The agency specified that the system could then spread eastward and peak in the evening and night across Mississippi and Alabama.
A particularly dangerous situation tornado watch was issued for portions of western and central Alabama and central to eastern Mississippi until 7pm on Wednesday.
The high risk areas covered in the warning included west-central Alabama, northern and central Mississippi, northeast Louisiana and far southeast Arkansas.
The latest outlook from the NWS on Wednesday afternoon slightly expanded the high risk area and increased the underlying likelihood of tornadoes across the southeast.
The service rarely offers such a severe degree of risk warning, with the last high-risk forecast being issued on 20 May 2019, in the southern Plains, according to The Weather Channel.
The NWS warned in a severe weather outlook on Wednesday that the incremental weather could also bring “scattered damaging winds, some hurricane force scattered large hail” noting some could be “baseball size”.
The outlook covered much of Mississippi, Alabama, Arkansas, parts of Louisiana, Tennessee, Missouri and Georgia.
The NWS warned that tornadoes will continue overnight across the south and told residents to prepare in advance, saying “your family’s life might depend on it.”
“Review your severe weather safety procedures for the possibility of dangerous weather today,” they said. “Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings.”
They specified that those who have been placed under tornado warnings should move to a place of safety: “Ideally in a basement or interior room on the lowest floor of a sturdy building.”
The widespread and substantial severe weather event is expected to continue into Thursday from southern Virginia southward into Florida and westward into parts of eastern Kentucky and eastern Tennessee.