Heavy precip continues into Thursday, flooding likely

February 26, 2019 – Rain and mountain snow, heavy at times, will continue into Thursday with increased flooding potential. Hazardous mountain travel persists into Thursday. Dry Friday, then more wet weather for the weekend.

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Baroclinic zone stretched across NorCal with embedded high PW plume (PWS > 1.25 inches in core). Radar showing heaviest precip attm directed across the Delta and Southern Sacramento Valley, and into the Motherlode and Northern Sierra Nevada. Mesoscale models showing precip increasing this evening as cold front currently near 128 W approaches. Model QPF indicating bulk of precip overnight will be from about I-80 north. With urban and small stream flooding already occurring, the addition of another 1 to 4 inches or rain in the Sacramento Valley, and 2 to 6 inches the foothills and mountains over the next 24 to 36 hours will further increase flooding potential.

As a result, an areal flood warning has been issued. Heavy snow continues in the mountains of Western Plumas and the Northern Sierra Nevada overnight with snow levels remaining around 5000 feet. Strong wind has been occurring in the Northern Sacramento Valley today with sustained wind up to 35 mph and local gusts approaching 50 mph. Forecast pressure gradients suggest strongest wind tonight will be ahead of and along the frontal boundary as it moves through.

Precipitation turns showery Wednesday morning in the post frontal AMS. Best shower probabilities tomorrow look to be over the foothills and mountains as snow levels trend up to around 6000 feet. Instability values look limited so held off adding a mention of thunderstorms in the Central Valley.

Wind expected to drop below advisory criteria Wednesday morning but remain breezy into Wednesday evening.

Cyclonic onshore flow will keep lingering showers into Thursday, mainly over the eastern portions of the Central Valley, extending into Motherlode and Sierra. Snow levels lower Thursday afternoon to around 4000 feet.

Drier weather forecast Friday into Friday night as short wave ridging moves through, then another Pacific storm tracks inland over the weekend.

Extended Discussion (Saturday through Tuesday)

The wet pattern continues through the extended period as multiple weather systems are expected to impact NorCal. The next system moves in overnight Friday, bringing Valley rain and mountain snow through Sunday. Although model consistency is still pretty low on specifics at this point, this is storm does not look to be nearly as wet as the current weather system. Liquid precipitation amounts of a third of an inch up to an inch are possible in the Valley with one to two inches possible in the foothills and mountains. Current model runs are warmer with this system, especially over the Sierra. Sierra snow levels now 5500 to 6500 feet. The northern mountain levels are still a bit lower at 3000 to 4000 feet early Saturday, rising to 4500 to 5500 feet by Saturday evening.

Light mountain showers could linger through Monday, otherwise dry conditions are expected early next week. Another weather system is expected to move in by midweek. Currently models are indicating this system could bring another round of significant precipitation, but confidence is very low this far out. Stay tuned to forecast updates for both of these weather systems as we hone in on the details.