The climate in Wyoming is semi-arid, with local desert conditions. Wyoming weather is cool, dry, and windy in comparison to most of the United States. Much of this is due to the topography of the state.
Summers in Wyoming are warm with July high temperatures averaging between 85 °F (29°C) and 95 °F (35°C) in most of the state. With increasing elevation; however, this average drops rapidly with locations above 9000 feet averaging around 70 °F (21°C). Summer nights throughout the state are characterized by a rapid cool down with even the hottest locations averaging in the 50-60 °F (10-14°C) range at night. In most of the state, the late spring and early summer is when most of the precipitation tends to fall. Winters are cold, but are variable with periods of sometimes extreme cold interspersed between generally mild periods, with Chinook winds providing unusually warm temperatures in some locations. Precipitation is highly dependent on elevation with lower areas in the Big Horn Basin averaging 5-8 inches (125 - 200 mm) making the area a true desert. The lower areas in the North and on the eastern plains typically average around 10-12 inches (250-300 mm), making the climate there semi-arid. Some mountain areas do receive a good amount of precipitation, 20 inches (510 mm) or more, much of it as snow, sometimes 200 inches (5 meters) or more annually. The record low temperature, –66°F (–54°C), was set 9 February 1933 at Riverside; the record high, 114°F (46°C), 12 July 1900 at Basin.
The climate of any area in Wyoming is largely determined by its latitude, altitude and local topography. When put together, these factors have a lot to do with airflow patterns, temperature variations, precipitation and humidity brought in by the weather systems that migrate eastward. In winter, Wyoming is often beneath the jet stream, or north of it, which accounts for its frequent strong winds, blasts of arctic air and precipitation, all the necessary ingredients for great snow conditions at Wyoming's northwestern ski areas. In summer, the jet stream retreats northward to somewhere over Canada, leaving the state's weather mild and pleasant at a time when the majority of Wyoming's visitors choose to arrive. Jackson, located at 6,230 feet above sea level and surrounded by mountains, can expect a high temperature in July of 80? F. The average is more likely to be 65? F. The closest National Weather Station (in Lander on the other side of the Wind River Mountains at 5,563 feet) reports slightly warmer July weather.
Weather and topography in Wyoming have more contrast than in most other states. Surface elevations range from the summit of Gannett Peak in the Wind River Mountains, at 13,804 feet, to the Belle Fourche River Valley in the state’s northeast corner, at 3,125 feet. Severe weather is not uncommon in Wyoming, with the state being one of the leading states for hail damage in the United States. The number of thunderstorm days vary across the state with the southeastern plains of the state having the most days of thunderstorm activity. Thunderstorm activity in the state is highest during the late spring and early summer. The southeastern corner of the state is the most vulnerable part of the state to tornado activity. Moving away from that point and westwards, the incidence of tornadoes drops dramatically with the west part of the state showing little vulnerability. Tornadoes, where they occur, tend to be small and brief, unlike some of those which occur a little further east.