As moisture from the Gulf of Mexico surges northward, areas from Texas to Iowa will be at risk for frequent downpours that could produce flash flooding.
Updated Sep. 30, 2021 9:23 PM EDT
Rounds of heavy rainfall are forecast to expand from the Gulf Coast region farther north into the Central states, and AccuWeather forecasters say the rainfall could be welcome news in some locations but problematic in others.
As a front remains stalled over the Plains and South Central states into Saturday, moisture will surge northward out of the Gulf of Mexico. Rising air associated with this stalled front over the South Central states will be the focus point for frequent rounds of showers and thunderstorms.
"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 AccuWeather Senior Meteorologist Matt 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.
Rain that has been falling in the center of the United States during the middle of the week was largely focused on Texas and Louisiana.
The top 36-hour rainfall reports in the South Central plains as of 6 p.m. local time Thursday, Sept. 30, 2021.
For locations such as southeastern Texas and Louisiana, where copious amounts of rain have occurred due to landfalling tropical systems this hurricane season, additional rainfall is not needed.
Both New Orleans and Houston received heavy rain from Hurricane Nicholas in the middle of September. With the added rainfall so far this week, both cities have now received over 8 inches of rain in September. Typically, Houston tallies 4.71 inches during an average September, while New Orleans records 5.11 inches.
Farther to the north, a completely different story has unfolded.
"Even with stormy weather to end September, places like Abilene, Texas, and Oklahoma City will be well below normal in terms of monthly rainfall," said AccuWeather Meteorologist Mary Gilbert.
Abilene has received just 0.40 of an inch of rain in September, which is only 15% of the normal of 2.67 inches. In Oklahoma City, even less rain has fallen. Just 0.35 of an inch of rain has been recorded, and that rain all fell in one day back on Sept. 4. This is just 9% of the 3.72 inches that is normal for September.
The U.S. Drought Monitor shows that much of Oklahoma is experiencing moderate drought conditions, while smaller portions of the state are dealing with severe or extreme drought.
The expected rainfall will be beneficial in some locations. However, it is not all good news.
"Too much rain falling at one time can lead to flash flooding issues as the ground simply cannot absorb the rainfall fast enough," said Gilbert.
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This is especially true when rain falls on exceptionally dry ground. When soils and the ground are dry for an extended period of time, the surfaces become less porous. In these situations, more water runs off than would typically be the case.
The aforementioned front is expected to remain in the same general location into the start of the weekend, due to a broad area of high pressure off the coast of the Southeast.
By Sunday, this high will finally begin to move farther offshore, and the cold front will be on the move. This will shift the chance of rain into locations such as Detroit, Cleveland and Pittsburgh.
Once the rain departs, dry weather is forecast in the middle of the nation through at least early next week.
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