March 17, 2021 – Dry weather continues today. Precipitation chances return Thursday and Friday. Winter Storm Watch from Thursday afternoon through Friday evening for West Slope Northern Sierra Nevada.
Discussion
Satellite imagery shows a large area of high-based stratus (5-7k ft msl) covering the northern third of the forecast area. Elsewhere, skies are mostly clear other than high clouds beginning to spread into the region ahead of the late-week trough.
Current temperatures and dew points are a little higher compared to 24 hours ago, and with more cloud cover compared to early Tuesday, early morning valley frost is expected to be far less extensive.
Dry weather will continue today. High clouds will become more extensive as the day progresses as the upper ridge axis shifts east into the Great Basin.
The next system begins to spread precipitation into far northern California late tonight and early Thursday. The bulk of the precipitation is expected later Thursday and Thursday night as the front and associated weak AR move gradually southeast.
QPF is expected to be a bit higher than the previous system with around a third to half an inch possible through much of the valley, and 1 to 2 inches over the foothills and mountains.
Snow levels will be higher with most of the heavier snowfall accumulations expected above 5-6k ft. The higher peaks may see 18-24 inches of accumulation through Friday. The winter storm watch remains in effect.
Precipitation turns more showery on Friday as the upper trough moves overhead. There may be enough instability for a few thunderstorms across the Sacramento Valley and surrounding terrain.
Some showers may linger over the mountains on Saturday, but overall drier weather is expected as the trough weakens.
Extended discussion (Sunday through Wednesday)
Dry weather expected Sunday as EPAC upper level ridging extends into NorCal. Short wave trough riding the ridge then drops SE across eastern portions of CA into the Great Basin Monday into Monday night.
Main threat of showers expected in the Shasta and Plumas mountains, and Sierra Nevada. Snow levels progged around 3500 to 5500 feet with little to no accumulations expected.
Drier weather returns Tuesday into Wednesday with warming temperatures and some breezy north to east wind.