Wyoming’s climate is largely determined by its midlatitude location in the interior of the North American continent. The eastern portion of the state lies within the Great Plains, while the central and western portions encompass a series of mountain ranges and basins. While the proximity of the jet stream frequently exposes the state to periodic storm systems, the lack of oceanic moisture sources leads to a mostly semiarid climate. Wyoming’s topographic variability causes large regional variations in precipitation across the state. Annual precipitation amounts range from less than 6 inches in the north-central part of the state to more than 25 inches in Yellowstone National Park (1991–2020 averages). Most of the state’s precipitation falls during spring and summer, although some areas in the mountains experience a peak during winter. Some high-elevation regions receive more than 200 inches of snowfall annually. The large range of elevations across the state (from about 3,100 to 13,800 feet) also causes wide variations in temperature. The state has mild to warm summers and cold winters. Typical winter minimum temperatures generally range from 5°F to 18°F, with lower values at higher elevations. Summer maximum temperatures typically range from the low 70s to mid-80s (°F), although temperatures are much lower at higher elevations. Due to the state’s semiarid climate, temperatures can vary widely from day to night.
Time series of observed and projected temperature change (in degrees Fahrenheit) for Wyoming 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 2.5 to positive 4.3 degrees. By the end of the century, projected increases in temperature range from 1.8 to 7.5 degrees under the lower emissions pathway, from 4.5 to 11.3 degrees under the intermediate pathway, and from 9.0 to 17.0 degrees under the higher pathway.
Annual average temperatures in Wyoming have increased almost 3°F since the beginning of the 20th century (Figure 1), and nearly every year of this century has been above the long-term average. The hottest year on record was 2012, with a statewide annual average temperature of 44.8°F, which was 3.8°F higher than the long-term (1895–2024) average. This warming has been observed in all seasons and is most evident in winter. Since 1995, winter and summer temperatures have averaged 1.8°F and 1.3°F above the historical average, respectively (Figures 2a and 2b), with summer average temperatures generally exceeding the extreme heat of the 1930s Dust Bowl era since the early 2000s. The highest number of very hot days occurred during the early 2000s and early 2020s (Figure 3a). While warm nights are rare in Wyoming, the number of these nights has generally been above average since the early 2000s (Figure 3b). Another indication of the overall warming trend is a generally below-average number of very cold days since the early 2000s, although the 2020–2024 period was slightly above average (Figure 4).
Two graphs of the observed (a) winter and (b) summer average temperatures for Wyoming from 1895–96 to 2023–24 and 1895 to 2024, respectively, as described in the caption.
Panel A: Winter Average Temperature
Y-axis values range from 8 to 32 degrees Fahrenheit. Annual values show year-to-year variability and range from 11.9 to 28.0 degrees. Five-year values also show variability and are mostly near or below the long-term average of 20.7 degrees between 1895 and 1989 but are all near or above average since 1990. The 1910 to 1914 period has the lowest 5-year value at 17.7 degrees, and the 1995 to 1999 period has the highest at 23.2 degrees.
Panel B: Summer Average Temperature
Y-axis values range from 56 to 68 degrees Fahrenheit. Annual values show year-to-year variability and range from 57.9 to 66.5 degrees. Five-year values also show variability and are mostly near or below the long-term average of 62.4 degrees between 1895 and 1999. Exceptions include the 1930 to 1934 and 1935 to 1939 periods. Since 2000, 5-year values are all above average. The 1905 to 1909 period has the lowest 5-year value at 60.6 degrees, and the 2020 to 2024 period has the highest at 64.7 degrees.
Two sets of paired graphs of the observed annual number of (a) very hot days and (b) warm nights for Wyoming (top) from 1950 to 2024 and for the contiguous United States (bottom) from 1900 to 2024 as described in the caption.
Annual and 5-year values show variability in all graphs.
Panel A: Very Hot Days
Wyoming
Y-axis values range from 0 to 20 days. Annual values range from 1.6 to 18.7 days. Five-year values are mostly below the long-term average of 8.3 days between 1950 and 1999 but are all near or above average since 2000. The 1990 to 1994 period has the lowest 5-year value at 5.1 days, and the 2020 to 2024 period has the highest at 13.1 days.
Contiguous US
Y-axis values range from 4 to 40 days. Annual values range from 7.0 to 36.6 days. Five-year values are below 16 days between 1900 and 1909, all near or above 16 days between 1910 and 1959, and all near or below 16 days since 1960 except for the 1980 to 1984, 2010 to 2014, and 2020 to 2024 periods, which are slightly above 16 days. The 1990 to 1994 period has the lowest 5-year value at 12.5 days, and the 1930 to 1934 and 1935 to 1939 periods have the highest at 27.1 and 24.9 days, respectively.
Panel B: Warm Nights
Wyoming
Y-axis values range from 0.0 to 1.5 nights. Annual values range from 0 to 1.1 nights. Five-year values are mostly below the long-term average of 0.2 nights between 1950 and 1999 but are mostly above average since 2000. The 1970 to 1974 period has the lowest 5-year value at 0.0 nights, and the 2020 to 2024 period has the highest at 0.4 nights.
Contiguous US
Y-axis values range from 4 to 28 nights. Annual values range from 7.5 to 26.2 nights. Five-year values are mostly near or below 16 nights between 1900 and 1994. Exceptions include the 1930 to 1934 and 1935 to 1939 periods with more than 18 nights. An upward trend is evident since the 1970 to 1974 period, which has the lowest 5-year value at 12.1 nights. All 5-year values since 1995 are above 18 nights. The 2010 to 2014 period has the highest 5-year value at 20.4 nights.
Paired graphs of the observed annual number of very cold days for Wyoming (top) from 1950 to 2024 and for the contiguous United States (bottom) from 1900 to 2024 as described in the caption.
Annual and 5-year values show variability in both graphs.
Wyoming
Y-axis values range from 0 to 6 days. Annual values range from 0 to 5.3 days. Five-year values are below the long-term average of 1.0 days between 1950 and 1959, mostly near or above average between 1960 and 1999, and all near or below average between 2000 and 2019. The 2020 to 2024 period is above average. The 2000 to 2004 period has the lowest 5-year value at 0.2 days, and the 1970 to 1974 period has the highest at 1.8 days.
Contiguous US
Y-axis values range from 0 to 6 days. Annual values range from 0 to 5.4 days. Five-year values are all above 1 day between 1900 and 1939, mostly below 1 day between 1940 and 1959, all above 1 day between 1960 and 1999, and below 1 day between 2000 and 2014. The 2015 to 2019 and 2020 to 2024 periods are slightly above 1 day. The 2000 to 2004 period has the lowest 5-year value at 0.5 days, and the 1915 to 1919 period has the highest at 2.4 days.
Precipitation in Wyoming varies widely from year-to-year. Statewide precipitation totals have ranged from a low of 11.0 inches in 2012 to a high of 20.5 inches in 1927 and show no long-term trend (Figure 5). There is also no long-term trend in the number of 1-inch extreme precipitation events for Wyoming (Figure 6).
Graph of the observed total annual precipitation for Wyoming from 1895 to 2024 as described in the caption.
Y-axis values range from 10 to 22 inches. Annual values show year-to-year variability and range from 11.0 to 20.5 inches. Five-year values also show variability, with no overall trend. Most are near or below the long-term average of 15.8 inches across the entire period; one exception is the 1995 to 1999 period, which has the highest 5-year value at 18.2 inches. The 2000 to 2004 period has the lowest 5-year value at 13.6 inches.
Paired graphs of the observed annual number of 1-inch extreme precipitation events for Wyoming (top) from 1950 to 2024 and for the contiguous United States (bottom) from 1900 to 2024 as described in the caption.
Annual and 5-year values show variability in both graphs.
Wyoming
Y-axis values range from 0.0 to 2.5 events. Annual values range from 0.2 to 1.9 days. Five-year values are below the long-term average of about 1 event between 1950 and 1959 but are mostly near or above average between 1960 and 2019. The 2020 to 2024 period is below average. The 1955 to 1959 period has the lowest 5-year value at 0.7 events, and the 2015 to 2019 period has the highest at 1.4 events.
Contiguous US
Y-axis values range from 6 to 12 events. Annual values range from 6.3 to 10.8 events. Five-year values are above 8.5 events between 1900 and 1909, mostly near or below 8.5 events between 1910 and 1989, and all above 8.5 events since 1990. The 1930 to 1934 period has the lowest 5-year value at 7.4 events, and the 2015 to 2019 period has the highest at 10.0 events.
During the summer months, the state experiences frequent thunderstorms, which can produce hail, lightning, and strong winds. Southeastern Wyoming lies in “Hail Alley,” the most hail-prone area in the country. On average, Cheyenne and surrounding areas record more than 6 days per year with reports of severe hail (1-inch diameter or larger). On August 1, 1985, a severe thunderstorm in Cheyenne dropped more than 6 inches of rain in just over three hours and produced hail of up to 2 inches in diameter. In some areas of the city, the hail piled up in 4- to 8-foot drifts. On June 6, 2020, Wyoming was one of the states hit by an exceptionally rare western-US derecho (a widespread, long-lived straight-line windstorm associated with a series of severe thunderstorms). This storm began in eastern Utah and tracked northeast over 750 miles before ending in North Dakota. Of the 339 total wind reports, 55 came from the state of Wyoming, with multiple reports of 80–95 mph winds.
Wyoming’s northern location and associated proximity to the jet stream also make it susceptible to the impacts of winter storm systems, including heavy snows, high winds, and low wind chill temperatures. In early 1949, a series of winter storms devastated the state, killing 17 people and hundreds of thousands of livestock. More recently (October 3–5, 2013), eastern Wyoming was hit by an early-season blizzard that knocked down power lines and closed many roads. Among long-term weather observing stations, Bates Creek No. 2 reported the highest snowfall amount of 25 inches over the 3-day period, 20 inches of which fell on October 5. The historic blizzard of March 2021 also resulted in unusually high snowfall amounts along and east of the Laramie Range. Snowfall rates of 2–3 inches per hour occurred at times and resulted in multiple interstate closures.
Chinook winds—warm and dry rapidly descending winds that occur along the eastern slopes of the Rocky Mountains—are a hazard unique to Wyoming and western mountain states. During the winter months, these winds can persist along the eastern slope of the Continental Divide and often bring large temperature increases that lead to rapid snowmelt and subsequent flooding. Chinook wind gusts are often strong enough to cause property damage.
Wyoming is a major source of water for other states, and changes in precipitation can have broad impacts beyond its boundaries. Water from the state’s rivers flows into four major river basins: the Missouri–Mississippi, Green–Colorado, Snake–Columbia, and Great Salt Lake. Yearly variations in late-season snowpack depths are large; for example, April 1 snow water equivalent (the amount of water contained within the snowpack) at Lewis Lake Divide has ranged from less than 20 inches to more than 50 inches since 1981 (Figure 7). Such variations have implications for water availability across the West, as snowmelt from the winter snowpack feeds many rivers and streams. In years with heavy snow cover, heavy rains during the spring thaw can cause rapid melting of the snowpack and lead to severe flooding. One of the worst floods in Wyoming’s history was the 1985 Cheyenne Flood. A summer thunderstorm led to flash flooding across the city, with more than 6 inches of rain falling in a 3-hour span, setting a state record for the most precipitation in 24 hours. The storm led to total damages exceeding $61 million and resulted in 12 fatalities and 70 injuries, most of which were due to the flooding.
Time series of the annual variations in April 1 snow water equivalent (SWE) at Lewis Lake Divide, Wyoming, from 1981 to 2024 as described in the caption.
Y-axis values range from 0 to 60 inches. Annual values show year-to-year variability and range from about 17 to 53 inches. Annual values show no clear trend and are mostly between 20 and 40 inches across the entire period. The highest annual values of 53 and 54 inches were recorded in 1997 and 1982, respectively, and the lowest values of 16.7 and 17.1 inches were recorded in 2001 and 2010, respectively.
Wyoming, like the rest of the Great Plains, is susceptible to droughts, which are occasionally severe (as defined by the US Drought Monitor). From 1999 to 2008, large portions of the state experienced drought conditions. The state then experienced several years of above-average precipitation until 2012, which was Wyoming’s driest year since historical records began in 1895. By October 2012, almost 90% of the state was in severe drought. The drought, along with high temperatures and high winds, resulted in one of Wyoming’s worst wildfire seasons, with more than 350,000 acres burned. Another severe wildfire season occurred in 2020; by October 2020, about 60% of the state was in severe drought and almost 340,000 acres had burned. However, the most notable wildfire season in recent years was 2024, which saw more than 820,000 acres burned—second only to the Yellowstone fires of 1988 that burned more than 1.7 million acres.
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 record 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. Increases in heat wave intensity are projected, but the intensity of cold waves is projected to decrease.
Under the intermediate emissions pathway, projected increases in total spring precipitation by midcentury are statistically significant for the north-central and northwestern portions of Wyoming but are less certain elsewhere (Figure 8). Statistically significant increases are also projected for annual precipitation (across northwestern and west-central parts of the state) and winter precipitation (in northwestern and west-central portions). There is uncertainty in projections for summer and fall precipitation. 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 rather than snow. This would reduce the 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 availability during the drier summer months. Heavier spring precipitation, combined with a shift from snow to rain, could increase the potential for flooding.
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. The state of Wyoming 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.
Wyoming
Wyoming is projected to see increases in total spring precipitation of 5 to 10 percent in the southern half of the state and statistically significant increases in the range of 5 to 15 percent across the northern half.
Contiguous US
Projected increases in total spring precipitation are as follows: up to 5 percent across a narrow strip running westward and curving northwestward from western Georgia into the Pacific Northwest; 5 to 10 percent in the Southeast, Mid-Atlantic, and Northeast, as well as southern areas of the Midwest, central portions of the Great Plains, and portions of the Northwest; and 10 to 15 percent in the northern areas of the Northeast, Midwest, and Great Plains, with statistically significant increases in the 10 to 15 percent range across the northern border of the country stretching from Maine to Montana.
Decreases of up to 10 percent are seen across the southern Great Plains and Southwest, including southern Texas, all of Arizona, and most of New Mexico and California.
Droughts, a natural part of Wyoming’s climate, are projected to increase in intensity due to higher temperatures and the associated increase in evaporation rates and soil moisture loss. This in turn will increase the frequency and severity of wildfires.
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