April 3, 2020 – Dry and mild weather expected today. A pair of storms move in over the weekend and continue into early next week bringing rain, gusty winds, chances for thunderstorms, heavy mountain snow, and travel issues.
One more day of dry and seasonably mild weather is expected today. Northerly winds are expected again today, but should be lighter than yesterday, gusting UP to 15 to 20 mph over the northern and central Sacramento Valley this afternoon.
Dramatic changes in the pattern take shape over the weekend as a pair of troughs impact the state. Significant late season snowfall across the mountains is likely along with Valley/foothill rain, scattered thunderstorms, along with gusty winds. While the initial closed low will bring unsettled weather to the region on Saturday, impacts will be somewhat limited given the progressive nature of the system. The bigger storm arrives Sunday with no break on Sunday and continues into Monday as a slow-moving, broad upper low barrels down from the Gulf of Alaska. More substantial travel impacts are likely across the mountains for those who must be out on the roads.
While 4 to 8 inches of snow will be possible across the mountains with the first leg of the weekend storms, conditions are going to become much more impactful on Sunday. Strong forcing with the approaching upper low accompanied by seasonably cold mid-level temperatures (running between -30 and -33C) will be the driver of significant snowfall to the mountains, particularly 4,500 feet and above. Hourly snowfall rates of 2 inches are possible within some of the heftier snow bands. On Sunday alone, some locations over the Sierra-Cascade range could reach 1 to 2 feet of snow with grand totals approaching 3 feet or more in some locales. A Winter Storm Watch continues from roughly early Saturday through late Monday morning for all elevations above 4,500 feet across the interior Northern California mountain ranges. Snow levels will range from 4,000 to 5,000 feet through Sunday night, lowering 3,500 to 4,000 feet by Monday. Snow intensity will decrease during the day Monday, with around another 3 to 6 inches of snow possible.
Down in the Valley and foothills, expect light to moderate rainfall on Saturday as the trough sweeps through. Forecast amounts generally ranging from 0.25 to 0.50 inches over the Valley with numbers closer to an inch across foothill locations. The associated cold front translates through during the middle of the day which is when precipitation will pick up in intensity. By Sunday afternoon, decent vertical shear profiles are noted in model soundings. This would support a threat for a few more organized thunderstorms if they were to evolve. Further inland, dynamics with the offshore upper low combined with focused upslope flow will raise amounts into the 1.50 to 2.50 inch range.
In terms of wind, periods of breezy southerly winds are likely on Saturday, given the strength of the approaching troughs. Valley wind gusts may reach 30 to perhaps up to 40 mph.
Temperatures will be unseasonably cool through the weekend into early next week, with Valley highs in the upper 50s.
Extended Discussion (Tuesday through Friday)
Closed upper low forecast to slowly dig along the CA coast through next week then eventually progress inland over SoCal. More progressive GFS moves low inland early Wednesday while EC is about 18 hours slower. Both scenarios keep unsettled weather over interior NorCal through Thursday. Best chances for showers in our CWA is in afternoons and evenings in the Northern San Joaquin, closer to the low center, and the Motherlode and Sierra Nevada. Drier weather returns next Friday.