After the record heat of the past couple of days, much cooler temperatures return through the Holiday weekend. Slight chances of showers Saturday into Monday in the Sierra and northern Sacramento Valley. Then, dry and breezy conditions return early next week.
Discussion
Skies remain clear across interior NorCal early this morning, though a band of mid and high clouds ahead of the approaching trough is just off to our northwest. Surface pressure gradients are beginning to reverse to onshore. In the areas from the Delta to around the Sacramento region, the return of the Delta Breeze has brought around 4-8 degrees of cooling compared to 24 hours ago with readings mainly in the upper 50s to mid 60s. Elsewhere, temperatures remain little changed to locally up 5-10 degrees compared to early Wednesday. From Marysville up into the Chico area, current temperatures remain very mild in the mid 70s to lower 80s.
Onshore gradients will continue to tighten today resulting in breezy south to west breezes by the afternoon. The onshore flow, along with synoptic cooling from the trough, will bring significant cooling today with many areas expected to see around 10-20 degrees of cooling from the record heat on Wednesday, especially areas closer to the Delta.
In addition to the wind and cooling, a few late day showers or thunderstorms will be possible over northern Shasta County as a short-wave moves onshore.
Cooling will continue through the holiday weekend as the trough moves ashore into the interior West. Scattered showers and a few thunderstorms will be possible over the northern Sacramento Valley and northern mountains, particularly Saturday and Sunday afternoons/evenings.
By Sunday, temperatures will be around 20-30 degrees cooler compared to yesterday.
Extended Discussion (Monday through Thursday)
Ensembles and clusters show the upper low moving into the Great Basin Monday, as this occurs onshore gradients will reverse and become offshore.
The EFI is highlighting portions of northern California for climatologically unusual north winds during the Monday-Tuesday timeframe, so will keep a close eye for any fire weather implications. Valley temperatures warm back into the 90s by Wednesday next week.