The National Weather Service (NWS) in Sacramento writes in their area forecast discussion today:
Near to slightly below normal temperatures are expected to persist through the week. Even cooler temperatures, breezy/gusty winds with showers and mountain thunderstorms possible late this week.
…
Ensembles and clusters show an anomalously cold low pushing
through northern California late Thursday and Friday, potentially
into Saturday.
The NWS mentioned this on Sunday, 8/18 on their Facebook feed:
Cooler than normal high temperatures observed this afternoon across interior NorCal. Sacramento (City) hit 89, Redding, Oroville, Vacaville and Modesto 88, Stockton, Tracy, Red Bluff and Marysville 87, Fairfield at Travis AFB 86, Paradise and Vallejo 80. In the Sierra Nevada, Blue Canyon reached 70 and South Lake Tahoe 75.
The national forecast from the NWS, seen above in the feature image, shows this trend extending into next week.