Tornadoes only occur when large thunderclouds
form. Many thunderstorm clouds DO NOT produce
tornadoes but some do. So, to understand tornadoes
you have to understand why thunder clouds
cumulonimbus clouds form in the first place.
Basically, it all comes down to 3 main
1. There has to be convergence of air at the
surface so that air is flowing horizontally from
opposing directions. When the air meets it has to
go somewhere and so it goes up. Another way to
make the air go up is to strongly heat the ground
surface due to solar heating. This warms the
ground air and because it is less dense the air
rises. So, this is called LIFT... there has to be
2. The second ingredient is that there needs to
be a source of warm MOIST air... that is air that
has a high relative humidity. this is important
because when warm moist air rises it condenses and
makes a cloud... when the water vapor becomes a
liquid droplet, heat is given off to the
surrounding air which then is less dense and rises
even FASTER.... this is why thunderclouds can form
so fast and grow to heights up to 20 km!!! In a
matter of minutes!
3. The third ingredient is wind shear. This
can be understood by recognizing that the wind
that blows horizontally does so at a speed that
can vary with height. So, say the wind is blowing
at 40 mph at 1 km above the surface at some
location. Then, at that same x,y spot but at 2 km
the speed is say 50 mph... This difference in
speed creates “vorticity” or spin.
Now we (meteorologists) use a number called the
lift index (LI) to say how all these
features come together to trigger possible
tornado... this index is called the lift index.
Typically the index is 0 or +1... A severe
thunderstorm has LI = -3... The LI over OK last
week was -8 !!!!
Tornadoes can develop when the LI is - 5 or -6
or -7 , -8 etc. Strongly negative value of LI.
Now, in that part of the mid west we have warm
moist gulf air, we have strong ground heating, and
because of the mixing of warm moist tropical air
(m T air = marine tropical) and dry cooler
continental polar air (cP), you see that we have
all the ingredients for intense thunder cell
development, and hence the POSSIBILITY of
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