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 EF4 damage in downtown Cullman, Alabama. | |
| Meteorological history | |
|---|---|
| Formed | April 27, 2011, 2:40 p.m. CDT (UTC−05:00) |
| Dissipated | April 27, 2011, 3:38 p.m. CDT (UTC−05:00) |
| Duration | 58 minutes |
| EF4 tornado | |
| on the Enhanced Fujita scale | |
| Highest winds | 190 mph (310 km/h) |
| Overall effects | |
| Fatalities | 6 |
| Injuries | 48+ |
| Damage | $1.1 million (2011 USD) |
| Areas affected | Cullman, Arab |
Part of the 2011 Super Outbreak and Tornadoes of 2011 | |
During the afternoon, a violent EF4 tornado touchdown in Cullman County and impacted the towns of Cullman and Arab in Northern Alabama, killing 6 and injuring a further 48 people. This tornado was part of the 2011 Super Outbreak, the largest tornado outbreak in United States history. The violent, multi-vortex wedge reached a peak width of 1 mile while reaching its peak intensity as a high-end EF4 tornado
Meteorological synopsis
On April 23, the Storm Prediction Center (SPC) began monitoring the potential for a substantial severe weather outbreak in the extended range.[1] As a shortwave trough tracked across portions of the Mid-South and southeastern United States, moderate instability and strong wind shear ahead of a trailing cold front was expected to promote the development of supercell thunderstorms capable of producing tornadoes, large hail, and damaging winds.[2] Two days before the event, on April 25, the SPC issued a moderate risk of severe weather encompassing portions of central and eastern Kentucky, middle and eastern Tennessee, northeast Mississippi, central and northern Alabama, and northwest Georgia. Due to the combination of rich low-level moisture, strong shear, and focused large-scale ascent, there was relatively high confidence across the outlined area for strong tornadoes – a tornado rated EF2 or higher on the Enhanced Fujita scale – and widespread damaging winds.[3] By the morning of April 27, the SPC upgraded to a high risk of severe weather,[4] noting that a dangerous tornado outbreak capable of producing several violent – EF4 tornado or stronger on the Enhanced Fujita scale – and long-track tornadoes was expected.[5][6]
Shortly before 12:00 p.m. CDT, the probability of tornadoes within 25 miles of a location was increased even further to 45%, a level exceeding even typical high-risk standards, for an area including Tuscaloosa. The forecast continued to emphasize the risk of strong/violent and very damaging tornadoes, as confidence increased even further regarding the risk of an extreme, high-end tornado outbreak. Throughout the afternoon hours, in the wake of two earlier mesoscale convective systems, the airmass across western and northern portions of Alabama began to quickly destabilize, with mixed layer convective available potential energy (CAPE) estimated in the 2500–4000 j/kg range and low-level dewpoints of 70–72 °F (21–22 °C) surging northward from Louisiana. Meanwhile, the wind shear environment became substantially more favorable as an 80–100 kn mid-level jet ejected eastward into the region.
- ^ Steve Goss (April 23, 2011). "Day 4-8 Severe Weather Outlook Issued on Apr 23, 2011". Storm Prediction Center. National Oceanic and Atmospheric Administration. Retrieved December 7, 2013.
- ^ Steve Goss (April 24, 2011). "Day 4-8 Severe Weather Outlook Issued on Apr 24, 2011". Storm Prediction Center. National Oceanic and Atmospheric Administration. Retrieved December 7, 2013.
- ^ Steve Goss (April 25, 2011). "Apr 25, 2011 0730 UTC Day 3 Severe Thunderstorm Outlook". Storm Prediction Center. National Oceanic and Atmospheric Administration. Retrieved December 7, 2013.
- ^ Ryan Jewell (April 27, 2011). "Apr 27, 2011 1200 UTC Day 1 Convective Outlook". Storm Prediction Center. National Oceanic and Atmospheric Administration. Retrieved December 7, 2013.
- ^ Ariel Cohen; Richard Thompson (April 27, 2011). "Apr 27, 2011 1300 UTC Day 1 Convective Outlook". Storm Prediction Center. National Oceanic and Atmospheric Administration. Retrieved December 7, 2013.
- ^ Ariel Cohen (April 27, 2011). "Public Severe Weather Outlook". Storm Prediction Center. National Oceanic and Atmospheric Administration. Retrieved December 7, 2013.