Strong storm for Northern California; active pattern continues statewide

Our midweek did bring a nice soaking rain to much of Northern California, with lesser amounts in the south. The system currently taking shape over the Eastern Pacific, however, appears to be significantly stronger. Recent infrared and water vapor satellite imagery indicates a moist plume interacting with a strong cold front, and a substantial amount of cold air following the front (as evidenced by significant open-cellular convective cloudiness).

Infrared Satellite Imagery of incoming storm system (NRL)


The storm system is expected to continue strengthening over the next 24 hours as it comes closer to the West Coast. Light warm advection-type rains may begin by tomorrow afternoon along the coast, but significant rainfall will hold off until Friday in most places. This system is expected to have stronger jet dynamics that the Tuesday event, and the atmosphere is likely to be much more unstable due to colder air aloft and the position of the jet exit region. As such, rainfall totals are likely to be uniformly higher than on Tuesday–perhaps in excess of 3-4 inches in the coastal mountains of NorCal and up to around 2 inches in the inland valleys. SoCal won’t see as much rainfall–perhaps 1-3 inches in the mountains and less than an inch elsewhere. Rainfall rates in the north (where convective activity is most likely) may be rather high, so some localized flooding problems are possible especially in places that saw more than an inch of rainfall yesterday. The models have been ramping up pressure gradients along the coast in the past couple of cycles, and the 00z GFS has 850mb winds from 50-55 kts early Friday. This could lead to some pretty significant gusts at the surface, especially given the likelihood of embedded convective elements in the cold frontal precipitation band that could bring these winds locally to the surface. Gusts to 50 mph or so are possible along the coast and in the hills, and possibly in the Central Valley, as well. Lightning is possible along the front, and may also be possible in the conditionally unstable airmass behind the front late Friday into early Saturday.

GFS 850 mb heights and wind field (NCEP)

After Saturday, California will see a brief break in the active pattern before a rather cold system moves in by next Tuesday. The models are still struggling a bit with the details of this system, but it does appear that a cold E. Pac. trough may pinch off into a cutoff low over CA and bring some very unstable conditions to much of the state. Stay tuned!