Cold storm this week

Today’s cutoff low produced some shower and thunderstorm activity in SoCal, which is still ongoing in the San Diego area. Light rainfall was widespread south of Santa Barbara, and some locations saw heavier amounts where convective downpours occurred. Not drought-busting rainfall, but every bit helps at this point. Conditions will become slowly drier over the next 12 hours before skies clear on Tuesday across the entire state for a sunny but cool day. All attention then turns to the approaching Gulf of Alaska storm system that will begin to impact the north part of the state late on Tuesday night. This system will be a cold one, and will be preceded by a moderately strong cold front. This cold front will actually be capable of producing some rather significant rainfall in NorCal late on Wednesday and early Thursday, along with some locally strong gradient-derived winds and possibly some thunderstorm activity. 1-4 inches of rain could fall in the North, with some higher totals possible. The front will maintain much of its strength as it drops south into SoCal, and could produce some heavy rain there, too. The main story, however, will be the very cold and unstable airmass that moves in behind the primary cold front. 850 mb temps will drop to nearly -6 C in the far north and as low as  -4.5 C around the Bay Area. The all-important -3 C isotherm may slide all the way south to the Los Angeles area by Friday, and 0 C temps at 850 mb will be experienced in Baja California. The result? Snow levels around 1000 feet (or perhaps a bit lower) will be experienced near Eureka, as low as 1500 feet in the Bay Area, 2000 feet in the LA County Mountains, and perhaps 2500-3000 feet in the mountains east of San Diego. Even though these snow levels will not be quite as low as they were in January of this year, the chance for precipitation when the cold air aloft will be present is much higher. As a result, some accumulating snow is possible over many of the hills in NorCal, and in the foothills of SoCal. In addition, lapse rates will become quite steep as the sun angle is now slightly higher than earlier this winter and potential insolation is greater. As a result, there is a pretty good chance of thunderstorm activity, possibly strong, over all of the state on Thursday. The heavier cores of convective showers may be able to produce some accumulating hail showers down to sea level, esp. in the north. Stay tuned, as this storm could bring very beneficial 2-4 foot snows to the Sierras…