Ken Clark

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Coldest Air of the Season for California

January 09, 2013; 2:04 PM

Just a quick update today. Back on Monday I wrote that a big change was going to take place from the Northwest south through California this week. That is already taking place now in the Northwest and moves south into California tomorrow. Really no big changes from my discussion on Monday.

Now I am going to get a little weather geeky for you here to show how big of changes take place.

In central California, the temperature at 850 mb (5,000 feet) this morning was around 13C. By sunup Thursday that will have dropped to 3 below zero C and down to 5 below zero C Thursday afternoon. The 500 mb height was around 577 dm, but this will fall to 537 dm Thursday afternoon. These are huge changes. Similar things happen in Southern California. The 850 mb temperature this morning was +14C but will be down to 1 below zero C late Thursday.

There will not be a lot of precipitation with this change. A few scattered showers will occur with the cold front in northern then central California tonight. The front will pass through Southern California first thing tomorrow morning with at best a stray shower. The upper-level trough itself will also probably produce scattered showers in central California, especially midday on. In Southern California, there will probably be a better chance for a shower inland from the coast in the afternoon and evening than with the front. Snow levels will fall to 1,000 feet or so around the Napa Valley to east of Sacramento, down to 1,500 feet in the Central Coastal mountains and southern Sierra and 2,000 feet in Southern California by later in the day. A dusting can occur down to the snow level with a few inches above 4,000 feet especially on west-facing mountains in the Sierra and north-facing mountains in Southern California.

Accompanying this change will also be a lot of wind Thursday. Coastal areas will get winds of 15-30 mph with gusts to 35-40 mph with similar winds in the Central Valley. In the Southern California deserts, winds will increase to 20-40 mph with local gusts to 55 mph that will cause blowing sand and dust. Outside of that area in Southern California, expect winds 15 to 30 mph.

Friday and Saturday are going to be cold days no matter where you are. The Central Valley will have highs in the 40s with lows at or below freezing with a hard freeze likely in the colder spots. There can be a frost right to the coast in Central California Friday or Saturday morning, but especially Saturday, with lows in the lower to middle 30s. Southern California coastal areas can have a frost Saturday morning. Freezes are likely in the coastal valleys of central and Southern California with the coldest spots having a hard freeze with temperatures in the 23- to 27-degree range in sheltered coastal valleys of the Central Coast and also inland Santa Barbara and Ventura counties.

The upper deserts Friday will struggle to get back to the upper 30s and lower 40s then dip into the mid-teens to low 20s by Saturday morning with Saturday during the day being as cold as Friday and Saturday night being frigid with teens again in the cold spots.

The lower deserts will have highs of only lower to middle 50s Friday and Saturday with lows both mornings of the weekend from the mid-20s in the colder spots to the lower to mid-30s in the more populated areas.

At the resorts, better really bundle up. Lows will be in the single digits with highs only in the lower to middle 20s.

Lastly, expect very rough surf and some coastal flooding tomorrow into Friday with dangerous rip currents. Breakers will be in double-digit heights on the favored west-facing beaches.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or


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Ken Clark
Ken Clark's Western U.S. weather blog tackles daily weather events with commentary from one of the most experienced and trusted Western U.S. weather experts.