Kevin Knupp, UAH: Detailed Study of U.S. Southeast Tornadoes
July 23, 2011
It was one of the deadliest tornado outbreaks in U.S. history.
satellite shows storm system moments before spawning tornado in Joplin,
Now scientists are organizing a research program to better understand
the tornadoes that blew through Alabama and other southeastern states on
April 27, 2011.
Scientists at the University of Alabama in Huntsville (UAH) are
analyzing radar data from that day, then merging the information with
detailed storm surveys and other data. They hope to learn more about how
the storms formed, what made the storms so powerful and what might be
done to make tornado warnings more effective.
The National Science Foundation (NSF) funds the project through a Rapid
Response Research (RAPID) grant, which enables support for fast-response
research tied to events such as tornadoes.
"Heavily forested rolling terrain and limited public awareness may
present unique challenges to tornado detection in this area and to
widespread dissemination of 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.
In addition to studying the physics of the storms, the team will look at
the psychology and sociology of storm warnings.
A graduate student from the University of Oklahoma and UAH student
volunteers and scientists 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 areas where there are only
countywide alerts," said Kevin Knupp, who leads UAH's severe weather
Data compiled by UAH scientist Tim Coleman shows about a ten-fold
increase in warnings among Memphis, Atlanta and Tallahassee since the
National Weather Service (NWS) 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
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 whether there was or was not a tornado on the
The UAH survey team is learning more about 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 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 are using data
from the NWS NEXRAD between Huntsville and Chattanooga, Tenn.; a dual-polarimetric
Doppler radar at the Huntsville International Airport and UAH's own
mobile dual-polarimetric Doppler that on April 27 was between the two
"Since we have three radars, we can reconstruct the wind field in detail
for each of the cells and squall lines that moved through," Knupp said.
"We had a full spectrum of storms, and it seemed that almost every storm
formed 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."
The dual polarimetric radars also picked signs of debris being thrown
into the sky by tornadoes, Knupp said. "The Cullman [Alabama] 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 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 what we saw in the radar to what was
being churned up by the tornado."
The detailed radar and surface data will also help 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.
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 [Alabama], I saw a heavy cast iron bathtub that was
upside down and completely disconnected from its plumbing. That was not
Knupp 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 spiders.
"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."