December 5, 2018 – Light rain and snow showers today, ending on Thursday. Mainly dry on Friday and Saturday with morning valley fog possible. Heavier rain and mountain snow possible early next week.
Upper level low pressure system off the coast with shortwave trough pivoting northward through the CWA this morning bringing scattered light showers mainly to the central part of the state. This shortwave will continue to pivot northward during the day reaching the northern part of the state by this afternoon. Precipitation amounts with this system are expected to remain light so impacts should remain minimal. The main upper low is forecast to drop southward off the SoCal coast on Thursday moving into the south state by Thursday afternoon. Therefore, expect shower threat to remain over the southern CWA Thursday then ending over the entire forecast area by Thursday night.
Mild upper low airmass will keep daytime highs today and Thursday just a little below normal. Brief upper ridging slides over the west coast on Friday bringing dry conditions and a little warming most areas. Fair skies and lingering surface moisture will bring a chance of morning valley fog. Upper ridge axis shifts east of the state by Friday night.
A shortwave trough moving into the Pacific Northwest on Friday night will bring a slight threat of showers to the coast range and northern CWA through Saturday. Again, precipitation amounts are expected to remain on the light side. Another, stronger Pacific frontal system will approach the coast Saturday night. Showers will be possible along the coast range by morning before bringing another round of precipitation to NorCal early next week.
Extended Discussion (Sunday through Wednesday)
A system is forecast to bring rain and snow to Northern California Sunday through Tuesday. Primarily dry conditions will be seen Sunday before precipitation moves across the area from the northwest by the late afternoon or evening. While there is still some disagreement in models on precipitation amounts, preliminary forecast snow amounts up to 10 inches look possible across passes. This will likely hinder travel in the mountains through early Tuesday. Precipitation amounts across the Valley look normal for this time of year with QPF amounts around a half inch.
There will likely be another break in precipitation later on Tuesday before another system approaches the northern Sacramento Valley late Tuesday night into early Wednesday morning.