Monday, 6 December 2021

Two storms to bring scattered showers to the Bay Area this week

November got off to a wet start but dry weather and unseasonably warm temperatures left Bay Area residents wondering when the next drop of rain would come.

The answer could come this week with two chances for light rain in the forecast and the possibility of a more precipitation in mid-December, according to the National Weather Service.

A trough of low pressure is moving over the Pacific Ocean and is expected to bring scattered showers Monday night into Tuesday morning, with a “couple hundredths of an inch” in the southern valleys and around a quarter of an inch in the North Bay, said NWS meteorologist Sean Miller.

Winds will be “breezy” with gusts ranging 20 to 30 miles per hour but only in higher elevations above 2,500 feet, Miller said.

Thursday will be more promising in terms of rain when another weather system could move in.

“It’s looking like Thursday will be a little bit stronger,” said NWS meteorologist David King. “It’s going to be more of a robust cold front and we’re going to see temperatures behind the front as it passes start to drop. It’ll start giving snow levels in higher elevations above 1,000 feet.”

There’s also the possibility for low-level frost in valley areas but “it’s not a slam dunk by any stretch of the imagination” in terms of snow, King said.

There is also the possibility for rain on the 13th or the 14th of the month, although it’s still too far out to be certain, Miller said.

After December started off with a mild heat wave, temperatures will start to “trend back closer to normal” this week with highs in the 50s and lows in the 40s at night,” according to Miller. After Thursday’s storm, temperatures are expected to cool down even more, with many of the valleys ranging in the 30s during the night.

The last time the Bay Area saw significant rainfall was a Nov. 9 atmospheric river storm that dropped 4.88 inches of rain on Middle Peak at Mount Tamalpais, 0.09 inches in San Francisco and 0.58 inches at the Oakland international airport. A much stronger Oct. 24 atmospheric river, a 5 on the UC San Diego Center for Western Weather and Water Extremes’ scale, drenched the region with 4.05 inches in one day in San Francisco, marking the city’s wettest October day on record.

There is currently a La Niña weather pattern occurring in the Pacific Ocean, which causes cold water to rise in the Pacific and can lead to droughts in the western parts of the country. Severe drought has ravaged California after two dry winters in a rows, sparking wildfires and straining power grids.

“When it got into November, it became really really dry and the fact that we’re getting a little rain with higher chances on Thursday, at least that’s an optimistic look,” King said. “It’s definitely positive because there’s no such thing as rain in California that isn’t beneficial but it’s not the type of forecasting we had with an atmospheric river with record-setting rainfall.”


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