[Even though storm prediction is improving, tornadoes are still
hard to predict, with a warning typically of only about 10 to 15
minutes. This is why tornado prediction is hard, and whats being done
to improve it.]
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WHY TORNADOES ARE STILL HARD TO FORECAST  
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Chris Nowotarski
March 31, 2023
The Conversation
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_ Even though storm prediction is improving, tornadoes are still hard
to predict, with a warning typically of only about 10 to 15 minutes.
This is why tornado prediction is hard, and what's being done to
improve it. _

Tornado touches down, Morgan Schneider/OU CIMMS/NOAA NSSL

 

_Meteorologists began warning about severe weather
[[link removed]] with the potential for tornadoes several
days before [[link removed]] storms
tore across the Southeast
[[link removed]]
and the Central U.S.
[[link removed]]
in late March 2023. At one point, more than 28 million people
[[link removed]] were under a
tornado watch [[link removed]]. But
pinpointing exactly where a tornado will touch down – like the
tornadoes that hit Rolling Fork, Mississippi
[[link removed]], on March 24, and
towns in Arkansas
[[link removed]],
Illinois [[link removed]] and
multiple other states
[[link removed]] on March 31
– still relies heavily on seeing the storms developing on radar.
Chris Nowotarski
[[link removed]],
an atmospheric scientist, explains why, and how forecast technology is
improving._

Why are tornadoes still so difficult to forecast?

Meteorologists have gotten a lot better at forecasting the conditions
that make tornadoes more likely. But predicting exactly which
thunderstorms will produce a tornado and when is harder, and that’s
where a lot of severe weather research is focused today.

Often, you’ll have a line of thunderstorms in an environment that
looks favorable for tornadoes, and one storm might produce a tornado
but the others don’t.

The differences between them could be due to small differences in
meteorological variables that aren’t resolved by our current
observing networks or computer models. Even changes in the land
surface conditions – fields, forested regions or urban environments
– could affect whether a tornado forms. These small changes in the
storm environment can have large impacts on the processes within
storms that can make or break a tornado.

[Scientists stand near a truck outfitted with measuring devices with a
dramatic storm on the horizon.]One way scientists gather data for
understanding tornadoes is by chasing storms. Annette Price/CIWRO
[[link removed]], CC BY
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One of the strongest predictors of whether a thunderstorm produces a
tornado relates to vertical wind shear
[[link removed]], which is how the wind
changes direction or speed with height in the atmosphere.

How wind shear interacts with rain-cooled air within storms, which we
call “outflow,” and how much precipitation evaporates can
influence whether a tornado forms. If you’ve ever been in a
thunderstorm, you know that right before it starts to rain, you often
get a gust of cold air surging out from the storm. The characteristics
of that cold air outflow are important to whether a tornado can form,
because tornadoes typically form in that cooler portion of the storm.

How far in advance can you know if a tornado is likely to be large and
powerful?

The vast majority of violent tornadoes form from supercells
[[link removed]], thunderstorms with a deep
rotating updraft, called a “mesocyclone.” Vertical wind shear can
enable the midlevels of the storm to rotate, and upward suction from
this mesocyclone can intensify the rotation within the storm’s
outflow into a tornado.

If you have a supercell on radar and it has strong rotation above the
ground, that’s often a precursor to a tornado. Some research
suggests that a wider mesocyclone is more likely to create a stronger
[[link removed]], longer-lasting tornado than
other storms.

Forecasters also look at the storm’s environmental conditions –
temperature, humidity and wind shear. Those offer more clues that a
storm is likely to produce a significant tornado.

What radar showed as a tornado headed toward Rolling Fork,
Mississippi, on March 24, 2023.

The percentage of tornadoes that trigger a warning
[[link removed]] has increased over recent
decades, due to Doppler radar [[link removed]],
improved modeling and better understanding of the storm environment.
About 87% of deadly tornadoes
[[link removed]] from 2003 to 2017 had an
advance warning.

The lead time for warnings has also improved. In general, it’s about
10 to 15 minutes
[[link removed]]
now. That’s enough time to get to your basement or, if you’re in a
trailer park or outside, to find a safe facility. Not every storm will
have that much lead time, so it’s important to get to shelter fast.

What are researchers discovering today about tornadoes that can help
protect lives in the future?

If you think back to the movie “Twister
[[link removed]],” in the early 1990s we were
starting to do more field work on tornadoes. We were taking radar out
in trucks and driving vehicles with roof-mounted instruments into
storms. That’s when we really started to appreciate what we call the
storm-scale processes – the conditions inside the storm itself, how
variations in temperature and humidity in outflow can influence the
potential for tornadoes.

Scientists can’t launch a weather balloon or send instruments into
every storm, though. So, we also use computers to model storms to
understand what’s happening inside. Often, we’ll run several
models, referred to as ensembles. For instance, if nine out of 10
models produce a tornado, we know there’s a good chance the storm
will produce tornadoes.

The National Severe Storms Laboratory has recently been experimenting
with tornado warnings based on these models, called Warn-on-Forecast
[[link removed]], to increase the lead time
for tornado warnings.

[A destroyed home with just one wall standing and furniture strewn
about in Rolling Fork, Mississippi, after the tornado March 24, 2023.]
[[link removed]]

An early warning can be the difference between life and death for
people in homes without basements or cellars. Chandan Khanna/AFP via
Getty Images
[[link removed]]

There are a lot of other areas of research. For example, to better
understand how storms form, I do a lot of idealized computer modeling
[[link removed]]. For that, I
use a model with a simplified storm environment and make small changes
to the environment to see how that changes the physics within the
storm itself.

There are also new tools in storm chasing. There’s been an explosion
in the use of drones – scientists are putting sensors into unmanned
aerial vehicles and flying them close to
[[link removed]]
and sometimes into the storm.

The focus of tornado research has also shifted from the Great Plains
– the traditional “tornado alley” – to the Southeast
[[link removed]].

What’s different about tornadoes in the Southeast?

In the Southeast there are some different influences on storms
compared with the Great Plains. The Southeast has more trees and more
varied terrain, and also more moisture in the atmosphere because
it’s close to the Gulf of Mexico. There tend to be more fatalities
[[link removed]] in the Southeast, too,
because more tornadoes form at night
[[link removed]].

[US map showing highest number of tornadoes in Mississippi, Alabama
and western Tennessee.]A map of severe tornado days from 1986 to 2015
shows a large number in the Southeast. NOAA Storm Prediction Center
[[link removed]]

We tend to see more tornadoes in the Southeast that are in lines of
thunderstorms called “quasi-linear convective systems.” The
processes that lead to tornadoes in these storms can be different, and
scientists are learning more about that.

Some research has also suggested the start of a climatological shift
[[link removed]] in tornadoes toward the Southeast.
It can be difficult to disentangle an increase in storms from better
technology spotting more tornadoes, though. So, more research is
needed.

_This article was updated March 31, 2023, with tornadoes in Arkansas
and the central U.S._[The Conversation]

Chris Nowotarski
[[link removed]],
Associate Professor of Atmospheric Science, _Texas A&M University
[[link removed]]_

This article is republished from The Conversation
[[link removed]] under a Creative Commons license. Read
the original article
[[link removed]].

* Science
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* meteorology
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* tornadoes
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* weather prediction
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