January 12, 2021 – Light precipitation will be possible north of I-80 through Wednesday. Otherwise, dry weather expected with areas of late night and morning valley fog. Temperatures warming to well above average late in the week.
Discussion
NorCal remains on the southern periphery of a strong AR aimed at the PacNW. Satellite imagery continues to show extensive high clouds covering the region while radar indicates light precipitation so far remaining mainly to the northwest of the forecast area. Despite the clouds, surface observations are indicating areas of light fog developing in the Central Valley to the south of Oroville as RH’s are running slightly higher compared to 24 hours ago, and short-term guidance indicates patches of thicker fog are expected once again around sunrise lasting until mid-morning.
Far northern California will remain on the warm side of the system today and Wednesday. Light precipitation is expected to spread further inland across NorCal today (into the northern half of the Sacramento Valley, and about as far south as I-80 in the northern Sierra Nevada) as warm-advection ramps up. Precipitation will decrease and retreat north tonight before another wave of warm- advection moves in early Wednesday.
QPF of 1 to 2 inches through Wednesday will be possible over the mountains of Shasta County to the north of Redding, with rainfall amounts expected to quickly taper off to the south. Snow levels will be above 7-8k ft, so accumulating snow will generally be limited to the highest peaks.
Strong ridging builds into the region late in the week and into the weekend bringing a return of dry weather, and possibly more extensive late night and morning fog. High temperatures will be around 10-15 degrees above average threatening daily record highs.
Extended discussion (Saturday through Tuesday)
Strong EPAC upper ridge will be dominant synoptic feature through the extended forecast period. This will result in dry weather with high temperatures upwards of 10 to 15 degrees above normal.