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2025 State Climate Summaries

IDAHO

Snake River Canyon, Twin Falls, Idaho by Jim Black
License: Pixabay Content License

KEY MESSAGES

Key Message1

Annual average temperatures in Idaho have increased about 2°F since the beginning of the 20th century, and 2015–2024 was the warmest decade on record. Under the intermediate and higher emissions pathways, historically unprecedented warming is projected during this century.

Key Message2

Total annual precipitation has been highly variable, with no clear long-term trend. Under the intermediate emissions pathway, statistically significant increases are projected in total annual precipitation and spring precipitation for western and east-central parts of the state by midcentury. Rising temperatures are projected to make future droughts more intense, potentially increasing the frequency and severity of wildfires.

Key Message3

Extreme precipitation events are projected to become more frequent, while higher temperatures are projected to cause a larger proportion of winter and spring precipitation to fall as rain rather than snow. These changes have the potential to increase flood risks. Earlier melting of the snowpack will decrease water availability during the already-dry summer months.

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. Average summer high temperatures generally range from less than 70°F at high elevations to almost 90°F in the valleys of southern Idaho (1991–2020 averages). Winter low temperatures are typically below freezing across the entire state. Wide ranges in elevation across the state affect regional precipitation. The lower-elevation regions of southern Idaho are shadowed by mountains, reducing the amount of moisture that can penetrate the area and resulting in generally low amounts of precipitation—less than 10 inches per year in some locations. By comparison, the higher elevations of northern and central Idaho receive much higher amounts of rain and snow, with some areas of the panhandle having annual precipitation totals of more than 70 inches. Approximately three-quarters of Idaho’s annual precipitation falls during the cool season (November–May) as a result of Pacific storms.

Figure 1 Observed and Projected Temperature Change
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Figure 1. Observed and Projected Temperature Change. For more details, consult the image description section following the caption.
Figure 1: Observed and projected changes (compared to the 1901–1960 average) in near-surface annual average air temperature for Idaho. Observed data are for 1900–2024. Projected changes for 2015–2100 were generated using global climate models to explore three possible futures, associated with lower, intermediate, and higher greenhouse gas emissions pathways (the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios, respectively). Temperatures in Idaho (black line) have increased about 2°F since the beginning of the 20th century (based on a linear trend). 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 (light gray shading). Less warming is expected under a lower emissions future (the coldest end-of-century projections being about 2.0°F warmer than the 1901–1960 average; blue shading) and more warming under a higher emissions future (the hottest end-of-century projections being about 12.9°F warmer than the hottest year in the observed record; red shading), while the intermediate emissions future leads to moderate warming (with end-of-century projections ranging from about 4.2°F to 11.2°F above the 1901–1960 average; dark gray shading). Adapted from Runkle et al. 2022. Data: NClimDiv and CMIP6.
Description

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 negative 4 to positive 20 degrees. Observed annual temperatures from 1900 to 2024 show variability and range from negative 2.8 to positive 4.5 degrees. By the end of the century, projected increases in temperature range from 1.9 to 7.9 degrees under the lower emissions pathway, from 4.4 to 11.3 degrees under the intermediate pathway, and from 8.5 to 17.8 degrees under the higher pathway.

Annual average temperatures in Idaho have increased about 2°F since the beginning of the 20th century (Figure 1), and 2015–2024 was the warmest decade on record. Statewide, the number of very hot days was mostly near or above average between the late 1910s through the early 1940s; more recently, the number of these days has generally been near or above average since the early 2000s, with the highest 5-year average recorded for the 2020–2024 period (Figure 2a). The number of warm nights has mostly been above average since the early 2000s, with some annual values exceeding the previous highs of the late 1920s and early 1930s (Figure 2b). A winter warming trend is reflected in a significant decline in the number of very cold nights, which has mostly been near or below average since the 1990s (Figure 3).

Figure 2 Observed Number of Very Hot Days and Warm Nights
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Figure 2. Observed Number of Very Hot Days and Warm Nights. For more details, consult the image description section following the caption.
Figure 2: Observed annual number of (a) very hot days (maximum temperature of 95°F or higher) and (b) warm nights (minimum temperature of 65°F or higher) for Idaho from 1900 to 2024. Dots show annual values. Bars show averages over 5-year periods. The horizontal black lines show the long-term (entire period) averages of (a) 11.4 days and (b) 1.4 nights. Note that this chart represents a statewide average; however, values for individual reporting stations vary greatly because of the state’s large elevation range. The number of very hot days has generally been near or above average since the early 2000s, with the highest 5-year average recorded for the 2020–2024 period. The number of warm nights has generally been above average since the early 2000s, with some years exceeding the previous highs of the late 1920s and early 1930s. Adapted from Runkle et al. 2022. Data: GHCN-Daily.
Description

Two graphs of the observed annual number of (a) very hot days and (b) warm nights for Idaho from 1900 to 2024 as described in the caption.

Panel A: Very Hot Days
Y-axis values range from 0 to 28 days. Annual values show year-to-year variability and range from 1.2 to 23.0 days. Five-year values also show variability and are all near or above the long-term average of 11.4 days between 1900 and 1944 except for the 1910 to 1914 period, but they are all near or below average between 1945 and 1999 except for the 1970 to 1974 period. Since 2000, all 5-year values are near or above average. The 1980 to 1984 period has the lowest 5-year value at 6.5 days, and the 1930 to 1934 and 2020 to 2024 periods have the highest at 14.8 and 15.4 days, respectively.

Panel B: Warm Nights
Y-axis values range from 0 to 7 nights. Annual values show year-to-year variability and range from 0 to 7.0 nights. Five-year values also show variability and are all below the long-term average of 1.4 nights between 1900 and 1914, and all near or above average between 1915 and 1939, and all below average between 1940 and 1999 except for the 1990 to 1994 period. Since 2000, 5-year values are all above average. The 1955 to 1959 period has the lowest 5-year value at 0.6 nights, and the 2020 to 2044 periods has the highest at 3.2 nights.

Figure 3 Observed Number of Very Cold Nights
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Figure 3. Observed Number of Very Cold Nights. For more details, consult the image description section following the caption.
Figure 3: Observed annual number of very cold nights (minimum temperature of 0°F or lower) for Idaho from 1900 to 2024. Dots show annual values. Bars show averages over 5-year periods. The horizontal black line shows the long-term (entire period) average of 8.0 nights. Note that this chart represents a statewide average; however, values for individual reporting stations vary greatly because of the state’s large elevation range. The number of very cold nights has mostly been near or below average since the 1990s. Adapted from Runkle et al. 2022. Data: GHCN-Daily.
Description

Graph of the observed annual number of very cold nights for Idaho from 1900 to 2024 as described in the caption.

Y-axis values range from 0 to 28 nights. Annual values show year-to-year variability and range from 0.8 to 25.6 nights. Five-year values also show variability and are below the long-term average of 8.0 nights between 1900 and 1909, all above average between 1910 and 1989 except for the 1940 to 1944 and 1965 to 1969 periods, and all near or below average since 1990. The 2000 to 2004 period has the lowest 5-year value at 4.0 nights, and the 1930 to 1934 and 1945 to 1949 periods have the highest at 12.5 and 12.1 nights, respectively.

Statewide, there is substantial variability but no overall trend in total annual precipitation over the 130-year period of record (1895–2024; Figure 4). Total annual precipitation has ranged from a low of 16.2 inches in 1935 to a high of 32.1 inches in 1996. Extreme precipitation events, which are relatively rare in Idaho, show year-to-year variability. The number of 1-inch extreme precipitation events has mostly been near or above average since the late 1990s; however, below-average values were recorded during the 2000–2004 period (Figure 5).

Figure 4 Observed Total Annual Precipitation
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Figure 4. Observed Total Annual Precipitation. For more details, consult the image description section following the caption.
Figure 4: Observed total annual precipitation for Idaho from 1895 to 2024. Dots show annual values. Bars show averages over 5-year periods. The horizontal black line shows the long-term (entire period) average of 23.7 inches. Annual precipitation varies widely but shows no overall trend. Adapted from Runkle et al. 2022. Data: NClimDiv.
Description

Graph of the observed total annual precipitation for Idaho from 1895 to 2024 as described in the caption.

Y-axis values range from 14 to 34 inches. Annual values show year-to-year variability and range from 16.2 to 32.1 inches. Five-year values also show variability and are all near or below the long-term average of 23.7 inches between 1895 and 1939 except for the 1905 to 1909 period but are mostly above average between 1940 and 1984. Since 1985, 5-year values are mostly below average. The 1935 to 1939, 1985 to 1984, and 2000 to 2004 periods have the lowest 5-year values at 20.95, 21.02, and 20.95 inches respectively, and the 1980 to 1984 and 1995 to 1999 periods have the highest at 28.8 and 28.0 inches, respectively.

Figure 5 Observed Number of 1-Inch Extreme Precipitation Events
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Figure 5. Observed Number of 1-Inch Extreme Precipitation Events. For more details, consult the image description section following the caption.
Figure 5: Observed annual number of 1-inch extreme precipitation events (days with precipitation of 1 inch or more) for Idaho from 1900 to 2024. Dots show annual values. Bars show averages over 5-year periods. The horizontal black line shows the long-term (entire period) average of 1.2 events, indicating that a typical station experiences one event per year. Note that this chart represents a statewide average; however, values for individual reporting stations vary greatly because of the state’s large elevation range. With the exception of the 2000–2004 period, the number of 1-inch extreme precipitation events has mostly been near or above average since the late 1990s. Adapted from Runkle et al. 2022. Data: GHCN-Daily.
Description

Graph of the observed annual number of 1-inch extreme precipitation events for Idaho from 1900 to 2024 as described in the caption.

Y-axis values range from 0 to 4 events. Annual values show year-to-year variability and range from 0.1 to 3.5 events. Five-year values also show variability and are above the long-term average of 1.2 events between 1900 and 1909 but are mostly near or below average between 1910 and 1994. Since 1995, 5-year values are all above average except for the 2000 to 2004 period. The 1935 to 1939, 1965 to 1969, and 2000 to 2004 periods have the lowest 5-year values at 0.86, 0.85, and 0.87 events, respectively, and the 1995 to 1999 and 2015 to 2019 periods have the highest at 2.1 and 1.9 events, respectively.

Total annual snowfall ranges from about 10 to 20 inches in the southern lowlands to more than 100 inches in the higher mountains (1991–2020 averages). 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 6).

Figure 6 April 1 Snow Water Equivalent (SWE) at Camp Creek, ID
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Figure 6. April 1 Snow Water Equivalent (SWE) at Camp Creek, ID. For more details, consult the image description section following the caption.
Figure 6: Variations in the April 1 snow water equivalent (SWE) at the Camp Creek, Idaho, snow course site (elevation 6,540 feet) from 1936 to 2024. SWE, the amount of water contained within the snowpack, is highly variable from year to year. There has been an overall decline in SWE since the highs of 1952 and 1969. The lowest value on record was recorded in 2015. Adapted from Runkle et al. 2022. Data: NRCS NWCC.
Description

Line graph of the annual variations in the April 1 snow water equivalent at Camp Creek, Idaho, from 1936 to 2024 as described in the caption.

Y-axis values range from 0 to 30 inches. Annual values show year-to-year variability and range from 2.2 to 24.8 inches. Annual values are mostly between 10 and 15 inches from 1936 to 1976, but they are mostly between 5 and 10 inches between 1976 and 2022. The highest values at nearly 25 inches occurred in 1952 and 1969, and the lowest values at less than 5 inches occurred in 1963, 1977, 2007, 2012, and 2015.

Extreme weather-related events in Idaho include severe winter storms, wildfires, floods, droughts, and heat waves and cold waves. Flooding occurs frequently in Idaho and can involve riverine flooding from snowmelt or extended precipitation (or both), flash floods from heavy precipitation events, and floods caused by ice and 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 conditions 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 1.5 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. The 2024 fire season was particularly destructive, with the Wapiti, Middle Complex, and other fires burning nearly 1 million acres in the state. More than half of Idaho suffered from extreme drought (as defined by the US Drought Monitor) in 2021, and large parts of the state continued to experience severe or moderate drought into 2025.

Under the intermediate and higher emissions pathways, historically unprecedented warming is projected during this century (Figure 1). Even under the lower emissions pathway, most projections show annual average temperatures exceeding historical levels by the middle of the century. However, projections for all three pathways show a large range of potential temperature increases, and some projections for the lower pathway are comparable to recent observed values. The intensity of heat waves is projected to increase, while cold wave intensity is projected to decrease.

Idaho is reliant on mountain snowpack for winter recreation and water supply. Rising temperatures are expected to raise the snow line (the average lowest elevation at which snow falls) and increase the likelihood that precipitation falls as rain instead of snow. This would cause the overall amount of land that is snow-dominated (areas where most precipitation falls as snow in the winter) to decrease and reduce water storage in the snowpack, particularly at those lower mountain elevations that are now on the margins of reliable snowpack accumulation. Higher spring temperatures are also expected to result in earlier melting of the snowpack, further decreasing water resources during the already-dry summer months.

Under the intermediate emissions pathway, statistically significant increases in total annual precipitation are projected by midcentury across east-central Idaho and portions of the western border with Washington and Oregon but are less certain elsewhere (Figure 7). Statistically significant increases are also projected for spring precipitation along the east-central border with Montana and Wyoming. There is uncertainty in projections for summer, fall, and winter precipitation. 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 is expected to increase the risk of flooding.

Figure 7 Projected Changes in Total Annual Precipitation
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Figure 7. Projected Changes in Total Annual Precipitation. For more details, consult the image description section following the caption.
Figure 7: Projected changes in total annual precipitation (%) for the middle of the 21st century (2041–2070) compared to the 1991–2020 average under the intermediate emissions pathway (SSP2-4.5 scenario). For areas with hatching, a majority of models project statistically significant changes and agree on the direction of change. For areas without hatching, less than half of models project statistically significant changes. Statistically significant increases of 5–10% in total annual precipitation are projected across east-central Idaho and portions of the western border with Washington and Oregon. Annual precipitation is also projected to increase throughout the rest of the state; however, these changes are not statistically significant. Adapted from Runkle et al. 2022. Data: CMIP6.
Description

Map of the contiguous United States showing the projected changes in total annual precipitation by the middle of this century as described in the caption. The state of Idaho is outlined in black.

Legend values range from less than negative 10 to greater than positive 15 percent. Note: unless otherwise specified, projected values are not statistically significant.

Idaho

The entire state of Idaho is projected to see increases in total annual precipitation of 5 to 10 percent, with statistically significant increases in the 5 to 10 percent range in the east-central region and along northwestern and southwestern portions of the borders with Washington and Oregon.

Contiguous US

Projected increases in total annual precipitation are as follows: up to 5 percent for most of the Southeast, as well as the central Midwest, central Great Plains, central West, and Northwest; and 5 to 10 percent for all of the Northeast, as well as portions of the Mid-Atlantic, Southeast, northern Midwest, northern Great Plains, and Pacific Northwest, with statistically significant increases in the 5 to 10 percent range for the Northeast, northeastern Midwest, and portions of the northern Great Plains and Pacific Northwest. 

Projected decreases of up to 5 percent are expected across most of Texas, New Mexico, and Arizona, as well as southern California.

Naturally occurring droughts are expected to be more intense because higher temperatures will increase evaporation rates and 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.

Details on observations and projections are available on the Technical Details and Additional Information page.
The compiled version of the 2022 State Climate Summaries, including the complete author list and recommended citations, is available on the Downloads page.

Authors
Laura E. Stevens, North Carolina State University
James Anheuser, North Carolina State University
Mark R. Essig, North Carolina State University
April D. Lamb, North Carolina State University
Thomas K. Maycock, North Carolina State University
Andrea L. McCarrick, North Carolina State University
Alexis Visovatti, North Carolina State University
Contributors
Jessicca Allen, Visual Communications Lead and PDF Layout, North Carolina State University
Jeff Bliss, Data Explorer Tool Development, National Environmental Mapping and Applications Center
Amy Camper, Visual Communications and PDF Layout, Innovative Consulting & Management Services, LLC
Ryan Cox, Web Application Engineer, North Carolina State University
Jacquelyn Crossman, Citation Management, NOAA NCEI Librarian, MPF-ZAI
Greg Dobson, GIS and Figure Development, National Environmental Mapping and Applications Center
David R. Easterling, Advisor, Future Climate, LLC, and Earth Knowledge, Inc.
Aaron Goodman, Web Developer, North Carolina State University
Katharine M. Johnson, Web Team Lead and GIS Analyst, North Carolina State University
Kenneth E. Kunkel, Advisor and Principal Research Scholar, North Carolina State University
Ciara R. Lemery, Figure and Production Coordination, Independent Contractor
Angel Li, Web Developer, North Carolina State University
Dave Michelson, Data Explorer Tool Development, National Environmental Mapping and Applications Center
Ronald Opio, Data Analysis and Figure Development, North Carolina State University
Xia Sun, Data Analysis and Figure Development, North Carolina State University
Xiangdong Zhang, Advisor, North Carolina State University
Acknowledgements
Tamara Houston, Regional Climate Center Review Coordination, NOAA National Centers for Environmental Information
Daniel McEvoy, Western Region Expert Review, Western Regional Climate Center, Desert Research Institute
Recommended Citation
Stevens, L.E., J. Anheuser, M.R. Essig, A.D. Lamb, T.K. Maycock, A.L. McCarrick, and A. Visovatti, 2026: 2025 State Climate Summaries for the United States: Idaho. [Update to Runkle et al., 2022: Idaho State Climate Summary 2022.] North Carolina Institute for Climate Studies Report NCICS-001-ID. North Carolina State University, Asheville, NC. https://doi.org/10.52750/605513

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