December 10, 2018 – Series of weak storms will pass over NorCal over the next several days but precipitation and impacts will be minimal with each of them. Valley fog will continue to be possible between systems.
Radar shows spotty light precipitation across interior NorCal spreading southward with the weakening cold front early this morning. Temperatures are milder compared to 24 hours ago and only patches of fog are present in the valley from around the Sacramento area southward. Current temperatures range from the mid teens to 20s in the mountain valleys to the upper 30s to mid 40s elsewhere.
The front will continue to weaken as it moves south into the San Joaquin Valley by this afternoon. Very light (generally less than a tenth of an inch), though spotty, amounts of precipitation will be possible today with around an inch or so of snow possible over the mountains. Clearing develops by this evening except for some lingering showers across the northern Sierra.
Developing north winds will limit widespread fog chances tonight and Tuesday morning, though some patchy fog could develop along the more sheltered east side of the Valley. Dry weather is expected Tuesday, but warm-advection ahead of a fast-moving system will result in increasing cloudiness during the afternoon. The brunt of that system will affect the PacNW, though some light precipitation will be possible across the far northern portion of the forecast area on Tuesday night as it skirts by to the north.
Stronger ridging will result in dry and milder weather Wednesday and Thursday, and northerly flow is expected to be strong enough to limit extensive fog development (particularly early Wednesday).
Extended Discussion (Friday through Monday)
Mid range models in a little better agreement in bringing a Pacific Frontal band through Norcal during the day on Friday. QPF values are not especially high with this one but snow levels are low enough that some mountain travel impacts are likely. May see a brief break in precipitation Saturday as flat upper ridge slides quickly across the west coast but overrunning precipitation could still bring a few showers north of Sacramento.
Next Pacific storm system moves quickly into NorCal next Sunday. ECMWF a bit slower than GFS with this one bringing this system into NorCal Sunday night. Models diverge going into early next week with varying amounts of upper ridging so uncertainty remains high for this time period. Daytime temperatures will remain around normal throughout the extended period with occasional breezy south winds as weather systems progress though.