An atmospheric river referred to as the "pineapple express" will bring heavy rain to parts of the Desert Southwest and Southern California over Halloween weekend, just over a week after destructive flooding plagued parts of Arizona, Nevada, New Mexico and Utah.

These atmospheric rivers often fuel heavy rain events in the West, especially in a stronger El Niño winter.

(COMPLETE COVERAGE: Super El Niño of 2026-27)

We'll discuss more about this pattern after laying out the important forecast details through this weekend.

When and where will these soakings arrive?

A larger batch of precipitation is arriving across the West and will continue to ramp up and spread further into the region as the weekend progresses.

Saturday overnight - early Sunday: Rainfall will really get going across much of the Southwest into early Sunday. The heaviest rain is expected for the greater Phoenix area, but pockets of heavy rain could spread as far north as Elko, Nevada. Los Angeles and San Diego could also see some rainfall.

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Sunday: An area of low pressure charged by this atmospheric river will move onshore and spread its heavy rain across the West. The heaviest rain is the red locations on the map below. While Phoenix just misses this region, it is still in the level 2 of 4 threat on this map. Flagstaff, Arizona; Zion National Park, Utah and pockets of northern New Mexico and southern Colorado could see the greatest rainfall and rainfall rates.

What are the potential impacts?

A more serious flash flood threat is in play for the Desert Southwest this weekend, but there will be some concern for wintry weather, too. Below are the current flood and winter weather alerts.

The ground is still saturated from the 2 to 5 inches of rain that soaked the area last week, triggering major flash flooding in northern Arizona, New Mexico, southern Colorado and southern Utah.

The map below shows total rainfall in the Southwest. Areas shaded in darker green and yellow could see more dangerous, widespread flash flooding.

The areas of greatest concern are:

• Elevations below snow level in southwestern Colorado and the immediate Four Corners area
• The Phoenix metro's north and east sides and the Mogollon Rim of northern Arizona
• The canyonlands of southern Utah
• Any ground scorched by recent wildfires, which is particularly susceptible to producing fast-moving debris flows, rock and mudslides, even in modest rainfall.

According to the National Weather Service in Flagstaff, Arizona, rivers such as the Little Colorado and Verde, could run high for days after this weekend's latest soaking.

If you had weekend plans to do any hiking in the parks of southern Utah, southern Colorado and Arizona, you should consider canceling. Fast-moving, life-threatening flash floods can sweep rapidly through slot canyons.

Over the higher elevations, this precipitation may fall as snow over the higher peaks of the Rockies and Sierra. This may lead to slippery travel mainly Sunday into Monday over mountain passes.

Record moisture for Halloween weekend?

What's fueling this soaking is a southward plunge of the jet stream near the West Coast.

That jet stream will pull a ribbon of deep tropical moisture called an atmospheric river into the Southwest.

This particular atmospheric river tap is originating from near Hawaii, something meteorologists nickname the "pineapple express."

It's not a strong version of either an atmospheric river or pineapple express, but the moisture fueling this heavy rain could be record-setting for this time of year.

According to the National Weather Service, the total moisture in the atmosphere over parts of Arizona, Colorado, Nevada and Utah could be 2 to 3 times the average for the end of October, near record amounts for Halloween weekend.

This could be a harbinger, given the tendency for a wetter Southwest during most stronger El Niños from fall through spring.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.