February 29, 2020 – A weather system will bring mountain and foothill snow, gusty winds, and cooler temperatures this weekend. Sierra travel will be impacted tonight due to periods of moderate snowfall. Dry and warmer early next week with breezy north to easterly winds.
Discussion
A surface cold front is moving through Northern California early this morning. This will bring cooler daytime temperatures to the area today with a temperature change of around 10 to 15 degrees from yesterday. Ensembles are still on track with a positively- tilted upper level trough deepening and moving through California this weekend. This trough will bring the return of precipitation to NorCal, though it will mainly be limited to the mountains and foothills. Precipitation will begin this afternoon over the souther Cascades as the lee side of the trough begins to move over NorCal, spreading south into the northern Sierra into the late afternoon and evening with periods of moderate snowfall possible.
Precipitation will continue through the night, with showers likely to linger through Sunday morning. This will be a colder system with snow levels initially 5000-5500 feet, lowering rapidly overnight to around 2000-2500 feet by Sunday morning. However, the majority of snowfall is expected before the snow levels begin to drop, so only light accumulation is expected below 5000 feet.
Model guidance has increased QPF slightly, so snow amounts have increased as well. Around 4 to 6 inches, locally up to 8 inches, are forecast at Sierra pass level. Since there has not been significant snowfall in quite a while, have decided to issue a Winter Weather Advisory in coordination with our neighbors from 4pm this afternoon through noon Sunday. Sierra travelers should prepare for periods of moderate snowfall, chain controls, and travel delays.
The trough axis is then forecast to slowly deepen and move south over California Sunday before slowly moving southeast Monday. Gusty north winds are expected Sunday as the surface pressure gradient tightens. The MFR-SAC gradient is forecast around 10-12 mb which will produce a decent wind event with Valley winds 20-30 mph with gusts up to 40-45 mph, especially over the northern and central Sacramento Valley. The strongest winds will be Sunday afternoon through evening before tapering off after 8pm. A Wind Advisory remains in effect from 10am to 8pm Sunday. Daytime temperatures will cool another 3 to 10 degrees Sunday with Valley highs in the upper 50s to low 60s and the mountains in the 20s to 30s.
Breezy conditions will continue through Monday as the upper trough continues to move southeast. Unfortunately, high pressure builds once again Monday into the week, bringing the return of dry weather and rising temperatures. Temperatures are forecast to quickly rise back to the upper 60s to low 70s in the Valley on Monday, and warming another few degrees Tuesday. HEC
Extended Discussion (Wednesday through Saturday)
Above average temperatures, sunny skies and somewhat breezy conditions will persist through Thursday. Models are trending towards a cooler and more unsettled pattern by next weekend. Projections this far out are likely to change, however there is enough indication of some possible moisture moving into our area that the forecast includes some low precip chances by the end of the extended forecast period.