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NOAA National Centers
for Environmental Information

State Climate Summaries 2022

IDAHO

Key Messages   Narrative   Downloads  

Lochsa River
Image by Jim Black from Pixabay

Key Message 1

Temperatures in Idaho have risen almost 2°F since the beginning of the 20th century. Under a higher emissions pathway, historically unprecedented warming is projected during this century.

Key Message 2

Winter and spring precipitation is projected to increase during this century. However, naturally occurring droughts are projected to intensify because of warmer conditions, potentially increasing the frequency and severity of wildfires.

Key Message 3

Higher temperatures are projected to cause more of winter and spring precipitation to fall as rain instead of snow, which may increase flood risks.

30 Cheval, Sun Valley Idaho
Photo by Thomas Hawk
License: CC BY-NC

IDAHO

Due to Idaho’s northerly latitude and location in the interior of North America, its climate has large seasonal temperature differences, with cold winters and pleasantly warm summers. Wide ranges in elevation affect regional precipitation. The low-elevation regions of southern Idaho are shielded by mountains to the east and west, reducing the amount of moisture that can penetrate the area and resulting in generally low amounts of precipitation. By comparison, the higher elevations of northern and central Idaho receive up to four times the amount of rain and snow. The majority of precipitation falls during the cool season (November–May). Idaho is reliant on mountain snowpack for water storage.

   

Figure 1

Observed and Projected Temperature Change
Time series of observed and projected temperature change (in degrees Fahrenheit) for Idaho from 1900 to 2100 as described in the caption. Y-axis values range from minus 3.9 to positive 16.6 degrees. Observed annual temperature change from 1900 to 2020 shows variability and ranges from minus 2.7 to positive 4.5 degrees. By the end of the century, projected increases in temperature range from 2.2 to 9.4 degrees under the lower emissions pathway and from 6.1 to 15.6 degrees under the higher pathway.
Figure 1: Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for Idaho. Observed data are for 1900–2020. 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 Idaho (orange line) have risen almost 2°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 during this century. Less warming is expected under a lower emissions future (the coldest end-of-century projections being about 2°F warmer than the historical average; green shading) and more warming under a higher emissions future (the hottest end-of-century projections being about 15°F warmer than the historical average; red shading). Sources: CISESS and NOAA NCEI.

Temperatures in Idaho have risen almost 2°F since the beginning of the 20th century (Figure 1). The year 2015 was the second-hottest (after 1934) since records began in 1895, with a statewide average temperature of 46.4°F. As with precipitation, Idaho’s temperature climate exhibits regional variation. In the southwestern city of Boise, the average (1991–2020 normals) high temperature in July is 92.7°F, while in the northern town of Coeur D’Alene, it is 82.8°F. In January, average low temperature is colder in Boise (25.5°F) than in Coeur D’Alene (26.2°F). Statewide, the number of very hot days (Figure 2) has been highly variable since 2000 but shows no overall trend. The number of warm nights (Figure 3) has been above average since 2000, exceeding the previous highest values of the late 1920s and 1930s. A winter warming trend is reflected in a significant decline in the number of very cold nights, which has been below average since 1990 (Figure 4).

   
Observed Number of Very Hot Days
Graph of the observed annual number of very hot days for Idaho from 1900 to 2020 as described in the caption. Y-axis values range from 0 to 25 days. Annual values show year-to-year variability and range from about 3 to 23 days. Multiyear values also show variability and are mostly near or above the long-term average of 12 days between 1900 and 1974 but are all near or below average between 1975 and 1999. With the exception of the 2010 to 2014 period, multiyear values are all above average since 2000. The multiyear periods of the late 1920s and 1930s, which are above average, have the highest multiyear values, and the 1980 to 1984 period has the lowest.
Figure 2: Observed annual number of very hot days (maximum temperature of 95°F or higher) for Idaho from 1900 to 2020. Dots show annual values. Bars show averages over 5-year periods (last bar is a 6-year average). The horizontal black line shows the long-term (entire period) average of 12 days (note that the average for individual reporting stations varies greatly because of the state’s large elevation range). The number of very hot days has been highly variable since 2000 but with no overall trend. The highest number of these days occurred during the late 1920s and 1930s. Sources: CISESS and NOAA NCEI. Data: GHCN-Daily from 10 long-term stations.
   
Observed Number of Warm Nights
Graph of the observed annual number of warm nights for Idaho from 1900 to 2020 as described in the caption. Y-axis labels range from 0 to 7 nights. Annual values show year-to-year variability and range from 0.6 to 6.0 nights. Multiyear values also show variability and are mostly near or above the long-term average of 2.1 nights between 1900 and 1939 but are all below average between 1940 and 1989. Since 1990, multiyear values are mostly above average. The 1950 to 1954 period has the lowest multiyear value and the 2000 to 2004 and 2010 to 2014 periods have the highest.
Figure 3: Observed annual number of warm nights (minimum temperature of 65°F or higher) for Idaho from 1900 to 2020. Dots show annual values. Bars show averages over 5-year periods (last bar is a 6-year average). The horizontal black line shows the long-term (entire period) average of 2.1 nights (note that the average for individual reporting stations varies greatly because of the state’s large elevation range). The number of warm nights has been above average since 2000, exceeding the previous highest values of the late 1920s and 1930s. Sources: CISESS and NOAA NCEI. Data: GHCN-Daily from 10 long-term stations.
   
Observed Number of Very Cold Nights
Graph of the observed annual number of very cold nights for Idaho from 1900 to 2020 as described in the caption. Y-axis values range from 0 to 30 nights. Annual values show year-to-year variability and range from about 1 to 27 nights. Multiyear values also show variability and are mostly near or above the long-term average of 12 nights between 1900 and 1989 but are all below average since 1990. The 2000 to 2004 period has the lowest multiyear value and the 1945 to 1949 period the highest.
Figure 4: Observed annual number of very cold nights (minimum temperature of 0°F or lower) for Idaho from 1900 to 2020. Dots show annual values. Bars show averages over 5-year periods (last bar is a 6-year average). The horizontal black line shows the long-term (entire period) average of 7.4 nights (note that the average for individual reporting stations varies greatly because of the state’s large elevation range). The number of very cold nights has been below average since 1990. The greatest number of these nights occurred during the 1945−1949 period, with a multiyear average of 12 nights. Sources: CISESS and NOAA NCEI. Data: GHCN-Daily from 10 long-term stations.

Total annual precipitation at long-term monitoring stations ranges from more than 40 inches at some northern mountain sites to less than 10 inches at sites in the southwest. Statewide, there is substantial variability but no overall trend in total annual precipitation for the 126-year period of record (Figure 5). However, the number of 1-inch extreme precipitation events has been above average for the past 16 years and has been trending upward since 2000 (Figure 6). A record-high number of events (more than 2 per year) occurred during the 1995–1999 period. The driest year on record for Idaho was 1935, with a total of 16.2 inches of precipitation, while the wettest was 1996, with 32.10 inches. The driest consecutive 5-year interval was 1928–1932, with an annual average of 20.1 inches, and the wettest was 1980–1984, with an annual average of 28.8 inches. Annual total snowfall ranges from about 10 to 20 inches in the southern lowlands to more than 100 inches in the higher mountains. Snowpack accumulation in the mountains is the state’s major source of water. It is highly variable from year to year and has generally declined since the mid-20th century (Figure 7).

   
Observed Annual Precipitation
Graph of the observed total annual precipitation for Idaho from 1895 to 2020 as described in the caption. Y-axis values range from 15 to 35 inches. Annual values show year-to-year variability and range from about 16 to 32 inches. Multiyear values also show variability and are mostly near or below the long-term average of 23.7 inches across the entire period. Exceptions include the 1980 to 1984 and 1995 to 1999 periods, which are well above average and have the highest multiyear values. The 1935 to 1939 and 1985 to 1989 periods have the lowest multiyear values.
Figure 5: Observed total annual precipitation for Idaho from 1895 to 2020. Dots show annual values. Bars show averages over 5-year periods (last bar is a 6-year average). The horizontal black line shows the long-term (entire period) average of 23.7 inches. Annual precipitation varies widely and shows no overall trend. Sources: CISESS and NOAA NCEI. Data: nClimDiv.
   
Observed Number of 1-Inch Extreme Precipitation Events
Graph of the observed annual number of 1-inch extreme precipitation events for Idaho from 1900 to 2020 as described in the caption. Y-axis values range from 0 to 3.0 days. Annual values show year-to-year variability and range from 0.2 to 2.7 days. Multiyear values also show variability and are mostly near or below the long-term average of 1.2 days between 1900 and 1994. With the exception of the 2000 to 2004 period, multiyear values are all above average since 1995. The 1915 to 1919 and 2000 to 2004 periods have the lowest multiyear values, and the 1995 to 1999 period, which is well above average, has the highest.
Figure 6: Observed annual number of 1-inch extreme precipitation events (days with precipitation of 1 inch or more) for Idaho from 1900 to 2020. Dots show annual values. Bars show averages over 5-year periods (last bar is a 6-year average). The horizontal black line shows the long-term (entire period) average of 1.2 days (note that the average for individual reporting stations varies greatly because of the state’s large elevation range). A typical station experiences 1 event per year. The number of 1-inch extreme precipitation events has been above average since 2005, with an overall upward trend since 1900. Sources: CISESS and NOAA NCEI. Data: GHCN-Daily from 10 long-term stations.
   
April 1 Snow Water Equivalent (SWE) at Camp Creek, ID
Line graph of the annual variations in the April 1 snow water equivalent at Camp Creek, Idaho, from 1936 to 2020 as described in the caption. Y-axis values range from 0 to 30 inches. Annual values show year-to-year variability and range from about 3 to 25 inches. Annual values are mostly between 10 and 15 inches from 1936 to 1975, but they are mostly between 5 and 10 inches between 1976 and 2020. A record-high value of nearly 25 inches occurred in 1952 and 1969, and record-low values below 5 inches occurred in 1963, 1977, and 2015.
Figure 7: Variations in the April 1 snow water equivalent (SWE) at the Camp Creek, Idaho, snow course site from 1936 to 2020. SWE, the amount of water contained within the snowpack, is highly variable from year to year. There is an overall decline in SWE since high values in 1952 and 1969. The lowest value on record occurred in 2015. Source: NRCS NWCC.

Extreme weather and weather-related events in Idaho include severe winter storms, wildfires, floods, droughts, and heat and cold waves. Flooding occurs frequently in Idaho; an estimated 90% of damages from natural disasters each year is attributable to riverine flooding, flash floods, or floods caused by ice/debris jams. The winter of 1996−97 brought tremendous amounts of snow (80–100 inches) to some parts of the state. Heavy rains and unusually warm temperatures produced significant amounts of snowmelt, resulting in disaster declarations for one-third of the state’s counties due to severe flooding and mudslides. Flash flooding typically occurs after intense thunderstorm events in the spring and summer. In 2012, Idaho experienced one of its most active fire seasons to date, with more than 1.6 million acres burned. Additionally, 11 of the state’s 44 counties were designated as primary natural disaster areas due to damages and losses caused by drought, excessive heat, and high winds. Extreme weather cost the state more than $400 million in property damages in 2012 alone.

Under a higher emissions pathway, historically unprecedented warming is projected during this century (Figure 1). Even under a lower emissions pathway, annual average temperatures are projected to most likely exceed historical record levels by the middle of the century. However, a large range of temperature increases is projected under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records. The intensity of heat waves is projected to increase, while cold wave intensity is projected to decrease.

Projected rising temperatures will raise the snow line—the average lowest elevation at which the snow falls. This will increase the likelihood that precipitation will fall as rain instead of snow, reducing water storage in the snowpack, particularly at lower mountain elevations that are now on the margins of reliable snowpack accumulation. Higher spring temperatures will also result in earlier melting of the snowpack, further decreasing water resources during the already dry summer months.

Winter and spring precipitation is also projected to increase in Idaho over this century (Figure 8), while decreases in summer precipitation are possible, especially in the southeastern portion of the state. However, even if overall precipitation increases, naturally occurring droughts will likely be more intense because higher temperatures will increase the rate of soil moisture loss during dry spells. The earlier melting of mountain snowpack may also lead to a reduction in soil moisture during the summer months. As a result, the frequency and severity of wildfires are projected to increase.

   
Projected Change in Spring Precipitation
Map of the contiguous United States showing the projected changes in total spring precipitation by the middle of this century as described in the caption. Values range from less than minus 20 to greater than positive 15 percent. Spring precipitation is projected to increase across most of the northern half of the United States, particularly in the Northern Great Plains, Midwest, and Northeast. Most of these projected increases are statistically significant across these areas. The projected change in spring precipitation is uncertain in central Colorado. The greatest decreases are projected for the Southwest United States. Idaho is projected to see the following increases: greater than 15 percent in the eastern panhandle and the southeastern part of the state, 5 to 10 percent in the western panhandle and south-central part of the state, and 0 to 5 percent along a sliver of the southwestern border. Statistically significant increases are projected for the southern panhandle and southeastern region.
Figure 8: Projected changes in total spring (March–May) precipitation (%) for the middle of the 21st century compared to the late 20th century under a higher emissions pathway. The whited-out area indicates that the climate models are uncertain about the direction of change. Hatching represents areas where the majority of climate models indicate a statistically significant change. Idaho is part of a large area of projected increases across the northern United States. Sources: CISESS and NEMAC. Data: CMIP5.

Extreme precipitation events are projected to become more frequent. The combination of more extreme precipitation events and more winter and spring precipitation falling as rain rather than snow will increase the risk of flooding during the cold season.

Details on observations and projections are available on the Technical Details and Additional Information page.

Lead Authors
Jennifer Runkle, Cooperative Institute for Satellite Earth System Studies (CISESS)
Kenneth E. Kunkel, Cooperative Institute for Satellite Earth System Studies (CISESS)
Contributing Authors
Rebekah Frankson, Cooperative Institute for Satellite Earth System Studies (CISESS)
Sarah M. Champion, Cooperative Institute for Satellite Earth System Studies (CISESS)
Laura E. Stevens, Cooperative Institute for Satellite Earth System Studies (CISESS)
John Abatzoglou, University of California, Merced
Recommended Citation
Runkle, J., K.E. Kunkel, R. Frankson, S.M. Champion, L.E. Stevens, and J. Abatzoglou, 2022: Idaho State Climate Summary 2022. NOAA Technical Report NESDIS 150-ID. NOAA/NESDIS, Silver Spring, MD, 4 pp.

RESOURCES

  • Gillis, S., B. Knapp, J. Wolf, J. Izo, K. McElligott, J. Reader, A. Peterson, D. VanSant, and N. Weller, 2011: Indicators of Climate Change in Idaho Report Summary: Understanding Climate Change and Its Impacts Through Indicators. University of Idaho, Moscow, ID, 15 pp.
  • Hayhoe, K., D.J. Wuebbles, D.R. Easterling, D.W. Fahey, S. Doherty, J. Kossin, W. Sweet, R. Vose, and M. Wehner, 2018: Our changing climate. In: Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II. Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart, Eds. U.S. Global Change Research Program, Washington, DC, 72–144. https://nca2018.globalchange.gov/chapter/2/
  • Knowlton, K., 2015: Climate Change Threatens Health. National Resources Defense Council, New York, NY. https://www.nrdc.org/resources/climate-change-threatens-health
  • 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. National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service, Silver Spring, MD, 83 pp. https://nesdis-prod.s3.amazonaws.com/migrated/NOAA_NESDIS_Tech_Report_142-6-Climate_of_the_Northwest_U.S.pdf
  • Lott, N., M.C. Sittel, and D. Ross, 1997: The Winter of '96-'97: West Coast Flooding. Technical Report 97-01. National Climatic Data Center, Research Customer Service Group, Asheville, NC, 22 pp. https://repository.library.noaa.gov/view/noaa/13812
  • MRCC, n.d.: cli-MATE: MRCC Application Tools Environment. Midwestern Regional Climate Center, Urbana-Champaign, IL. https://mrcc.illinois.edu/CLIMATE/
  • NOAA NCEI, 2013: State of the Climate: Wildfires for Annual 2012. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, Asheville, NC. http://www.ncdc.noaa.gov/sotc/fire/201213
  • NOAA NCEI, n.d.: Climate at a Glance: Statewide Time Series, Idaho. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, Asheville, NC, accessed May 7, 2021. https://www.ncdc.noaa.gov/cag/statewide/time-series/10/
  • NOAA NCEI, n.d.: U.S. Climate Normals [30-Year Normals 1991–2020]. National Oceanic and Atmospheric Administration, National Centers for Environmental Information, Asheville, NC. https://www.ncei.noaa.gov/products/us-climate-normals
  • NRCS NWCC, n.d.: Snowpack: Snow Water Equivalent (SWE) and Snow Depth [Camp Creek, ID]. Natural Resources Conservation Service, National Water and Climate Center, Portland, OR. https://www.nrcs.usda.gov/wps/portal/wcc/home/snowClimateMonitoring/snowpack/
  • Spracklen, D.V., L.J. Mickley, J.A. Logan, R.C. Hudman, R. Yevich, M.D. Flannigan, and A.L. Westerling, 2009: Impacts of climate change from 2000 to 2050 on wildfire activity and carbonaceous aerosol concentrations in the western United States. Journal of Geophysical Research: Atmospheres, 114 (D20). http://dx.doi.org/10.1029/2008JD010966
  • State of Idaho, n.d.: Idaho Floods! A Flood Awareness Guide for the Gem State. State of Idaho, Boise, ID, 48 pp. https://adacounty.id.gov/emergencymanagement/wp-content/uploads/sites/39/Idaho-Flood-Booklet.pdf
  • The White House, n.d.: The Threat of Carbon Pollution: Idaho. The White House, Washington, DC, 2 pp. https://obamawhitehouse.archives.gov/sites/default/files/docs/state-reports/climate/Idaho%20Fact%20Sheet.pdf
  • USDA NRCS, n.d.: Current Water Year Data. U.S. Department of Agriculture, Natural Resources Conservation Service, Boise, ID. https://www.nrcs.usda.gov/wps/portal/nrcs/detail/id/snow/products/?cid=nrcs144p2_047788

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