The Washington PostDemocracy Dies in Darkness

California sees major drought improvement as onslaught of storms ends

More than 32 trillion gallons of rain have inundated the state since late December

The Salinas River rises on the morning of Jan. 13 in Salinas, Calif. (Paul Kuroda/For the Washington Post)
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Since late December, at least nine major storms have socked California, dumping up to 20 feet of mountain snow in the higher elevations, a widespread 15 to 25 inches of rain in the valleys and about 32 trillion gallons of water overall on the previously parched state. At least 20 people have died in the three-week barrage of deluges and windstorms.

Now the state welcomes a respite and the opportunity to take advantage of tranquil weather to repair damaged roadways and infrastructure as floodwaters subside.

The toll extreme weather took in the U.S. during 2022, by the numbers

The rain has been a blessing from a drought standpoint. Three months ago, 41 percent of the state faced “extreme” or “exceptional” drought, according to the federal drought monitor. That percentage has since dropped to zero, although more mild levels of drought still cover most of the state.

What happened to the atmospheric rivers?

Between Dec. 20 and Jan. 15, at least nine atmospheric rivers blasted California like a fire hose — only shutting off for short intervals. Atmospheric rivers are narrow strips of deep subtropical moisture generated by ocean storms. Their moisture can originate from as far away as Hawaii.

Atmospheric rivers can carry a billion pounds of moisture overhead every second, the bulk of which is most heavily concentrated a mile up in the atmosphere. That’s why the mountains often pick up the most precipitation.

Every winter features atmospheric rivers. Where along the West Coast they hit, however, varies from season to season. Since they’re dragged east by low-pressure systems, they’re at the mercy of the storm track, which is influenced by the jet stream.

Atmospheric rivers transfer massive amounts of water over thousands of miles, bringing flooding and winds to wherever they make landfall. (Video: John Farrell/The Washington Post, Photo: Melina Mara/The Washington Post)

For the past month, the jet stream has been swooping southwest to northeast in the eastern North Pacific. That’s allowed a conga line of low-pressure systems to develop and track toward the California-Oregon border, each of which pulled atmospheric rivers into California. That west-to-east jet stream pattern has since broken down, resulting in a storm track unfavorable for West Coast atmospheric rivers.

In California, a drought turned to floods. Forecasters didn’t see it coming.

How long will this break last?

Stagnant high pressure is in the process of building west of Vancouver Island. This dome of high pressure will deflect the jet stream northward. That will lead to a lengthy stretch of dry weather as the high-pressure zone fends off any intrusions of the jet stream, atmospheric rivers or moisture. In other words: no storms, no atmospheric rivers.

A look at a long-range weather model shows a significant surplus of rainfall and mountain snow compared to average in northwestern British Columbia and adjacent southeast Alaska. That’s an indicator of how far north the atmospheric rivers will be nudged. They don’t look to return to California anytime soon.

That said, there are some indications that the high-pressure ridge could weaken in early February, which would allow the return of more active weather. It’s too early for specifics, but California might not be done with atmospheric rivers for the winter.

Is the drought over?

The drought isn’t over, but there has been significant improvement on multiple fronts. California desperately needed this rainfall, although too much of a good thing too quickly can be a recipe for problems.

If you were to average out all the precipitation that fell in California between Dec. 26 and Jan. 17, 11.47 inches would have fallen everywhere across the state.

At the start of the water year in late September, 94 percent of California was gripped by varying degrees of drought; the number has since dropped to 43 percent, and the remaining drought is classified as “moderate” or “severe,” rather than extreme or exceptional.

More beneficial than the rain is the longer-term storage of moisture in the Sierra Nevada snowpack. Some places at the highest elevations have seen up to 20 feet of snow in the past four weeks.

In the central Sierra Nevada, the snowpack is at 255 percent of normal, and in the southern Sierra, close to three times the normal amount.

Sierra snow is sometimes even more valuable to California than liquid rain, since it remains at higher elevations and more gradually melts, pacing the release of waters. That will allow more of the water to be captured by California’s aquifers, supplying agricultural operations and hydropower.