January 5, 2018 – Scattered showers this morning. Rain and high elevation snow today as frontal system moves through. Showers ending Saturday then dry Sunday. A stronger and wetter storm moves through Monday and Tuesday.
Discussion
Pacific cold front now moving onto the coast with EKA radar picking up precipitation over the northwest corner of the state. This system will be moving across the north state today. Ahead of this system, a shortwave trough is bringing a few light showers this morning mainly over the higher elevations. Fog has formed this morning at many valley locations but increasing cloud cover should keep it from becoming significantly dense. For the most part, precipitation should remain fairly light today but orographics could bring heavier precipitation over the Shasta county mountains this morning and over the Sierra this afternoon. Snow levels remain high today at generally above 7000 feet so impacts due to snow will be minimal at pass levels.
Front moves into the Sierra tonight then east of the state on Saturday. Snow levels drop to between 5500 and 6500 feet on Saturday but by then precipitation rates drop off significantly. Upper ridge builds on Saturday which should bring an end to any shower activity by evening.
Skies should remain mainly cloudy through the day but daytime highs are still expected to come in several degrees above normal. Upper level ridge slides across the west coast on Sunday so second day of this weekend looks dry with above normal daytime temperatures continuing. Fair skies in the morning will allow valley fog to form thanks to plenty of residual surface moisture from today’s system.
GFS a little quicker with approach of next Pacific system bringing precipitation into NorCal by 12z Monday. ECMWF holds off on precip onset for about 6 hours bringing rain into central California by mid day Monday. This system looks to be bit wetter and on the order of a moderate winter storm. Snow levels will still be fairly high but may drop to pass levels so will need to keep an eye out for winter mountain travel impacts.
Extended discussion (Tuesday through Friday)
Good agreement between the latest operational runs of the GFS and ECMWF with a more significant weather system affecting the region Tuesday as an upper trough moves across NorCal. This system looks a fair bit wetter than this weeks’ weather systems. Snow levels should start out rather high once again but will lower as the trough moves in.
There is also pretty good model consensus in the eastern Pacific ridge rebuilding on Wednesday bringing drier weather across NorCal. A series of short-wave troughs then move through the PacNW late in the week, and depending on how far south they sag, far northern CA may see some light precipitation.