Wyoming offers sharp contrasts in its weather. You may hike for weeks, experiencing only an occasional cooling rain. Or, particularly in the mountains, you may encounter fog and rain so heavy you can only see a few feet in front of you for days. At the higher elevations, snow and hail can occur at any time of the year. At both high and low elevations, be prepared for electrical storms.
Thru-hiking the CDT in Wyoming is complicated by the fact that it begins in the mountains, drops to near desert conditions in the basin, and then climbs to the tundra. Hiking south to north, you begin near an elevation of 10,000 feet in the Sierra Madre. The trail loses 3,500 feet by the time it reaches Rawlins on the southern fringe of the Great Divide Basin. From there it winds its way north across the hot, dry basin, then climbs through the forested foothills and on to the tundra of the Wind River Range. The high point of 11,120 feet above sea level is reached among these rugged peaks. The CDT drops out of the clouds just south of Green River Lakes, and spends its last few hundred miles somewhere between 7,500 and 9,000 feet in the Teton Wilderness and on the high plains of Yellowstone. Over this wide variance in altitude, annual precipitation ranges from an average of less than 8 inches at places in the Basin to over 40 inches in the Wind River Range. To this diversity in altitude, add a 4-degree change in latitude across the state.
Lower elevations, below 8,000 feet, will be almost free of snow by late May, but back roads can still be rough and muddy, occasionally blocked by deep, slow melting snowdrifts. Sudden and paralyzing spring blizzards can occur into June. The first two weeks of June are a good time to be in the Great Divide Basin. The flowers bloom early at this elevation. By mid-summer they are dry, thin shadows of themselves, while their alpine cousins are in full bloom. Wildlife is active in May and June also, their attention focused on mating, home building, and rearing their young. There is usually still plenty of water available from runoff. Be prepared for storms at any time of the year. Shelter from the elements is important, but a deep rut in the road or a patch of sagebrush may be all that’s available.
The higher elevations are not clear of snow until early or mid July, and expect it to be later than earlier. The tundra above 10,500 feet retains large patches of snow throughout the summer. Stream crossings can be difficult if not impossible until early August. Late summer above 8,000 feet is wonderful, as the crowded trailheads and overused trails will attest. The days are long and warm and it rains less often. You may experience long stretches of dry, warm days. Be vigilant and always stay prepared for rain or snow.