Unsettled weather returns to Northern California this week. Cooling trend will bring below average temperatures to the region into the start of the weekend. Chances for showers are also possible through Saturday with best chances over the mountains. Breezy winds at times will also be likely.
Satellite imagery indicates pre-frontal clouds are starting to reach far northwestern California and will slowly make their way into interior Northern California through the day today. Some clouds from the closed low just off the Southern California Coast have also spread northward into the southern San Joaquin Valley this morning. Lingering wildfire smoke will mean hazy skies in the morning before more substantial clearing is expected as the trough off the Pacific Northwest Coast edges closer and onshore flow continues to increase over the region. The San Joaquin and Sierra will be the last areas to see improvement in smoky conditions. Cooler temperatures are expected today as we transition into a more unsettled pattern. Highs today are forecast to drop around 10 degrees today compared to Monday’s highs. Highs across the Valley will generally be in the 80s which is near normal for this time of year. Breezy winds, particularly over exposed ridge tops and wind prone areas will be possible today with gusts generally from 15 to 25 mph. Dry conditions are expected for much of the region but some light showers could start to reach our the interior coastal range tonight.
Wednesday will see temperatures decrease further with below average highs in the 70s forecast across the Valley. Increasing humidities and light shower chances will spread across the region with best chances for measurable precip over the higher terrain. Ensemble guidance is coming into better agreement about the trough elongating down the West Coast before splitting into somewhat separate features. The southern piece of the trough could lead to some shower chances over the Sierra Thursday into Friday with a quarter to a half inch possible. The EFI depicts cooler temperatures also sticking around Thursday through Saturday as the trough slowly makes its way over central California. The cool air in place could also support some short lived snow over the highest terrain, generally above 7500 feet. Breezy winds will also be possible at times.
Extended Discussion (Saturday through Tuesday)
Unsettled weather will slowly be moving out of our region for the start of the weekend. Ensemble guidance expects short wave ridging to lead to dry and warmer conditions by Sunday before another trough digs into our region early next week. This next trough is looking to have less marine influence with more of a land/coastal based origin leading to very minimal shower chances over the mountains and drying northerly winds possible through the Valley. Uncertainty is present with exact location of the trough and has yet to come into good agreement in dynamic cluster analysis. The depth and location of this trough will greatly influence expected impacts for Northern California. Some clusters would produce fire weather concerns for the Valley while other scenarios would likely lead to more moderate impacts. It is also worth noting the EFI has a stronger signal for gusty winds through the Valley early next week.