High Wind — S Sierra Mtns, California

2011-12-01 to 2011-12-02 · S Sierra Mtns, California

Wider weather episode

This is the continuation of the Mono wind event from November 30th. This continued through December 2nd.

December began with an upper-level trough over the region and a low pressure center over the Desert Southwest. Northeast winds flowed around the low and knocked over numerous power line poles and trees throughout the central San Joaquin Valley, the Sierra Nevada foothills and Yosemite National Park. Fresno was also hit hard by power outages due to downed poles; this prompted a local emergency in the city during the afternoon of the 1st. Fresno County reported about $2 million in damages due to the strong winds. Mariposa County and especially near the town of Mariposa, numerous large trees were toppled by the high winds. Numerous large trees were downed in Yosemite National Park, with power outages and blocked roads in Yosemite Valley.

Winds gusted to 45 mph at Fresno-Yosemite International Airport on December 1st, just shy of the record gust for December of 48 mph'on December 28th, 1991. Winds gusted to 60 mph at Tioga Pass, and over 50 mph at Coalinga. Trees were blown down at several locations, including Clovis and Mariposa.

Officials at Devils Postpile National Monument in eastern Madera County reported widespread forest destruction in the monument with numerous large trees downed. In addition roads were closed for months and several outbuildings were also damaged.

An automated station at the summit of Mammoth Mountain a few miles to the east of Devils Postpile recorded sustained wind speed of 150 mph, and gusts in excess of 150 mph (the limit of the anemometer). Therefore wind gusts with this storm were estimated around 200 mph at the peak of the event early on December 1st. Red's Meadow in Devils Postpile is aligned in a NNE to SSW direction which favored the extreme downslope wind pattern from the nearby Sierra Peaks during this storm. The historic magnitude and duration of this event was caused primarily by an extreme pressure gradient set up between strong low pressure in the desert SW and strong high pressure off the Pacific NW coast.

This high wind event was known as a severe and relatively rare Mono Wind event; where winds flow over the Sierra Nevada and down into the foothills from the east instead of the typical westerly direction. These winds allow the air to warm adiabatically; temperatures rose dramatically in much of the San Joaquin Valley compared to the previous day.

Yet despite the severe winds, the southeastern part of the San Joaquin Valley remained almost completely wind sheltered and areas of dense fog developed during the night of November 30th-December 1st along a corridor stretching from Visalia south to Bakersfield.

Source: NOAA Storm Events Database, event_id 355398. Narrative written by the NWS forecast office that issued the report.