March 3, 2020 – Dry through Thursday with well above normal daytime temperatures. Some record highs likely today and Wednesday in the Central Valley. Chance of precipitation late Friday into the weekend.
EPAC high extends inland over NorCal and will be dominant synoptic feature for the next several days. Unseasonably strong subsidence will result in highs today and Wednesday at near record levels with some new records likely to occur. Record high temps forecast at KRBL, and KSCK today; and KSAC, and KSCK Wednesday.
With 1036 mb surface high extending inland through Oregon into the Great Basin, and thermal troughing over interior NorCal, some breezy northerly wind expected again today in the Sacramento Valley, Delta, and locally in the Coastal Range. However, wind speeds will be lighter compared to Monday, in the 10 to 20 mph sustained range with local gusts up to 30 mph. Pressure gradient weakens by Wednesday morning.
Heights begin to fall Thursday as upper ridging shifts into the Intermountain West while deep upper low from GOA digs SE towards the West Coast. Highs remain about 10 to 15 degrees above normal Thursday, but are forecast below record values. Clouds begin to increase from the NW Thursday afternoon as associated Pacific frontal system approaches.
Baroclinic zone progged to push inland Friday with a threat of some light precip beginning over Shasta county by the evening. Synoptic cooling and increasing cloudiness Friday will result in a drop of about 6 to 12 degrees in max temps. Front then moves slowly across Interior NorCal Friday night through Saturday. Model QPF differences exist attm, but main theme is light precipitation expected in the Central Valley with orographic forcing favoring moderate amounts over the mountains of Shasta and Western Plumas, and over the Northern Sierra Nevada Saturday.
Extended discussion (Saturday through Tuesday)
Ensemble models continue to indicate an upper level trough will move through NorCal on Saturday, bringing precipitation to the forecast area. Precipitation expected to become widespread Saturday as a surface front and the trough axis move through. Showers could continue through Sunday and Monday, mainly limited to the mountains and foothills, as ensembles depict a closed low deepening just offshore. Current guidance has backed off on Valley precip chances somewhat with only light showers expected at this time. Travel impacts are expected in the mountains as upslope flow will likely produce more precipitation than the Valley, though it is not clear at this time how impactful this system will be. There is low confidence in precipitation amounts and specific timing details at this time due to model inconsistencies. Snow levels forecast to fall to around 4000-5000 feet by early Saturday morning after the surface front passes, then falling down to the upper foothills Saturday night. Gusty southerly winds are expected Saturday with the trough passage.