Thread by @Weather_West

Thread on very strong inbound CA storm. A cold & clear morning will quickly give way to increasing clouds, NorCal valley rain & snow down to 1,500-2,000 ft (locally lower) later this PM. Current satellite imagery shows this strengthening system off the coast. (1/10) #CAwx

Tonight, a rapidly intensifying cold front will sweep across NorCal. This front will be unusually well defined, for a CA winter storm, and will replace an already cold airmass with...another cold airmass! (2/10) #CAwx

The cold frontal passage is expected to be quite dramatic across NorCal in the overnight hours. A convective "narrow cold frontal rainband" (NCFR) will likely develop, which could bring a period of torrential rain or snow to many areas, as well as possible lightning. (3/10) #CAwx

Extremely heavy precipitation is possible for a 30-60+ minute period when this NCFR feature moves ashore. Over an inch of rain could fall per hour in some spots. This portion of the event poses a high threat of debris flows in/near recently burned areas. (4/10) #CAwx

In addition to torrential rainfall, the cold front/NCFR will be accompanied by very strong wind gusts across much of NorCal. In fact, high-res models are suggesting potential for gusts of 60-70 mph even in lower elevation places. Widespread power outages possible. (5/10) #CAwx

Meanwhile across the northern and central Sacramento Valley, a very rare heavy snowfall event will unfold. Some places near the Valley floor (near Redding and even Red Bluff) could see a foot or more of accumulation (!). Some lighter snow possible even south of that. (6/10) #CAwx

That very rare, heavy & wet snowfall in the North Valley could lead to widespread disruption and power outages. Meanwhile, extremely heavy snowfall (multiple feet) is likely at slightly higher elevations above 2,000ft. Mountain travel may become impossible. (7/10) #CAwx

Then, on Wednesday, the #AtmosphericRiver/associated cold frontal rainband will likely stall along Central Coast (near border of Monterey/SLO counties). High-res models are suggesting potential for *extreme* 48hr rainfall accums, & very high flood/mudslide risk there. (8/10)#CAwx

The Hwy corridor and Big Sur, as well as the Dolan/River Fire footprints, appear to be at very high risk in this scenario. Other models aren't quite as aggressive with rainfall totals here, but still suggest a high likelihood of 10-15 inches. (9/10) #CAwx

Finally, on Thurs, the cold front/AR will shift southward down the coast. Impacts will be less severe in SoCal than across northern&central CA, but this will still be a pretty robust system as it brings a briefer period of heavy rain/snow to SoCal. (10/10) #CAwx

The new @NWSBayArea morning forecast discussion uses some very pointed language regarding risks associated with potentially extreme rainfall near Big Sur over the next 48 hours. #CAwx