An atmospheric river referred to as the "pineapple express" could 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.

This latest round of rain will be fueled by a low-end pineapple express, a type of atmospheric river that often fuels heavy rain events in the West, especially in a stronger El Niño winter.

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

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

When and where will these soakings arrive?

There are two rounds of soaking rain ahead:

1. Thursday and Friday: Western Texas, parts of New Mexico and Arizona
2. This weekend: In mainly Southern California, it will increase starting Saturday, peaking early Sunday. In the Southwest, rain and some high mountain snow will increase late Saturday, continue into Sunday and linger in some areas Monday.

What are the potential impacts?

Local flash flooding is possible from the first round of rain in parts of western Texas including Lubbock and Midland.

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A more serious flash flood threat is in play for the Desert Southwest.

That's because 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.

It's also because some of these areas will see both rounds of rain in a span of just three days.

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

The areas of greatest concern are the Phoenix metro's north and east sides, the Four Corners and San Diego County's foothills and high country. Also, any ground scorched by recent wildfires is particularly susceptible to producing fast-moving debris flows, even in modest rainfall.

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 in the 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 off 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.