Four days of destruction
April 25-28 marks a four day stretch on the calendar known for one of the deadliest and most destructive tornado outbreaks in United States history. Storms that occurred during that stretch of days caused $4 billion in damage.
April 27 marked the peak of the episode. Despite the continued advancements in technology and increased lead time on warnings through the years, that date was the deadliest due to tornadoes in the United States since 1925. 199 tornadoes caused 316 fatalities in five states. Compare that single day to all of 2014 thus far in which just 119, mainly weak, tornadoes have claimed no lives.
Over the span, four tornadoes garnered the highest possible rating based on their damage-EF5. In a typical year, one or fewer tornadoes are assigned that rating. The four EF5 twisters struck (in order) Philadelphia, MS., Hackleburg-Phil Campbell, AB., Smithville, MS. and Fyffe/Rainsville, AB.
The Philadelphia tornado ripped pavement off of the ground, completely leveled strong brick houses and killed three. The Hackleburg-Phil Campbell twister ripped homes off of strong foundations tossing them several hundred yards, ripped apart and twisted high-voltage power-line trusses and killed 72. The violent Smithville storm lifted one pickup off of a driveway never to be seen again, completely scoured vegetation from the ground and killed 23. In the Fyffe/Rainsville storm, a school bus was ripped clean off of its frame, trees were debarked and 25 were killed.
This outbreak also produced the infamous EF4 Tuscaloosa, AB. Tornado that would kill 44 and injure 1,000. As it moved through a high populated area, the storm was well photographed and documented by local TV stations and sky cameras. Whole communities were leveled and debris from the destructions was reported to be falling from the sky over 20 miles away in Birmingham, AB.
The four day event came together as the final in a series of upper level storms moved into the Great Plains. Much colder than its predecessors, the atmosphere was able to rapidly destabilize. An unusually strong surface low pressure system then developed in Arkansas and was steered northeastward. As this storm formed, low-level winds greatly increased. Surface southerly winds of 10-15mph crossed nearly 50mph southwesterly winds aloft. This change of vertical wind speed and direction is known as shear and is an ingredient needed to create highly-organized, rotating storms. A strong jet stream aloft, gave storms plenty of "breathing-room" and ensured that they could propagate forward for a long duration. The strong southerly winds quickly replenished tapped moisture from strong morning thunderstorms in Southern Mississippi and Alabama. Behind the early storms, clearing allowed maximum sunshine and the returned moisture to rapidly destabilize the atmosphere.
The outbreak was well forecast. Meteorologists saw the setup days in advance issuing their highest severe weather risk and most strongly worded statements. The rarest of National Weather Service Storm Prediction issuances, the Particularly Dangerous Situation Tornado Watch, which is sometimes seen less than once a year, was used 10 times during the four day event.
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