Climate and Weather: Wind River Range
Wyoming’s outstanding feature is its majestic mountains and none is more spectacular than the Wind River Range. The highest point in the Winds is Gannett Peak at 13,785 feet, but there are many other peaks nearly as tall. Since the Wind River Range lies in a general northwest-southeast direction, it is perpendicular to the prevailing westerlies, therefore, it provides an effective barrier which forces air currents moving in from the Pacific Ocean to rise and drop much of their moisture along the western slopes. The resulting air flow often increases wind velocity across the mountains, bestowing the range with its well-deserved name.
The Continental Divide runs down the spine of the Winds, leaving most of the drainage areas to the east. The run-off drains into three great river systems: the Columbia, the Colorado, and the Missouri. Snow accumulates to considerable depths in the high mountains and many of the streams fed by the melting snow furnish ample quantities of water for irrigation of thousands of acres of land.
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Because of its elevation, the Wind Rivers have a relatively cool climate. Above the 6,000 feet level the temperature rarely exceeds 100° F. For most of the State, mean maximum temperatures in July range between 85° and 95° F. With increasing elevation, average values drop rapidly. A few places in the mountains at about the 9,000 foot level have average maximums in July close to 70° F. Summer nights are almost invariably cool, even though daytime readings may be quite high at times. For most places away from the mountains, the mean minimum temperature in July ranges from 50° to 60° F. Of course, the mountains and high valleys are much cooler with average lows in the middle of the summer in the 30s and 40s with occasional drops below freezing.
In the wintertime it is characteristic to have rapid and frequent changes between mild and cold spells. The majority of cold waves move southward on the east side of the Divide. Many of the cold waves are not accompanied by enough snow to cause severe conditions. In January, the coldest month generally, mean minimum temperatures range mostly from 5 to 10° F. In the western valleys mean values go down to about 5° below zero. The record low for the State is -66° F observed February 9, 1933, at Yellowstone Park. During warm spells in the winter, nighttime temperatures frequently remain above freezing. Chinooks, warm downslope winds, are common along the eastern slopes.
Numerous valleys provide ideal pockets for the collection of cold air drainage at night. Protecting mountain ranges prevent the wind from stirring the air, and the colder heavier air settles into the valleys often sending readings well below zero. It is common to have temperatures in the valleys considerably lower than on the nearby mountain side. January, the coldest month, has occasional mild periods when maximum readings will reach the 50s; however, winters are usually long and cold.
For most of the range, sunshine ranges from 60 percent of the possible amount during the winter to about 75 percent during the summer. Mountain areas receive less, and in the wintertime the estimated amount over the northwestern mountains is about 45 percent. In the summertime when sunshine is greatest – not only in time but also intensity – it is characteristic for the mornings to be mostly clear. Cumulus clouds develop nearly every day and frequently blot out the sun for a portion of the afternoons. Because the altitude provides less atmosphere for the sun’s rays to penetrate and because of the very small amount of fog, haze, and smoke, the intensity of sunshine in unusually high.