Cool and unsettled weather pattern into next week. Shower chances remain across far northern California through this evening. A stronger system will bring a better chance of showers and mountain snow early next week. Mountain snow, Valley & foothill rain, widespread thunderstorm chances, & breezy winds early next week, heaviest snow Sunday.
Discussion
Pattern change is well underway with the big cool down that began Thursday with the initial short-wave brushing across far northern California. Partly to mostly cloudy skies cover the region early this morning as we’re in-between systems.
Onshore surface pressure gradients have relaxed a bit, but local southerly breezes in the teens to lower 20s mph persist in the valley and foothills while a few gusts in the 30-40 mph range continue across the higher elevations.
Next short-wave moves in later today and tonight. Ahead of it, a cold front will push south again this afternoon and evening resulting in tighter surface gradient and a return of more widespread gusty south to southwest winds.
Moisture will be pretty limited behind the front, but increasing forcing with the approach of the short-wave will lead to scattered showers across the northern mountains later this afternoon into this evening, with a few showers possible in the northern Sacramento Valley and northern Sierra.
Enough instability is also present for a few thunderstorms across Shasta County into this evening. A relative break in the weather is expected Saturday, then the main upper trough is forecast to settle in across the region early next week leading to several days of more widespread shower and thunderstorm activity along with even cooler temperatures.
It’s a little early to pin down the finer details, but ensembles have been trending toward potential for impactful snowfall across the northern Sierra Sunday afternoon and evening.
Extended Discussion (Tuesday through Friday)
Long wave trough off the West Coast with embedded short wave Tuesday brings a threat of showers to much of the CWA. Lingering mountain showers possible over the Sierra Nevada Wednesday. Another short wave trough progged across northern portions of the forecast area Thursday.
Drier weather expected Friday with some breezy north to east wind as EPAC upper ridging builds inland. Below normal high temperatures expected Tuesday through Thursday, then warming to slightly above normal Friday.