Brief update today. Summary: Cold and unstable with low snow levels days 2-5. Possible deep freeze and local sea-level flurries days 5-9. Large uncertainty beyond day 2.
The initial cold front is currently moving across far NorCal as expected, and will usher in dramatically colder conditions over the next 24 hours. Showers will begin increasing tomorrow from north to south, with snow levels quickly dropping to 1000 feet in the far north, 2000 feet in the Bay Area, and 3000-4000 feet south to Los Angeles by late Saturday. By Sunday, reinforcing cold air will be pulled in from the Canadian interior and snow levels will drop further, and will vary from between sea level to 1000 feet on the north coast, the Valley floor to about 1000 feet in the N. Sac. Valley, and 500-2000 feet in the Bay Area (depending on time of day and intensity of precip). It is possible that snow levels will drop even further by Wednesday, but the amount of precip in NorCal by that time is questionable. SoCal will see snow generally as low as 2500-3000 feet, though by Wednesday these could drop even lower if there is still precipitation around. Convective instablity will be significant, and I fully expect scattered heavy showers with lots of small hail and isolated lightning strikes. The models now appear to be developing strongly meridonal (N-S) flow just off our coast by Wednesday, which is the kind of pattern that truly can bring deep freezes along with snow flurries to just about any location in the northern half of the state and possibly even SoCal. Precip in such a pattern would be very low, but would probably fall as all snow. Certainly stay tuned–this has been only one side of a rather flip-floppy forecast lately (and the flip side is cold and dry weather, but not exceptionally so).