PHOENIX, ARIZONA — Widespread flash flooding threatens the Southwest today, Wednesday, September 16, as a surge of tropical moisture fuels heavy thunderstorms across Arizona, New Mexico, southern Utah and southwestern Colorado. A weather system moving out of the Gulf of California is pulling exceptional moisture into the region, prompting a Moderate Risk for excessive rainfall across parts of Arizona and New Mexico, according to an Excessive Rainfall Outlook from Max Velocity valid today and updated at 2:41 a.m. CDT.
Moderate Risk for Excessive Rainfall Targets Phoenix and Tucson Today
Today’s outlook places the highest-end Moderate Risk category directly over the Phoenix metro, extending south to include Tucson, along with a separate, smaller Moderate Risk pocket near Albuquerque. That designation, carrying roughly a 40 percent probability of numerous flash floods, represents the top tier reached anywhere on today’s map, reflecting forecasters’ high confidence that rainfall rates across those specific zones will be intense enough to quickly overwhelm drainage.
Weather System Out of the Gulf of California Fuels the Flash Flood Threat
The moisture driving today’s threat is being pulled north by a weather system moving out of the Gulf of California, drawing exceptional tropical moisture directly into Arizona and New Mexico. That kind of deep, tropical-origin moisture feed is far richer than typical monsoon moisture, giving today’s thunderstorms the fuel to produce unusually heavy rainfall rates over a relatively compact stretch of the Southwest.
Disturbance Attempted Tropical Cyclone Formation, a Feat Achieved Only Once Since 2018
In an ironic twist, forecasters noted the same disturbance responsible for today’s moisture surge actually attempted to organize into a tropical cyclone over the Gulf of California itself, something that has happened only once before in that body of water. The only prior example on record is Tropical Depression Nineteen-E, which formed in the Gulf of California back in 2018, making today’s system a genuine rarity even though it ultimately failed to fully organize.
Phoenix Metro and Desert Washes Face Torrential Downpour Risk
Across Arizona, forecasters warned that torrential downpours could quickly overwhelm urban areas like the Phoenix metro, where impervious surfaces and storm drains can struggle to keep pace with intense rainfall rates. The threat extends beyond the city itself to normally dry desert washes throughout the region, which can transform into fast-moving, dangerous flows within minutes once heavy rain begins falling upstream, even in areas that appear completely dry beforehand.
Ruidoso Burn Scars Face Highly Dangerous Flash Flood Threat in New Mexico
In New Mexico, the greatest concern centers on repeated rounds of heavy rain over the Sacramento Mountains, which forecasters say will create a highly dangerous flash flood threat for the sensitive burn scars near Ruidoso. Burn scars strip away vegetation that would normally slow and absorb rainfall, allowing water to run off far faster and in much greater volume than unburned terrain, a combination that has produced some of the most dangerous flash flooding events in recent years across the burned areas surrounding Ruidoso.
Southern Utah and Southwestern Colorado Slot Canyons Face Broader Heavy Rain Risk
A broader heavy rain risk also extends into southern Utah and southwestern Colorado, where forecasters warned that rapid runoff could easily funnel into steep terrain and popular slot canyons. Those narrow, deep canyon systems are notoriously dangerous during flash flooding because water can rise with almost no warning far downstream from where the actual rain is falling, a hazard that has claimed lives in the region during past flash flood events tied to sudden, intense rainfall.
Slight and Marginal Risk Stretches From Albuquerque and El Paso to Denver
Surrounding the highest-end Moderate Risk zones, a much broader Slight Risk, carrying roughly a 15 percent probability of scattered flash flooding, covers most of Arizona, New Mexico, southern Utah and southwestern Colorado, including Albuquerque and El Paso. An outer Marginal Risk band, at roughly 5 percent for isolated flash flooding, extends the footprint even farther, reaching as far north as Denver and as far east as Kansas City.
Separate Slight Risk Corridor Also Stretches From Omaha to Des Moines and Rockford
Today’s national Excessive Rainfall Outlook also highlights a separate corridor of Slight and Marginal Risk stretching from near Omaha through Des Moines and into Rockford, well removed from the Gulf of California moisture surge affecting the Southwest. Residents across both highlighted regions, the Southwest’s Moderate Risk corridor and the Midwest’s separate rainfall zone, should stay weather aware today as heavy rainfall threatens to develop in each area.
