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Fundamental Elements
Wind gradient causes the formation of rotating cylinders...
The following illustrations outline the key elements
of Severe Weather systems; in this specific example, a Supercell.
The storm profiled here began in eastern Kansas and
moved across Missouri on the afternoon of April 10, 2001.
This sounding animation runs from 7:00 pm (CDT) April
9 through 7:00 pm April 10 -- for Jefferson City, MO. (about
100 miles west of St. Louis).
The meteograms below profile wind and conditions for Lambert Field, St. Louis.
Lambert Field @ 21z (4:00 pm) -- April 10, 2001
The analysis below is based on the Eta computer model from the surface to 24,000 msl. The tops of the cells associated with this storm are expected to be about 39,500 msl. The storm track should be from 268 dT at 33 knots. This analysis predicts 1/2 inch hail. Convective Available Potential Energy, is a measure of the cumulative buoyancy of a parcel as it rises, in units of Joules per Kilogram. CAPE values larger than 1,000 J/Kg represent moderate amounts of atmospheric potential energy. Values exceeding 3,000 J/Kg are indicative of very large amounts of potential energy, and are often associated with strong to severe weather. The red area depicts the difference between the temperature of a lifted parcel of air in relation to the temperature of the surrounding air mass -- hence its bouncy. A lifted parcel cools at the Dry Adiabatic rate, until condensation occurs and the cloud forms. The parcel then cools at the Saturated Adiabatic rate. In this profile the surrounding air mass is significantly cooler than the lifted parcel rising within it -- enhancing its bouncy.
Key points to look for:
-- wind shear (significant change in wind
direction in relation to altitude will indicate rotation)
-- CAPE totals exceeding 1,000 J/kg
-- note the direction and speed of storm
movement
-- note the expected Tops (cclEL and lfcEL)
St. Charles, Mo @ 21z (4:00 pm) -- April 10, 2001
(38.8, -90.5)
National Weather Service Observations -- Summary
A complex of showers and thunderstorms moved through parts of Missouri
and Illinois during the
morning and afternoon hours on April 10, 2001. The cool outflow
from the thunderstorms created an
east-to-west oriented boundary just south of Interstate 70 from
western Missouri into southwest Illinois.
Later in the afternoon, a thunderstorm developed over eastern Kansas
and moved east-northeast into
west central Missouri. When the thunderstorm crossed the boundary,
it turned east and tracked just
north of it into Southwest Illinois. Tornadoes were reported in
Johnson and Pettis counties before the
storm entered the NWS St. Louis county warning area. A brief tornado
also was reported 3 miles north
of California in Moniteau county. Tornadoes were then reported near
Fulton, Wright City, Wentzville,
Lake St. Louis, and Granite City Illinois.
Recent research on tornadoes has shown thunderstorms that interact
with boundaries are more likely to
produce tornadoes. Boundaries are an added source of instability
and rotation for tornadic
thunderstorms. See the surface map below for the location
of the boundaries on this day.
In addition to the tornadoes, this large thunderstorm produced widespread
hail along its track with
numerous reports of golfball to baseball sized hail in both Columbia
and the northern suburbs of St.
Louis. Many homes and businesses were damaged by the hail, as were
22 planes at Lambert
International Airport.
The surface map analysis from 11:00 AM on April 10, 2001. A low pressure
center is located over
western Kansas. A stationary front extends east from the low
through Missouri and Illinois. An
outflow boundary from earlier convection is located south of the
main stationary front.
A good look at the supercell as it moved across central Missouri
and into Boone and Moniteau
County. The storm cell kept its basic structure and intensity
all the way from eastern Kansas to west
central Illinois. Large hail, damaging winds, and the occasional
tornado were reported all along and
north of Interstate 70.
This narrative of a close encounter with a supercell was written
by a trained spotter from the
MidMoSkywarn Association. He wanted you to know that even
though he was well equipped to
recognize severe weather and take the appropriate actions to avoid
possible injury, it is sometime
unavoidable. Tornado spotting can be very risky at times and
should be left to trained professionals like
those from the spotter group in Central Missouri.
Always observe safety rules when confronted by severe weather.