Heavy Rain and Flash Flooding can be Dangerous
The heavy rain threat is going to be very serious from Arizona and New Mexico all the way into the Central Plains and Midwest today through tomorrow. The remnants of Hurricane Polo are moving northward through Mexico and will continue transporting a tremendous amount of tropical moisture into the United States.
Even though Polo will weaken considerably as it crosses the mountains of Mexico, the moisture associated with the system will remain intact. That moisture will spread northward into Arizona and New Mexico, fueling thunderstorms and widespread areas of heavy rainfall.
Arizona and New Mexico
The most immediate concern is across Arizona and New Mexico, where heavy thunderstorms will develop today. Rainfall totals could range from around 1 inch to locally 6 or 7 inches in the areas that receive repeated or particularly intense thunderstorms.
For the Desert Southwest, that amount of rain can be extremely significant. Flash flooding could develop quickly, especially across desert areas, normally dry washes, mountain canyons, and areas with steep terrain.
Some locations could experience serious flash flooding as thunderstorms repeatedly move over the same areas. Given the rainfall these areas have already received recently, additional heavy rain could make the flooding threat even more dangerous.
Flooding Spreads Eastward
As the moisture plume associated with Polo continues moving northeastward, the heavy rain and thunderstorms will spread into the Plains and eventually the Midwest.
The threat will extend from Kansas and Nebraska into Iowa and surrounding areas, with additional flooding possible as the system moves east over the next couple of days. Areas receiving repeated thunderstorms could see rapidly rising water levels and significant runoff.
Flood Safety
If you encounter a flooded roadway, do not drive through it. You cannot reliably determine how deep the water is or how quickly it is moving, and floodwaters can sweep vehicles off the road even when the water does not appear particularly deep.
Turn around, don't drown.
The Bottom Line
This is a potentially major flooding event from the Desert Southwest into the Plains and Midwest. Tropical moisture from Hurricane Polo will produce heavy thunderstorms and periods of torrential rain, with some locations potentially receiving several inches of rainfall.
The greatest immediate threat is across Arizona and New Mexico, particularly in desert and mountainous terrain, but the flooding threat will expand eastward into the Plains and Midwest over the next two days.
Be prepared, stay alert, and never drive through flooded water.