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Bassfield–Pachuta, Mississippi

Bassfield–Pachuta, Mississippi

EF4 tornado
A home near Cantwell Mill, Mississippi (northeast of Bassfield), that was swept off its foundation by the tornado.
Highest winds	190 mph (310 km/h)
Max. rating1	EF4 tornado
Fatalities	8 fatalities, unknown injuries
1Most severe tornado damage; see Enhanced Fujita scale

During the afternoon of Easter Sunday, 2 isolated supercells developed across southern Mississippi, one of whch went on to produce a high end EF4, which would cause extreme damage across its track through the towns of Bassfield, Soso, Moss, Heidelburg and Pachuta. It was the strongest tornado since 2015, and was responsible for the loss of 8 lives.

Meteorological synopsis

Satellite image of the extratropical cyclone responsible for the outbreak across the Southeastern United States at 21:56 UTC on April 12

For weeks throughout March and into April, an expansive area of high pressure built across the Southeast United States, contributing to abnormally warm temperatures across much of the country. The United States as a whole experienced its seventeenth warmest March, continuing the pattern that persisted throughout winter. In particular, many locations along the U.S. and Mexican Gulf coasts saw record warmest temperatures for the month. Calm weather associated with the high-pressure area induced rapid warming of the Gulf of Mexico waters to their highest values in the modern record—greater than 2 °C (3.6 °F) above the 1971–2010 average—as well as a moistening of the air near the surface. Increased instability associated with anomalously warm and moist air from the Gulf of Mexico has been associated with an increased risk of severe weather and tornado activity.

The first indications of organized severe weather came on April 8, when the Storm Prediction Center (SPC) outlined 15% probabilities for severe weather within 25 mi (40 km) of a point from central Texas eastward into the Florida Panhandle and eastern Georgia valid for April 11–12. These threat areas were later refined with the introduction of a day-3 moderate risk, the fourth of five threat levels, across northeastern Louisiana through central Alabama on April 10. Historically, the SPC issues one day-3 moderate risk every year, and half of those over the previous decade were later upgraded to High risk, the highest threat level. Over subsequent days, a significant mid-level shortwave trough progressed eastward across the United States. By the pre-dawn hours of April 12, mid-level cooling associated with the feature overspread the Edwards Plateau, Hill Country, and much of central Texas. Accordingly, an intense line of severe thunderstorms developed along a dry line while vigorous convective development formed farther east. These thunderstorms were initially isolated in nature but soon coalesced into a mesoscale convective system as they encountered an enhanced corridor of warm air streaming northward, as well as very strong wind shear. This storm complex progressed across northern Louisiana through the late morning and early afternoon hours, contributing to multiple tornado debris signatures. One such tornado in Monroe was rated EF3 strength. In advance of the line, a lifting warm front aided in the formation of a very moist, highly unstable, and highly sheared environment across and northeastern Louisiana and much of Mississippi. Accordingly, the SPC issued a particularly dangerous situation tornado watch into the late evening hours.

A weather balloon launch from Jackson, Mississippi, at 18:00 UTC revealed the presence of a capping inversion across the region. This cap was expected to weaken across central Mississippi, while forecasters expressed more uncertainty about its longevity across southern Mississippi and Louisiana. As a small area of low pressure progressed across northwestern Mississippi, it caused surface winds to turn out of the east-southeast, enhancing the potential for tornadoes. As a cluster of storms across central Mississippi progressed toward the northeast, it began to reintensify and develop supercell characteristics with an attendant threat of strong tornadoes. Farther south, two distinct supercells developed within an environment where long-tracked, significant tornadoes were favored, both exhibiting extremely strong rotation and distinct debris signatures. Based on previous storm structures in similar environments, the SPC remarked that "this is an exceptionally rare event" and estimated tornadic winds of 170–205 mph (274–330 km/h) on the first supercell, consistent with a tornado of EF4 or EF5 intensity. After conducting damage surveys, meteorologists identified two violent tornadoes with the first supercell, one that killed four people northwest of Salem to southwest of Bassfield and a second that killed eight people from south of Bassfield to southwest of Pachuta, both of EF4 intensity. An EF3 tornado was identified with the second supercell.

Storm development and track

Six minutes after the first EF4 tornado lifted far southwest of Bassfield, another violent, long-tracked tornado touched down south of the town spawned by the same supercell. A tornado emergency remained in effect for Bassfield due to the first tornado, giving substantial warning as the second developed. As it approached Bassfield, a large "donut hole" or BWER (Bounded Weak Echo Region) was noted on radar over the town, and in the next frame a pronounced debris ball was visible. Shortly after, the tornado quickly intensified and enlarged in size, reaching EF4 intensity as it demolished mobile homes and debarked trees. A cinder block business building was destroyed with its slab largely swept clean; four people were killed at this location.

The tornado reached peak intensity at high-end EF4 as a wood-frame metal-roofed cabin was swept clean of its foundation and a truck was thrown 300 yards (270 m). The tornado continued to grow in size, reaching its peak width of 2.25 miles (3.62 km) west of Seminary. An entire forest was leveled with extreme debarking to some trees and thousands to millions of trees damaged. Dozens of farm structures were damaged or destroyed. Multiple vortices and an intense core were evident in the damage path. A tornado emergency was extended ENE downwind of the storm for Seminary, Mississippi and Collins, Mississippi; one of several issued for the storm . with a photo being carried 121 miles downstream into Tuscaloosa, Alabama. One house was reported to have had its plumbing fixtures ripped out, indicative of very intense winds. The Storm Prediction Center issued a mesoscale discussion stating that a tornado with winds of 170-205 mph was likely ongoing, and that it was an 'exceptionally rare event'.. The storm then narrowed to 1.7 miles (2.7 km) and weakened to EF3 intensity, but continued to cause extreme tree damage and significant structural damage near Centerville. It then moved into Soso, causeing major damage to homes, churches, and destroying a convenience store and other structures at low-end EF4 intensity. EF4 damage continued in Moss, where nearly every structure was damaged and numerous homes were destroyed. The tornado finally dissipated after causing tree and roof damage in Pachuta. The most intense damage from this tornado is still being reviewed

The tornado was estimated by the NWS to have been at least 2.25 miles wide, making it the widest tornado in Mississippi history and the third-widest in the US on record, just behind the 2004 Hallam tornado. The tornado was also long-tracked, with a length of 68 miles. Damage was severe to the point the path of the tornado could be seen from satellite imagery. The tornado was given the preliminary rating of a high-end EF4 with estimated winds of 190 mph on April 16.