By AccuWeather senior meteorologist
Updated Apr. 30, 2021 10:43 AM AKDT
"Drought often ends with flooding rain" is a common refrain heard from AccuWeather meteorologists. In Texas, that is expected to be the case this weekend as much of the state gets hit with needed rain thanks to a slow-moving storm system.
The weather patterns that have been keeping soaking rain away have been fairly strong and generally diverting storms from much of Texas in recent weeks. The last stormy pattern in these semi-arid portions of the Lone Star State was during the deep freeze when multiple storms combined with frigid air to bring snow and ice in February.
Heavy rains have recently been falling over the South Central states, but Texas had generally been on the fringe of those storm systems. That changed this week as downpours expanded in some of the central and eastern areas. Dallas picked up nearly 1.50 inches of rain on Thursday with San Antonio was belted by more than 2.50 inches on Wednesday.
When a storm-free pattern persists, it generally takes a potent storm system to snap that dry weather pattern. Often storms of that caliber are so strong that one extreme is followed by another.
On Friday, a large storm was situated in the middle part of the atmosphere over northern Mexico and crawling eastward. Even though the storm is not tropical in nature, it is forecast to draw on Gulf of Mexico moisture and interact with a stalled front that is already in place and producing heavy rain in portions of eastern Texas and Louisiana. This is the same frontal zone that contributed to rainfall in Dallas and San Antonio recently.
This radar image, taken Friday morning, April 30, 2021, shows light rain in green, moderate rain in yellow and intense rain in red. (AccuWeather/NOAA)
As the storm makes steady northeastward progress through the weekend, it is expected to produce rainfall rates of 1-3 inches per hour in some locations, which is enough to cause flash flooding.
By mid-morning Friday, about 2-4 inches had already fallen in the parts of southeastern Texas, including the Houston area. Flash flood watches were in effect for the region, and there had been multiple reports of flooding on roadways, according to local officials.
Prior to the storm, soil moisture conditions ranged from average in the northeastern corner of the state to exceptional drought in south Texas and the state's western counties, according to the United States Drought Monitor. While this storm will not affect the western and west-central portions of the state, it will drench many areas farther to the southeast.
For millions of people in Texas, this will be a beneficial rainstorm.
The storm is likely to bring a broad area of 1- to 2- and 2- to 4-inch rainfall amounts in central and eastern Texas, according to AccuWeather Senior Meteorologist Randy Adkins.
Even though the rain may be welcomed by many, especially by agricultural and hydrological interests, too much of a good thing is likely to unfold in localized areas, and the situation could become dangerous.
A rather large swath of 4-8-inches of rain with an AccuWeather Local StormMax™ of 16 inches is forecast from east of San Antonio to just south of Austin to areas west of Houston and finally locations north of Brownsville, Texas, according to Adkins.
"But you don't have to be right within this zone to be at risk for flooding," Adkins said.
In many cases, that 4-8 inches of rain could wipe out the rainfall deficit from the start of the year.
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Due to the dry state of the ground, the intense rainfall may not have a chance to soak in but may instead run off at a rapid pace. In mostly urban areas, prior drought conditions do not matter as paved and concrete surfaces absorb only a small amount of moisture.
"Some of the rain on the northern edge in northeastern Texas and western Louisiana is likely to consolidate southward and break up for a time into Friday night," AccuWeather Senior Meteorologist Dan Pydynowski said, "But as the storm rolls out from Mexico, it will expand northeastward once again this weekend."
Motorists should use extreme caution during their travels into Saturday. Rainfall of the magnitude anticipated can rapidly inundate low water crossings and underpasses. Some secondary roads may be unsafe and ponding can occur on portions of major highways that drain poorly.
Motorists are strongly urged to adopt the "Turn Around, Don't Drown" slogan from the National Weather Service on their commutes. AccuWeather forecasters caution that the flooding could pose multiple concerns. They say the water may be much deeper than it appears, the road may have been washed away beneath the water or water levels may be rising as a vehicle tries to pass through. Merely several inches of water can cause some vehicles to drift.
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In addition to the likelihood of heavy rain and flooding, thunderstorms associated with the system can bring locally heavy, gusty and even severe with isolated high winds and hail.
As the storm swings northeastward, heavy rain will end from west to east across coastal Texas but will expand northeastward over the central Gulf Coast states this weekend.
The core of the rain is expected to be centered over Louisiana, Arkansas, Mississippi and southern Missouri on Sunday.
"Even though the rain may not be as intense in this zone when compared to southeastern Texas, much of this area is not in drought and may only be able to handle a moderate amount of rain with flood-related problems," Pydynowski said. "Portions of Arkansas and Missouri were hit with several inches of rain earlier this week."
Most of the major rivers in the central Gulf states have dipped below flood stage in the past couple of weeks, based on information from NWS hydrologists. It is possible that enough rain falls in this zone to slow or halt the recession and lead to some rises on area rivers next week.
The same storm is forecast to produce a broad zone of rain over Midwest and Eastern states during the first part of next week as well.
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