February 28, 2020 – Dry with above normal daytime temperatures again today. Cooler with gusty wind this weekend along with a threat of showers, mainly in the foothills and mountains. Dry and warmer early next week with breezy north to east wind.
Pacific frontal system approaching the PacNW attm as lower latitude closed upper low progresses towards the CA coast. Abundant mid to high level cloudiness, associated with closed low, lifting up into the area today. Cloudiness will help to lower max temps, but highs will still be well above normal with potential new records in the Southern Sac/Northern San Joaquin Valleys.
Frontal system tracks into the PacNW tonight into early Saturday, then secondary colder short wave trough digs offshore near 130W tomorrow. Increased dynamic/orographic forcing over the Shasta mountains by the afternoon could result in some scattered light showers. Significant cooling expected Saturday with locally breezy conditions. High temperatures are forecast 10 to 15 degrees lower than today.
Associated upper low then progged to dig south through the CWA Saturday night and Sunday. CAA continues over the area Sunday with breezy to windy conditions. Potential for some showers over Interior NorCal, spreading from north to south, Saturday night and Sunday. However, with limited available moisture, best chances for precip will be over the eastern foothills and mountains. Snow levels lower into the foothills Sunday, as snow ratios increase, but little to no accumulations expected at those elevations. Bulk of snow will fall over the higher elevations of Western Plumas mountains and Sierra Nevada. 2 to 5 inches of snow are possible at pass levels Sunday with locally up to near 8 inches over the higher elevations of the Sierra Nevada, south of Highway 50. Main threat of precip for the Central Valley looks to be along the east side, with only a few hundredths expected. Wind speeds continue to ramp up Sunday, with potential for wind advisory in the Northern and Central Sacramento Valley, extending into the western foothills and Coastal Range, Sunday afternoon into evening.
Shower threat winds down Sunday evening as upper low digs into SoCal and upper ridging drops in from the north. Breezy conditions continue Sunday night into Monday under strong northerly flow aloft and EPAC surface high building inland through OR into the Great Basin. AMS warms Monday under increased subsidence and downslope flow. Highs Monday return to above normal with upper 60s in the Central Valley, 40s to low 60s for the mountains and foothills.
Extended discussion (Tuesday through Friday)
The extended period will start out dry and mild as a ridge of high pressure builds back over interior NorCal. Forecast highs in the Valley will be in the low to mid 70s, with mountain locations in the mid 40s to low 60s. These temperatures are forecast to be 5 to 10 degrees above average for early March. Locally gusty north winds are expected through Tuesday.
Deterministic and ensemble guidance show signs that the ridge may break down late next week. This would suggest the possibility for some precipitation making it down to interior NorCal. However, confidence in any specific details is low at this time.