Severe storms that are expected to push across the Southern United States on Wednesday through Thursday night are likely to lead to damaging winds, hail and tornadoes, some of which will occur after dark, forecasters warned.

The risk of severe weather stretches from Texas to Kentucky on Wednesday and from the Gulf Coast of Alabama to the shore of Lake Erie in western New York on Thursday. In most areas there will be a risk of storms capable of producing damaging winds and some hail. While the tornado threat will mostly be contained to the South, forecasters with the Storm Prediction Center said that tornado-producing storms were possible as far north as Ohio.

Severe storms are expected across portions of the Lower MS Valley today into tonight, with damaging wind gusts, large hail, and tornadoes all likely. Strong tornadoes are possible tonight near the MS River. Be sure to have multiple ways of receiving watch and warning information. pic.twitter.com/gDrSwrU8jV

In Memphis, where there was a risk of tornadoes on Wednesday evening, Andy Chiuppi, a National Weather Service forecaster, said that the worst storms would occur after the sun goes down.

People should not go outside, he said; they’re going to have to trust the warnings and respect them. On Wednesday morning, it didn’t feel like the muggy, 70-degree conditions that people associate with tornado weather, Mr. Chiuppi said. By late Wednesday afternoon, that muggier, moist air will move into the region, creating the environment for tornadoes to form.

With that weather settling in late in the day, he said, “some people may not be as alert.”

Forecasters like Mr. Chiuppi are most worried about isolated storms called supercells that form ahead of a main line of storms. These supercells have the potential to create tornadoes, some of which could be strong, across portions of eastern Arkansas, northern Mississippi and western Tennessee on Wednesday evening.

“Supercells oftentimes have a higher frequency of producing stronger tornadoes,” Tony Lyza, a coordinating meteorologist for the PERiLS project, a collaboration of researchers from nearly a dozen universities, different divisions of the National Oceanic and Atmospheric Administration and the National Science Foundation to study storms in the Southeast that are capable of producing tornadoes. Mr. Lyza and a team of 70 to 80 researchers are in the South this week to study the severe weather.

On Thursday, this team will be waiting for the storms to arrive. Forecasters from the Storm Prediction Center say that several tornadoes are possible over Mississippi and Alabama, some of which may be strong.

The researchers are less focused on the supercells that may cause these stronger tornadoes to form and more on the main line of storms that are expected to develop and sweep through Mississippi and Alabama on Thursday. Those storms are then expected to move into Georgia and Florida overnight on Thursday as the system weakens.

“Tornadoes that form in these long lines of storms are a little bit more difficult to predict and especially to warn for because the circulations often formed quickly,” Mr. Lyza said. Even though these tornadoes are often weaker, on average, parts of Mississippi and Alabama are still vulnerable to them because of their larger mobile home populations and because these storms often happen at night.

Around 30 teams of researchers will deploy a variety of equipment in eastern Mississippi and western Alabama on Thursday, including mobile radars, uncrewed aerial systems, trucks with instruments attached and different kinds of portable devices designed to measure lightning and the atmosphere within and around storms.

However, there is some uncertainty on exactly when and where the storms will begin to move into eastern Mississippi.

Even though the researchers started planning last week for a possible deployment on Thursday, the forecast has continually shifted.

In recent days, Mr. Lyza said, it did not seem as if the weather would be severe. But over the last day or so, he said, “we’ve seen this trend towards better indications of more significant severe weather coming into Mississippi and Alabama.”

But he said there were still questions about how significant this severe storm system would be. “It’s just a trickier forecast,” he said, “even than usual.”

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