Portland Climate Statistics

Temperature

Portland's annual average temperature has warmed by about 3 degrees F since 1940. This warming trend is statistically significant. The warmest year on record was 2015. The warming rate over the most recent 30 years is greater than the warming rate over the entire record. Data updated through 2023.

Portland's annual average daily maximum temperature has warmed by about 2.6 degrees F since 1940. This warming trend is statistically significant. The warming rate of the most recent 30 years is greater than the warming rate over the entire record. Data updated through 2023.

Portland's annual average daily minimum temperature has warmed by about 3.4 degrees F since 1940. This warming trend is statistically significant. The warming rate of the most recent 30 years is similar to the warming rate over the entire record. Data updated through 2023.

Portland's winter average temperature has warmed by about 2.1 degrees F since 1940. This warming trend is statistically significant. Winter is defined as December-February. The warmest winter on record was 2015. The last 30 years have seen no trend. Data updated through 2024.

Portland's summer average temperature has warmed by about 4.6 degrees F since 1940. This warming trend is statistically significant. Summer is defined as June-August. The warmest summer on record was 2015. The most recent 30 years exhibit a greater warming rate than over the entire record. Data updated through 2023.

Portland's spring average temperature has warmed by about 2.7 degrees F since 1940. This warming trend is statistically significant. Spring is defined as March-May. The warmest spring on record was 1992. The warming trend over the most recent 30 years is slightly greater than over the entire record but is not statistically significant. Data updated through 2024.

Portland's fall average temperature has warmed by about 2.9 degrees since 1940. This warming trend is statistically significant. Fall is defined as September-November. The warmest fall on record was 2022. The warming trend over the most recent 30 years is consistent with the trend over the entire record. Data updated through 2023.

Charts show the seasonal mean temperature for each year starting in 1940. The solid gray line shows the linear trend of the 1940-present time period. The solid blue line shows the linear trend over the most recent 30-year period. The dashed blue line shows the standard 30-year 1991-2020 climatological average while the gray dashed line shows the average for the entire record. The thick black line is the 10-year running mean.

*Computed trends are based on a linear fit. These should be interpreted as approximate since trends may not be linear in reality.

**Significance is assessed using a Mann-Kendall test at the 5% level.

Linear trends in annual averages of daily mean temperature ending in the year indicated on x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in degrees F per year and significant trends are indicated with a black dot.

Linear trends in spring averages of daily mean temperature ending in the year indicated on the x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in degrees F per year and significant trends are indicated with a black dot.

Linear trends in winter averages of daily mean temperature ending in the year indicated on the x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in degrees F per year and significant trends are indicated with a black dot.

Linear trends in summer averages of daily mean temperature ending in the year indicated on the x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in degrees F per year and significant trends are indicated with a black dot.

The sign and magnitude of a trend can depend on the starting and ending point of the trend calculation. The charts in this section show the linear trend in daily mean temperature based on different starting and end points in the trend calculation. Trends computed over short time spans are both positive and negative, sometimes large and rarely significant. Longer trends tend to be less variable, with most significant trends being positive (warming). The natural internal variability in Portland's temperature climatology is also apparent in these figures.

Linear trends in fall averages of daily mean temperature ending in the year indicated on the x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in degrees F per year and significant trends are indicated with a black dot.

Portland now experiences about 21 more days above 85 degrees F per year, on average, than it did in 1940. This increasing trend is statistically significant. The record number of days of 85 degrees or warmer was in 2021 and 2022. Data updated through 2023.

Portland now experiences about 11 more days above 90 degrees F per year, on average, than it did in 1940. Thi3s increasing trend is statistically significant. The record number of days of 90 degrees or warmer was in 2018. Data updated through 2023.

Portland now experiences about 1 more day above 100 degrees F per year, on average, than it did in 1940. This increasing trend is statistically significant. The record number of days of 100 degrees or warmer is tied between 1941, 1977, 2021, and 2022. Data updated through 2023.

The hottest day of each year has warmed by about 4.9 degrees F since 1940. This warming trend is statistically significant. The hottest day on record was in June 2021. Data updated through 2023.

The hottest night of each year has warmed by about 5.3 degrees F since 1940. This warming trend is statistically significant. The hottest night on record was in June 2021. Data updated through 2023.

The coldest night of each year has warmed by about 5.8 degrees F since 1940. This warming trend is statistically significant. Data updated through 2023.

The number of days that drop below 32 has decreased by about 18 days since 1940. This decreasing trend is statistically significant. Data updated through 2023.

The coldest day of each year has warmed by about 3.1 degrees F since 1940. This warming trend is not statistically significant. Data updated through 2023.

The number of days that never warm above freezing have decreased by 2.8 days since 1940. This decreasing trend is not statistically significant. Data updated through 2023.

(Left) Record cold days are still set, although more records for cold stays stand in the earlier half of the data record. (Right) Most records for cold nights were set prior to 1980, with a large reduction in the number of records cold nights being set in recent decades. Data updated through 2023.

(Left) More record warm days have been set in the later half of the data record, although the increase in the frequency of setting new record warm days has only increased gradually. (Right) The majority of record warm nights have been set in the later half of the data record. Recent years have seen many record warm nights set indicating that extreme warm nights are increasing at a greater rate than extreme warm days. Data updated through 2023.

The number of fall days that drop below freezing has declined by about 2.4 days since 1940. This decreasing trend is not statistically significant. Updated through 2023.

The number of summer days with a high cooler than 65 degrees has declined by about 3.5 days since 1940. This decreasing trend is statistically significant. Updated through 2023.

The number of winter days that drop below freezing has declined by about 10.5 days since 1940. This decreasing trend is statistically significant. Note winter is defined as Dec, Jan, Feb of a calendar year, not as a coherent season. Updated through 2023.

The number of summer days with a high cooler than 70 degrees F has declined by about 9.3 days since 1940. This decreasing trend is statistically significant. Updated through 2023.

The number of spring days that drop below freezing has declined by about 5.6 days since 1940. This decreasing trend is statistically significant. Data updated through 2023.

The number of summer days with a high cooler than 80 degrees F has declined by about 21 days since 1940. This decreasing trend is statistically significant. Updated through 2023.

The average winter diurnal temperature range (Tmax-Tmin). The negative trend is statistically significant. Data updated through 2024.

The average summer diurnal temperature range (Tmax-Tmin). There is no trend. Data updated through 2023.

The average spring diurnal temperature range (Tmax-Tmin). The negative trend is not statistically significant. Data updated through 2023. The negative trend is statistically significant and the mean spring diurnal temperature range has decreased by about 1.4 degrees since 1940.

The average fall diurnal temperature range (Tmax-Tmin). The negative trend is statistically significant and the mean fall diurnal temperature range has decreased by about 1.6 degrees since 1940. Data updated through 2023.

The diurnal temperature range is the difference between the daily high and daily low temperature. The shoulder seasons exhibit a significant decrease in the mean diurnal temperature range while summer and winter do not.

Precipitation

Portland's annual mean precipitation has decreased by about 2 inches since 1940. This decreasing trend is not statistically significant. Data updated through 2023.

Portland's winter mean precipitation has decreased by about 1.4 inches since 1940. This decreasing trend is not statistically significant. Data updated through 2024.

Portland's spring mean precipitation has increased by about 1.3 inches since 1940. This increasing trend is not statistically significant. Data updated through 2024.

Portland's summer mean precipitation has decreased by about .38 inches since 1940. This decreasing trend is not statistically significant. Data updated through 2023.

Portland's fall mean precipitation has decreased by about 1.1 inches since 1940. This decreasing trend is not statistically significant. Data updated through 2023.

There are no significant trends in Portland's mean annual or seasonal precipitation climatology. Portland's precipitation climatology is, however, characterized by a large degree of natural variability including on the year-to-year and multi-year time scales. Dashed lines indicate the 1991-2020 climatological mean and the thick black line is the 10-year running mean.

The mean annual precipitation rate in Portland has decreased by about .02 inches/day since 1940. This decreasing trend is not statistically significant. Data updated through 2022.

The number of rainy days in a year in Portland has increased by about 2.4 days since 1940. This increasing trend is not statistically significant. Data updated through 2022.

The number of days in a year with over 1 inch of rain has decreased by about 2.9 days since 1940. This decreasing trend is not statistically significant. Data updated through 2022.

The amount of rain falling on the wettest day of the year has shown essential no change over the 1940-2022 period in Portland. Data updated through 2022.

The number days with any precipitation in winter shows essentially no trend. Note winter is defined as Dec, Jan, and Feb of a calendar year, not a coherent season. Data updated through 2023.

The number of days with any precipitation in spring has increased by over 7 days since 1940. This increasing trend is statistically significant. Data updated through 2023.

The number of days with any precipitation in summer shows a decreasing trend, however the trend is not statistically significant. Data updated through 2023.

The number of days with any precipitation in fall shows essentially no trend in Portland. Data updated through 2023.

Linear trends in annual mean precipitation ending in the year indicated on x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in inches per year and significant trends are indicated with a black dot.

Linear trends in spring mean precipitation ending in the year indicated on x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in inches per year and significant trends are indicated with a black dot.

Linear trends in winter mean precipitation ending in the year indicated on x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in inches per year and significant trends are indicated with a black dot.

Linear trends in fall mean precipitation ending in the year indicated on x-axis and beginning 2-30 years prior as indicated on the y-axis. Trends are in inches per year and significant trends are indicated with a black dot.

The charts in this section show the linear trend in annual mean precipitation based on different starting and end points in the trend calculation. Trends computed over short time spans are both positive and negative, sometimes large and rarely significant. Longer trends tend to be less variable, however there is no indication of a systematic climate change signal in any season's precipitation. Natural internal variability in Portland's precipitation climatology is clearly apparent in these figures.

Scatter plots show seasonal mean temperature versus seasonal total precipitation for each year. Years falling to the left of the vertical red line were cooler than the long-term (full record) average. Years falling to the right of the vertical red line were warmer than the long-term (full record) average. Years falling above the horizontal green line were wetter than the-term (full record) average. Years falling below the horizontal green line were drier than the long-term (full record) average. Years from 2010 to present are in red.

Atmospheric Circulation

There is little change in the number of ridge days over Portland in winter.

There has been an increase in winter trough days over Portland in winter. Troughs are less common than ridges because the mean circulation pattern of Pacific Northwest in winter has a stationary ridge.

Ridges and troughs are types of atmospheric circulation patterns that affect temperature and precipitation. They can be defined several ways. Here we define a ridge day if the 500 hPa geopotential height over Portland has a zonal anomaly of 100 meters or greater. A trough day is when the zonal anomaly is -100 meters or less. This follows Loikith et al. (2022). In general, ridges are associated with warmer and drier than average weather while troughs are the opposite. All charts are updated through 2021.

There has been a decrease in ridge days over Portland in spring.

There has been an increase in trough days over Portland in spring.

There has been little change in the number of ridges days over Portland in summer.

There has been a decrease in trough days over Portland in summer.

There has been a small decrease in fall ridge days over Portland during fall.

There has been an increase in trough days over Portland during fall.

All seasons except for summer show a positive trend in trough days and a negative trend in ridge days. It should be noted that ridges and troughs do not have to be directly overhead for them to cause weather impacts.