September 22, 2020 – Chance of showers over the Shasta and Coastal mountains Wednesday night and Thursday, otherwise dry weather expected. Temperatures close to average this week, then hot, dry, and potentially windy conditions return over the weekend.
Discussion
Band of high clouds is moving across NorCal early this morning associated with short-wave passing to the north of the region. Otherwise, skies are clear. Increased onshore flow is gradually bringing improved air quality inland from the coast, but it has been a slow process. Good air quality now covers the northern San Joaquin Valley and extends about halfway up the Sacramento Valley, but the southerly flow is also pooling unhealthy air across the north end of the Sacramento Valley.
Onshore flow will continue across the region today as the initial short-wave lifts out and another weaker one brushes the far northern part of the state. Temperatures will be down a few degrees compared to Monday. Brief ridging will bring slight warming and lighter winds on Wednesday.
Next upstream trough forecast to move through the PacNW on Thursday. It will push a weakening frontal system into NW California on Wednesday night and Thursday with only very light QPF expected over the far NW corner of the forecast area. Dry and warmer weather returns beginning Friday.
Extended Discussion (Saturday through Tuesday)
High pressure builds over interior Northern California over the weekend into early next week. This will result in a warming trend with above normal temperatures. Highs by Monday/Tuesday in the Central Valley will be in the upper 90s to around 100, hottest in the Northern Sacramento Valley, with 80s to low 90s for the mountains and foothills. Breezy north to east wind develops Saturday and continues into early Tuesday. Combination of wind, hot temperatures and low humidity will bring elevated fire weather conditions.
