Cold and wet week ahead for California

Yesterday’s system brought a considerable amount of convective activity to much of California, especially southern parts. There wasn’t really any severe weather, but many cells did contain small hail/lightning through the day. An even more impressive duo of cold convective storms will impact the entire state later this upcoming week, though…

GFS depiction of low thicknesses and precipitation over NorCal with first low. (NCEP)

The first storm, due in to NorCal by later Tuesday, will bring some light to moderate rain along the frontal band. The real interesting stuff, though, comes with the subsequent cold-core low center that moves directly over the northern part of the state. Thicknesses drop to sub-530 dm levels in the north and 850 mb temps drop to around -2 to -3 C, which will bring low snow levels and increased lapse rates. Preliminary snow levels appear to be in the 1500-2000 foot range in the far north, 2000-2500 feet around the Bay Area, and perhaps as low as 3000-3500 feet along the Central Coast. These numbers are not especially out of the ordinary for a cold March system. Convective precipitation will be widespread in NorCal, and thunderstorms are quite likely in some places especially if there are sunny breaks in the cloudiness that act to enhance surface heating. I do expect to see a lot of heavy downpours, small hail, and probably scattered lightning strikes. [ad#post-ad-w]

The second (and much more significant) system is slated to move into California by Friday. This system has considerably more cold air associated with it, which is saying something. There is presently a great deal of model uncertainty regarding this system: the GFS depicts a very cold and very unstable pattern with moderate precipitation overall while the ECMWF has a cold and unstable (but less so) pattern with heavy precipitation. The main difference is that the ECMWF brings the low more offshore, which attenuates the cold air aloft but entrains more moisture. Either way, it will be an active and interesting pattern statewide. If the GFS progs turn out to be close to reality, 850 mb temps could drop below -4 C in NorCal and snow levels could fall below 1000-2000 feet in places. Convective chances would be even higher in this scenario, and thunderstorm coverage would be rather high across the state (with the potential for some severe weather if NorCal remains in the jet exit region). We’ll have to see which scenario wins out in the coming days…

GFS depiction of very low thicknesses and significant precipitation over California (NCEP)