The Pineapple Express is an airborne river. Another one is drenching California.

Another Pineapple Express has been bringing massive April showers to California since Thursday. And this one is so big it may set records.

A Pineapple Express is an example of an atmospheric river, a channel in the atmosphere that moves vast amounts of moisture. This kind forms over Hawaii (hence “pineapple”) and directs moisture toward the West Coast. Daniel Swain, a University of California Los Angeles climate scientist, told Vox last month that it channels “more water than the Mississippi River.”

The last Pineapple Express hit the West Coast in late March, bringing torrents of rain that caused flooding and mudslides and triggered evacuations in Southern California.

Now, the National Weather Service is expecting up to 8 inches of rain through Saturday further north — in the Santa Clara Valley and parts of the San Francisco Bay Area. It’s also calling for 6 to 8 inches snow parts of the Sierra Nevada. The ongoing downpour has already caused accidents and spin-outs on freeways.

For California, which has suffered years of drought and is still reeling from its worst fire season ever, rain is a welcome relief.

But getting so much at once can be disastrous. The fire-charred landscape, denuded of vegetation, does little to retain water and is vulnerable to deadly mudslides. California has already seen 21 deaths from mudslides this year.

“The main concerns we have with this atmospheric river include moderate to heavy rain across the region, urban flooding and ponding of water on roads, flooding of creeks or streams, and also the possibility of mudslides and debris flows for recent burn areas,” said Scott Rowe, a meteorologist at the National Weather Service’s San Francisco Bay Area office, during a briefing.

Will you support Vox’s explanatory journalism?

Most news outlets make their money through advertising or subscriptions. But when it comes to what we’re trying to do at Vox, there are a couple of big issues with relying on ads and subscriptions to keep the lights on:

First, advertising dollars go up and down with the economy. We often only know a few months out what our advertising revenue will be, which makes it hard to plan ahead.

Second, we’re not in the subscriptions business. Vox is here to help everyone understand the complex issues shaping the world — not just the people who can afford to pay for a subscription. We believe that’s an important part of building a more equal society. And we can’t do that if we have a paywall.

So even though advertising is still our biggest source of revenue, we also seek grants and reader support. (And no matter how our work is funded, we have strict guidelines on editorial independence.)

If you also believe that everyone deserves access to trusted high-quality information, will you make a gift to Vox today? Any amount helps.

One-Time Monthly Annual

$5/month

$10/month

$25/month

$50/month

Other

$

Yes, I'll give $5/month

Yes, I'll give $5/month

We accept credit card, Apple Pay, and Google Pay. You can also contribute via