California Experiencing a Seesaw of Wet and Dry Weather

After a week of toasty weather that sent the mercury climbing above even normal summer temperatures in some spots last week, California is getting a brief respite: A storm system is set to cool things off and bring rain and snow back to the thirsty state on Wednesday.

Brief is the key word, though, as warm and dry weather — though not quite as blistering as last week’s — is expected to return for the weekend and stick around through the end of the month.
 

February, typically one of the wettest months of the year for California, has been a disappointment this year for those hoping for meaningful drought relief, especially given a strong El Niño. While winter storms have improved the situation somewhat, they haven’t come close to erasing the drought.  But there is a glimmer of hope on the horizon, with signs that March could bring a return to wet weather.

Winter storms, fueled by one of the strongest El Niños on record, finally returned to California this year, after several hot, dry winters in a row — aided by a push from global warming — ushered in a deep drought. While those storms dumped plenty of snow on the Sierra Nevada mountains, building up a key water resources, not everywhere in the state has benefitted. Much of Southern California was still well below normal precipitation levels even before last week’s heat wave brought a disconcerting case of déjà vu.

The ridge of high pressure that set in last week was reminiscent of the one that camped out over the West over the last few winters. The sunny, warm weather knocked down the Sierra Nevada snowpack to below-normal levels, though it still remains far above last year’s meager showing.

Record temperatures were broken in spots throughout the state, with some daily highs topping 90 degrees around Los Angeles. (Overall, record highs are outpacing record lows as the world warms.) Such hot weather can drive up water demand, potentially worsening the drought situation, something that usually isn’t as much of an issue in the mild winter months.

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Credit: NWS

This week’s storm system has managed to push its way past that high pressure ridge, and with a tap into tropical moisture sources, it could bring some decent rain to the whole state and a foot or two of snow to mountain areas, Daniel Swain, a PhD student of climate science at Stanford University, said in a blog post. It will also bring temperatures back down to more seasonable levels.

But that rain and snow is a relative drop in the bucket. It “does nothing to make up for the past two weeks of dryness,” state climatologist Michael Anderson said in an email.

“All in all, this system will be enough to water the plants, freshen the ski slopes, and clear the air, but it won’t accomplish much in the way of drought relief,” Swain wrote.

After the rains clear, high pressure slides right back in, bringing a return to warm, dry weather.

It’s not unusual to have long stretches without storms in winter in California, Swain said, but Californians had been hoping that El Niño would juice February rains based on what had happened in previous El Niño winters. Why that hasn’t happened isn’t an easy question to answer, but every El Niño is different, and even small shifts can mean big changes in its impacts.

Forecast models suggest that the usual waltz of high and low pressures in the atmosphere will cause a shift back to wet weather in March, according to Swain. However, nothing is certain, and “with each passing dry week it’s getting decidedly harder to make up the accumulated seasonal deficits in Southern California,” he wrote.

There is still some time, though, and Californians have their fingers crossed.

“We will have to wait and see what transpires through the rest of winter and spring to see where each locale stands and what impacts are in play,” Anderson said.