An unusual deep low pressure area off of the coast of Baja California is funneling copious tropical moisture over the Southwestern United States. Rain has been falling all morning in SoCal as far north as Santa Barbara. Almost everyone has seen some rain, and totals of over 0.75 inches have been suprisingly widespread. The rain actually appears to be increasing, with more developing and enhancing offshore. A precipitible water plume of nearly 2 inches is focused on Arizona, but SoCal will continue to see period of occasionally heavy rain for the next 12-24 hours. Convective parameters are not great, but there is some cold air aloft moving in from the north and with such a saturated atmoshperic column combined with east-side diffluence/divergent flow aloft there exists a small possibility of some thunderstorms developing today. The rainfall has been heavy enough to trigger flooding over the recent burn areas, and some fairly serious debris flows could occur in the vicinity of the recent fires near San Diego. Significant flooding is even more likely in Arizona, where rainfall on the order of 3-4 inches could fall. This storm has been handled terribly by the deterministic models, and sort of took us by suprise (the extent and magnitude of the rain, at least). This actually helps out quite a bit in SoCal (if we can escape damage from debris flows), putting a damper on further wildfire activity for a few weeks at least. NorCal has not seen one drop of rain from this system, though–just cold and clear up here. The system will eventually turn into the Midwest’s first major winter storm of the season, with blizzard conditions developing over the Plains States. After the weekend excitement exits SoCal, our attention shifts north…
An extremely powerful baroclinic storm system will undergo bombogenesis off of the Oregon coast early next week. The extreme temperature differentials at the 850 mb level will fuel explosive development of this storm system as it approaches the coast on Monday, with a 120kt jet streak at 850 mb! If that were taken literally, 130+ mph wind gusts would be possible near the surface in western Washington and Oregon. Winds probably won’t get quite that strong, but I fully expect to see some gusts over 100 mph. 12-15 inches of rainfall will be possible in a 24 hour period on SW-facing slopes, so some significant flooding is possible (especially given the lowland snow that is supposed to fall in the days preceding this warm storm. Seattle could see 3 or 4 inches of the white stuff on Sunday!). Heavy rain and strong winds will impact the far NorCal coastal areas to a lesser extent, with 2-3 inches of rainfall and 60 mph gusts possible. However, there are some indications that even in the absense of heavy rainfall, some pretty strong winds could occur at higher elevations near the Bay Area and the Sierras. Stay tuned about this one–there could actually be some pretty severe wind damage in some places as a result of this storm. Even with all this active weather, however, Central California, the part of the state that need rainfall this time of year to replentish the aquifers and reservoirs, will see very little over the coming week. The GFS is now indicating the potential for a retrogressive cold low over CA beyond day 7, with cold temperatures and possibly some showers. At least the monotony has been broken in some places…
