Strong tornadoes hit Mississippi. Here’s what made them unusually dangerous.

Gov. Tate Reeves (R) said that a search-and-rescue response was underway and that the state was in contact with local emergency managers and first responders. The governor estimated that 275 homes and 50 apartments were damaged or inaccessible in Lamar County, as were 200 in Lincoln County and a dozen in Lamar County.

As of early Thursday, 17 people were reported to be injured.

Why the tornadoes were so severe

Rain-wrapped tornadoes are especially dangerous. They resemble innocuous-looking curtains of rain; there’s no way to, from the outside, ascertain what lurks within.

Rain-wrapped tornadoes are especially common across the Deep South. That’s where robust Gulf of Mexico moisture leads to low cloud bases, obscuring storm structure. Pine forests also release additional moisture to the lower atmosphere, leading to fog and even more low clouds – not to mention, the trees block the sky from view.

Storms in the Deep South are more likely to be waterlogged; the wetter midlevels of the atmosphere are less conducive to hail production, but more supportive of torrential downpours and flooding.

Tornadoes in the Deep South are also faster-moving on average, carving longer paths.The larger pockets of mobile homes in the region can increase the Deep South’s risk and vulnerability in a tornado. You’re far more likely to be killed by a tornado if in a mobile home than in a permanent structure.For this storm, the National Weather Service Storm Prediction Center had indicated the potential for several tornadoes, including an isolated strong tornado, with an enhanced (Level 3 of 5) risk of severe weather around southern Mississippi and southwest Alabama.

The main source of uncertainty was whether the rotating supercells would evolve. Or whether storms would merge into messy clusters and windy squall lines while being undercut by an approaching cold front.

The latter would have reduced tornado risk appreciably.

Instead, however, several things happened.

There was a slightly stronger cap – a lid of hot air a mile above the ground that suppresses warm surface air – at the midlevels of the atmosphere. The cap prevents that surface air from rising and forming storms. The presence of a subtle cap, rather than no cap, meant that only a few air pockets could rise and form storms.

The result was a couple of dominant supercells that neither merged nor had to compete for resources in the volatile environment.

There was also a bit of a stronger trigger ahead of the main cold front, and gathering air at the surface. Colliding air forced a couple of air pockets to rise, generating those isolated rotating supercells.

Wind dynamics also were more supportive for tornadoes than initially thought.

Weather models had simulated southerly surface winds, whereas there was a small corridor of south-southeasterly surface winds in southern Mississippi. That subtle easterly component to the surface winds contrasted against stronger southwesterlies aloft. Tall storms felt those changing winds with height and rotated profusely.

Outlook for Thursday

The Storm Prediction Center is outlining a slight (Level 2 out of 5) risk of severe weather for the Florida Panhandle and extreme northern parts of the peninsula.

A remnant band of thunderstorms along the cold front was sagging southeast and was expected to weaken into the midafternoon hours. Only an isolated tornado threat is anticipated. The main concern will be locally gusty winds along the front.