You heard about it.
Maybe you even saw it.
Maybe you’ll never be the same.
They started several days ago, the storms. They travelled across the central, southern, and eastern parts of the country in waves; one after another. At one point they even had the U.S. adorned with tornado watches that extended all of the way from northern Michigan to the southern Texas. We knew it would be bad. But few would have guessed it would be like it was.
The events of Wednesday April 27, 2011 will reverberate through the towns of the southern United States for many years to come, and they will likely reverberate through the meteorological community for decades. As meteorologists, many of us watched in horror as we saw live feed of the tornadoes going through Tuscaloosa and making their way to Birmingham. Many of our number sacrificed rest that night in order to continue to put out the watches and warnings that would hopefully notify the public they needed to find safe shelter. Many more stayed awake in order to ensure that friends and family were taking the impending threat seriously and finding safe quarters in which to sleep. We all hoped that these efforts would not be in vain, but when the sun rose the next day and cast light on the damage and casualties, many couldn’t help but wonder if things could have been done better, or if something might have gone wrong.
Meteorologists knew days in advance that conditions would likely be favorable for severe convection across much of the country in these last few days of April 2011. As April 26 and 27 came closer, forecasts were able to become more precise. On Monday, April 25, the Storm Prediction Center (SPC) issued both Day 2 and Day 3 convective outlooks that indicated a moderate risk of severe weather potential over parts of Dixie Alley. By 13:00 UTC (9:00 am EDT) on April 26, the SPC had issued a high risk of severe weather potential over parts of Texas, Arkansas, and Louisiana and indicated that there would be an elevated threat of significant tornadoes (of damage intensity EF2 or greater) for the rest of the day in and around this area. As the day went by, the high risk was extended east to include parts of Mississippi. It should be noted that the severe threat was also indicated as being present over much of the rest of the southeast. Preliminary storm reports suggest that the tornado outbreak started in earnest around 22:00 UTC (6:00 pm EDT) in northeast Texas, about 9 hours after the SPC had issued a high risk for the potential of severe weather. The first tornado watch on this day was issued for northeast Texas, southwest Arkansas, and northwest Louisiana at 18:45 UTC (2:45 pm EDT) and was in effect until 10:00 pm local time. This watch was also the first of three Particularly Dangerous Situations (PDSs) issued that day, suggesting forecasters believed there was a real threat for a serious severe weather outbreak that could include long track, violent tornadoes. Indeed, an 18:00 UTC sounding taken at Shreveport, Louisiana indicated high levels of convective available potential energy (CAPE, a measure of buoyancy in the atmosphere) and vertical wind shear, suggesting that supercell thunderstorms would be likely if convection were to be initiated, or if it traveled into the area.
Areas of the south started the next day in SPC issued high risks. By 12:00 UTC (8:00 am EDT), this high risk area included portions of Mississippi, Alabama, Tennessee, and Georgia. The first tornado watch was issued for a much of Mississippi and Alabama at 7:25 UTC (3:25 EDT), for a line of storms passing through the region – remnants of the convective activity that occurred in Texas and Louisiana the day before. By about 13:00 UTC (9:00 am EDT), that initial line had passed through Alabama and left the area with patchy clouds and continued southerly flow (which enabled air from the Gulf to keep supplying the region with warmth and moisture). 18:00 UTC (2:00 pm EDT) soundings from Mississippi and Alabama show high CAPE, amble low level moisture, and incredible low level wind shear (with winds at 10 to 20 knots at the lowest levels which veer (turn clockwise) with height and increase to 50 to 60 knots at the 700 mb level, which is still relatively low in the atmosphere). Such conditions are, again, conducive to the formation of supercell thunderstorms, and as forcing was available that could spawn convection (in the form of a cold front and associated upper level low that was able to provide extra support for storms), watches began anew for the southern states in the early hours of the afternoon. The first of four PDSs for the day was issued at 16:05 UTC (12:05 pm EDT) for almost the entire state of Mississippi, and was in effect until 7:00 pm local time (a similar tornado watch was issued for Alabama just under two hours later). The first tornado reports that were associated with this new threat started coming in shortly before 19:00 UTC (3:00 pm EDT), from northern Mississippi.
We knew it was going to happen. The information was out there. But still, this severe weather outbreak is now seen as one of the most deadly in American history, second only to the March 18, 1925 tornado outbreak that killed upwards of 700 people. It will make people rethink what they know about the weather, and how they respond to it. The atmosphere does not make much distinction between a city and a forest, nor does a tornado discriminate between a home and an empty lot or a derelict shanty. All we can do is respect the weather, be alert, and move out of the way when we need to...
More than 100 tornadoes occurred on April 27, 2011. I can’t say for sure how many; we may not know for days.
More than 300 people died on April 27, 2011 as a result of tornadic storms. I can’t say for sure how many; we may not know for days.
What went wrong? If you aren’t a meteorologist or storm chaser and are interested in helping the National Weather Service and SPC figure out how they can improve storm watches and warnings, please e-mail nssl.outreach@noaa.gov to take their survey.
Sometimes the strength of a storm is so strong, even a full brick home with a basement offers no protection. An entire house and the basement contents are literally sucked out and are forever lost, along with the lives of those who tried to save themselves.Photo and thought courtesy of Dennis Sherrod, Alabama native and chairman of Alert 1 Weather. To contribute to their effort to provide relief and assistance to Alabama residents impacted by the storms, visit alert1weather.org
