Periods of rain, snow, and breezy winds through Wednesday with flooding concerns and mountain travel impacts. Additional storms expected late this week and weekend. Continued rises on area creeks and streams; limited mainstem river flooding expected the rest of this week. Potential for storm track to shift north of California middle to end of next week.
Discussion
The trough has shifted east as short-wave ridging moves into NorCal. Radar is still showing some lingering scattered showers mainly along I-80 and northward early this morning. Warm-advection is beginning to ramp up with the approach of the next system, and IR imagery shows a well defined maturing baroclinic leaf with the system off the coast.
Expect to see light to moderate rain develop across interior NorCal early this morning with snow picking up again across the northern Sierra where snow levels are expected to gradually climb from around 4k ft early this morning to above 6k ft by this evening.
Southeasterly breezes will also pickup again today with gusts of 25-35 mph expected in the valley. The heaviest QPF over the next 24 hours is expected across the Coast Range, mountains of Shasta County and the Feather River basin – areas where south to southeast flow will generate the greatest orographic enhancement. These areas will likely see around 2-3 inches of additional rain with some areas north of Redding possibly seeing 4 inches.
A Flood Watch is in effect for these areas from later this morning through Thursday morning. For the valley, the north end will likely see around an inch with amounts tapering as you head south. Around a half inch is expected in Sacramento and a quarter inch across the northern San Joaquin Valley.
Snow will pick up again this morning across the northern Sierra. Snow levels will also begin to gradually rise through the day, and will likely be at or above the higher pass levels later tonight. 4-8 inches of additional snowfall accumulation is expected at the higher pass levels with up to a foot over the peaks.
Winds will likely be a bit “lighter” compared to recent days. The Winter Storm Warning will be allowed to expire at 4 AM, replaced by a Winter Weather Advisory in effect through 4 AM Thursday.
The next incoming trough will take its time arriving as it digs offshore. Precipitation will retreat north and westward tonight and Thursday as the warm front lifts up into far northern California.
The next cold front is forecast to stall over northwest California where heavier QPF will be focused before the approach of the trough nudges the front inland on Friday. Still some uncertainty on the details on how quickly this will evolve and how far west the precipitation will retreat tomorrow.
Recent hi-res models have been indicating that moderate precipitation may hang in across the Coast Range and northern half of the Sacramento Valley on Thursday, so this is something we’ll be watching closely for potential increased flood impacts.
The wet pattern continues with another system forecast to move in on Saturday. This one may be a little more vigorous, but quick hitting as another negative-tilt trough swings through.
Expect to see potentially higher precipitation rates, but shorter duration. Winds will also likely be a bit stronger with another round of gusts above 40 mph through the Central Valley.
Extended Discussion (Sunday through Wednesday)
Showers expected Sunday as we are on the tail end of an exiting weather system. Looking upstream, models continue a strong zonal polar jet extending across the Pacific which remains focused into CA.
This will result in additional rounds of precipitation and their associated impacts: flooding, wind, mountain snow, etc… as multiple storms track through over the extended forecast period.