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.
This big difference in elevation explains why the city of Powell, in the north at 4,400 feet has a mean annual July temperature of about 7˚ F higher than the town of Evanston in the southwest corner, at 6,800 feet. It also explains why so many locals head for the mountains in the summer to camp, fish for brookies or relax in the cool, dry mountain air. A typical July high in Sheridan is 70˚ F, while 40 miles west atop the Big Horns at Burgess Junction, the average July temperature is 55˚ F. The warmest temperature ever recorded in Wyoming was 114˚ F at Basin (3,870 feet) on the west slope of the Big Horns – a day when everyone went to the mountains.
Wyoming is located deep in the interior of the North American continent, far from any moderating influence of oceans. Wyoming, therefore, has some long winters, but also some pleasant summers. When traveling across the state, summer or winter, it's common to experience several climatic zones, due to the state's size and diverse topography.
Generally speaking, summer visitors can expect summer daytime temperatures to run in the 70s and 80s. Ninety-degree days are rare anywhere in the state and over 100˚ are almost unheard of. The air cools quickly after sundown. It can get downright cold in the mountain towns and in places like Yellowstone National Park. Wyoming folks sleep under blankets most nights and are never far away from a warm jacket.
A typical Wyoming summer day will start out bright and sunny. Clouds will appear on the western horizon about noon and thunderheads will develop in mid-afternoon. Scattered, isolated thundershowers will dot the landscape in late afternoon and early evening. Some can be severe with wind and hail, especially on the eastern plains, but the chances of getting wet in any given location are slim. Wyoming is mostly a fairly dry, low humidity place in any season.
Autumn in Wyoming is a pure delight. Most places will start to see snow in mid-September, but winter weather won’t start to stick until late November. For most of the two months in between, the state enjoys a special season called Indian Summer, with warm days, cool nights and spectacular colors. It’s a delightful change-of-season experience.
Weather is one of the most pleasant and interesting things about living in Wyoming. Enjoy your trip to the Cowboy State. Bring a jacket.