Three dozen people perished in a devastating rampage of storms that began Easter weekend and unleashed more than 100 twisters across much of the South and Southeast. Three of the tornadoes were deemed “violent,” reaching EF4 strength with winds topping 165 mph. The toll tied 2020 as the deadliest year for tornadoes since 2011.
In the wake of Sunday and Monday’s vicious storms, National Weather Service meteorologists have fanned out across the areas hardest hit, collecting clues found in the damage to piece together information about the storms’ intensities.
Meanwhile, satellites peering down from above have illustrated the destructive potency of the storms. Vast expanses of mowed-down vegetation mark the twisters’ paths, and while rebuilding will soon begin, the scars left in the landscape could take decades to heal.
The scar of a storm
Peter Forister is a meteorologist pursuing a master’s degree in geography and meteorology at Virginia Tech. He used satellite data to produce maps highlighting where the devastating Mississippi tornadoes carved their paths of destruction.
His method centers on comparing the health of vegetation, particularly in heavily forested regions, before and after a tornado strikes. By plotting the difference in two satellite-derived quantities, Forister was able to determine where once-verdant forests had been torn up and denuded.
His findings show that damage associated with the Soso, Miss., tornado reached an astonishing two miles wide — or more. The National Weather Service in Jackson, Miss., reported Wednesday that the storm had a preliminary width of “at least 2 miles,” placing it in a rare category of enormous tornadoes.
Land temperature reveals a twister’s path
Others have used satellites to measure the temperature of the land surface. Forests and vegetation often help to regulate the temperatures of the ground; when a forest is chewed up by an enormous lawnmower-like tempest, the bare ground heats up faster than the surrounding forest.
The MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA’s Aqua satellite measures the surface temperature of land in miniature grid boxes. A scan of the satellite on April 14 detected a heat signature southeast of Collins and northwest of Laurel, Miss., where the EF4 tornado plowed through.
Satellites capture a storm’s intensity in Mississippi
Satellite imagery provided by Maxar Technologies shows farm buildings dashed to pieces in Seminary, Miss., following the EF4 tornado’s passage. While the destruction is immense, the steel truss farm buildings shown swept away above (top half of image) often succumb to winds in the EF1 to EF2 range, meaning that their destruction cannot be used as a damage indicator to qualify for an EF4 rating.
For further evidence of warehouse-style buildings’ susceptibility to high winds, look just a few hundred yards to the south — at least one building is left somewhat recognizable with a roof partially intact. That home appears to have been the most well-constructed structure visible in the satellite shot.
However, there’s also an outbuilding or barn just to the north with a metal roof that was left unrecognizable. Moreover, on the west side of the street, a home — likely a modular or manufactured home — appears to have been carried off its footprint to the east, where it collapsed about 50 feet away. Fragments of its roof can still be seen.
Then, a metal-roofed building to the north looks to have been largely demolished, yet a section of its roof remains — indicating that part of the building was perhaps left intact. Meanwhile, the site-built structure just to the north was wrecked.
It’s likely that there may have been tornadic subvortexes involved, or smaller funnels within the boiling behemoth that caused strips of highly intense and irregular damage.
A Tennessee tornado’s caprice seen from above
That sort of meteorological caprice can be seen on Angie Drive in East Chattanooga, Tenn., which was hit by an EF3 tornado overnight Sunday into Monday. Some homes can be seen left uninhabitable, while neighboring residences escaped with barely a scratch.
The East Brainerd Elementary School in East Chattanooga suffered serious roof damage from the twister; it’s estimated that winds in this area peaked in the EF2 range, the tornado expanding in width near the Drake Forest neighborhood. The school was closed due to covid-19 concerns until April 24 at the earliest.
What happened there offers a particularly interesting example of how damage is so dependent on construction styles. All of the sections of roof that were peeled away from the building came from the second floor — not from single-story parts of the building with only one floor. Construction on the building began in 2013 and wrapped up in 2015.
Google Maps street view indicates the first floor of the building was likely constructed with brick and heavier materials, while the second floor is probably composed of hefty amounts of sheet metal.
The second floor also has much larger windows, which, when broken by tornadic debris, likely allowed more air to enter the second floor and contribute to lifting the roof off the building.
The second floor also appeared to have longer expanses of gabled roofs, which are more vulnerable to tornadic winds than hip roofs. The majority of first-floor segments of the building appear to be covered by hip roofs. The first floor proved particularly well-constructed.
Sunday’s and Monday’s storms conjured up the power of the atmosphere. Each satellite image is a reminder of a tornado’s furious power — and a testament to the importance of knowing how, and when, to shelter.