Hazardous mountain travel conditions, heavy rain and very strong winds this weekend

January 5, 2019 – Wet weather returns today with valley rain and mountain snow. Periods of hazardous mountain travel expected today through the middle of next week due to heavy snow and gusty wind. Gusty winds in the central valley and foothills today and again late Sunday. Brief break in precipitation Thursday and Friday with possible return of precipitation next weekend.

Discussion

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Initial precipitation from a Pacific cold front currently a few hundred miles off the coast is starting to show up on EKA radar at this time. Satellite imagery showing an abundance of high cloud cover over the CWA this morning ahead of the front but this cloud cover only having a minor impact on morning temperatures now running just a few degrees above 24 hours ago. Even some central valley fog has formed again from about Marysville southward.

Models fairly consistent in bringing frontal precipitation into western California during the morning hours and into the Sierra by afternoon. During this time, surface and upper level pressure gradients increase bringing a rapid increase in wind speeds. Models still showing wind advisory criteria wind speeds so have left advisory for the lower elevations in place.

For the higher elevations, combination of wind and heavy snowfall justify winter storm warning now in place for the coast range and Shasta county mountains this morning and for the Sierra Cascade range this afternoon.

Cold front lingers over the Sierra tonight as upper trough moves onto the coast keeping showers going through the night and bringing decreased windspeeds. A return of more steady precipitation occurs quickly as yet another Pacific cold front moves into the north state Sunday afternoon.

As with today’s system, this relatively cold system will keep snow levels below major passes and bring another round of strong southerly winds. Winter storm warning remains in place through the weekend as snowfall is not likely to show much of a break over the higher terrain but the strong winds will drop off between fronts tonight and Sunday morning. The Sunday afternoon wind speeds look as strong as today’s so another wind advisory will likely be needed at some point for Sunday afternoon and evening.

Upper ridge builds slightly on Monday but not enough to keep warm advection precipitation out of the forecast so Monday looks like a day of light showers and higher snow levels. Winds will be a little lighter under the ridge Monday but still rather breezy. Next in the series of Pacific storm systems to march into NorCal hits the north state coast Tuesday afternoon and evening. This system will bring another round of steady precipitation but with higher snow levels than current weekend systems.

Extended Discussion (Wednesday through Saturday)

A Pacific frontal system is expected to move across the area Wednesday morning, bringing Valley rain, high elevation snow, and breezy to gusty winds. Early QPF estimates suggest less than an inch of precipitation across the Valley, and about 0.50-1.50 inches over the mountains Wednesday into early Thursday. Snow levels could remain around 5500 feet.

Mainly dry conditions expected on Thursday, except for some lingering showers over the northern mountains. Forecast guidance indicates a storm system moving into the region late Friday into Saturday. However, models continue to show differing solutions, with the 00z GFS run digging the system into SoCal. Pattern appears to remain active heading into early next week, although confidence is low given model differences.