February 17, 2024 – Active weather returns this weekend into next week. Rain, isolated thunderstorms, mountain snow and gusty winds are expected at times through the holiday weekend, heaviest Sunday night into Monday.
Discussion
Storm number one is approaching early this morning with extensive cloud cover overhead and radar picking up areas of virga or very light precipitation. Winds are generally light and temperatures remain very mild, in the upper 40s to lower 50s across the Central Valley, and mainly in the 30s to lower 40s over the mountains.
Precipitation will begin to spread inland later this morning and through the afternoon as warm-advection increases. The period of heaviest precipitation will be this evening as the cold front moves through. There will also be a chance for thunderstorms this evening with the mid-level short-wave trough moving across the region.
Gusty southerly wind will also increase by this afternoon as surface pressure gradient tightens ahead of the approaching cold front. Gusts of 40-45 mph will be possible in the Sacramento Valley and adjacent foothills into this evening and a Wind Advisory has been posted.
A Winter Weather Advisory remains in effect for elevations above 6000 feet from later this morning through early Sunday morning, when periods of difficult travel will be possible.
The second storm system is trending stronger than the first one and will arrive Sunday afternoon and bring periods of moderate to heavy rain, mountain snow, gusty winds and isolated thunderstorms through early next week.
A Winter Storm Warning remains in effect for the Sierra and Western Plumas/Lassen Park area above 5500 ft.
The National Blend of Models (NBM) has a 55-95% probability of 12 inches of snow or greater over 72 hours through Monday night, with a 40-80% probability of 24 inches of snow or more.
Mountain travel is highly discouraged while the Warning is in effect, as potential impacts include difficult to impossible travel conditions, snow covered roads, chain controls, reduced visibility and road closures.
Widespread moderate to heavy precipitation will bring concerns for minor flooding of urban and poor drainage areas, slick roads, longer than normal travel times, and moderate rises on rivers and streams. The NBM has a 80-100% probability of 1 inch of rain over 72 hours through Monday night for much of the Valley and foothills, with a 50-80% probability for 2 inches mainly in the foothills and in the Valley north of Interstate 80 over the same timeframe.
A FloodWatch has been issued from Sunday afternoon through Wednesday morning for much of the Valley, foothills and Coast Range.
The Extreme Forecast Index (EFI) also highlights a strong signature for CAPE over much of interior NorCal with the second storm, and this is matched by the NBM with probability of 20-40% for thunderstorm development on Monday.
We will be keeping a close eye on how this trends as we get closer. When thunder roars, go indoors!
Periods of gusty southerly winds are expected, and winds are trending stronger for the second storm compared to the first one. The NBM shows a 50-90% probability of wind gusts greater than 40 mph on Sunday and Monday, with a 40-80% probability of wind gusts greater than 47 mph on Monday. Gusty southerly winds may cause loose objects to blow around, create difficult driving conditions for high profile vehicles, and bring down tree branches.
Plan ahead for impactful weather over the next several days, and always check the weather forecast and road conditions before heading out the door
Extended Discussion (Wednesday through Saturday)
Lingering showers possible Wednesday as upper troughing moves through interior NorCal, best chances over the mountains. Forecast then trends drier Thursday into Saturday with warming temperatures under upper level ridging.
Models differ with progression of ridge and upstream upper low. More progressive EC/NBM brings a threat of showers over southern half of CWA Saturday afternoon into night as low weakens and moves into SoCal.