Intense storms were brewing Thursday across the southern tier of the United States, marking the fourth day of an unusually prolonged episode of severe weather. The pattern should start winding down by Friday after having caused at least 4 fatalities and widespread damage yet to be tallied. At least two people were killed in Tennessee on Wednesday afternoon by a powerful twister that crossed Interstate 64 south of Nashville.
The main culprits for this week’s rampage of severe weather are a broad, cold upper low bordered by a powerful west-to-east jet stream that’s pushed across the entire northern half of the nation, together with warm low-level inflow from the Gulf of Mexico bearing near-record levels of moisture for early May. Multiple frontal systems along the jet stream have spawned daily rounds of severe thunderstorms. A few of the tornadoes have been intense, including one rated EF4 on the Enhanced Fujita Scale that devastated the town of Barnsdall late on Monday, May 6.
From Monday through midday Thursday, and after filtering for duplicate reports, the NOAA/NWS Storm Prediction Center (SPC) had tallied an eye-popping total of 84 tornado reports, 606 severe hail reports (hail at least 1” in diameter), and 359 reports of severe wind (gusts to at least 58 mph). This comes after April produced 300 confirmed tornadoes, the largest total on record for that month outside of the Super Outbreak month of April 2021.
For Thursday afternoon into early Friday, SPC placed much of the South from northern Texas and Louisiana to southern Mississippi, Alabama, and Georgia under an enhanced risk (level 3 of 5) of severe weather.
Two main threats were looming for Thursday:
Giant hail. On Wednesday, Dallas-Fort Worth International Airport (DFW) recorded a muggy dew point of 78 degrees Fahrenheit. That’s the highest surface moisture value ever observed at DFW so early in the year. This juicy air, getting heated by the May sun on Thursday, will spawn intense thunderstorms across North Texas on Thursday afternoon that will race eastward across Louisiana and into the Southeast as the night unfolds, perhaps making it all the way to the Atlantic coast by midday Friday.
Multiple runs of the short-range HRRR forecast model were projecting storms to build and intensify rapidly near the DFW area by late afternoon. Some of the nation’s most destructive hailstorms on record have slammed the DFW area, and SPC warned that historical analogs suggest some of Thursday’s storms could produce hail 3 to 4 inches in diameter (i.e., baseball-plus to grapefruit-sized).
Potential derecho. Thursday’s pattern also bears some of the warning signs for development of a derecho, a long-lived corridor of extreme high winds. Pockets of severe wind gusts above 50-60 mph are a near certainty, but it was too soon to know with confidence whether the delicate balance of storm structure, instability, and upper-level conditions will be aligned to produce a truly sustained derecho.
Jeff Masters contributed to this post.