Cooling onshore flow ends heatwave


WEATHER WATCH: Governor Jerry Brown declared a State of Emergency in Tulare, Mariposa, and Madera counties due to wildfires ravaging the region. An air quality alert is also in effect for Three Rivers and Sequoia National Park due to smoke.

There is a town-wide power outage scheduled for Thursday, Sept. 14,
from 2 am to 12 pm.


That extended heatwave that had nearly all of the western U.S. trapped under a ridge of high pressure finally relented during the Labor Day weekend as an onshore flow of cooler ocean air eventually brought seasonal temperatures for at least the next seven to 10 days. By the workweek, daytime highs will be in the 80s, nearly 20 degrees cooler than just a few days ago.
On Sunday, Sept. 3, the convection associated with all that stagnant hot air caused some isolated locales to experience wacky, windy weather highly unusual for the dog days of summer.
Weather gurus often use the term “convection” interchangeably with thunderstorms. But that’s wet convection; convection can be dry too. Essentially, convection is the vertical transport of heat and moisture in the atmosphere, especially by updrafts and downdrafts.
During Labor Day weekend, Kaweah Country witnessed a battle of sorts between hot air, moist at times, and cooler air aloft trying to force the scorching heat up and over the Great Western Divide. Most of the tug-of-war occurred Sunday with the more pronounced effects in the higher elevations.
Lightning strike in Three Rivers— Lightning touched down above South Fork Drive, striking a tree near the AT&T cell tower and causing a mid-afternoon spot fire. The quick response of the National Park Service helicopter that deposited some bucket loads of water on the blaze prevented the fire from becoming potentially dangerous.
Lightning strike in the Sierra— Near Jennie Lake in Giant Sequoia National Monument, three people were reported to have been struck by lightning. A source following the incident stated that they were transported to Fresno for treatment by a CHP helicopter.
A rare wind event— In Mineral King, wind gusts of 40 to 50 mph played havoc with a quota-filled backpacking weekend. In the Mineral King, the high winds swirled through the valley from sunup to sundown Sunday. There was no major damage reported, but there were trees down, lots of branches falling, a couple rockslides, and high waves on the lakes that rim the valley. The weekend also featured plenty of thunder and, in two separate downpours, dumped pea-sized hail and an inch of rain.

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