PHOENIX, AZ — The flood threat continues to increase across the Southwest heading into Monday, with a Level 3 of 4 Risk for excessive rain and flooding now in place across portions of the region. A deep plume of tropical moisture associated with Hurricanes Odalys and Polo will surge north as a strong upper-level trough digs into the West, creating a favorable environment for widespread showers and storms capable of producing torrential rain and potentially significant flash flooding.
Highest Concern Where Storms Repeat Over the Same Areas
The greatest flooding concern will be concentrated where storms repeatedly move across the same locations or produce extremely heavy rainfall rates over a short period of time. Burn scars, normally dry washes and arroyos, slot canyons, low-water crossings, urban areas, and steep terrain will all be particularly vulnerable to rapid runoff and flash flooding under this setup, as these terrain features are especially prone to quickly channeling and concentrating fast-moving water.
The Level 3 Risk zone, highlighted in red on the outlook map, is centered over portions of Arizona, New Mexico, and southern Utah, encompassing communities including Flagstaff, Gallup, and Monticello, where the combination of terrain and moisture makes for the most dangerous flooding potential.
Heavy Rain Extends Across a Much Larger Area
Beyond the highest-risk zone, heavy rain will extend across a much larger area surrounding the Level 3 Risk, affecting parts of the broader Southwest, Four Corners, and Great Basin regions. Tropical moisture will spread from Southern California and the Desert Southwest north and northeast into parts of Arizona, Nevada, Utah, New Mexico, and surrounding areas. Even outside the highest-risk zone, localized significant flash flooding will remain possible wherever the heaviest storms happen to develop.
Not a One Day Event
This developing situation will not be confined to a single day. As the western trough moves east and Polo’s tropical moisture becomes incorporated into the larger storm system, the heavy-rain threat will gradually shift toward the Southern and Central Plains. Texas and Oklahoma will become increasingly important areas to watch as deeper moisture interacts with the approaching system, setting the stage for additional rounds of heavy rain and storms heading into Tuesday and Wednesday.
Beneficial Rain Comes With Real Risk
Forecasters note that some of this rain will be extremely beneficial for drought-stricken areas across the Southwest, offering meaningful relief after an extended dry stretch. However, tropical moisture this deep can also produce a substantial amount of rain in a very short period of time, meaning the same system delivering welcome drought relief also carries genuine flash flooding danger for communities in its path.
A Potentially Significant Multi Day Event
The overall pattern is setting up for a potentially significant, multi-day heavy-rain event stretching from the Southwest and Great Basin into the Southern Plains, with flash flooding likely to be the primary concern in the hardest-hit areas. Residents throughout this broad corridor, from Arizona and New Mexico through Texas and Oklahoma, are advised to stay closely tuned to forecasts as this evolving situation continues to develop over the coming days…