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High Sierra Thunderstorm, Tuolumne Meadows
A regular feature of High Sierra weather during Summertime are local thunderstorms.
These thunderstorms are the most powerful expression of the relationship between the Valley and the Sierra Nevada. During most of the year the weather in the Sierra is a product of a vast system of energy distribution operating on a planetary scale.
Typically, the storms that bring our Winter snows begin thousands of miles away in the Bearing Straight.
This is not the case for Summer thunderstorms in the Sierra.
These powerful storms are generated by local heat and evaporation generated in the San Joaquin Valley, pushed up the Western Flank of the Sierra on the wings of Pacific breezes, and cooled rapidly by the climb. This violently transforms hot Valley air fat with moisture into cold air sweating moisture, and this transformation can be felt in Earth shaking thunder and seen as massive bolts of lightening highlighting torrential downpours, all topped off by great sunset shows as the storms tear themselves apart at twilight.
Delightful, but dangerous. Violent T-Storms are not always the outcome of Valley heat.
During Summertime heating trends in the Valley determine the daily progression of local weather in the Sierra. When temps are lower than 100 degrees in the Valley the evaporative clouds pushing up the Sierra are minimal, and the daily cycle of clouds and clearing will not threaten thunderstorms.
But when temps in the Valley hit 100 degrees the T storm mechanism can begin operating. If a heat wave breaks out in the Valley a multi-day "heat pump" can begin operating, with each day's rising temps pushing powerful storms like clockwork up the West flank and Sierra Crest, to explode into violent thunderstorms and torrential downpours. These daily storms die with each days sunset, when the energy source of this vast heat pump, the Sun, sets.
It is each Sierra backpacker's obligation to observe the recent trends and changes in the daily weather pattern. If the pattern is forming daily thunderstorms (generally they form between 2 and 3 pm, but sometimes things get weird) it is your obligation to make sure any high crossings of open spaces do not coincide with nearby thunderstorm activity.
In this page's embedded video I had already arrived and set up camp at the backpacker's camp at Tuolumne Meadows before the thunderstorm broke out.
I was ready, as thunderstorms dotted the last couple of days of my trip across the North Yosemite Backcountry in late June and early July of 2013.
Listening to the rain tapping on my tent was delightful, while the thunder and lightening gave an edge of excitement to this otherwise tranquil scene.