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Weather is extremely important for aviation, and controllers need to know how to read weather reports and understand how the weather will impact operations.
The real world ZSE ARTCC produces a regular pre-duty weather briefing which is a helpful summary of current weather affecting ATC.
For details on these topics and much more, see the vZAB seminar on aviation weather.
METAR/TAF clouds are in AGL (above ground level)
METAR/TAF winds are in true heading
Flying is done in magnetic heading
In ZSE, subtract 20 from the true wind to get the magnetic wind heading
The general rule is: If you read it, it's true. If you hear it, it's magnetic.
Minimums
Minimums
For aircraft to fly at an airport under Visual Flight Rules, the weather must meet specific minimums: 3 miles visibility and 1000 foot ceilings. The ceiling is defined as the lowest BKN or OVC layer.
If the visibility is at least 1 mile, airplanes may request Special VFR to enter or depart the airport area.
METAR
METAR
METeorological Aerodrome Reports
METARs typically come from airports. Reports are generated once an hour, but if conditions change significantly at a staffed location, a report known as a special (SPECI) may be issued.
A typical METAR contains data for the temperature, dew point, wind direction, and speed, precipitation, cloud cover and heights, visibility, and barometric pressure. A METAR may also contain information on precipitation amounts, lightning, and other information that would be of interest to pilots or meteorologists such as a pilot report or PIREP, color states, and runway visual range (RVR).
METARs and TAFs have many abbreviations and acronyms. Click here to see a list. Another helpful site is metar-taf.com which provides a plain text description and graphical depiction of the conditions in the METAR and TAF.
Here is a METAR taken from KHIO:
METAR KHIO 192253Z 12012KT 10SM SCT019 BKN055 09/04 A2966 RMK AO2 SLP044 T00890044
Each item of the METAR is decoded as follows:
METAR: Type of Report
KHIO: Station Identifier: Portland-Hillsboro Airport
192253z: Date and Time: 19th day of the month at time 22:53 Zulu
12012KT: Wind Direction and Speed: Wind is 120° true at 12 knots
10SM: Visibility, at least 10 statute miles (a METAR will not show anything beyond 10SM)
SCT019: Clouds Scattered at 1,900 feet AGL
BKN055: Clouds Broken at 5,500 feet AGL (which will be the ceiling)
09/04: Temperature 9° Celsius, Dewpoint 4° Celsius
A2966: Altimeter setting is 29.66 inches of mercury (inHg)
RMK: Remarks follow...
AO2: This is an automated station with a precipitation discriminator (rain vs. snow)
SLP044: Sea Level Pressure 1004.4 hPa
T00890044: More precise temperature: 8.9° Celsius, dewpoint 4.4° Celsius
TAF
TAF
Terminal Area Forecasts
TAFs are issued at least four times a day, every six hours, for major civil airfields: 0000, 0600, 1200 and 1800 UTC, and generally apply to a 24- or 30-hour period, and an area within approximately five statute miles from the center of an airport runway complex. Not all airports with a METAR will have a TAF.
Here is a TAF taken from KHIO:
KHIO 192323Z 2000/2024 12011KT P6SM BKN060
FM200500 09004KT P6SM SCT025
FM201400 VRB03KT 5SM BR BKN025
FM202000 VRB03KT P6SM SCT250
KHIO: Station I.D
192323Z: Date and Time, 19th day of the month at time 23:23 Zulu
2000/2024: Valid Time Period, Starts on the 20th day at 00:00z, Ends on the 20th day at 24:00z
12011KT: Wind 120° at 11 Knots
P6SM: Visibility More than 6 Statute Miles
BKN060: Clouds Broken at 6,000 feet AGL
FM200500: From the 20th day at 05:00z
09004KT: Wind 090° at 4 Knots
P6SM: Visibility More than 6 Statute Miles
SCT025: Clouds Scattered at 2,500 feet AGL
FM201400: From the 20th day at 14:00z
VRB03KT: Wind Variable at 3 Knots
5SM: Visibility 5 Statute Miles
BR: MIST
BKN025: Clouds Broken at 2,500 feet AGL
FM202000: From the 20th day at 20:00z
VRB03KT: Wind Variable at 3 Knots
P6SM: Visibility More than 6 Statute Miles
SCT250: Clouds Scattered at 25,000 feet AGL
Practice using the information on this page to decode the following METAR:
METAR KHIO 100553Z 09006KT 2SM -RA BR SCT005 BKN010 OVC016 05/04 A3007 RMK AO2 DZE0457RAB0457 SLP193 T00500039
SIGMETS and AIRMETs
SIGMETS and AIRMETs
These are types of weather advisories that are issued for pilots about weather phenomena which may affect safety of aircraft operations. You will see these in aviation weather briefings. The main importance for ATC is knowing what kinds of significant weather might be expected that will affect airport operations or aircraft routing. More detail is available in AIM 7-1-6.
sigmets
sigmets
Significant Meteorological Information
A SIGMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena which is expected to affect the safety of aircraft operations. The key word here is that this weather could be significant to any aircraft.
There are three main types of SIGMET:
Volcanic Ash
Tropical Cyclone
Other
Thunderstorm types
Turbulence types
Mountain waves
Icing/Sleet/Hail
Dust or sand storms
Radioactive Cloud
The US has an additional type of SIGMET: the Convective SIGMET. This is issued for one of three types of thunderstorms:
Line
Area
Embedded
airmets
airmets
Airmen's Meteorological Information
An AIRMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena that may affect the safety of aircraft operations, but at intensities lower than those which require the issuance of a SIGMET. They are intended to inform all pilots but will be of more importance to VFR flights or aircraft operations particularly sensitive to hazardous weather.
There are three types of AIRMET identified by phonetic letters:
Sierra - Ceiling and visibility
IFR (Ceilings less than 1000 feet and/or visibility less than 3 miles affecting over 50% of the area at one time)
Extensive mountain obscuration
Tango - Turbulence
Moderate turbulence
Sustained surface winds of 30 knots or greater
Non convective low−level wind shear
Zulu - Icing
Moderate icing along with freezing levels
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