November 28, 2017 – Dry weather this week outside of a few showers across far northern California this afternoon and evening. Patchy valley fog may develop each morning. Next storm system arrives Saturday.
Upper level high pressure ridge centered over the west coast this morning bringing fair skies to the CWA. Only wild card is possibility of valley fog. Stable conditions, surface moisture from yesterdays rain and clear skies will make at least patchy fog likely but still not sure how dense this fog will become. Most locations will see a little warming today. Exception will be the far northern CWA where the tail end of a shortwave trough moving through the Pacific Northwest will bring some cloud cover and a little cooling.
Shasta and Tehama county coast range may see some very light rain this afternoon with the northern Shasta mountains seeing a slight threat of showers this evening as the trough lifts to the north and east. Remainder of CWA will see little impact from this system.
Upper ridge rebuilds over west coast on Wednesday bringing a little warming all areas. Meanwhile, surface high pressure moves in over the Pacific Northwest behind the retreating trough resulting in a tightening northerly surface gradient across NorCal. This will bring breezy north winds on Wednesday.
Strongest winds will be in the northern Sacramento valley especially west side. The breezy north winds will last into Wednesday night and this may restrict valley fog formation to the northern San Joaquin valley and south of Sacramento.
Lighter winds are expected on Thursday as another shortwave trough skims the north state as it moves through the Pacific Northwest. This system remains farther north than the system moving through this afternoon and will have even less impact. Thursday daytime temperatures may even warm slightly. High pressure remains over the west coast on Friday for continued fair skies and above normal daytime highs but lighter north winds could allow morning valley fog to slip farther north of Sacramento.
Extended discussion (Saturday through Tuesday)
Lots of uncertainty for the forecast this weekend and early next week as latest operational model runs of the GFS and EC are showing little consistency in handling the incoming weekend trough. Have deferred to the previous forecast and made only minor changes.