January 11, 2018 – Chance of light precipitation north of Chico today, otherwise dry through the weekend with above normal temperatures. Night and morning valley fog likely. Next chance of precipitation late Monday or Tuesday of next week.
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Dirty ridge over the west coast bringing varying amounts of cloud cover to the forecast area this morning. Many locations are seeing clearing under the ridge while lingering surface moisture helps to keep a low cloud deck in parts of the central valley. The central and southern Sacramento valley and delta have remained clear through the morning hours, however, and some light fog has formed there. A shortwave riding over the top of the west coast ridge will bring a chance of light rain north of about Chico. Upper level ridge axis amplifies over the west coast tonight and Friday. Stable conditions and clearer skies south of about Chico will allow fog again southern Sacramento and northern San Joaquin valleys and delta. This fog could become locally dense. A slight chance of light rain far northern forecast area will finally be pushed north of the CWA by Friday morning as the ridge builds. Fair skies and warming airmass with bring up daytime highs to several degrees above normal. High amplitude ridge will bring fair skies through the weekend with daytime highs expected to come in 10 or more degrees above normal. Fog will likely be an issue again night and morning hours valley locations. Upper ridge axis begins to shift east of the state by late Sunday in advance of a Pacific storm system pushing into the eastern Pacific. This will bring a change back to a wetter pattern early next week.
Extended discussion (Monday through Thursday)
The upper ridge will weaken and shift eastward early next week as a series of frontal systems push into the area. The first of these should arrive late Monday or Tuesday. The GFS has fluctuated quite a bit with the timing and amount of precipitation this system will bring. The ECMWF has been a bit more consistent, keeping the bulk of precipitation north of Interstate 80 during the day Tuesday.
Confidence remains high in a second, colder storm system moving through the region late next week and bringing widespread precipitation. With lower snow levels projected, this second storm system has the potential to bring greater snow accumulations over the mountains than most of the weather systems thus far this season.