Flooding rain strikes Dallas metroplex, with more on the way across the South
The corridor from northern Texas and southern Oklahoma to central portions of Mississippi is within a zone of unfolding heavy rain that will persist into the middle of the week. Drenching, drought-easing, deluge and dangerous are terms that AccuWeather meteorologists are continuing to use to describe the unfolding event. An entire summer's worth of rain can pour down in a matter of days in some locations, forecasters warn.
Already, this risk has become a reality in the Dallas-Fort Worth metroplex. As slow-moving, heavy thunderstorms dumped rain on the sprawling region, flash flood warnings were first issued late Sunday night. Within a couple of hours, reports of street flooding were already pouring in.
By Monday afternoon, some areas in the city picked up more than 15 inches of rain. Monday evening, the flooding turned deadly when Dallas County Judge Clay Jenkins reported that a 60-year-old woman was killed when her vehicle was swept away in the flood waters.
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About 60% of the south-central United States remained in severe drought or worse as of the latest report from the United States Drought Monitor. But, that percentage soon may be substantially reduced should a vast area of over 4 inches of rain unfold as AccuWeather meteorologists suspect over the next several days.
During the period from June 4 through Aug. 9, Dallas only saw a few drops of rain, compared to the normal amount of about 6 inches. It was a similar story for much of Texas and Oklahoma during the same stretch. A couple of rounds of thunderstorms have visited some locations since Aug 9, but while these have led to highly-isolated flash flooding, they may be just a drop in the bucket compared to what is forecast to unfold into midweek for some communities.
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"A stationary frontal boundary draped from northern Texas to the Interstate 20 corridor in Louisiana and Mississippi will be recharged with tropical moisture from the Gulf of Mexico and the southwestern United States," says AccuWeather Storm Warning Meteorologist Robert Spinetti. "This convergence of weather systems and moisture will lead to excessive rainfall."
A massive swath of 2-4 inches of rain will extend from near the New Mexico border in northern Texas to central Alabama into midweek. "Within this zone, there is the potential for a pocket of 8-12 inches of rain from near Dallas to northern Louisiana," Spinetti warned.
An AccuWeather Local StormMax™ of 20 inches could be realized anywhere in the 2 to 4-inch zone or higher, but is most likely in northeastern Texas and northern Louisiana. "It's hard to imagine that how rainfall of that magnitude with high rates of runoff would not be tremendously disruptive and potentially dangerous and damaging," AccuWeather Chief On-Air Meteorologist Bernie Rayno said.
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Rapid runoff can occur in any urban area given the pattern. Where downpours persist, some streams and rivers can experience substantial and rapid rises, despite prior soil moisture conditions.
"Hourly rainfall rates could reach 2-3 inches with 6 inches or more possible in 12 hours or less," AccuWeather Senior On-Air Meteorologist Mark Mancuso added. The normal total rainfall during the three-month period from June 1 to Aug. 31, in Dallas is about 8 inches. In Shreveport, the rainfall average increases to about 11 inches. Both of these cities and others could pick up three months' worth of rain in as many days or less.
In much of Texas and in parts of Oklahoma, the dry landscape and hard soils are prone to rapid runoff in any downpour. Farther to the east, the soil becomes progressively wetter due to rounds of showers and thunderstorms in recent weeks.
Given the likelihood of repeating downpours and the potential for excessive rainfall with the setup, commuters, home and business owners and emergency management officials should be prepared for flooding. There is a significant risk to lives and property.
While the frontal zone is forecast to sag slowly southeastward into midweek, the steadiest and heaviest rain may avoid areas from I-20 in west-central Texas to the Hill Country, Spinetti said.
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Last week, a tropical rainstorm that nearly evolved into a tropical depression moved ashore and brought 5-10 inches of rain along portions of the Rio Grande.
A storm system that develops along the front will continue the downpour threat from mid-to-late week in the Southeast states.
As this area of disturbed weather lingers along the southern Atlantic coast, waters over the Gulf Stream will have to be watched for some tropical development around next weekend, Spinetti said. Much of the Gulf and Atlantic coast states will be in a wet pattern for the week ahead.
Drier air should end the flooding risk in northwestern Texas, north-central Texas and southern Oklahoma by Tuesday. But, as one area dries out another zone may trend wetter. Tuesday to Thursday may bring the best opportunity for drenching downpours and the greatest risk of flash flooding from Austin and Houston to near San Antonio and Victoria, Texas.
A tropical disturbance that AccuWeather meteorologists were watching closely over the southwestern Gulf of Mexico, ran into dry air and more hostile development conditions near the Mexico coast on Saturday night. The system failed to evolve into a tropical depression. While localized thunderstorm activity from this system will be drawn northward into parts of coastal Texas, most of the rain from the system and the downpour zone in the northern part of the state should not reach the lower Rio Grande Valley.
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