Flash flooding and severe storms were expected to spread from the Four Corners into New Mexico and the Southern Plains

The National Weather Service’s Weather Prediction Center said in a short-range forecast issued at 408 p.m. EDT on Oct. 22 that numerous to widely scattered instances of flash flooding and severe weather were expected across the Four Corners and the Southwest through the morning of Oct. 23, with the threat then shifting east into New Mexico and the Southern Plains. The discussion was written by forecasters Asherman and Kebede and covered the period from 00Z on Oct. 23 to 00Z on Oct. 25.

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Everything in this article describes what forecasters said would happen. It does not report observed rainfall totals, flood damage or rescues, because the forecast documents do not contain them, and no storm reports or local flood warnings were consulted. Forecasts of this kind can overstate or understate what happens at any one location, which is why the risk levels below are expressed as probabilities.

What the Oct. 22 discussion said

The setup, in the Weather Prediction Center’s discussion, was a deep upper-level low over California pushing showers and thunderstorms ahead of it. Tropical moisture was being drawn in ahead of a cold front moving through the Desert Southwest, and that combination is what the forecasters tied to the flash flooding expected across the Four Corners and the scattered severe weather expected across the Southwest through Friday morning.

The same discussion also covered a lee-side cyclone expected to form over the Northern High Plains, which is a separate part of the forecast. On the Southwest threat, it said the heavy rain and severe weather threat would shift east with that cold front over the following 48 hours, reaching New Mexico and the Southern Plains. In the summary at the top of the product the forecasters listed excessive rainfall and severe weather affecting California, the Southwest and the Four Corners, along with a developing low that would bring much cooler weather to the central United States over the weekend.

The excessive rainfall risk levels that followed

A day later, the center’s Excessive Rainfall Discussion, issued at 0806Z or 404 a.m. EDT on Oct. 23, put numbers on where the risk sat. For the 24 hours beginning at 12Z that Friday it called for a Slight Risk of excessive rainfall across portions of New Mexico, far West Texas and southern Colorado, with a broader Marginal Risk over much of New Mexico and southern Colorado. The Slight Risk area included the Sacramento Mountains and nearby urban areas and burn scars.

Looking one day ahead, the same document put a Marginal Risk over parts of Utah and northern Arizona in the Four Corners region, where isolated flash flooding was possible, and a Slight Risk from West Texas through eastern New Mexico, southeastern Colorado and far western Kansas. For the third day it extended a Slight Risk across the central and southern High Plains, from northeastern New Mexico to western Kansas, and for the fourth day it placed a Marginal Risk across the central to southern High Plains, including parts of western Oklahoma.

The center’s Excessive Rainfall Outlook page defines the risk as the probability that rainfall will exceed flash flood guidance within 25 miles of a point, with Marginal meaning at least 5 percent and Slight at least 15 percent. Its first-day map, issued at 0803Z on Oct. 23, listed about 1,171,725 people and 16,561 square miles under the Slight Risk and about 1,756,804 people and 102,644 square miles under the Marginal Risk.

Why the forecasts stressed roads and burn scars

The Slight Risk area in New Mexico was described as including burn scars and urban areas around the Sacramento Mountains, the kinds of locations where heavy rain over a short time is most likely to cause trouble for roads and drainage. The National Weather Service’s Turn Around Don’t Drown page makes the road risk concrete: six inches of fast-moving water can knock over an adult, twelve inches can carry away most cars, and two feet can carry away SUVs and trucks. The page cites the Centers for Disease Control and Prevention for the finding that more than half of flood-related drownings occur when a vehicle is driven into hazardous water. It also warns against driving around barriers on a flooded road, since the pavement may have collapsed under the water.

Beyond the window of these products, the center’s medium-range discussion, issued at 1932Z on Oct. 23, said rain and thunderstorms were possible from Oct. 26 to Oct. 30 across the south-central United States and the southern and central Plains, with modest totals and some isolated higher amounts. It added that totals may increase later in that week, depending on how the pattern evolves. That product did not identify a specific flood threat for the Southwest, New Mexico, Texas or Oklahoma, so the flash flood forecasts above are the ones tied to those areas.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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