A brief cool down today and Wednesday, then seasonably hot weather returns by late-week. A few showers and thunderstorms will be possible later today near the Sierra crest.
The closed low off the coast has begun to shift a bit to the north and east overnight. Increasing lift ahead of it has resulted in a few late-night thunderstorms over eastern Shasta County. Radar shows a few showers continuing to redevelop in that area and move quickly to the north.
Satellite imagery shows clear to partly cloudy skies across the rest of interior NorCal as we remain on the western periphery of monsoonal moisture moving up from the south. Onshore surface pressure gradients remain similar to 24 hours ago, but the increase in mid and high clouds has lead to a little milder temperatures across most of the region. Current readings range from the 60s to mid 70s across the Central Valley.
The early morning showers and thunderstorms over eastern Shasta County are expected to end before sunrise as the low edges a bit closer and shifts the zone of lift further to the northeast.
Afternoon Sierra thunderstorms are expected to be mainly east of the crest today, but areas south of I-80 may see a few storms along the crest. The low is forecast to accelerate northward off the coast of the PacNW tonight and Wednesday.
Breezy south to southwest winds will develop later this afternoon and continue into this evening. Highs today and Wednesday are forecast to be down a bit compared to Monday.
Seasonably hot weather will return for the second half of the week as high pressure over the middle of the US expands westward.
Extended Discussion (Saturday through Tuesday)
Ensemble guidance is in agreement a low pressure system will be just off the Pacific Northwest Coast for the start of the extended forecast period. Thereafter, cluster analysis indicates models diverge slightly into early next week. The low may push onshore with lingering troughing along the coast. High pressure also builds into northern California leading to a warming trend with triple digit highs possible for the northern Sacramento Valley by Sunday. Heat risk remains low to moderate as onshore flow continues over the region helping keep overnight temperatures near normal.