Thru-Hiker's Guide to America
Excerpted from Thru Hiker's Guide to America by E. Schlimmer
The John Muir Trails short hiking season is due mainly to snow, which is still on the ground in early summer and starts again in early fall. Snowfields can last well into summer and on very high passes some actually ride out the entire season. Starting your end-to-end hike too early, perhaps in late May, means you will face snowfields and dangerous stream crossings. Most streams along the John Muir Trail are not bridged, and you may find whats usually a mild-mannered drainage has turned into a ripping brown torrent. Be aware that you may be delayed quite a bit if you attempt to traverse the JMT before the first of July.
The majority of days on the trail are beautifully sunny. Temperatures can range greatly, from the upper seventies and even the mid-eighties during the afternoon to below freezing at night. The numerous clear days combined with the high elevation means a thru-hiker can get fried pretty quickly by the sun. The dangerous stream fords and the sun are the biggest concerns on the JMT... okay, besides the lightning... all right, and the bears... and the possible summer snowstorms. But thats it. Really!
With the pleasant afternoon temperatures come intense lightning storms, as on the Colorado Trail in the Rockies. Keep your eyes peeled for cumulonimbus clouds, especially after noon, and retreat from ridgelines if you hear thunder.
Because much of the trail is 2,000 to 8,000 feet above surrounding towns, the average temperatures listed above may not be of much use to the JMT thru-hiker. For example, Lone Pine is located more than 10,000 vertical feet below the summit of Mount Whitney. You could estimate that the temperature on the summit of Mount Whitney is 35 degrees cooler than that in the valleys below. Do your research concerning weather. The Pacific Crest Trail Association posts weather links on their website, including ones that give the Sierra Nevada snowpack from the previous winter.
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Details mentioned in this article were accurate at the time of publication