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State Climate Summaries

WASHINGTON

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WASHINGTON

Washington’s location in the heart of the middle latitudes exposes it to frequent storm systems associated with the mid-latitude jet stream. Its climate varies widely from the western to the eastern parts of the state due to the physical barrier of the Cascade Mountains. The Pacific Ocean provides abundant moisture, causing frequent precipitation west of the Cascade Mountains that is orographically enhanced in some places. The eastern side generally receives less precipitation due to blocking of moisture by the mountains. Temperatures in the central and eastern portions of the state are not as strongly moderated by the ocean and exhibit a greater annual range compared to the western side of the state.

 

Figure 1

Observed and Projected Temperature Change

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Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for Washington. Observed data are for 1900–2014. Projected changes for 2006–2100 are from global climate models for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions). Temperatures in Washington (orange line) have risen around 1.5°F since the beginning of the 20th century. Shading indicates the range of annual temperatures from the set of models. Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Historically unprecedented warming is projected to continue through the 21st century. Less warming is expected under a lower emissions future (the coldest years being about as warm as the hottest year in the historical record; green shading) and more warming under a higher emissions future (the hottest years being about 11°F warmer than the hottest year in the historical record; red shading). Source: CICS-NC and NOAA NCEI.

Since the beginning of the 20th century, temperatures have risen approximately 1.5°F and temperatures over the past three decades have been warmer than any other historical period (Figure 1). The year of 2015 was the hottest on record with a statewide average temperature of 50.0°F, 3.9°F above the long-term average. The overall warming trend is evident in the number of days with extreme nighttime temperatures. Since 1990, the state has seen below average numbers of very cold nights (nights with minimum temperature below 0°F) and below freezing days (days with maximum temperature below 32°F) (Figure 2a). Warm nights (days with minimum temperature above 60°F in Eastern Washington and above 65°F in Western Washington) have been above average since 1990 (Figure 3). The number of very hot days (days with maximum temperature above 95°F) has been quite variable, with numbers well above average occurring in the first decade of the 21st century, but below average numbers occurring over 2010–2014 (Figure 2b).

Figure 2

Figure 2a

2a

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Figure 2b

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Figure 2c

 

2c

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Figure 2d

2d

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Figure 2: The observed (a) number of very cold nights (annual number of days with minimum temperature below 0°F) for Eastern Washington and freezing days (annual number of days with maximum temperature below 32°F) for Western Washington, (b) very hot days (annual number of days with maximum temperature above 95°F for Eastern Washington and above 90°F for Western Washington), (c) annual precipitation, and (d) extreme precipitation (annual number of days with precipitation greater than 1 inch for Eastern Washington and greater than 2 inches for Western Washington), averaged over 5-year periods. The values Figures 2a, 2b, and 2d are averages from all available long-term reporting stations (for Western Washington 7 for both temperature and precipitation and for Eastern Washington 9 for temperature and 11 for precipitation). The values for Figure 2c are from NCEI’s version 2 climate division dataset. The dark horizontal lines represent the long-term average. Since 1990, Washington has experienced below average below freezing days and very cold nights, indicative of warming in the region. The state has experienced a variable number of hot days since 1990. Both annual precipitation and the number of extreme precipitation events have varied widely since the beginning of the 20th century. Source: CICS-NC and NOAA NCEI.

Observed Number of Warm Nights (Eastern Washington and Western Washington)

 Observed Number of Warm Nights (Eastern Washington and Western Washington)

Figure 3: The observed number of warm nights (annual number of days with minimum temperature above 60°F for Eastern Washington and above 65°F for Western Washington) for 1900–2014, averaged over 5-year periods; these values are averages from all available long-term reporting stations (9 for eastern Washington and 7 for western Washington). The dark horizontal lines represent the long-term average. The number of warm nights is highly variable, with a typical station averaging 3–4 such days annually. Since 1990, the number has been well above the long-term average. Source: CICS-NC and NOAA NCEI.

Annual precipitation exhibits wide regional variations across the state. Portions of the Olympic Peninsula receive upwards of 150 inches of precipitation annually, while annual totals average less than 10 inches along the Columbia River in eastern interior Washington. Statewide annual precipitation has ranged from a low of 26 inches in 1929 to a high of 54.95 inches in 1996. The driest multi-year periods were the late 1920s, early 1940s, and late 1980s while the wettest periods were the 1950s, early 1980s, and late 1990s (Figure 2c). The driest 5-yr period on record was 1926–1930 with an annual average of 34.6 inches while the wettest was 1995–1999 with 51.0 inches. Washington has not experienced any long-term trend in the number of extreme precipitation events (Figure 2d).

Most of Washington’s precipitation falls during the winter months and the Cascades can receive upwards of 400 inches of snowfall annually. Snowpack in the mountains provides an important source of water during the drier summer months (Figure 4). Precipitation falling as rain instead of snow can have negative impacts on critical industries, such as the timber and agricultural industry, which are also vulnerable to extreme temperatures.Wildfires during the drier summer months are of particular concern. The 2015 wildfire season was the most destructive in Washington’s history, with over 1 million acres burned, more than 6 times the average.

Fish Lake Snow Course

Fish Lake Snow Course

Figure 4: Time variations in April 1 snow water equivalent at the Fish Lake, Washington, snow course site. Snow water equivalent is a common measure for the amount of water contained within the snowpack. Snowpack water content varies widely from year to year, but with a general downward trend. The extremely low snowpack levels in 2005 (3rd lowest) and 2015 (record lowest) were due to below average precipitation and very warm temperatures during the first three months of the year. Source: USDA Natural Resources and Conservation Service.

Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a lower pathway of greenhouse gas emissions, temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records (Figure 1). Overall, warming will lead to increases in heat wave intensities but decreases in cold wave intensities. Unlike in other parts of the United States, Seattle and other urban areas are rarely exposed to very high temperatures. Future heat waves, particularly an increase in the frequency of hot nights, could stress these communities, which are not well adapted to such events.

Temperature increases will affect basins with significant snowmelt contributions to streamflow. Projected rising temperatures will raise the elevation of the snow line in the mountains. This will increase the proportion of precipitation falling as rain instead of snow, leading to less snow accumulation during the winter. Rainfall is expected to be the dominant form of precipitation across the majority of the state by the end of the 21st century. Higher spring temperatures will also result in earlier melting of the snowpack, with average snowpack projected to decline by up to 70% by the end of the 21st century. This will further decrease water availability during the already dry summer months and increase the risk of spring flooding due to earlier spring peak flows. Projected increases in heavy rainfall events by mid-century could further increase flood risk. Reductions in summer flow (projected to occur in 80% of the state’s watersheds) will have important ecological implications, and are of particular concern in some areas from hydropower and irrigation water supply perspectives.

Increasing temperatures raise concerns for sea level rise in coastal areas. Since 1880, global sea level has risen by about 8 inches. It is projected to rise another one to four feet by 2100 as a result of both past and future greenhouse gas emissions due to human activities (Figure 5). Sea level rise has caused an increase in tidal floods associated with nuisance-level impacts. Nuisance floods are events in which water levels exceed the local threshold (set by NOAA’s National Weather Service) for minor impacts. These events can damage infrastructure, cause road closures, and overwhelm storm drains. As sea level has risen along the Washington coastline, the number of tidal flood days has also increased, with the greatest number occurring in 2010–2011 (Figure 6).

 

Past and Projected Changes in Global Sea Level

Past and Projected Changes in Global Sea Level

Figure 5: Estimated, observed, and possible future amounts of global sea level rise from 1800 to 2100, relative to the year 2000. The orange line at right shows the most likely range of 1 to 4 feet by 2100 based on an assessment of scientific studies, which falls within a larger potential scenario range of 0.66 feet to 6.6 feet. Source: Melillo et al. 2014 and Parris et al. 2012.

Observed and Projected Annual Number of Tidal Floods for Seattle WA

Observed and Projected Annual Number of Tidal Floods for Seattle WA

Figure 6: Number of tidal flood days per year for the observed record (orange bars) and projections for two possible futures: lower emissions (light blue) and higher emissions (dark blue) per calendar year for Seattle, WA. Sea level rise has caused an increase in tidal floods associated with nuisance-level impacts. Nuisance floods are events in which water levels exceed the local threshold (set by NOAA’s National Weather Service) for minor impacts, such as road closures and overwhelmed storm drains. The greatest number of tidal flood days (all days exceeding the nuisance level threshold) occurred in 2010–2011 at Seattle. Projected increases are large even under lower emissions pathway. Near the end of the century, under a higher emissions pathway, some models project tidal flooding to occur 200 days per year. To see these and other projections under additional emissions pathways, please see the supplemental material on the State Summaries website (http://stateclimatesummaries.globalchange.gov) Source: NOAA NOS.

Although projections of overall annual precipitation are uncertain, summer precipitation is projected to decrease (Figure 7). Drier conditions during the summer could increase reliance on diminishing snowmelt for irrigation. Additionally, drier summers, along with higher temperatures and earlier melting of the snowpack, would tend to increase the frequency and extent of wildfires.

 

Projected Change in Winter Precipitation

Projected Change in Winter Precipitation

Figure 7: Projected changes in winter precipitation (%) for the middle of the 21st century compared to the late 20th century under a higher emissions pathway. Winter precipitation is projected to increase throughout Washington, but these changes are small relative to the natural variability in this region. Source: CICS-NC, NOAA NCEI, and NEMAC.

Lead Authors:
Rebekah Frankson, Kenneth E. Kunkel
Contributing Authors:
Sarah Champion, David Easterling, Laura Stevens, Karin Bumbaco, Nick Bond, Joe Casola, William Sweet
Recommended Citation:
Frankson, R., K. Kunkel, S. Champion, D. Easterling, L. Stevens, K. Bumbaco, N. Bond, J. Casola, and W. Sweet, 2017: Washington State Climate Summary. NOAA Technical Report NESDIS 149- WA, 4 pp.

Resources

  1. Bumbaco, K. A. et al., 2013. History of Pacific Northwest Heat Waves: Synoptic Pattern and Trends. Journal of Applied Meteorology and Climatology, 52, 1618-1631.
  2. Kunkel, K.E, L.E. Stevens, S.E. Stevens, L. Sun, E. Janssen, D. Wuebbles, K.T. Redmond, and J.G. Dobson, 2013: Regional Climate Trends and Scenarios for the U.S. National Climate Assessment. Part 6. Climate of the Northwest U.S., NOAA Technical Report NESDIS 142-6, 75 pp. [Available online at https://www.nesdis.noaa.gov/content/technical-reports]
  3. NAS, 2012: California sea level projected to rise at higher rate than global average; slower rate for Oregon, Washington, but major earthquake could cause sudden rise, published June 22, 2012, retrieved January 5, 2017, National Academy of Sciences. [Available online at http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=13389]
  4. NOAA, cited 2016: Climate at a Glance: U.S. Time Series, published December 2016, retrieved on December 30, 2016, National Oceanic and Atmospheric Administration National Centers for Environmental Information. [Available online at http://www.ncdc.noaa.gov/cag/]
  5. NOAA, cited 2016: Climate of Washington, National Oceanic and Atmospheric Administration. [Available online at https://www.ncdc.noaa.gov/climatenormals/clim60/states/Clim_WA_01.pdf]
  6. NOAA, cited 2017: State of the Climate: National Overview for July 2014, published online August 2014, retrieved on January 5, 2017, National Oceanic and Atmospheric Administration National Centers for Environmental Information. [Available online at http://www.ncdc.noaa.gov/sotc/national/201407]
  7. Snover, A.K, G.S. Mauger, L.C. Whitely Binder, M. Krosby, and I. Tohver, 2013: Climate Change Impacts and Adaptation in Washington State: Technical Summaries for Decision Makers. State of Knowledge Report prepared for the Washington State Department of Ecology. Climate Impacts Group, University of Washington, 130 pp. [Available online at http://cses.washington.edu/db/pdf/snoveretalsok816lowres.pdf]
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