March 24, 2020 – Widespread showers return today thru Wednesday with mountain snow leading to hazardous mountain travel conditions. Showers linger into Thursday. Dry and milder late this week.
Discussion
Secondary cold front moving into northwest CA early this morning as upstream cold upper trough closes off to the southwest of Vancouver Island. Satellite imagery shows clouds filling in across most of the region the past several hours and radar has begun to indicate a few light showers popping up over the northern Sierra. Current temperatures are mainly in the 30s across the mountains with 40s to lower 50s in the Central Valley.
Shower activity will become more widespread today as the front gradually shifts southeast and stronger short-wave ejects from the base of the trough across NorCal during the afternoon. Snow will likely pick up this afternoon across the northern Sierra, and GFS and EC ensembles still indicating around 6-10 inches of snow accumulation at KBLU thru Wednesday, heaviest later this afternoon and tonight. Travel impacts likely increase for this area by this afternoon.
Main thunderstorm threat area for this afternoon still appears to be across the northern half of the Sacramento Valley as previously mentioned short-wave and associated mid-level winds overspread the area. Heavy rain, small hail and gusty winds likely the primary threat with stronger storms, but total shear does hint at non- zero potential for some longer-lived storms.
Shower chances continue across the region on Wednesday (as the upper trough moves overhead) before decreasing Thursday and Friday as short-wave ridging gradually replaces the trough. Temperatures will remain well below average today and Wednesday before moderating a bit late in the week.
Extended Discussion (Saturday through Tuesday)
Short wave trough moves through interior NorCal over the weekend with model differences on timing and strength. Attm, Saturday afternoon looks like the highest probability of seeing some precipitation with best chances over the mountains. Overall QPF looks light with snow levels around 4000 to 5500 feet. Model differences increase early next week. EC and ensembles tend to favor a drier solution with warming temperatures under upper level ridging.