Brief low snow event in NorCal

Filed in Uncategorized by on December 26, 2007 52 Comments

The next 36 hours could prove to be rather interesting in parts of NorCal. Strong cold air advection is taking place as a Gulf of Alaska system moves south. Only isolated showers–with snow levels in the 1500-2000 foot range–are currently occuring. 3 PM temperatures near sea level on the north coast are running 38-44, and 31-38 at 2000 feet. Temps at 2000 feet in the Bay Area are running 35-40 this afternoon, with very cold 20-30 mph winds yielding wind chills in the low 20s. Temperatures will continue to drop over the next 12 hours as the sun sets, more cold air moves in aloft and winds begin to die down a bit. Interior valley locations will see some 20-25 degree readings tomorrow AM, and even parts of the Bay Area’s urban core will see lows in the 29-34 degree range. By early AM (3-4 AM or so) clouds will begin to move in ahead of an incoming weather system. Although the incoming system is not particularly cold, the bottom 10,000 feet of the atmosphere will remain quite cold for this area because the mid-level cloud deck will act as a “lid,” trapping radiationally cooled air near the surface. As a result…temperatures will struggle to reach 40 degrees throughout NorCal tomorrow, even near the coast and elsewhere at sea level. Precipitation will move in by late PM, and with evaporational cooling and the surface cold layer some snow or sleet could fall all the way to sea level as far south as the northern Bay Area. No real accumulation is expected below 1000 feet, but this would still be a very rare event. Above 1000 feet, up to 1-2 inches of snow accumulation could occur before precipitation switches to mainly rain by midnight below 2000 feet. The Northern Sacramento Valley and the Motherlode stand to see actual snow accumulations of 1-2 inches (places like Redding, Chico, Grass Valley, Colfax, etc.). Stay tuned, as these types of events can always be even more dramatic than expected or can peter out just before occuring (it’s a very fine line between liquid/frozen precip, esp. in CA). After a few days of cool and unsettled weather (with some more strong offshore winds for SoCal), we will see several days of dry (and actually quite mild) weather. Rain chances increase again by late next week, however…we certainly could use a Pineapple Express right about now…