This system has met or exceeded all expectations–in terms of heavy SoCal rainfall, significant thunderstorm activity, and even very low snow levels. Although shower activity has decreased substantially across most of the state from its peak this PM, more showers and isolated thunderstorms will redevelop mainly over or near coastal areas by the early morning hours as the cold core of the low–and its associated vorticity maximum–move slowly south along the CA coast. This is where things get interesting. Temperatures from the Bay Area northward–regardless of elevation–have uniformly fallen into the 30s (currently 36 in San Rafael). Many sea level sites are currently below 35 degrees, and some have already dropped to freezing or below. With the uptick in showers expected by sunrise, and further radiational cooling over the next six hours, I would expect at least some snow to fall all the way to sea level from the Bay Area northward (except, probably, on the beaches), and this may even be more widespread than currently forseen. It is possible that showers will be so sparse that very few areas see snow, but I fully expect to see pictures of unexpected winter wonderlands in the morning. SoCal will see snow levels drop below 2500 feet tomorrow, with local sites as low as 1000 feet or even a little lower seeing brief snow showers tomorrow morning or Wednesday morning. Thunderstorm activity may occur once again tomorrow from the Bay Area southwards, and given the locally severe activity over the past 24 hours and increasing instability near San Diego, some large hail or even a tornado or two remain within the realm of possibility. Once the precip and clouds clear by Tuesday night in the north and Wednesday night in the south, very cold overnight temperatures will lead to a significant and potentially damaging deep freeze over much of the state, with widespread lows in the low to mid 20s in more inland areas. Highs even in the sunshine will not make it out of the 40s this week in NorCal. The current GFS has discarded the “warm storm” scenario and is going with a remarkably long-lived cold and wet pattern. We could see more showery, convective, and cold weather with potentially low snow levels through the rest of December. It appears that a larger than normal number of Californians may see a white Christimas this year…
