Winter Storm in California, October 21 to 22, 2012

By the 19th, high pressure began to weaken and exit the region, while marine-cooled air moved inland from the Pacific Ocean and allowed temperatures to cool by several degrees. In addition, a relatively cold low pressure system was approaching the Pacific Northwest and continued to move toward central California through the next couple of days. Consequently, temperatures cooled another several degrees by the 21st. The storm system arrived by the early morning hours of the 22nd and brought rain and snow to the region. This system was the first winter-like storm to impact the southern Sierra Nevada in terms of snowfall.

The cold front tapered off to the south as it moved through central California. Most of the precipitation fell north of Kern County. Fresno received a quarter inch of rain, and around a tenth of an inch fell in parts of Kings and Tulare Counties, but rainfall in the south end of the San Joaquin Valley was measured only in the hundredths. Up to a foot of snow fell above 7000 feet in the Southern Sierra Nevada.

An unseasonably cold airmass moved into the central California interior behind the cold front. High temperatures in the central and southern San Joaquin Valley north of Bakersfield were only in the 60s, with Fresno tying its record low maximum temperature for October 22nd of 63 degrees, set in 1889. The south end of the San Joaquin Valley was a little warmer, with highs in the lower 70s.

An east-Pacific upper-level ridge slowly built into California, with its progress impeded by a broad trough that covered much of the eastern half of the United States and Canada. Temperatures warmed to near normal by the 25th, and, after one day of near-persistence, continued warming to above normal on October 27th and to as much as 12 degrees above normal by October 30th.

The average temperature for Fresno for October was 69.1 degrees, for the 8th warmest October on record. The average temperature for Bakersfield was nearly a degree cooler at 68.2 degrees.