October 4, 2018 – October 4, 2018 – Showers today ending from the west tonight. Mainly dry Friday except a few showers possible northern mountains. Breezy to strong north winds over the weekend with drying and increased fire danger. Dry early next week with temperatures a little below normal. A chance of showers again northern mountains around mid week.
Upper low pushing through southern California over night now in the southern Great Basin. There is still a few showers this morning over the northern Sierra associated with this departing low. Meanwhile, an upper trough dropping into the Pacific Northwest is bringing some light showers to the northwest corner of the state. The upper trough is forecast to dig southeastward through northern California today bringing a chance of showers to most of the forecast area. The highest chance of showers will be over the Sierra Cascade range this afternoon.
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Cloud cover and cooler airmass will bring down daytime highs today down to between 5 and 10 degrees below normal. Showers end from the west tonight as the upper trough shifts east of the state. Friday looks dry most areas but another shortwave trough tracking through the Pacific Northwest Friday afternoon will bring a threat of showers to the Shasta county mountains Friday afternoon and evening. Models show this trough digging into the Great Basin Saturday as high pressure builds over the eastern Pacific.
Northerly flow between these two systems combined with a strong northerly surface gradient will bring breezy to strong northerly winds to much of the forecast area over the weekend. The northerly winds will bring lowering RH values Saturday with a little more drying Sunday. Current forecasts keep minimum RH values generally above 20 percent on Sunday so not expecting critically low moisture. Daytime highs are expected to remain below normal.
Extended Discussion (Monday through Thursday)
Dry weather with northerly winds continues into Monday, though winds are expected to decrease in strength, gusting to around 20 mph in the Valley. High temperatures are expected to be near average. Gradual cooling is expected Tuesday and Wednesday as a low drops into the Great Basin, with just a slight chance of light showers over the Sierra.