December 14, 2017 – Dry and mild weather into early next week with chilly nights in the valleys.
Discussion (Today through Sunday)
Overnight model analysis and water vapor imagery continued to show a large amplitude upper level ridge in place over California with plenty of dry air in place. Mostly clear skies during the early morning hours allowed for cool temperatures across the area with valley temperatures in the low to mid 30s and lower 20s for the higher elevations.
Latest model guidance shows the upper level ridge of high pressure maintaining strength through today and tonight. High temperatures across the area today will range between 5 and 15 degrees higher than average. Clear skies tonight will allow for rapid cooling with frost and patchy fog in some valley locations.
The upper ridge will break down Friday as a quick moving trough of low pressure slides through northern California Friday night. With a lack of atmospheric moisture ahead of the trough, not much precipitation is expected. There is some decent agreement for some light rain for the mountains north of Redding between GFS/ECMWF/NAM, so placed a slight chance of precipitation in the forecast. North winds will increase for the valley and create some gusty conditions Saturday into Saturday evening.
The quick trough moves through the region by Saturday night and another ridge builds for Sunday and into the beginning of next week, keeping dry and warm conditions across the forecast area.
Extended discussion (Monday through Thursday)
High pressure will continue to bring mild daytime temperatures and cool overnight lows through early next week. Models have come into to agreement with a cold Pacific storm system dropping south mid-week. This system breaks down the ridge rather rapidly and brings a few impulses of precipitation across Northern California. Have introduced precip chances Wed-Thur to reflected possible pattern change. This is the first run of model agreement(GFS/Euro) and relatively low confidence remains.