|THE PERFECT TORNADIC ENVIRONMENT
METEOROLOGIST JEFF HABY
A tornado is a violently rotating column of air from a storm that is in contact with the ground. There are
several ingredients that go into producing this wonder of nature. These ingredients include instability,
wind shear, moisture, lifted condensation level, cap, and surface influence.
Instability: The higher the instability the stronger the updraft strength. In order to have a tornado a
thunderstorm needs to be present. Thus, at least a minimal amount of instability needs to be present. Tornadoes
can occur when instability is weak, moderate or high. There is a tendency for stronger tornadoes when
instability is higher but instability by itself can not forecast tornadoes.
Wind shear: The wind direction changing with height and the wind speed changing with height contribute
to wind shear. This ingredient is very important for tornadic environment. If wind shear is weak the
chance for a tornado is very low. In order to develop and sustain the rotation of a tornado there needs to
be wind shearing air currents.
Moisture / Lifted Condensation Level: This ingredient is important for the development
of a storm. Without significant moisture a
thunderstorm will have too much dry air in order for the Lifted Condensation Level
to be close to the surface. A storm that develops in an environment with a moist
boundary layer and has a LCL close to the surface has a better tornadic potential than
when the boundary layer is dry.
Cap: The cap or lid can be an energy building aid in the boundary layer. A nice cap can aid in
allowing only stronger storms to develop. The stronger storms have a greater tornadic potential. If the
cap is weak and rain and storms develop all over the place then there is less energy to focus into any
Surface influence: The surface influence is an often overlooked ingredient. Irregularities of the
surface can focus higher wind shear and low level convergence over certain areas. This can
enhance the tornadic potential. Subtle surface cover changes and topographic features can
focus initial storm development in places where uplift from surface convergence is more intense.
So what is the perfect tornadic environment? There really isn't an exact one since it is how all the
ingredients come together that determines the likeliness of a tornado. I will though list a
hypothetical situation that would be a great situation for a tornado:
Instability (1,500 J/kg), Wind shear (very strong especially from surface to 3,000 meters above surface), LCL
that is within 750 meters of surface, a
moderate cap that breaks, and a surface convergence boundary to focus thunderstorm development. This
situation will have a strong updraft that is twisted near the surface by the wind shear. The LCL near the
surface allows good alignment of the updraft and wind shear. The moderate cap
breaking and surface convergence allow a focus for a storm to develop.