UAH to make detailed study of deadly April 27 tornadoes
- HUNTSVILLE, Ala. (July 11, 2011) -- Scientists at The University of Alabama in Huntsville are organizing a research program to better understand the deadly outbreak of tornadoes that killed more than 240 people in Alabama and other Southeastern states on April 27.
Supported by a one-year, $150,000 grant from the National Science Foundation (NSF), the UAHuntsville team will analyze radar data from that day, then merge that information with detailed storm surveys and other data. They want to learn more about how the storms formed, what made that day's storms so
unusually powerful, and what might be done to make tornado warnings more effective.
In addition to studying the physics of the storm, the team will also look at
the psychology and sociology of storm warnings. A graduate student from the
University of Oklahoma, UAHuntsville student volunteers and faculty are
interviewing survivors to learn more about how and when people reacted to
that day's repeated tornado warnings.
"One thing we're after is whether people are desensitized because the false
alarm rate is so high, especially in counties where there are only
countywide alerts," said Dr. Kevin Knupp, who leads UAHuntsville's severe
weather research team.
Data compiled by UAH post-doctoral student Tim Coleman shows that there has
been about a ten-fold increase in warnings between Memphis, Atlanta and
Tallahassee since the Weather Service installed the NEXRAD Doppler radar
system, and that about 80 percent of all warnings are "false."
The increase in warnings is due in large part to the NEXRAD radar's ability
to spot "rotation" inside a storm system. Installed between 1993 and 1997,
the five NEXRAD radar units in Alabama are also better at detecting small
tornadoes than the previous system: In the years since NEXRAD was installed,
the number of small tornadoes (EF-0 and EF-1) documented by the National
Weather Service in Alabama has increased almost threefold, while the number
of larger tornadoes has stayed roughly the same.
"Before NEXRAD we didn't know these rotational elements along squall lines
were so prevalent," Knupp said. "If a small tornado didn't cause property
damage or wasn't reported, we might never know about it. Now we can see the
rotation, pinpoint the location, then go out afterward and look for damage
to confirm that there was or was not a tornado on the ground."
The UAH survey team is trying to determine how the public judges the threat
of dangerous weather.
"Did people perceive these tornadoes as dangerous?" Knupp asked. "There were
tornado watches posted hours before the storms hit, and some of the tornado
warnings went out 15 or 20 minutes or more in advance. Did people dawdle
because they thought there was no need to rush to take shelter?
"It apparently takes visual images to make some people react. Of course, if
we need pictures of an approaching tornado to make people take shelter, then
we've got a problem."
In their analysis of the storm data, Knupp and his team will use data from
the NWS NEXRAD between Huntsville and Chattanooga, a dual-polarimetric
Doppler radar at the Huntsville International Airport, and UAHuntsville's
own mobile dual-polarimetric Doppler, which on April 27 was stationed
between the two stationary radars.
"Since we have three radars, we can reconstruct the wind field in detail for
each of the cells and squall lines that moved through that day," Knupp said.
"We had a full spectrum of storms that day and it seemed that almost every
storm was forming a tornado."
The radar data will be compared to detailed aerial reconnaissance of the
"The damage path is really the fingerprint of the tornado," Knupp said.
"That is why it was so urgent to do this reconnaissance quickly, before the
cleanup or re-growth could erase the clear tracks."
NSF is funding this project through a Rapid Response Research (RAPID) grant,
which enables support for fast-response research tied to events such as
"Heavily forested rolling terrain and limited public awareness may present
unique challenges to tornado detection in this area, as well as to
widespread dissemination and effective public response to severe weather
warnings," said Brad Smull, program director in NSF's Division of
Atmospheric and Geospace Sciences, which funded the RAPID award.
The dual polarimetric radars also picked signs of debris being thrown into
the sky by tornadoes, Knupp said. "The Cullman storm had very high
reflectivity up to 20,000 feet. That was debris being lofted to 20,000 feet.
These storms were very efficient at that.
"We will look at Google Earth to see what was in those areas before the
storms hit. Was it metal buildings, a residential area, forest or fields?"
he asked. "We can use that information to relate was we saw in the radar
with what was being churned up by the tornado."
The detailed radar and surface data will also help the scientists determine
whether other factors, such as surface roughness, topography or gravity
waves, played a role in forming or strengthening tornadoes.
Knupp assisted with the NWS surveys of the April storm tracks, including
track of the tornado that went through Hackleburg and Phil Campbell.
"I talked to one woman who took shelter in her bathtub," he recalled. "Her
house went one way and her tub went another. There was a post that pierced
the tub, but she walked away from it.
"In Hackleburg, I saw a heavy cast iron bathtub that was upside down and
completely disconnected from its plumbing. That was obviously not
"I was surprised at the relatively large number of storm shelters in the
area, even those that were just storm pits -- a mound of dirt with a door
facing north or south," he said. "There have been reports that some people
were fearful of getting into their storm shelters due to a fear of snakes or
"Let me tell you, I have a near phobia of spiders, but I would get into a
storm pit if there was a tornado warning."
Radar impage from the National Weather Service Hytop (KHTX) radar at 6:34 a.m. CDT (1134 UTC), showing a large mesoscale cyclonic circulation and its associated banded structure. This circulation feature was associated with 15 EF-0 to EF-2 intensity tornadoes.
Radar reflectivity from the UAH Advanced Radar for Meteorological and
Operational Research (ARMOR) showing reflectivity curls associated with
cyclonic circulations near the leading edge of a squall line at 1:23 p.m.
CDT (1623 UTC). These circulations were directly associated with 7 EF-P to
ARMOR radar reflectivity showing the parent supercell storm at 3:33 p.m. CDT (2022 UTC).
ARMOR radar reflectivity showing multiple tornado supercell storms at 4:30 p.m. (2130 UTC).
Damage near Tanner, AL, from the EF-5 tornado that also hit Phil Campbell
and Hackleburg, AL. The concrete slab of a small house, foreground, and the
area surrounding the slab were wiped clean of most debris. (Photo by Kevin
Dr. Kevin Knupp monitors instruments launched aboard a helium balloon into violent storms on April 27. (UAH/ESSC photo)