Pineapple Express Storm to Blast 35 States: Halloween Flash Floods, Heavy Snow and a Cross-Country Deluge

LOS ANGELES — A moisture-rich atmospheric river known as a Pineapple Express is set to drench California and the Desert Southwest over Halloween weekend, forecasters said on 29 and 30 October 2026, kicking off a cross-country storm system expected to bring dangerous weather to as many as 35 states in the days that follow.

The system, fuelled by El Niño steering the Pacific jet stream over the southern tier of the United States, will arrive in two rounds, according to forecasts from the FOX Forecast Center and The Weather Company, with the heaviest rain in Southern California expected early on Sunday. Forecasters warn of flash flooding on already saturated ground, heavy snow in the mountains, and a later severe-weather threat as the storm marches east into the Plains and Midwest for Election Day.

It is a forecast, not yet an outcome — and forecasters stress that exact rainfall totals and the location of the worst severe weather remain uncertain. But the ingredients are unusually potent for late October: tropical moisture drawn from near Hawaii, atmospheric moisture levels two to three times the late-October average in parts of the Southwest, and ground already soaked by last week's rain.

Illustration: A band of tropical moisture streaming from the Pacific toward California and the Southwest. This is an AI-generated illustration, not a real photograph.

What Happened

Forecasters describe a two-stage event. Starting on Friday, 30 October, a strong upper-level low near the Pacific Northwest coast will pivot a well-defined Pacific jet toward the Southwest, allowing a secondary low to develop and draw rich Pacific moisture inland into Saturday, the FOX Forecast Center said. The first round of rain will affect western Texas and parts of New Mexico and Arizona through Friday, with flash flooding possible around Lubbock and Midland, according to The Weather Company forecast reported on 30 October.

The second, more significant round intensifies across Southern California and the wider Southwest from Saturday into Sunday, with Southern California's heaviest rainfall expected early Sunday. Moderate-to-heavy soaking rains are forecast for Los Angeles and San Diego by Saturday, likely disrupting Halloween plans. In San Diego, measurable rain on Halloween is rare — there have been only nine such Halloweens since 1850, the most recent in 1987, Fox Weather noted.

Through Monday morning, the system will push inland across the Southwest, spreading rain eastward. Widespread totals of 1 to 2 inches or more are expected across portions of Arizona through Monday, with up to 5 inches possible from Phoenix to Flagstaff, the FOX Forecast Center said. Flagstaff has already recorded 5.69 inches of rain so far in October; another 3 inches, as forecast, could bring significant flash flooding, and a level 2 out of 4 flash flood threat is in effect through the weekend.

Illustration: Floodwater rushing along a desert road in the Southwest under storm clouds. This is an AI-generated illustration, not a real photograph.

Background

The danger is amplified by what came before. Parts of the Southwest received 2 to 5 inches of rain last week, saturating the ground and contributing to major flash flooding across northern Arizona, New Mexico, southern Colorado and southern Utah, according to the forecast summary. When soil is already saturated, even moderate additional rain runs off quickly instead of soaking in — which is why forecasters are flagging the northern and eastern Phoenix metropolitan area, the Four Corners region, and the foothills and high country of San Diego County as areas of greatest concern.

Burn-scarred ground adds a second hazard. Areas recently affected by wildfires can produce fast-moving debris flows even when rainfall amounts are relatively modest, and floodwaters in narrow canyon systems can become life-threatening. Hiking plans in parks across southern Utah, southern Colorado and Arizona face particular risks, forecasters warned, because flash floods can move rapidly through slot canyons with little warning.

At higher elevations, the same system brings a very different hazard: snow. Cold air trapped aloft will produce snow from the Sierra to the Rockies, with the southern Rockies seeing the highest totals, between 12 and 18 inches, according to the FOX Forecast Center. Mountain passes could turn slippery, particularly from Sunday into Monday, and the Sierra is also in line for snow as the atmospheric river's moisture meets colder air.

An atmospheric river is a long, narrow corridor of concentrated moisture in the atmosphere. A Pineapple Express is the best-known type in the eastern Pacific: it draws deep tropical moisture from near Hawaii toward the West Coast. Forecasters note that the approaching system is not considered a particularly strong atmospheric river in its own right, but its moisture content could approach seasonal records — the National Weather Service forecasts atmospheric moisture levels across parts of Arizona, Colorado, Nevada and Utah reaching two to three times the average for late October.

Why It Matters

First, the timing matters. Halloween weekend puts large numbers of people outdoors in the evening — including children trick-or-treating — in cities where heavy rain is forecast. Southern California's soaking rains arrive on Saturday, and forecasters say the heaviest rain there comes early Sunday, so outdoor plans across the region face disruption through the weekend rather than a single passing shower.

Second, the scale matters. November is expected to begin, in Fox Weather's words, "with a bang": a powerful storm that could deliver dangerous weather to 35 states. That is not a single-state flood story but a continent-spanning system, with each region facing a different hazard — flooding in the Southwest, snow in the mountains, and severe storms further east.

Third, the system is a reminder of how El Niño reshapes autumn weather. By helping steer the Pacific jet stream over the southern tier of the country, El Niño is funnelling tropical moisture into a region that is simultaneously recovering from last week's flooding and, in other parts of the West, still dealing with wildfire-scarred landscapes. The combination of saturated soil, burn scars and a second moisture surge is what turns a wet weekend into a dangerous one.

Illustration: Heavy snow falling over a mountain pass as a snowplow clears the road. This is an AI-generated illustration, not a real photograph.

What Happens Next

Later on Monday, the storm begins moving into the Plains and Midwest. Heavy rain could increase the risk of flash flooding across the Plains, and nearly 40 million Americans are under a large level 1 out of 4 flash flood threat from Texas to Wisconsin on Monday, according to the FOX Forecast Center. Ahead of the storm, a new area of low pressure across the Plains will likely form, drawing warm, moist air northward.

That warm air will then interact with an approaching cold front, which may allow severe storms to develop from Tuesday into Wednesday. Forecasters say the atmosphere is becoming primed for severe storms from Texas into parts of the Southeast by early in the week through midweek, but they caution that models disagree on exactly where the low will form and how strong it will become — so the severe-weather map remains uncertain.

From Wednesday onward, the storms continue into the East, potentially bringing heavy rain on Thursday and Friday to major cities on the I-95 corridor, from Raleigh, North Carolina, to Washington, D.C., New York City and Boston — in some cases their first rain in nearly two weeks. For the Southwest, the advice through the weekend is simpler: avoid flooded roads and slot canyons, watch for debris flows near burn scars, and check the latest National Weather Service warnings before travelling, especially over mountain passes.

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FAQ

What is a Pineapple Express?

It is a type of atmospheric river — a long, narrow corridor of concentrated moisture — that draws deep tropical moisture from near Hawaii toward the West Coast of North America. When that moisture reaches land, it can produce prolonged heavy rain and mountain snow.

Which areas face the greatest flash-flood risk this weekend?

Forecasters flag the northern and eastern Phoenix metropolitan area, the Four Corners region, and the foothills and high country of San Diego County, along with western Texas around Lubbock and Midland in the first round. Saturated ground from last week's rain and wildfire burn scars raise the risk further.

How much rain and snow are forecast?

Widespread totals of 1 to 2 inches or more are expected across portions of Arizona through Monday, with up to 5 inches possible from Phoenix to Flagstaff, according to the FOX Forecast Center. The southern Rockies could see 12 to 18 inches of snow, with snow also expected from the Sierra to the Rockies.

Will the storm affect areas beyond the Southwest?

Yes. The system is expected to bring dangerous weather to as many as 35 states as it moves east, reaching the Plains and Midwest on Monday, with severe storms possible from Texas into the Southeast from Tuesday into Wednesday, and heavy rain reaching the I-95 corridor later in the week.

Is this forecast certain?

No. Forecasters stress uncertainty, particularly for the severe-weather threat early next week, where models disagree on where the Plains low will form and how strong it will become. Rainfall totals and exact locations may shift as the system develops, so residents should follow updated National Weather Service warnings.

Sources

Fox Weather, "Cross-country storm to blast 35 states with flooding, storms and even snow", 29 October 2026 (FOX Forecast Center forecasts; National Weather Service moisture outlook); The Weather Company forecast via Suara Garut, "Pineapple Express Threatens California and Southwest With Flooding", 30 October 2026 (two-round rainfall outlook; National Weather Service atmospheric moisture forecast).