March 29, 2020 – Unsettled weather continues today with rain showers and mountain snow showers. There is a slight chance of thunderstorms this afternoon west of I-5. Threat of showers persists in the north Monday through Tuesday morning, otherwise drier and much warmer into the middle of next week.
Latest radar indicates shower activity is increasing over mountains and foothills this morning as a shortwave trough moves onshore. Profiler at Colfax shows snow levels currently at 4600 feet. Visibility has dropped to 1/4 mile at Blue Canyon Airport in snow at 5280 feet. Kingvale has seen about an inch of new snow, with around 1-2 inches at Blue Canyon. Some chain controls are now in effect across portions of I-80, Highways 50, 4, 88, 108, and 36 (Visit quickmap.dot.ca.gov for current conditions). An additional 2 to 3 inches of snow are forecast through today. Mountain motorists should allow extra time for travel and be prepared for winter driving conditions, bringing a winter kit including chains.
Precipitation amounts so far have ranged from less than 0.05″ to 0.20″ in the Valley to around 0.25 to 0.75″ in the northern mountains and northern Sierra. An additional 0.10 to 0.25 is expected through this afternoon. There is a slight chance of thunderstorms this afternoon west of I-5 given the potential for some clearing behind the front. HREF is showing best chance of thunderstorms over the Delta and western portions of the Central Valley. Main threats are small hail, brief heavy downpours, and gusty winds if storms develop.
By early next week, a trough tracking through the Pacific NW and its associated frontal boundary will bring a chance of showers to the northern mountains and the northern Sacramento Valley Monday through Tuesday morning. Best dynamics will remain north of the forecast area; thus, expected precipitation amounts will remain generally under a tenth of an inch. Elsewhere, conditions will remain dry with increasing cloud coverage generally north of I-80. Regarding temperatures, highs are forecast to gradually warm up early next week, and will rise to slightly above normal by Tuesday. Forecast highs on Tuesday will be 5 to 10 degrees warmer than Monday, with Valley highs in the low 70s.
Extended discussion (Thursday through Sunday)
Deterministic and ensemble guidance support increasing heights across the region as an amplifying ridge builds over the West Coast. This should result in dry conditions and above normal highs (generally 5-15 above average).