(This story, originally published Monday morning, was updated with tornado rating information.)

Storms erupted over the Southeast on Sunday, spawning dozens of tornadoes that proved both destructive and deadly. Twenty-three people have been confirmed dead, a number that may rise as recovery operations continue Monday.

The tornado deaths from this event alone outnumber the count from the previous two years combined over the entire United States.

The tornado responsible for the 23 deaths, in Alabama’s Lee County, was given a preliminary rating of EF-4 on the 0-5 Enhanced Fujita scale for tornado intensity with estimated winds up to 170 mph. It is the first EF-4 tornado to hit the U.S. since April 29, 2017 in Canton, Texas, ending a record long streak without a twister this strong in the U.S.

A tremendous temperature contrast between the north-central and Southeast United States set the backdrop for this devastating storm outbreak. Temperatures from Montana to Minnesota hovered below zero Sunday afternoon (with wind chills around minus-40) while South Florida soared into the mid-80s — a difference of more than 90 degrees.

The region struck by the twisters sat in a volatile zone on the northern fringe of the warm and humid air, right up against the leading edge of the bitter Arctic chill.

As temperatures swelled into the 60s and 70s on Sunday afternoon, storms developed explosively, feeding off the unstable air.

A total of 97 tornado warnings were issued throughout the day. They dotted the map for a continuous 7 hours 51 minutes, marking the most tornado warnings to be issued in a single day since Dec. 23, 2015.

The National Weather Service logged at least three dozen tornado reports Sunday as twisters swept across four states: Alabama, Georgia, Florida and South Carolina.

The EF-4 rated tornado, responsible for the 23 fatalities, struck Lee County, Ala., around 2 p.m., tracking 30 miles east to north of Columbus, Ga., before dissipating.

Hardest hit were rural areas between Beauregard and Smiths Station, Ala. A tornado warning was issued 23 minutes in advance, then upgraded to an extremely rare and desperate “tornado emergency” 10 minutes later.

It is the deadliest tornado since the infamous Moore, Okla., tornado of May 20, 2013, in which 24 perished.

A second “large and extremely dangerous tornado” swept through an almost identical path less than an hour later.

Radar scans showed tornadic debris carried to an astounding 18,000 feet. That combined with the observed forest and structural damage indicated 170 mph winds commensurate with the EF-4 range.

A billboard torn off in the storm was carried 20 miles northeast to near Hamilton, Ga. The half-mile-wide tornado could be the first “violent” tornado to hit the United States since April 29, 2017.

Another strong tornado narrowly missed Macon, Ga. — whizzing through Houston County, Ga., at speeds of up to 60 mph.

Cairo, Ga., also took a direct hit by a twister 20 minutes after nightfall. Radar displayed a “tornado debris signature,” remnants of structures and vegetation lofted into the sky, suspended over the town.

That same telltale radar signature appeared farther north near Eufala, Ala., where a tornado tracked through the north side of town — remarkably with no injuries reported. It was rated an EF-2.

The tornadic storms coalesced near a warm front draped over Alabama’s Capital Heartland region and the southern Piedmont region of Georgia.

“Temperatures stayed in the 40s and 50s in the northwest half of Central Alabama,” wrote the National Weather Service in Birmingham, “while south of the warm front, readings got up into the 60s along with some 70s.”

Stalled warm fronts are also known to enhance the low-level convergence of air and spin critical for tornado formation. The front also served as a focusing mechanism, triggering storms and allowing them to track over some of the same areas repeatedly.

That same Weather Service office reported flurries just after nightfall — illustrative of how dramatic the clash of air masses was.

Despite the high impact, tornado outbreaks like this are not uncommon during the early spring in the Southeast. As warmth builds while winter lingers, the seasons battle it out — first over Dixie Alley in March, the threat shifting toward Ark-La-Tex in April, and finally the Plains and “Tornado Alley” in May.

Sunday’s arsenal of fierce storms did not feature the high contrast typical of Great Plains supercells, which allow storm spotters, chasers and eyewitnesses to see them coming from great distances. Instead, a dozen or more tornadic supercells were embedded in a large mass of rain. Even though warnings were issued for these storms, they were frequently disguised.

Survey teams will be dispatched across the South on Monday, assigning official ratings and conducting studies of the damage left in the wake of Sunday’s horrific storms. Preliminary data suggests between 15 and 20 touched down, at least half a dozen of which will be deemed “significant” and one or two “violent.”