Cool weather continues today along with a chance of mountain showers and thunderstorms. Dry weather and warming temperatures return beginning Sunday.
Discussion
Satellite imagery shows the upper low closing off over far northern California. Radar indicates showers and thunderstorms have diminished across the northern half of the forecast area from Friday evening, but a few showers continue from Tehama and Plumas Counties northward. Onshore flow persists, but surface pressure gradients have weakened as cooler air spreads across the region.
Cool and unsettled weather will continue today with most shower activity likely confined to the foothills and mountains, but a few may occur elsewhere as stronger vorts slide through the trough. With the low overhead, overall shear will be pretty weak most of the day, so the primary threat with storms will likely be some brief heavy rain and small hail with stronger cells.
Shear does increase some later this afternoon as the low drifts a bit to the east, and hail may become more of a threat with stronger cells as forecast soundings indicate some healthy CAPE (~ 250-500 j/kg) over the northeastern portion of the forecast area. Otherwise, showers will likely taper off this evening as the airmass stabilizes and the trough edges into Nevada. Highs today will remain unseasonably cool (around 10-20 degrees below average).
Weak troughing will remain in place over NorCal Sunday into early next week but warm air will still build in from the southeast. This will warm temperatures in the lower elevations back into the 80s Sunday, into the 90s on Monday, and triple digits again beginning on Tuesday.
We will also see northerly winds develop Monday with lowering humidity. Gusts up to 20 mph will be possible over the Sacramento Valley during the afternoon.
Extended Discussion (Wednesday through Saturday)
Ensembles indicate onshore flow will prevail through Saturday, as weak troughing continues to influence interior NorCal. EFI suggests above normal temperatures for the extended forecast period. Temperatures will start to gradually cool after Wednesday, with Valley temperatures dropping down from triple digits back to the upper 90s by Friday, remaining a few degrees above average. Another trough will slowly approach the region late-week, however it looks like dry conditions will prevail through the extended.