Prediction and Safety
Tornado Alley
Tornadoes affect every State in the US. However,
the bulk of them are concentrated in the wide
flat expanse of land between the Rocky Mountains
in the west, and the Mississippi River in the
East. This is known as Tornado Alley –
home to some of the most extreme weather phenomenon
on earth.
The reasons for this are both geographic and
climactic. Tornadoes are more common here in
the central plains because warm, humid air from
the Gulf of Mexico collides with cooler, drier
air coming down from Canada.
These converging weather fronts create the
huge storm clouds that sometimes generate tornadoes.
Since Tornado Alley lies isolated from the influences
of both Atlantic and Pacific Ocean storms, the
unique conditions necessary for tornadoes to
form occur more often here than anywhere else.
Predictions
Though tornado forecasting has vastly improved
over the past few decades, predicting where
a tornado will touch down next is virtually
impossible. Meteorologists observe the development
of temperature and wind flow patterns in the
atmosphere. It is these factors which create
moisture, instability, lift, and wind shear
needed for ‘tornadic’ thunderstorms
to develop. However, forecasting severe weather
more than two days in advance is little more
than guesswork.
A fleet of mobile radars known as Doppler on
Wheels (DOWs) are based around tornado prone
areas in America. DOWs record minute details
of tornado features, including eyes and inflow
jets, and wind speeds on and above ground level.
Arguably, the most valuable source of information
on tornado science and behaviour comes from
grass-roots level.
A network of storm chasers and tornado watchers
across the United States compile data on tornadoes
as they happen. This can sometimes be a very
dangerous task. Spotters feed live information
to America’s National Weather Service as
the tornados develop. This can often mean being
what normal people would regard as suicidally
close to a twister.
Twister Safety
Just 20% of America’s twisters are rated
at F2 and above. Even so, that’s still
200 tornadoes every year with winds of over
200mph. The amount of F4 and above tornadoes
clocks up just 20 a year, and thankfully F5
monster tornadoes generally strike just once
a year. This is still enough to kill an average
of 60 people a year in the US alone, and cause
billions dollars-worth of damage.
Even a relatively gentle twister can send a
piece of wood crashing through a brick wall
as if it was made of paper. The safest place
to shelter from a tornado is below ground level
in a basement. Amazingly, it’s estimated
that less than half of the houses in Tornado
Alley have cellars.
Experts recommend that people living in tornado-prone
areas without basements should line the walls
of a room in the house with 10mm steel sheeting.
Ideally, this would be an windowless corridor
in the interior of the home surrounded and protected
by other rooms. The family should cover themselves
with mattresses and cushions to prevent injury
from flying glass and debris.
Death From Above
Safety experts from America’s Storm Prediction
Centre recommend a list of tornado warning signs
to look and listen for:
Strong, persistent rotating storm clouds.
Whirling dust or debris on the ground under
a cloud base.
Hail or heavy rain followed by either dead calm
or a fast, intense wind shift.
A loud, continuous roar or rumble, which doesn't
fade like thunder.
Small, bright flashes near to ground level beneath
a thunderstorm which indicated that power lines
are being snapped by very strong wind.
On average, people living in their path have
just 18 minutes warning to take shelter for
an approaching tornado. However, public awareness
of tornado safety is extremely high in Tornado
Alley, and consequently casualties are often
lower than other parts of the USA.
On May 3rd 1999 an incredible 66 tornadoes
trashed Oklahoma leaving a 38-mile trail of
devastation into Oklahoma City itself. The biggest
of these twisters – an F5 - damaged almost
8,000 buildings and caused over a billion dollars
worth of damage. Despite this incredible destruction,
fewer than 40 people were killed. People in
these parts know to keep an eye on the sky.
