Supercells can prove to be one of the most spectacular
weather phenomena. This storm near Lamesa, Texas on May 14, 1997 moved
extremely slowly (5 to 10 mph), produced spectacular striations around
its main updraft and provided a 2 hour long show on storm structure.
Supercells are the most dangerous type of thunderstorm, due to its intense
rotating updraft the storm is able to last for several hours. The strong
updraft allows the storm to produce hail stones that can range in size
from marble to as large as a softball. Supercells also produce high winds,
flash flooding and all strong to violent tornadoes.
Some supercells exhibit rapid rotation at their mid levels that can appear quite obvious to even the most casual observer. It is these storms that usually produce large hail and/or tornadoes.
Above are two examples of supercells with strong mid level rotation.
On the left is the supercell responsible for producing the F-5 tornado
that devastated much of Oakfield, Wisconsin on July 18, 1996. On the right
is the supercell from July 25, 1997 that produced two tornadoes near Madison, Wisconsin.
There are three distinct types of supercell, the type of supercell is dependent on updraft orientation and how much precipitation is falling from the base of the storm. The three types are called dryline (LP) classic and collapsed (HP).
Above are examples of an LP supercell (left) and an HP supercell,(right).
Sometimes supercells do not easily fit into one category or another:
On the left we have a storm that has a large precipitation core but
no updraft on the forward flank (as in the case of an HP supercell). On
the right we have the leading a supercell that was beginning to transform
as it was absorbed into a squall line a short time later.
Supercells can produce large hail, high winds, microbursts, flash flooding and tornadoes.
On the left we have a hailstone near Odessa, TX (May 26, 1999) and
on the right is a tornado just northeast of Panhandle, TX on May 29, 2001.
Many supercells actually turn out to be relatively harmless. This happens most often when a storm remains out over open country, but it can also be due to a nearby storm that causes the supercells early demise.
Above we have a supercell with an impressive wall cloud that stayed in open country south of Scottsbluff, Nebraska on May 21, 1998. On the right we have an LP supercell near Lamesa, Texas that stayed out over open country and farm fields on May 14, 1997.
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Brian William Jalas.