Impacts & Causes of the Unusual Cold, Snowy & Stormy 2009~2010 Winter

 
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Introduction: During the winter of 2009-2010 a rare combination of known factors in earth’s climate variability systems -- the Arctic Oscillation and North Atlantic Oscillation in the Atlantic. El Nino, the Pacific Decadal Oscillation and Pacific/North American Pattern in the Pacific and the Indian Ocean Dipole -- influenced the Northern Hemisphere winter from North America, across Europe to eastern Eurasia - as far east as Mongolia, China and Korea.

This has been a highly unusual northern hemisphere winter; extremely cold and snowy in some regions, stormy in others - yet Canada had its warmest winter on record, parts of the the Arctic and tropical sea temperatures were unusually warm.

According to records going back to 1950, this winter saw one of the strongest El Nino events, combined with the most negative Arctic Oscillation (and also with a negative North Atlantic Oscillation) yet seen during a winter.
(Screenshot below from: AccuWeather. Text added by site administrator.)
Over the USA in particular this combination produced a remarkable winter, with several major snowstorms and record cold in the southern states. It also produced a memorable spring with historic floods, and very varied weather.


Over northern Eurasia the Arctic Oscillation was the dominant factor, causing a much colder than
usual winter. The jet stream also directed storms towards the Atlantic island of Madeira, the Mediterranean region and North Africa.

El Nino events typically bring wet, cool stormy conditions to many US states; this added to the cold.

El Nino
also fuelled storm fronts that moved up from the Pacific to the USA; when these ran into the cold Arctic air they generated very heavy snowfalls.

Satellite image below of snowstorm over NE USA. February 4th-7th 2010. Source: NOAA. Note tail leading back to the Pacific.
On February 4th-7th, and again between February 9-11th, two El Nino fuelled winter storms pummelled the north-east United Sates. These two systems combined broke records for snowfall in Washington, DC and New York. Another great snowstorm occurred between February 23rd-28th.

El Nino fuelled storms over USA at time of Snowmageddon and Snoverkill. Feb. 4th-11th

Above: NOAA animation based on imagery collected from NOAA's GOES-12 satellite, February 2010. These storms generated huge snowfalls.

Earlier, a series of major El Nino fuelled Pacific storms had pounded California, causing flooding and mudslides.

Unusually bad weather continued into March 2010. After having record snowfalls between December and February, the north-east USA then suffered storms (seasonal Nor'easters) that produced record rainfall totals by the end of March.

According to Accuweather, 22 storms passed over the USA's east coast region in the 2009-2010 winter; drenching it with 30-40 (76-101cm) inches of precipitation [snow and rain]. The average is 20-25 (20-63 cm) inches. These rains, combined with a saturated ground and previous snow-melt, produced widespread and historic flooding. This was immediately followed by an abnormal heatwave; with over 100 records for high temperature at this time of year broken over the USA's Midwest and north-east. Source.

Storms also impacted the north-west USA during March. In the Midwest and Southern Plains several storms crossed the region (it was also tornado & severe weather season by then), and in late March 2010, a great snowstorm crossed eastern Oklahoma, western Arkansas and north eastern Texas. Texas had its second snowiest winter on record.

As well as the great cold and snow other extreme weather events occurred worldwide; great storms, floods, heat-waves and droughts; also due to the current El Nino in the tropical Pacific. This winter's El Nino has been the strongest since the powerful El Nino of 1997/98.  (A warming of Eastern Pacific waters of 1.5 degrees C in 09/10, compared with 2.7 degrees C in 97/98.)

In S. China and SE Asia a severe drought took place during December, January & February; likely to last until the El Nino fades away; in places it is now the worst drought for at least 60 years.

This rare combination of events has given people the world over a memorable, often extreme, winter.
Sadly, this winter also claimed lives and devastated many homes and livelihoods; the power of nature can affect all of us. NB: The meteorological winter is defined as being December, January and February. (I also continue coverage through March into Spring.)

The first-half of this page looks at this winter's global impacts, in North America, Europe, Asia and elsewhere in the world (
videos help illustrate these). The lower-half of this page takes a detailed look at this winter's causes. Near the bottom of the page I also look at the 2010 spring outlook; and at whether this winter is just a weather anomaly, or a sign of a shift in climate? - Of either 'global cooling' or 'global warming'?

I link to sources and additional information where possible (Blue & Underlined); but bear in mind pages get retired, moved, blogs updated etc; so if you get a Page-Not-Found try a Google search on the topic.

Impacts of the 2009 - 2010 Winter: North America-

For the USA it was the coldest winter in 25 years. Various cities and areas of the USA saw this winter become one of their top five snowiest &/or coldest winters since their records began. For a few States and cities the 2009/2010 winter took the top spot for snowfall or cold. For more detail on the USA see Here, Here and Here. NOAA’s report on the USA's 2009-2010 winter season is here.

8th January 2010

The overall continental USA temperature anomaly was minus 1.771 C; which makes February 2010 the coldest for the continental USA since February 1979. An unusually negative Arctic Oscillation caused 'blocking' areas of high pressure that diverted the paths of the Jet Streams, this allowed cold polar air to spill southwards over the U.S.A.

There were four major NE snowstorms; one in December 2009, three in February 2010. New York City set a record for the snowiest month since its records began with nearly 36.9 inches (93.7 cm) of snow in February 2010, beating the previous high of 30.5 inches (77.47 cm) set in March 1896. Philadelphia and Baltimore also saw their snowiest winters ever. 

Snowmageddon: February 4th-7th 2010 - See below.

Both the south and south-east regions of the USA experienced their seventh coldest February on record. Meanwhile, warmer-than-average temperatures dominated the extreme north-west and north-east climate regions of the USA.
The cold migrated down to the South!

For Louisiana it was its fifth coldest February. Alabama, Georgia and Texas each had their sixth coldest. It was the seventh coldest February in Arkansas, while both Mississippi and South Carolina experienced their eighth coldest. Source: NOAA.

For Houston, Texas, the winter of 2009 - 2010 was one of the coldest in the area since record keeping began.

The cold Arctic air reached as far south as Florida; in early January 2010 it suffered unaccustomed cold and frosts.


Graphic from Accuweather. Used under fair-use/educational/non-commercial terms.

This was later followed by the cold air mixing with air
coming from the Gulf of Mexico, caused by El Nino in the Pacific, carrying moisture that resulted in snow and ice coating Florida's roadways and fields.

Both the months of January 2010 and February 2010 were the 6th coldest on record for Tampa (Florida) since records began in 1890. (December was around normal.) For Miami Beach (Florida) it was the coldest winter on record.

Florida overall had its fourth coldest February. The first 3 months of 2010 were the coldest ever reported in Miami Beach, Naples, and West Palm Beach, and was among the coldest winters ever for Ft. Lauderdale and Miami. El Nino conditions also resulted in the coldest March on record in Miami Beach; second coldest in West Palm Beach. It also remained wet over much of Florida.

For the period of December, January & February it was the coldest three-month stretch ever recorded for Florida overall; its coldest winter on record. Source: Here and Here.

Late December 2009 saw a snowstorm that brought up to 20 inches (50 cm) of snow across America's eastern seaboard. See also Wikipedia: North American Blizzard of 2009.

February saw three major snowstorms over north-eastern parts of the USA; originating from storms coming from the tropical Pacific, bringing moisture-rich air over the USA to meet the cold air pushed down from the Arctic. This clash of airstreams generated major snowfalls.

The first was named Snowmageddon (Feb 4th-7th) by the media. See also: Snowmageddon' Brings Washington to a Standstill. Also video above.

February 9th - 11th 2010

Snowmageddon was followed a few days later (Feb 9th-11th) by another great snow-storm across the eastern USA. This was dubbed variously 'Snowmageddon 2', 'Snoverkill', 'Snowapocalypse' & Snowtorious B.I.G! by sections of the media.

Snowverkill: February 9th -11th 2010

Yet another very heavy snowfall occurred in the last week of February (23rd-28th). Named Snowicane by one weather service, this brought protests of 'Enough of these bad puns' from a snow (and hype) weary public.

Catskill Mountains after Snowicane

February was Washington DC's second-snowiest month on record, with 32.1 inches. In contrast, in March it had no measurable snow, and set a record by having no freezing days at all.

This year's snowfall in both Kansas City (Kanas) and Tulsa (Oklahoma) gave them both one of their top five snowiest winters. For Texas it was the second snowiest winters ever (including the March totals), only half-an-inch short of the record; if it snows again in April a new record could be set. (The Texas Weather Service recognizes that snow can occur in North Texas from November through to April.) Source: NOAA.

El Nino in the Pacific generated a series of storms that slammed into California in the week of January 17th-22nd, and also drove storm fronts that drenched Nevada, Arizona and New Mexico.

One of the California storms 2010 - by Mrarteest

These El Nino fuelled storms also generated massive amounts of snow at high elevations. 84 inches (213cm) of snow fell on Mount Baldy, in Los Angeles County. 112 inches (284 cms) were estimated to have fallen at Kaiser Point in the Sierra Nevada Mountains. Heavy snows also fell in North and Central New Mexico and Arizona.

The storms continued across the USA; a strong winter storm brought a wide variety of weather including rain, thunderstorms, freezing rain, sleet and snow to West Texas on the 28th of January.

El Nino typically brings wetter-than-normal winters across the southwestern and southern United States due to an active subtropical jet stream.

Storms and snow continued through February well into March. On March 21st/22nd (Spring equinox) a major snowstorm struck across eastern Oklahoma, western Arkansas and north eastern Texas. Source. 20 inches of snow fell in some places. See also Here, Here and Here.

This helped Texas have its second snowiest winter on record (#1 was 1977/78.) It is likely that El Nino will continue to fuel further storms well into spring after March.

Violent storms caused injuries and destruction in Carolina on 28th March.

Temperatures across the continent were also highly variable, and changed over short periods of time. Warm and sunny one day; cold, windy and nasty the next!

The north-east US suffered great rainstorms during March (seasonal Nor'easters). (El Nino events typically produce more Nor’easters. Source: Development of Nor'easters during El Nino Years. L. Hoppe and D. Smith. United States Naval Academy. 2005. Link on this page.)

As March drew to a close a final slow moving rainstorm passed over the north-east US coast; the third such rainstorm that month. Below: Satellite image of rainstorm over NE USA. March 2010. Source NOAA. Graphic from AccuWeather. More on Nor'easters Here.

Satellite image above from NOAA. Graphic above from Accuweather. Used under fair-use/educational/non-commercial terms.

In 2010, Boston, Massachusetts, & Providence, Rhode Island all broke their previous March rainfall records. Over 14.5 inches (35.5 cm) of rain fell in March 2010 in Boston, the second wettest month ever since its records began in 1872. For New Jersey the period of March 2009 to March 2010 also turned out to be the wettest 12-months, of any 12-month interval, dating back to 1895. Many areas suffered flooding due to saturated ground and already swollen rivers..

Providence (Rhode Island) recorded more than 16 inches (38 cm), its rainiest ever month, since records began. Source. Blue Hill Observatory in SE Massachusetts also set a record for wettest month ever (since 1955), with 18.79 inches (47.7 cm).

Rhode Island - 31st March 2010

Philadelphia set a record when the total precipitation (snow & rain) for February and March 2010 reached 12.68 inches (32 cm); the city's highest total for the two-month period (7.3" in March alone) since records began being kept in 1873.

New York City set a new March record for rainfall (10.68 inches - 27 cm) in 2010; following on from its record snowfall in the previous months! Many NE regions were seriously challenged by flooding. See also Here.

Connecticut flooding : 30th March 2010

Rainfall totals on Monday 29th March 2010 surpassed 2 inches (5 cm); from North Carolina to Massachusetts, with amounts nearing 4 inches in spots. Over a dozen daily rainfall records fell in this area on this day. Extensive flooding resulted. These rains were almost immediately followed by much warmer weather across the north-east, with temperatures reaching 80 degrees F (27 degrees C) on the Easter weekend. See also: Here.

The Pacific north-west also had wild March weather, that brought heavy rains (snow at high elevations) and strong winds.

As March 2010 ended, violent storms had swept across much of the USA, bringing strong winds, low temperatures, heavy rains and snowfalls; it was also the annual severe weather season. 

Warmth and high temperatures (27 degrees C + (80 degrees F) then appeared at the end of March 2010. Many towns across the US plains set records for high temperatures in a March. On March 30th in Denver, temperatures peaked at 27.2 degrees C (81 degrees F). Chicago had its warmest April 1st since 1946, temperatures reached 83 degrees F (28 degrees C). The seasonal spring battle to banish winter was underway.

Overall the USA averaged warmer-than-normal conditions in March 2010. Warmer in the north, colder in the south.

It was the warmest January-March period for Maine, Vermont and New Hampshire. By contrast, the three-month stretch was the coldest ever for Florida, the second coldest for Louisiana, and the third coldest for Mississippi and Alabama. Source.

The March temperature averaged across the contiguous United States was 44.4 degrees F, which is 1.9 degrees F above the long-term average. Source.


However, the 2009-2010 winter was highly unusual in that some northern regions of continental north America remained relatively snow-free and warm, during its coldest months; whilst regions further south were colder and received heavy snowfalls.

At the same time as Snowmageddon, Vancouver - host city of the 2010 Winter Olympics - was trucking snow up to its ski-slopes, as its warmest winter on record threatened to leave the ski-runs snow free. (See also The El Nino Effect and Other Climate Variability Factors sections below.)

For Coeur d’Alene (Idaho) and Spokane (Washington State), 2010 will go down in the records books as the least snowiest for both locations. Minnesota had a snowless March for the first time in 130 years of records. Syracuse (NYS) had the lowest amount of snow for any March since 1951.

Much of the north of the continent was notably warmer and less snowy than in the south, Canada in particular. Some U.S. forecasters named this 'The upside-down winter'  with lots of snow in some places where it usually doesn't fall and relatively little in some where it usually does. For more on this see also: Here, Here, Here and Here - and below.

 Canada actually had its WARMEST, driest winter (Dec, Jan & Feb) on record! (Source: Environment Canada.)

January 2010 in Vancouver (Canada) was the warmest since record keeping began in 1937. Not a good omen for the Winter Olympics held there in February 2010; unseasonal warm, wet weather continued throughout February. (Typically, an El Nino event brings warmer than average temperatures to Vancouver, and cooler than average conditions to Florida.)

Vancouver - February 15th 2010

Fairbanks in interior Alaska had its lowest amount of snowfall this winter since 1952/53.

In Toronto, Canada's biggest city, the temperature departure for the winter was nearly 2 degrees F above normal. Montreal was warmer than usual by more than 6 degrees F.

Temperatures 8 degrees F to 12 degrees F above normal spread over wide swathes of Yukon, Northwest Territories, Nunavut, British Columbia and Manitoba and the sprawling vastness of Labrador and Quebec, where half of the province's twelve largest cities experienced their warmest or second warmest January on record. This warmth extended as far south as Newfoundland and New Brunswick. Canada had its second-warmest January on record (since 2003).

Graphic from Accuweather. Used under fair-use/educational/non-commercial terms.

February also turned out to milder and drier than normal; the average daily high of 7.3 degrees C was well above the normal of 3.6 degrees C. See also Here, Here and Here. March continued warm; Ottawa and Toronto had a snow free month; their first since record keeping began in 1845. Alberta and Saskatchewan had a dry fall and winter and faced drought by April. Ottawa had record temperatures of 25 degrees C (77 degrees F) in early April.

Environment Canada reports that winter 2009/10 was 4 degrees C above normal, making it the warmest in 63 years since nationwide records were first kept in 1948. It was also the driest winter on the 63-year record, with precipitation 22 per cent below normal nationally, and down 60 per cent in parts of Alberta, Saskatchewan and Ontario. Source.

Seattle in Washington (USA) had its warmest January in 120 years of record keeping; both Oregon  and Washington states recorded their 4th warmest January. For more on this see Accuweather.

As the Jet Stream & cold Arctic air retreated northwards snow finally fell on Vancouver's Olympic venues at the end of March, a month after the games finished. Wet, snowy and stormy weather began to affect the north-west, extending down to northern California.

In the Arctic seas, for Iceland the 2009-2010 winter season was unusually warm - the temperature was 1.6 degrees C above average in Reykjavík.

Impacts of the 2009 - 2010 Winter: Europe and Asia

Northern and Western Europe and northern Eurasia weren't so lucky as to have an upside-down winter. Stockholm in Sweden had its heaviest snowfall since 1982. There was also record snowfall in Moscow (23/02/10).

It was the coldest UK winter for 31 years (since 1978/79). In Scotland it was the coldest for almost 50 years (since 1962/63). Source.

This UK winter has been the third coldest in the last 50 years and 10th coldest in the last 120 years
. Source. (For more detail see: Wikipedia: Winter of 2009–2010 in the United Kingdom,
Winter of 2009–2010 in Europe,)

Even though it's been the coldest winter in the UK for 31 years, the individual months have not themselves been the coldest in 31 years. December was the coldest since 1996, January was the coldest since 1987 and February was the coldest since 1996. It's been the prolonged nature of this winter's low temperatures - over the three month period - that made this record.

January 5th 2010. Yorkshire UK - ITN news

Hoseda-Hard in Russia recorded minus 56.4 degrees C (-70 F) on  February 19th - the second coldest temperature ever measured in Europe. (On the following day the temperature in Birni-N'Konni in Niger hit  44.3 degrees C (112 degrees F), the second warmest temperature ever recorded in the Northern Hemisphere in a February. Source. Niger was also in the grip of a major drought and famine.)

Overall it was the coldest Russian (and Siberian) winter for 30 years. (NB: This was also claimed in 1998!)

By the end of February in Mongolia, after weeks of heavy snowfalls, fierce winds and temperatures as low as minus 58 degrees C, 2.3 million livestock had perished this winter, and an additional 3 million may die by summer (summer grazing will be late) according to the Mongolian government. Source and Here. (This winter followed a very dry 2009 summer.)

Mongolia - 14th March 2010

Parts of north and north-western China struggled through snowstorm after snowstorm during one of its coldest winters in decades. (See also here.) On January 6th, temperatures in Beijing dropped to -16.7°C (1.9°F); its lowest temperature in the first ten days of January since 1971. Source.

Heavy Snow in North China - January 10th 2010

In the north-western region of Xinjiang-Uyghur these snowstorms are the worst in six decades. More than 11,000 houses collapsed in Yining County due to damage by blizzard and rainstorms.

On December 22, a blanket of heavy snow fell upon large parts of Japan and South Korea, causing the deaths of 10 Japanese and 3 South Koreans. Eleven inches (28 cm) of snow fell in Seoul, South Korea on the 3rd January, the greatest snowfall amount in a day since records began in 1937. See also: Wikipedia:Winter storms of 2009–2010 in East Asia, Winter storms of 2009–2010.

The Mediterranean region had an unusually cold and stormy winter. A Negative NAO winter favours a stormy mid-Atlantic and the prevailing storm track (Jet Stream) moves southwards over the Mediterranean. (Source.) This brings increased storm activity and rainfall to southern Europe, the Mediterranean and North Africa. (This winter the tropical Atlantic waters were also the warmest on record for a February, and the 2nd warmest anomaly for a month since 1948. Source.)

Screenshot from weatheronline.co.uk Arrows added by site administrator. Image used under fair-use/educational/non-commercial terms.

A stormy Atlantic and the southern track of the Jet Stream this winter produced major flooding and 48 deaths on the island of Madeira on February 20th.

February 20th 2010 - RubenvTV ‎- Dramatic footage

The Jet Stream also helped steer the Atlantic storm Xynthia (Cynthia), with hurricane force winds and rain, towards Spain, Portugal and France during the last weekend of February, producing widespread devastation and over 50 deaths.

Xynthia - February 27th - 28th 2010

Southern Spain had one of its coldest and wettest winters overall in years. On March 8th the city of Barcelona and north-eastern Spain received its biggest snowfall since 1962.

The cold air returned a few days later (March 10th) to the Mediterranean, bringing the first snowfall since 1962 to many areas of Spain, France, Italy and Greece. This turned out to be the last gasp of the European winter; shortly afterwards the AO edged up into a positive phase and most of Europe and the USA experienced warm spring conditions.

South of France - March 10th 2010

In Morocco heavy rains caused floods and mudslides that killed several people; heavy rains there were also blamed for a Minaret collapse that killed over 80 (Being in a poor state of repair also contributed.).

Heavy rains also affected other Mediterranean countries such as United Arab Emirates and Turkey.

Israel, however, managed to buck the trend by having its longest hot spell in a February for 38 years, with temperatures reaching 20/30 degrees C (86 F). It is thought that high pressure over Europe brought warm air from deserts in the Middle East towards the Israeli coast. Another heatwave arrived in mid March.

In March seasonal sandstorms combined with strong winds to close ports on the Suez Canal  for a few days.

At the end of March the Arctic Oscillation again dipped into a negative phase, and cold and snow returned to the UK; particularly to Ireland and Scotland. Cold, wet and occasionally windy conditions affected the parts of the UK not affected by snow. See also: Here.

Atlantic storms and a cold blast from the Arctic (caused by the AO dipping into a negative phase) combined to cause more drifting in high grounds.


December 2009 Northern Hemisphere sea-ice extent was the 4th lowest since satellite measurements began in 1979 and was slightly below December 2008 levels. January 2010 Northern Hemisphere sea-ice extent was the 4th lowest since measurements began in 1979. In February 2010 Arctic sea ice extent continued to track below the average, and near the levels observed for February 2007.

Ice extent was unusually low in the Atlantic sector of the Arctic, but above normal in the Bering and Baltic seas; a large number of ships became stuck in ice in the Baltic Sea in February. See also: graphic near top of page.

The warmth wasn't evenly distributed across the Arctic. Ice growth in the Bering Sea was sufficient that the extent of ice-covered Arctic Ocean had nearly returned to the 1979-2000 average. Being newly formed this ice is likely to be thin and unlikely to remain for long. Over other areas of the Arctic Ocean it had been warmer than average. On the Atlantic side of the Arctic, ice coverage was unusually low in the Atlantic sector; including the Barents Sea, part of the East Greenland Sea, and in the Davis Strait. Source: National Snow and Ice Data CenterSee also: Here and Here.

1st April 2010: Alaska Dispatch report

Lake Superior in continental northern America had unusually low amounts of ice in early March 2010; 73% of the lake was ice-free, compared to an 'average' year's 40% at the same time of year. Source.

Heat distribution has also been highly anomalous (and unevenly distributed) in the Arctic (see below) this winter due to large anticyclones over Greenland and Scandinavia, overall it has been an unusually warm Arctic winter.

But, according to Rutgers University Global Snow Lab February's northern hemisphere winter snow extent was the second highest on record, at 52,166,840 km2. (The highest was February 1978.)

It was also the second highest snow extent for the continental USA. However, for Eurasia on its own snow cover was only joint-seventh (with 1986).


El Nino 2010 Impacts: Worldwide

On the Pacific side of the USA El Nino caused a series of storms and heavy flooding in California; the El Nino wind pattern also swept cold, winds and rains across to Florida.

El Nino brought heavy rains and flooding in Peru, Bolivia and MexicoIn contrast Ecuador had its worst drought in 40 years. Venezuela and Nicaragua also suffered from severe drought.
Brazil, Uruguay and Argentina were hit by heat waves and intense rains.

Flooding in Peru - 27th January 2010

Conditions in Brazil, Colombia and Venezuela caused a sharp rise in cases of the tropical disease dengue fever; 146,000 cases were reported in the first three months of the year, of which 79 were fatal. Source.

In the mid Pacific Hawaii had the worst drought conditions of the USA. El Nino tracked rain clouds north of the islands.

Hawaii - Mid February 2010

See also: Snow, Floods, Heat-waves as El Nino Wallops the Americas.

At the same time North China had heavy snowfall (see above), Southwest China reported severe drought and a shortage of drinking water in Yunnan, Sichuan, and Guizhou provinces in February and March, affecting over 50 million people in the south-western part of the country; with no end in sight after six months with no rains.

SW China: 20th March 2010

Yunnan province is experiencing its worst drought in six decades. Source.

Drought in Southwest China - March 2010

SE Asia, Malaysia and the Philippines also suffered from this severe El Nino drought at this time.

Philippines - February 27th 2010

Singapore's February 2010 was the driest month in 140 years, since 1869, when records of rainfall first started.

El Nino rains brought relief (and floods and some deaths) to drought stricken Kenya, Uganda, and parts of Ethiopia, Somaliland and northern Tanzania

Kenya - 5th March 2010

In West Africa Niger, Ghana, Burkina Faso, Cape Verde, Chad, Gambia, Guinea Bissau, Mali, Mauritania and Senegal all suffered unusually hot temperatures for a February - and droughts. (See also here.)

For central Australia, February 2010 was one of the wettest months since January 2001. A number of stations in the Alice Springs area recorded a year's worth of rainfall in just 11 days; extreme flooding affected parts of Queensland and New South Wales. (El Nino & the Indian Ocean Dipole both have major effects on Australia's weather. El Nino conditions prevailed in 2009-2010 at the same time as the waters of the Coral Sea, to Australia's north, were also warm; unusual for an El Nino.)

Queensland Flood 2010

NB: January 2007, February 2003, April 1998, January 1995, March 1983 and February 1973 also all produced heavy rainfalls over parts of northern and eastern Australia; it tends to signify the decay of the El Nino event.

On February 12th a major storm struck Sydney, which recorded 2.5 inches (6.5 cm) of rain in just one hour helping make the month the second-wettest February in eight years.

On 6th/7th of March a super-cell thunderstorm crossed Melbourne (Australia); up to 1.5 inches (3.8 cm) of rain fell in about 30 minutes along with very large hailstones causing considerable flooding and damage. Melbourne had its second wettest March since 1989; it was also the city's hottest month since 1974. Source.

All these are thumb-prints of an El Nino.

A number of forecasters are suggesting that ENSO neutral conditions may occur by early summer.

In the north Pacific the Pacific/North American Pattern (PNA) was in a positive phase contributing to warm weather on the western seaboard of Canada and colder conditions on the eastern side of the USA. (See Other Climate Variability Factors section below.)

See also: CapitalWeatherGang - Now you know the power of El Nino


But it wasn't cold or snowy everywhere:  

Graphic from Accuweather. Notice the Upside-Down conditions over the Arctic and USA. Used under fair-use/educational/non-commercial terms.

The town of Exmouth, in Western Australia recorded record heat of 48.9 degrees C (121.82 degrees F) on the 2nd January 2010. Source. (It's summer in the summer hemisphere.)

The Australian city of Melbourne sweltered through its hottest night since 1902 on 11th January 2010, with temperatures topping 34 degrees Celsius (93 degrees Fahrenheit).

In Western Australia Perth had just recorded the joint-hottest summer (December, January & February) in its110-year record. Perth also endured its driest summer since records began in 1897, with just 0.2 millimetres (0.01 inches) of rain falling in December, January and February. Source. This ended when a severe storm struck the city on 23rd March.

January 12th 2010

All of Western Australia sweated through its hottest ever summer (December, January and February), recording average temperatures close to 30 degrees Celsius (86 F). Its hottest summer in the 60-year state-wide record. (Source.)

Hobart in Tasmania had its warmest March for more than a century.

Temperatures in Taipei City (Taiwan) reached 31.8 degrees Celsius Friday 26th February, a record high for the city for that month. In Manila (Philippines) temperatures hit 35.8 C in early March.

Across Vietnam high temperatures and parched rivers during January and February are shaping up to produce its worst drought in more than 100 years.

Rio de Janeiro in Brazil experienced temperatures of 46.3 degrees Celsius in February 2010 in the worst heatwave to hit Rio de Janeiro in 50 years. See also here.

A late February heatwave killed 250 ostriches from heat exposure in temperatures of more than 50 degrees Celsius in the Klein Karoo in South Africa.

Shimla in northernmost India, known as the 'Queen of Hills' because of its cool climate, had the warmest January in the past six years. Shimla recorded an average high of 15.4 degrees Celsius in January this year, which was 3.8 degrees above average for this time of the year. But a cold snap around 2nd and 3rd January killed more than 200 people in northern India, mostly in Uttar Pradesh, in accidents in heavy fog.

By late March maximum temperatures were above normal by 5-10 degrees Celsius over many parts of north-west, central and north-east India. March overall was the second warmest ever recorded.

On 8th January 2010 parts of coastal Alaska were warmer than Florida.

The anticyclones (high pressure) also resulted in an unusually warm Arctic, with air temperatures locally at 5.6 to 8.4 degrees C (10 to 15 degrees F) warmer than they should be in certain areas.

If you look at the Greenland region on the two images below - towards the centre of each - that is where the high pressure is; cold air was being displaced away either side and down towards the mid latitudes.

Image above from: Capital Weather Gang: A virtual tour of the cold (and not so cold). Original source: NSIDC.

At Goose Bay in Newfoundland on January 7th 2010, temperatures were barely getting below zero, the average minimum for January there should be minus 23 degrees C. (Minus 9.4 degrees F.).

In Canada unseasonably warm weather and heavy rain led to the closure of one of Vancouver's Olympic premier ski venues (January 13th 2010), one month before the 2010 Winter Olympics were scheduled to start, in an attempt to conserve the snow for the games. (See also here.)

Vancouver, Seattle and Portland all experienced a winter of rain and wind, but much warmer than usual with temperatures around the 10°C mark. See also here. Port Angeles in Washington State (USA) may have had its warmest January on record in 2010.

Bulgaria also experienced record warm temperatures. The thermometer reached 17 degrees C in many places with temperatures in Sofia on January 7th, 2010, soaring up to 14 degrees C (57.2 degrees F). In the northern town of Veliko Tarnovo temperatures reached 22.4 C. (72.32 F); at a time when the country should be blanketed by snow and temperatures be well below freezing.

In Crete on New Year's Day the temperature reached 30°C (86F), a new all-time record for Europe in January.

Although there has been freezing weather in places as far afield as Mexico, Florida, China and the UKthe Arctic, Greenland, Africa and southern Asia and SE Asia have been warmer than usual.

Overall the northern hemisphere winter or global temperatures as a whole may turn out to be no colder than in previous years, it's just that the heat is being distributed differently. This turned out to be the case for January 2010.

Globally, January 2010 was the 4th warmest January on record, with global ocean temperatures the 2nd warmest on record, according to NOAA. See also: Winter Olympics Forecast: Near-Record Warmth


Screenshot from USA Today.El Nino Fuelled Record Global Warmth in January. Used under fair-use/educational/non-commercial terms.

In 2010 the tropical Atlantic waters were the warmest on record for a February and the 2nd warmest anomaly for a month since 1948. (Source.)

Image above from weatherunderground.com. Image used under fair-use/educational/non-commercial terms.

The South Atlantic saw a
tropical cyclone
form in March. off the Argentinian coast; only the 7th ever recorded since the first in 1974. See also Here

Global temperatures in January and February 2010.

Though hard to believe, especially if you were in a region subject to below average temperatures, January 2010 was anomalously warm compared with those similar months from recent previous records. See also Here
and below.

NASA's Goddard Institute for Space Studies rated February 2010 the second warmest in the 32-year record, behind February 1998 (also during an El Nino event).

I give sources below, including two from Dr Roy Spencer, a scientist who 'double checks' the official figures.

BBC News: Why Was it Cold in the UK, But Not Across the World?

Dr Roy Spencer: I’ve determined that the warm January 2010 anomaly IS consistent with AMSR-E sea surface temperatures from NASA’s Aqua satellite.

Dr Roy Spenser: February was second warmest in the 32-year record, behind Feb 1998. The El Nino is still the dominant temperature signal.

However, the USA's National Oceanic and Atmospheric Administration's (NOAA) National Climatic Data Centre ranked February as the sixth warmest. See also Here. March was the warmest on record globally.

See also: Washington Post Capital Weather Gang. A virtual tour of the cold (and not so cold).

See also: If It’s That Warm, How Come It’s So Damned Cold? Hansen et al.

See also: New Scientist. Errors and Lies Thrive in Cold Weather.

See also: WeatherOnline: The 'Big' Freeze, 2009-10 - Unprecedented, or What?

See also: Klimaat: 2010: A winter of extremes: Cold in Europa, Siberia and the US, but Above Normal Globally


Causes: Why Was The 2009-2010 Winter So Cold, Snowy and Stormy?

An atmospheric pattern developed over the Arctic Circle region that flushed cold air away from the North Pole towards the mid-latitudes, where many of us in the N. Hemisphere live.

This pattern, known as ‘high-latitude blocking’ (caused by the negative phase of the Arctic Oscillation, or -AO) is essentially a large area of high pressure (anticyclone) in the atmosphere over far northern latitudes.
 
Saturday 9th January 2010. A large area of high pressure stretched from Northern Ireland across northern Britain
and the North Sea to Scandinavia.
High pressure also stretched over parts of Greenland, Baffin Bay and NW Canada.
The thicker back lines across the UK indicate the main areas of snow showers. More are over the Atlantic.
On this day low pressure in the Mediterranean  is spreading active weather fronts northwards across Europe & towards south-east England.
Met Office Synoptic Chart. 07.30 on Saturday 9th January 2010.
 
Below: AO Index (updated daily). January 12th, 2010.
Graphic from US National Weather Service Climate Prediction Centre. Used under fair-use/educational/non-commercial terms.

Screenshot from Metchck.com. (The UK warmed for a while from 17th Jan.) Used under fair use/educational/non commercial terms.

The Arctic Oscillation is part of the North Atlantic Oscillation (NAO), this was also in its negative phase.

Screenshot from Metchck.com. The red bars indicate a positive phase, the UK came out of its big freeze in these days.
Used under fair use/educational/non commercial terms.
The AO and NAO are known together as the northern hemisphere annular mode. When sea-level pressure is above normal over the polar region and below normal over the Mediterranean, the annular mode is said to be in a low or negative index. When reversed it is in a high or positive index. When in its low index state there are frequent excursions of cold polar air extending into the Eurasia and the USA. Below: charts for Feb. 2010, the period of Snowmageddon etc in the USA.

Screenshot above from Metchck.com. Used under fair use/educational/non commercial terms.
Screenshot above from Metchck.com. Used under fair use/educational/non commercial terms.

Met Office Synoptic Chart: Feb. 15th 2010. (Extreme cold hits Florida.)  Anticyclones remain over Greenland and Scandinavia.
Screenshot above from Metchck.com. Used under fair use/educational/non commercial terms.

When the NAO is in its positive phase the storm-track doesn’t bring down the intensely cold air from the Arctic. Instead, it drops into Quebec and the Canadian maritimes; a large subtropical high is set up in the Atlantic which keeps the south-eastern United States warmer than normal.
When in NAO is in its negative phase (as during the 2009/2010 cold winter spell), the main branch of the jet stream brings the cold, Arctic air down into the Central United States, then down to its south-east. The only warm spots on the continent would be the Canadian Maritimes and Newfoundland  over to Greenland.

.

High pressure pushes cold air downwards; as that air gets nearer the Earth's surface it's forced outwards and away, sending cold air toward us.

This high-latitude blocking pattern (-AO) was the strongest on record for a December in 2009 - and continued into mid February 2010. The pattern consisted of two blocking anti-cyclones:

The first was over Greenland and it prevented (blocking) the usual warmer, damper westerly winds from reaching Europe across the Atlantic, by steering the high-altitude jet stream far to the south of Britain, leaving the country and north-western Europe exposed to winds from Russia, Scandinavia and the Arctic Ocean. This anticyclone also pushed large amounts of cold, Arctic air from the north, southwards, towards the United States. e.g. Below.

Charts above from weatherunderground.com. Image used under fair-use/educational/non-commercial terms.

The second anti-cyclone is the Siberian anti-cyclone (Siberian High) that was over much of northern Eurasia (during the coldest spell high pressure also stretched from above Northern Ireland, across northern Britain and the North Sea to Scandinavia) and also supplied much cold air to areas further south and east such as eastern regions of the USA, as well as to western Europe and across to China.

The Siberian High is an intense, cold anticyclone that forms over eastern Siberia in winter; lasting from late November to early March and is associated with cold air and winters over East Asia.

(NB: during any winter a number of High pressure zones (anti-cyclones) form over high latitude areas.)

Negative Arctic Oscillation (AO) conditions allows Arctic air to spill southwards into eastern North America more readily.

Negative AO winters tend to bring cold winters to Europe (winds were from the north and east) whilst the prevailing storm-track (Jet Stream) moved south towards the Mediterranean Sea.

This also brought increased storm activity and rainfall to southern Europe and North Africa.

North Western Europe's prevailing winds generally bring weather from the south-west and west; but during the coldest period of 2010 the wind blew from the north and east.

This led to increased snowy conditions and also brought sub-zero temperatures to North Western Europe from the Arctic, Scandinavia and Siberia.

Image below of the UK covered in snow taken by NASA's Terra satellite on 7th Jan. 2010. Photo: NASA. Click here to go to much larger version.

See also: Washington Post - Blame the North Pole and the Equator

See also:
Times Online: Weather eye: Jet stream is Driving Force Behind Continued Winter

See also: NPR: Frozen In France? Thank The Arctic Oscillation - plus:

Washington Post:: Capital Weather Gang. How Did this happen?

New York Times: Feeling That Cold Wind? Here’s Why.

Baltimore Sun: North Atlantic Oscillation blamed for cold spell.

The Scotsman: Villain of the Winter's Tale Lies in Greenland.

UCAR: Brrr: The AO is Way Low.

Nashua Telegraph [USA]: High Pressure in Polar Latitudes is Forcing Colder Air South.

Business Sustain: The winter of 2009 - 2010 - 'The big freeze'

Skeptical Science: 2009-2010 Winter Saw Record Cold Spells

NY Times: Polar Pressure, Snowstorms and Sea Ice


Role Of The Jet Stream In The 2009-2010 Winter

There are 2 major jet streams in the Northern Hemisphere. The sub tropical - aka Pacific or mid-latitude- Jet Stream and the Polar - aka high-latitude - Jet Stream. The Polar Jet stream is found at the boundary between cold air to the north and warm air to the south. The sub-tropical jet (along with the influence of the Gulf Stream) flowing across western Europe often helps it have mild (if wet and stormy) winters.

A ridge of high pressure over north western North America and trough of low pressure over eastern North America caused conditions that allowed warm air from the Pacific to flow into high latitudes (the PNA pattern and El Nino also favour this), whilst cold Arctic air moved southwards, deep into the USA; the position of the Polar Jet was shifted far southwards.
The sub-tropical (pacific) jet was also pushed further south; both jets meander in course so the sub-tropical jet also rose and fell in latitude. This jet was responsible for the storms that struck California and the heavy rains that fell on Nevada, Arizona and New Mexico in the week of January 27th-22nd 2010. See also Here.

The blocking areas of high pressure produced by the Arctic Oscillation (See also below) diverted the course of the Jet Stream over Eurasia. The sub tropical Jet was over the Mediterranean & North Africa; hundreds of miles south of its usual position for a European winter. This allowed cold Arctic air to extend further southwards; cold air was coming down from the north and northeast instead of warmer air blown across the Atlantic by the sub tropical jet that usually Europe usually gets.

Images from: Wrex.com 13WeatherAuthority blog. Used under fair use/educational/non commercial terms


The weather that western Europe normally gets in winter (brought by the sub-tropical Jet Stream) was diverted south towards Spain, the Mediterranean and North Africa where it was unseasonably wet and stormy for this time of year. e.g. See chart below.

Screenshot from weatheronline.co.uk Image used under fair-use/educational/non-commercial terms. Arrows added by site administrator.


When thinking of the vast area that forms the northern hemisphere bear in mind that cities and towns in America share one important thing with many cities and towns in Europe and Asia - the same line-of-latitude.

Denver [Colorado] & Philadelphia [between New Jersey and New York] in the USA, Madrid in Spain, Ankara in Turkey, Baku in Azerbaijan, Beijing in China and Hamhung in North Korea are all situated approximately* along latitude 40 degrees north. (* Within one degree [plus/minus] latitude of the 40 degrees north line-of-latitude. NB: All these countries [and India] are in the northern hemisphere.)

When cold air from the Arctic circle spreads out southwards then all the places named above above can be equally affected; particularly as during this winter they found themselves to the north (cold) side of the Jet Stream as it moved to the south.

The Arctic Oscillation (AO) refers to the changes in the strength of the atmospheric pressure (measured at sea level) in the Arctic and the mid-latitudes. In early January 2010 it was in an extreme negative phase (the most negative Arctic Oscillation pattern in 60 years of record keeping); above-normal pressure over the polar region and below-normal pressure over the mid-latitudes, with weaker zonal (west to east) winds (the Jet Stream in particular) resulting in greater movement of frigid polar air into middle latitudes.

The above normal pressure over the polar region displaces cold air to the south and also displaces the course of the sub-tropical Jet Stream (aka southern Jet) in the northern hemisphere; this results in colder, wintry weather across Northern Europe, Northern America and Eurasia. (When the jet stream is strong it's course is fairly straight and Arctic cold does not penetrate very far southward. When the jet stream is weaker it zig-zags, with its southward excursions allowing frigid Arctic air to reach ordinarily warmer climes.)

In February 2010 the warmer tropical waters an El Nino produces also resulted in more moisture in the atmosphere. El Nino also generates stronger winds across the USA; these carry the moisture towards a collision with the cold Arctic air towards the Atlantic seaboard resulting in major snowfalls. Other variability systems were also at work. (See below.)

This confluence of climate variability systems, and the strength of the Arctic Oscillation, resulted in extremely harsh, cold winter conditions with heavy snowfall in many regions across the northern hemisphere. (Scroll down to Why the 2019-2010 winter was unusually cold and snowy below for explanation.)

The most dominant features have been regions of high pressure - anticyclones or Highs - over Greenland, Scandinavia and Siberia. These anticyclones forced colder air away from the Arctic and down into northern America, western Europe and parts of central and eastern Asia. Wind direction changed from the west to come instead from the north and east.

The blocking high pressure was so strong that mild maritime air from the North Atlantic moved west into eastern Canada and the Canadian Maritimes, producing unseasonably mild weather and few storms.

The Greenland
anticyclone blocked the usual path of the Jet Stream, forcing it to swerve well away from its usual course. (below)

Image fromTechnorati's Lynn Voedisch blog: Used under fair use/educational/non commercial terms.


The cold many of us experienced in the winter of 2009/2010 was a weather phenomenon, not a climate phenomenon. It is not connected to climate change, but is part of earth's natural climate variability.

In fact we appear to be experiencing a repeat of the same factors that produced extremely cold winters in 1963 and 1978 (See The North Atlantic Oscillation and the Historic Record below). Source.

The Arctic Oscillation forms part of the larger North Atlantic Oscillation (NAO).

The NAO also was in a negative phase: i.e. above-normal pressure over Iceland; below-normal pressure over the Azores; in Northern Europe this is usually associated with below-normal temperatures.

Image from Tim's Weather Blog. Used under fair-use/educational/non-commercial terms.

The NAO index for the month of December 2009 was -1.93, which is the third lowest NAO index since 1950 for a winter month (December, January, or February). It went even lower in early January 2010. (See below.)


Above: NAO Index. January 17th 201. The UK came out of its Big Freeze from the 16th onwards, temperatures rose above freezing.
Image from US National Weather Service Climate Prediction Centre Used under fair-use/educational/non-commercial terms.

The only winter months with a lower NAO index were February 1978 (-2.20) and January 1963 (-2.12). January 1963 was one of the coldest months on record in the both United Kingdom and the eastern regions of the USA. Source plus US National Weather Service.
In 1963 anticyclones to the North and East of the UK, brought bitterly cold air over Britain. A depression tracked to the South, and brought heavy snowfalls to England, Wales, and Scotland.

The mean maximum temperatures for January 1963 was more than 5 degrees C (9 degrees F) below average over most of Wales, the Midlands and Southern England, and in some places 7 degrees C below average (12.6 degrees F).
1963 was
the coldest winter in the UK for 200 years.

We don't have sufficient records (to my knowledge) to demonstrate that these are similar conditions to those that produced the extremely harsh winter of 1946/47, but it I believe it likely to be the case.
 
That winter (46/47) was followed by a summer with temperatures well above average, so there may be something to look forward to.

Looking back, it seems that strong and weak jet streams tend to cluster in groups: a series of mild and stormy winters, followed by three or four cold and snowy ones. We can identify the cold clusters in the past half-century: 1962-65, 1968-70, 1978-82, 1985-87 and 1994-97.

In late January and early days of February 2010, after some days in its positive phase, the Arctic Oscillation returned to its negative phase by . This was the period major snowstorms - Snowmageddon etc - affected parts of the USA.

Screenshot above from Metchck.com. Used under fair use/educational/non commercial terms.

What we can't yet tell is whether the  conditions experienced this winter will just be for 2009-10, or will prove to be part of a cluster that extends through winters from to 2009 to 2012? Only time will tell.

See also:
"The AO is a measure of north-south differences in air pressure between the northern mid latitudes and polar regions. When the AO is positive, pressures are unusually high to the south and low to the north. This helps shuttle weather systems quickly across the Atlantic, often bringing warm, wet conditions to Europe. In the past month, however, the AO has dipped to astoundingly low levels - among the lowest observed in the past 60 years. This has gummed up the hemisphere's usual west-to-east flow with huge 'blocking highs' that route frigid air southward."  Source: Snow, ice and the bigger picture. Robert Henson. Guardian Online

El Nino refers to warmer-than-normal waters in the central to eastern Pacific Ocean along the equator, it is the warm phase of the El Nino Southern Oscillation (ENSO). See video below.

El Niño Explanation

El Nino plays its part in affecting conditions over the USA this winter. The west and the south of the USA, especially Californiathe Gulf Coast states and Florida, typically sees cooler and wetter conditions in a typical El Nino winter because of the stronger influence of the subtropical jet stream.

El Nino events vary widely from event to event, with different distributions of sea-surface warming and wind-pattern changes. Just as no two snowflakes are the same, so no two El Ninos are the same. (NB: There is also a recently identified variation to the 'classic' El Nino known as an El Nino 'Modoki'. The 2009-2010 winter doesn't appear to be connected to one of these.)

The 2009/2010 El Nino has been the 'strongest' since 1998. It is the 5th 'strongest' El Nino since 1950; only 1973, 1983, 1992, and 1998 saw stronger El Nino conditions during January-February than in 2010, as measured by the MEI (Multivariate ENSO Index). Source: Multivariate ENSO Index (MEI) page. 5th March 2010. NOAA. Also screen-shot below.

In the USA El Nino typically brings beneficial winter precipitation to the arid South-west, less wintry weather across the North (counteracted in 2009/2010 by the Arctic Oscillation) and a reduced risk of Florida wildfires. ie. It's wetter.

The South-west experiences increased precipitation and seasonal snowfall during the mature winter phase of an El Nino. The opposite is found for the north-western USA.

In the North-east, in a line that extends up the Appalachian Mountains from central Virginia through Maryland and New Jersey to western Vermont, more snow falls in this region during an El Nino year.

Northern Texas shows the greatest increase in snowfall in mid-winter during El Nino years.

El Nino's negative impacts can include damaging winter storms in California and increased storminess across the southern United States. El Nino also produces cooler than average temperatures across the southern US States; demonstrated again this El Nino winter.

Image source: NOAA. Image used under fair-use/educational/non-commercial terms.

El Nino can be blamed for a very moist atmosphere that produces heavy precipitation in some regions worldwide when it occurs. El Nino also is associated with drought in other regions of the world, as it alters global precipitation patterns.

(La Nina, the negative (cool water) phase of ENSO, also produces alterations to global weather patterns, if of a different nature. El Nino/La Nina are sometimes seen as opposite sides of the same coin, though this is far from an exact analogy.)

El Nino conditions formed in the equatorial Pacific last year (summer 2009) and currently continue. This El Nino is the strongest since that of the 1997/98; at present its sea temperatures are above normal, the warmest for at least 12 years.

The Australian Meteorological Bureau reports (6th Jan. 2010): Central Pacific Ocean temperatures remain well above El Nino thresholds. Trade wind strength returned to near normal over the past fortnight, slightly reducing the excessive warmth of the equatorial Pacific Ocean. However, significant areas remain more than 2 degrees C above average at the surface, and over 4 degrees C warmer than normal at depth. Source.

Those warm waters (heat = energy) helps to both feed more moisture into the Jet Streams that circle earth and generate stronger high altitude winds - both of which add fuel to storm systems.

Storm tracks are pushed farther south producing more clouds, rain, severe weather and cold over those areas.

Image source: Dr Cane on iBankcoin Image used under fair-use/educational/non-commercial terms.

However, this winter the effects of El Nino have not been typical because the negative phase of the AO/NAO temporarily diverted cold air further south than normal. Both of those phenomena will have contributed to temperatures and conditions across the west, south and east of the USA during the 2010 winter. 

e.g. Chart below showing wind directions (and indicating temperatures) over south-east and eastern USA.

The upper air-stream comes from the AO; the lower air-stream is being influenced by El Nino in the Pacific.

Chart above from Weatherunderground.com January 13th 2010. Image used under fair-use/educational/non-commercial terms.

When moisture rich air crosses a region receiving colder air from the northern Atlantic, then that moisture condenses and falls as snow. e.g. Moscow Times: Record Snowfall Blankets Moscow.

If the air is not cold enough to produce snow then the precipitation falls as rain; sometime in record and destructive amounts. e.g. In the Portuguese Madeira Islands more than 3 inches of rain fell in one hour during the height of the flooding; this can be traced to a strong jet stream far south of its normal position, brought about by the negative AO (El Nino also alters the Jet Stream's behaviour); an unusually warm tropical Atlantic also contributed. See: Floods: Death Toll Rises To 40. See also: YouTube videos.

If the air remains cold and dry then frosts and cold temperatures result.

See also: Oregon Live: Mild January Weather A Reflection Of Typical El Nino Year
"El Nino conditions, the warming of the equatorial Pacific Ocean surface waters off the coast of South America, occur about every two to six years. The phenomenon tends to spell drier and warmer winters in the Pacific Northwest, wetter storms in the Southwest and colder winters in the South. This year's El Nino (2009-10) is the strongest since the winter of 1997-98, when powerful storms tore into Southern California, toppling beach-side homes and dumping feet of rain in the Southwest. ‘California gets hammered, and Florida gets as cold as Maine.’"

See also: El Nino Packs a Punch Far Beyond Soggy California

See also: Capitalweathergang: El Nino-linked weather arrives with a vengeance

See also: Temperature Trackers Watch Waxings and Wanings of Our Watery World

Plus: WWAYTV: El Nino Brings Southern Winter Storms

Signon-San-Diego news: El Nino Just Getting Warmed Up

Newser: Blame El Nino for Recent Storms

NOAA: Forensic Meteorology Solves the Mystery of Record Snows

El Nino and its Effect on the Southeast U.S

Effects of El Niño on Streamflow, Lake Level and Landslide Potential. US Geological Survey.

 Click here for a page on Historic El Ninos and a list of links to good websites devoted to ENSO.


Other Climate Variability Factors & The 2009-2010 Winter
 
Warm waters in the tropical Atlantic also fuel winter storms along the eastern seaboard of the USA, boosted as they cross the warm Gulf Stream. (This year these waters were the warmest on record for a February and the 2nd warmest anomaly for a month since 1948. Source.)

Much of the snow on the US eastern seaboard comes from Atlantic coastal storms encountering cold air over the land; as the moisture laden air meets cold air, instead of rain-storms areas get snow-storms.


The Pacific/North American Pattern (PNA) is a wintertime pressure pattern in the North Pacific. The positive phase of the PNA pattern is associated with above-average temperatures over western Canada and the extreme western United States, and below-average temperatures across the south-central and south-eastern U.S.

Screenshot above from NOAA. Used under fair use/educational/non commercial terms.

The PNA influences weather from Shanghai, China, to Atlanta, Georgia, every month except June and July.
A positive pattern forms when air masses over the warm waters of Hawaii and in the cool waters of Alaska's Aleutian Islands start a circulation pattern that sweeps east into North America. There the pattern interacts with a high ridge of air over the northern Rockies and a deep trough over the southern states.

During the winter of 2010 the PNA was in a positive phase. A positive PNA carries tropical moisture into British Columbia, and the United States ends up with cold and stormy weather in the Midwest and South-east; cold in the East and warmth in the West; and tornadoes - and even snowstorms - along the Gulf Coast, as polar air meet warm, moist air in the South.
Screenshot above from Metchck.com. Used under fair use/educational/non commercial terms.

Although the PNA pattern is a natural mode of climate variability, it is also strongly influenced by the El Nino Southern Oscillation (ENSO) phenomenon. The positive phase of the PNA pattern tends to be associated with Pacific warm episodes (El Nino), and the negative phase tends to be associated with Pacific cold episodes (La Nina).

The northern Pacific PDO (Pacific Decadal Oscillation) was in its warm phase. This added to  the warm moist-air in the northern Pacific.

In the Indian Ocean the dipole mode phenomenon (an increase in temperatures across the western parts of the Indian Ocean) causes colder weather patterns in its the western regions, and wetter weather in East Africa; though El Nino is also known to influence weather patterns over Africa, India and China.

Research suggests that an autumn positive (warmer) phase of the Indian Ocean dipole can also induce heavy snow over eastern Eurasia - e.g. Mongolia, Korea and Japan - during the following winter and spring seasons. This appears to have happened during the winter of 2009 - 2010, adding to the heavy snow-falls over Northern China, Korea and Mongolia. Source

 Chart above from weatherunderground.com January 13th 2010. Image used under fair-use/educational/non-commercial terms.

The positive phase of the Indian Ocean dipole during an autumn is associated with the warm (El Nino) phase of the El Nino Southern Oscillation (ENSO) over the Pacific. (As occurred this winter.)

Recent research also suggest teleconnections between the Indian Ocean dipole and ENSO may provide a means of refining forecasting El Nino events. See also here.

In a study in Nature Geoscience (21/02/2010) by Takeshi Izumo of the Research Institute for Global Change in Yokohama, Japan researchers analysing sea surface temperatures between 1981 and 2009 have found that a negative phase of the dipole - a warm western and cool eastern Indian Ocean - is an efficient predictor of El Nino 14 months before its peak, and similarly, a positive phase in the Indian Ocean Dipole often precedes La Nina."

See also: AccuWeather: It Is Not Just El Niño! El Nino & PDO

See also: Eric Berger's science blog: Why Has This Winter Been So Cold?

and: Greg Postel's weather blog: Why Did This Winter Start So Cold?

See also: Understanding Global Climate Patterns

See also: Teleconnections and Oscillations. Climate Events and What They Mean

See also: El Nino Climate Pattern Shows Effect on US Winds

As for why such large high pressure zones (-AO) formed over the Arctic in the first place in 2009-2010, one explanation I've seen is this: "What caused the cold outbreak was a stratospheric warming event during late Nov / early Dec. This caused the polar vortex to slow...split in two...and reverse direction...creating an anti-cyclonic (clock-wise) circulation aloft. The reversal took ~3 weeks to propagate to the surface...creating HIGH pressure over the pole....which in turn created favourable conditions for arctic outbreaks and high-latitude blocking...such as the one currently observed.
These reversal events occur preferentially during years (such as this one) where an east wind is observed in the tropical stratosphere...the quasi-biennial oscillation - QBO...and solar activity (sunspots) is low. Above normal snowfall in eastern Eurasia this fall played a significant role in initiating the stratospheric warming event."
Judah Cohen: Atmospheric and Environmental Research.

This may be related to the effect of the Indian Ocean dipole - and a teleconnection with El Nino (see above) - though this is speculative.

See also: 'Improved Skill of Northern Hemisphere Winter Surface Temperature Predictions Based on Land–Atmosphere Fall Anomalies.' Cohen & Fletcher. 2007.

See also: Also this Predicting Winter video (YouTube) and article at Sciencentral.

See also: Scientists Verify Predictive Model for Winter Weather - The National Science Foundation. See also: Here


Currently: These extreme cold spells, historically, haven't lasted for the same duration as an entire negative AO or NAO; and both the AO & NAO can switch from negative to positive modes within a matter of weeks.

This happened over NW Europe in mid January 2010, the NAO entered a positive phase, temperatures quickly rose, the Jet Stream moved northwards and brought warmer, moister air to the UK and the snow quickly melted.

In February 2010 the Arctic Oscillation again dipped into a negative phase. This saw the period of
Snowmageddon in the USA; snow also returned to parts of the UK, particularly southern parts. There was also
record snowfall in Moscow (23/02/10).

The PNA was in a mainly positive phase in March 2010. The AO & NAO currently fluctuate between negative and positive. High pressure remains over Greenland, but over Scandinavia and much of northern Europe it has been replaced with low pressure.
Screenshot above from Metchck.com. Used under fair use/educational/non commercial terms.
As the effects of the AO fade, El Nino will continue to dominate weather patterns once the cold spell has ended, until El Nino too fades to ENSO neutral conditions.It looks as if the configuration of factors that were responsible for this unusual winter (a strong El Nino and highly negative phases of the Arctic Oscillation & NAO) are now coming to a close.

El Nino is now losing strength, though likely to linger into summer. At present it is fuelling a stormy severe weather & tornado season in the USA, drought remains across SE Asia and South China.

The main Jet Stream over Europe is still to the south, over the Mediterranean region; but is now showing signs of moving northwards. It looks as if we're seeing a return to our 'normal' type of spring conditions, in Europe at least, but that is likely to include a few storms too.

If El Nino disappears by early summer then this year's Atlantic Hurricane season is likely to be much more active than last years (El Nino suppresses hurricane formation. (I've done a short explanation near the bottom of this page.)

NB: Metcheck.com has a page showing the day-by-day status of the NAO, AO and PNA as they each develop over the course of the current month. To go to it click Here.

It is now Tornado season in the USA. In the Pacific the cyclone season runs from December through to April; In the western Pacific are currently two cyclones; Cyclone Ului (which struck the Australian coast) and Cyclone Tomas (which struck Fiji) on 15th/16th March. In the Indian Ocean the cyclone season runs from April to December. China was engulfed in a major sandstorm in late March.

For a map showing current and anticipated positions of the Jet Stream over Europe, MetCheck have a page doing just that.


Does The 2009-2010 Winter Mean There's Global Cooling?

Some newspaper articles used this to winter predict 30 years of cooling, or of such winters. This I believe to be erroneous, if not active
disinformation.
See also here and here

If you want a reminder as to the difference between weather and climate there’s one here

A conjunction of a strong El Nino with an extremely negative Arctic Oscillations (and other factors that influence our weather) are  rare events. It is unlikely we will see those conditions repeated winter after winter; this combination will probably occur again one-day, but is highly unlikely to become the norm. One day, week, month or winter is called weather, not climate. Nor does weather in one part of the globe, at one time, represent a global trend. See also: Bear in Mind it wasn't Cold Everywhere section above.

There may be a short cluster of cold winters (see above) due to a negative NAO; but this exceptional winter can be explained by known factors that influence our weather systems, as described above. The cold and snow many of us experienced was a weather phenomenon, not a climate phenomenon. It is not connected to climate change but is part of earth's natural climate variability.


Does The 2009-2010 Winter Mean There's No Global Warming?

If you want a reminder as to the difference between weather and climate there’s one here.

a) Background natural climate variability (weather such as this winter) continues regardless of any longer term changes in climate.

b) Earth’s temperature rose by around 0.8 degrees C last century. Did you think that would banish winter forever?
Even a rise of 6 degrees C won’t do that. Many northern regions experience winter temperatures down to around minus 40 degrees C, or even lower.
The seasons will still continue regardless. (This is Earth, not Narnia!)
What’s more important about any change in earth’s temperature, both now and in the past, are the consequent changes to ocean/atmosphere interactions and precipitation patterns.
Some regions would get much wetter, some much dryer.

c) To detect climate change we must always look at trends, over decades. (See also below.)

See also: NOAA: Can Record Snowstorms & Global Warming Coexist?
See also: Is The Globe Really Warming?

Could Global Warming Cause Snowier Winters?

A warmer atmosphere carries more moisture. When warm air meets cold air it condenses and falls as precipitation. If the temperature is below zero then it falls as snow. El Nino and the PNA pattern were the cause of greater moisture in the atmosphere over eastern USA in February, and anomalously warm temperatures for much else of the world (see above), but snowy winters could be signals of a warming world, if sea temperatures were also rising.

There are only three requirements for a record snow storm:

1) An atmosphere warm enough to hold large amounts of moisture.
2) A near-record amount of moisture in the air (or a very slow moving storm) meeting 3 below.
3) Temperatures cold enough to form snow.

The record 2010 USA snowfalls: Snowmageddon, Snoverkill & Snowapocalypse weren't caused by water vapour suddenly 'just' turning to snow over those regions affected; rather travelling storms of water vapour rich air collided with masses of colder air, then the sudden change in temperature caused the water vapour to turn to snow. The water vapour came from outside the region the snow fell on (and the cold air was over).

El Nino/La Nina events could be good examples of how small changes in ocean temperatures can have major global impacts on weather patterns. El Nino/La Nina fortunately appear and disappear every few years, so we see their impacts as events that also come and go. But if any changes in ocean temperatures were to be more permanent, then those impacts would change regional climates over much longer time-scales.

One of the projections of climate change is of changes to amounts of precipitation in some regions; some will get dryer, others wetter; given that winter seasons will still occur, so could greater snowfalls occur.

As always it will be long term trends that need to be studied - as will also the behaviours of the climate variability systems: e.g. El Nino, the NPA pattern, NAO/AO etc.

See also: Thomas misrepresents climate science to claim "global warming is a falling doctrine"

See also: Discover magazine: Once Again, Cold Weather Doesn’t Disprove Global Warming

See also: CapitalWeatherGang: Blizzards "consistent with" climate change

See also: TimesOnline: If Global Warming is Real Why is it Cold?

See also: Cold Snaps Plus Global Warming Do Add Up

See also: Does record snowfall disprove global warming?

See also:
It's so Cold, there can't be Global Warming video, below:

It's So Cold There Can't be Global Warming

See also: WeatherUnderground: Heavy Snowfall in a Warming World

See also: Capital Climate: Some Further Thoughts On SuperStorm 2010


El Nino and Hurricanes: NB: One positive effect of the current El Nino is that the Caribbean and Gulf States of the USA had a quieter than average hurricane season in 2009. El Nino is so powerful he even can defeat  a hurricane!

El Ninos tend to increase the amount of wind-sheer blowing west-to-east across the tropical Atlantic; this inhibits hurricanes forming by disrupting the conditions that favour their formation.

These winds prevent hurricanes forming their familiar towering cylindrical shape by sheering off their tops or distorting them so they break-apart. A few hurricanes manage to make landfall, but not as many as in a non El Nino year.

It is expected that El Nino will be gone by summer 2010, so this year's hurricane season will be more active than last years.


Weather & Climate Variability Sites Worth Keeping An Eye On Include:

WeatherUnderground - AccuWeather - Metcheck - LiveWeatherBlogs - Washington Post: Capital Weather Gang. - MetOffice - NOAA -

NOAA CPS - WeatherOnline - 13 Weather Authority Blog - Australian Bureau of Meteorology - UM Weather - Environment Canada-weather -

World Weather.org - Unisys.comA further list (of mainly US) weather sites is here.

Tim Dennell. Sheffield. UK.

I have been running this page since early January 2010. I started it to satisfy my own curiosity as to why this winter had been so cold in the UK, but as the 2009-2010 winter turned out to be exceptional I had no choice but to continue updating it.
I also have an interest in El Nino events; it is clear that El Nino plays a significant role in climate variability - and altered weather patterns worldwide this winter.

The winter of 2009 - 2010 is now over. El Nino impacts of course will continue until it fades away; the cyclone and tornado seasons are underway, this year's Atlantic hurricane season is likely to be active; but other than any linkage with El Nino events these are seasonal occurrences and not connected with the factors that caused the exceptional winter of 2009-2010.

Should a similar conjunction of events (-AO plus strong El Nino etc) occur at some point in the future then I hope this page will give people something to compare winters with.
Those that experienced the 2009-2010 winter first-hand should also find it of interest.

Videos sourced from YouTube.
Images
used in page header sourced from Flickr, used under Creative Commons licence.
Other images
and screen-shots used under fair-use/educational/non-commercial terms. I have credited source where possible.

This site: Creative Commons licence. Share-alike. Yeah, you can copy and paste too. Attribution's always nice.
If you like this page please link to it and post the URL into site comments, aggregators etc.
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I also run - and am developing - a site devoted to looking at the causes and consequences of the Medieval Warm Period.
I also produced a site devoted to the Paleocene Eocene Thermal Maximum.

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used under fair-use/educational/non-commercial terms.
My email is: climatehistory@googlemail.com