March 19, 2020 – Lingering showers possible today, mainly over the Sierra Nevada, otherwise drier weather expected into the weekend with warming temperatures. Widespread rain and mountain snow returns late Sunday into the middle of next week.
Large closed upper low centered over west-central NV this morning is continuing to produce a few light showers over Stanislaus and Tuolumne counties. Some patchy light fog being reported by surface observing systems in the Southern Sac Valley attm. Expect fog development to remain patchy and short lived as boundary layer remains somewhat mixed given current synoptic pattern. Upper low progged to dig towards SoCal today with cyclonic wrap around flow keeping a threat of light showers, mainly over the Sierra Nevada. Elsewhere dry weather expected across interior NorCal today with warming temperatures. Highs today forecast to be about 5 to 10 degrees warmer than Wednesday but remaining slightly below normal.
Upper low progged to retrograde slightly Friday over Central CA and fill. Models suggest a continued slight chance of afternoon showers over the higher elevations of the Sierra Nevada. Additional warming tomorrow with forecast highs near climatology.
Upper low continues to retrograde off the coast early Saturday, then move back onshore as it further weakens. Meanwhile next significant 533 DM low, currently off VRISL, digs off the West Coast. This feature will be the next significant system to impact our forecast area. Models suggest associated precip will spread in from the SW over the CWA Sunday night and Monday. System looks to produce another round of lower elevation rain and significant mountain snow. In the meantime, above normal temperatures expected over the weekend with upper 60s to lower 70s in the Central Valley and 50s to 60s for the mountains and foothills.
Extended discussion (Monday through Thursday)
An active pattern will re-emerge next week as a pair of systems are set to impact northern California. Models show a closed low moving into central sections of the state early Monday which brings a return of precipitation to the region. Eventually a more impressive trough enters the picture which maintains wet weather though at least mid-week.
Yet another upper low originating from the Gulf of Alaska will be cold in nature with snow levels likely around 3,000 to 4,000 feet. While it will not have substantial moisture to tap into, the system is forecast to be fairly dynamic. The combination of energetics with the upper trough with strengthening upslope flow will raise the potential for moderate to locally heavy snow across the Sierra-Cascade range.
At this juncture, 1 to 2 feet of snow looks possible through Wednesday with higher amounts toward mountain summit level. Overall, it will be a cool, unsettled pattern with abundant cloud cover and below average temperatures.