Winter Weather — Tulare Cty Foothills, California

2012-12-12 to 2012-12-13 · Tulare Cty Foothills, California

Wider weather episode

A weak storm system moved through northern California during the night of December 4th, and moved south the next day bringing a few showers to Merced and Mariposa Counties by noon. Ahead of the storm, patchy dense fog developed in northern Kings County during the early morning hours of the 5th. This was a warm storm, and low temperatures on December 5th were again above normal. The low at the Fresno-Yosemite International Airport on the 5th was 52 degrees, tying the record high minimum temperature for the date. The low at Fresno the next day was even warmed, bottoming out at 55 degrees. This broke the old record high minimum temperature for the 6th by 3 degrees. For the seven days from November 30th through December 6th, Fresno broke or tied the record high minimum temperature on six days.

In the wake of the storm of December 5th-6th, an upper-level ridge formed over the eastern Pacific. The circulation around the ridge set up a northwest flow aloft over California, bringing cooler temperatures. 'Cooler' was a relative term, however, as temperatures were still above normal.

The upper-level ridge also brought a stable environment to the central California interior. This triggered the development of night and morning fog over parts of the central and southern San Joaquin Valley on December 9th through the 11th. December 11th also saw the approach of the next Pacific storm system, which reached the central California interior that night. This storm brought up to 15 inches of new snow to the higher elevations of the Southern Sierra Nevada, and 3 inches of snow as far south as Frazier Park. Snow levels fell into the upper foothills in the cold airmass behind the front, dropping to around 3500 feet during the afternoon of the 12th.

The storm moved east of the region during the morning of December 13th, leaving only a few showers over the Kern County deserts. Behind the departing trough, another east-Pacific upper- level ridge built into the state, bringing more fog to the central and southern San Joaquin Valley.

The airmass was drier the next morning, and in the absence of fog, radiational cooling allowed lows in the central and southern San Joaquin Valley to drop into the upper 20s to around 30.

Source: NOAA Storm Events Database, event_id 427346. Narrative written by the NWS forecast office that issued the report.