January 4, 2019 – Dry today, then wet weather returns this weekend. Periods of hazardous mountain travel possible Saturday through middle of next week due to heavy snow and gusty wind. Gusty winds in the central valley and foothills Saturday.
Upper ridge axis has now shifted into the Great Basin. This has allowed a great deal of high cloud cover to spill over the ridge and into northern California. Clearer skies from about Oroville south has allowed some light fog to form in the central valley but so far nothing too dense. An offshore Pacific frontal band will approach the coast today but the daytime hours should remain dry under high cloud cover.
Not expecting much change in high temperatures today even with high cloud cover due to warm air advection ahead of the front. Current timing moves offshore front on to the NorCal coast by 12z Saturday with models sweeping it across the state during the day. Timing has been quite consistent but precip amounts have not with GFS remaining consistently wetter than the ECMWF.
Either way, with snow levels below major pass levels, mountain travel issues a high likelihood with several inches to 2 feet or more of snow expected at the higher elevations. In addition to the valley rain and mountain snow, strong south winds are expected ahead of the front on Saturday.
Surface Gradients from MFR to SAC are forecast by the GFS to top 12 mb with 925 mb winds Saturday afternoon indicating 40 knots or higher. Have issued wind advisory for much of the central valley and interior coast range from 15z Sat through 03Z Sunday when pressure gradients should relax behind the front. Showers continue Saturday night through Sunday as upper through swings across the region.
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Next frontal system pushes through quickly on the heels of the first bringing another round of steady precipitation into the north state as early as Sunday afternoon. Combination of relatively low snow levels and precipitation amounts will bring more mountain travel impacts Sunday night into Monday so more winter weather hazard products will likely be needed for this time period. Another round of increased wind is expected Sunday afternoon through Monday but at this time, this wind event does not look as strong as on Saturday.
Extended Discussion (Tuesday through Friday)
A cold front will approach the area on Tuesday with lingering showers expected during the morning hours for communities north of I-80. The frontal system is expected to make it to the north Coast late in the evening and arriving into our CWA early Wednesday morning. Models continue to struggle with the exact timing and strength with this system, but valley rain, mountain snow, and gusty winds are to be expected with this system. They do have some similarities though for Thursday with both keeping lingering moisture around the area and building a ridge on Friday.