AccuWeather map, 9/29/21.
SIOUX FALLS, S.D. (KELO.com) — A surge of rainfall is expected across the southern Plains and South Central states this week as winds steer moisture inland from the Gulf of Mexico, resulting in rainfall amounts for the center of the United States that could produce flash flooding.
“The overall pattern in the Plains will remain fairly stationary, allowing for thunderstorms to develop over the same area through the rest of the week,” said AccuWeather Senior Meteorologist Matt Rinde. This pattern is being slowed by blocking from systems to the east.
In a typical weather pattern, these storms would likely get shoved eastward with the flow of the atmosphere. Instead, moisture from the Gulf of Mexico will be held in place over the top of the south-central region, allowing showers and thunderstorms to repeatedly impact much of Texas, Oklahoma, Louisiana and Arkansas each day this week.
Showers and thunderstorms will also stretch farther to the north into the Plains during the balance of this week.
“Not only will the day-to-day thunderstorms allow for heavier rainfall totals, but there is also a risk for training storms on any given day,” said Rinde.
When storms “train” this means they move over the same region in a relatively short period of time, similar to the way a train moves over its tracks repeatedly.
“This means that during a particular afternoon, thunderstorms could repeatedly hit the same areas and cause flash flooding,” explained Rinde.
Flash flooding occurs within six hours of heavy or excessive rainfall, according to the National Weather Service (NWS). Due to the sudden nature of this phenomenon, forecasters urge residents to make sure they have a way to receive weather warnings.
Residents should also avoid going into basements or anywhere underground if a flash flood watch or warning has been issued for their area. Motorists are cautioned to never drive through flooded roadways and to beware of changing visibilities when thunderstorms become heavy. Just 6 inches of water in a flash flooding event can cause cars to lose control or stall, according to the Federal Emergency Management Agency (FEMA).
One potential bright spot with the rain is that it is headed to places that have been drier than normal this month.
“Most of the rain will hit areas where drought has been re-emerging in recent weeks,” said AccuWeather Senior Meteorologist Alex Sosnowski.
Places like Oklahoma City haven’t had measurable rainfall since Sept. 4, putting the city at only 9% of average rainfall for the month. Tulsa, Oklahoma, has only reported 3% of average in September. In fact, nearly 40% of the state of Oklahoma is in moderate drought, according to the United States Drought Monitor. Omaha, Nebraska, and Wichita, Kansas, have also fallen behind monthly rainfall averages.
Oftentimes, drought-ridden areas can be at a greater risk of flooding. When the ground is dry, it has difficulty absorbing heavy amounts of rain. This allows the water to build on top of the earth, which causes flooding. Not all areas in the central U.S. are in need of rain. Some parts of the Gulf Coast region have already had more than their fair share.
“Parts of southeast Texas and western Louisiana will get more rain after hits from the tropical season,” said Sosnowski.
New Orleans has received over 7 inches of rain throughout the month of September so far, mainly from Hurricane Nicholas, which brought heavy rain to the city shortly after it made landfall in Texas. The Big Easy has so far recorded over 150% of average rainfall for the entire month. Houston also reported an incredible amount of rain from Nicholas, putting the monthly total to date at over 7 inches, which is 159% of normal for September.
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A general 2-4 inches of rain with an AccuWeather Local StormMax™ of 7 inches is forecast to fall over the central and southern Plains states and part of the Mississippi Valley through the end of this week. Portions of coastal Texas and Louisiana are among the locations that could experience close to 7 inches due to the rounds of heavy rain.
As of the midday hours on Wednesday, the evolving wet weather pattern had already unloaded 3.54 inches of rain on Lake Charles, Louisiana, and 2.23 inches on San Antonio and 1-2 inches on the Houston metro area since the start of this week.
As the week ends, rainfall is not expected to come to a halt. AccuWeather forecasters are also monitoring an area of low pressure expected to move across the Southwest this weekend, which is anticipated to weaken or move east into early next week.
“This low pressure area will draw up a good amount of moisture from Mexico and transport it north into the southern Plains,” said AccuWeather Lead Long-Range Senior Meteorologist Paul Pastelok.
The greatest amount of precipitation will likely occur across western Texas and Oklahoma, with storms continuing to train and bring the risk for flash flooding.
