Bay Area Remains In a Drought Following Storms, Likely Will Not Reach Seasonal Average for Rainfall

SFIST-04-Feb 2021

Sure, we just saw a lot of rain get dumped on us — some places more than others — but we need a whole lot more, as meteorologists around the Bay Area keep saying.

"The storm did make a dent in the precipitation deficit, but it definitely did not erase it," says National Weather Service forecaster Drew Peterson, speaking to SFGate. "In th... Bay Area, we're kind of halfway where we need to be. At this point, it's a question of how much under normal we're going to be. Each day that passes under normal, it's harder and harder to catch up."

During last week's atmospheric river event, downtown San Francisco saw 2.06 inches of rain over the course of 72 hours, and on Monday night another half inch fell. But with a total of just over 17 inches of rain in the past 19 months, the city is as 46% of normal — and this is the third driest period the city has seen since record-keeping began in 1849.

An #AtmosphericRiver can have a big impact on seasonal rain totals, as can be seen by comparing totals before and after the recent AR event. Percent of normal increases were much greater farther to the south (#SanJose, #Salinas) where the AR persisted for much longer. #CAwx

The rainfall deficits across Northern Calif and the Sierra for the past 19-months continue to grow; with many in the top 10 driest on record. San Francisco and San Jose are the 3rd driest since records began.

The Sierra snowpack is growing, which is good news, but it is still well below the seasonal average. As the Mercury News reports, the snowpack was at 38% of normal before last week's storms, and now it has risen to 68% of normal, so a good deal more snow needs to fall in order for the snowpack to catch up. After some snow on Wednesday, that may rise to 70%.

"If you look at the amount of rain that has fallen over the last 19 months, most places are about half of normal,” says Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay and former NWS meteorologist, who compiled the rainfall data seen in the above tweet. "Last year we began digging a big hole. And this year we continued digging. We would need something monumental and probably catastrophic to get out of it."

Sierra Snow Boost: the jump from 40% of average to 66% of average to date in the last 10 days quantified: Was 5.5" avg snow depth 1.7" SWE, Now 27.3" and 5.7" SWE #CAwx #Sierra

Last February, as you may recall, San Francisco saw zero rain — there was a 38-day dry spell, in fact, that didn't get broken until March 7. And that wasn't even a La Nina year when such winter dry spells are typical in parts of California.

This year's La Nina pattern pushed the rainfall well past December into the new year, and while there's still a chance for drenchings in late February or March, there's not much in the forecast yet.

As NWS Bay Area tweeted this morning, February 2020 was matched only by February 1864 in terms of dryness, and the wettest February on record was in 1998, during the legendarily wet El Nino of that winter.

Taking a look at February extremes for #SanFrancisco:
Warmest high temperature 81° Feb 26, 1986
Coldest low temperature 31° Feb 6, 1989
Driest 0.00" Feb 1864 and Feb 2020
Wettest 14.89" Feb 1998 and was the wettest monthly total for SF during the strong '97-'98 El Nino.

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