April 3, 1974-The Super Outbreak
(Information courtesy of: http://www.april31974.com/)

The
forecast for Wednesday April 3, 1974 was for showers on the East coast and for

thunderstorms across the Midwest. In the heavens, a storm of an overwhelming

magnitude was forming. Children went to school, people went to work and
lives
went on as normal until the second worst storm of the 1900's struck.
Tornadoes
broke across the heartland with such an intensity and frequency
never seen before in
the United States. Homes and schools destroyed. Loved
ones lost. This site looks at
the events of that day .This site is dedicated
to the 315 people who lost their lives in
this storm and to the over 5,000
people who were injured.

Why it happened...

The approximate cause of the huge tornado
outbreak of April 3-4, 1974, in roughly
layman's language, was the result of
a number of important factors coming together
at the right critical time. A
very vigorous upper level atmospheric disturbance,
along with a strong polar
jet stream lead to the amplification and general
strengthening of a low
pressure region to the east of the Rocky Mountains. As this
low pressure
region, with its counterclockwise rotation moved eastward, it became
more
and more intense and caused a great deal of warm, moist air to move into the

Ohio river valley from the Gulf of Mexico. The natural rising of the
surface, warm,
moist air was inhibited by an upper atmospheric layer of warm
dry air from the dry
southwest region of the country.

At the
interface of the lower, warm, moist air and the upper, dry air was a large

region subsidence, where the air was sinking onto the lower moist air. This
large
sinking air mass region acted like a lid on the lower, moist air to
keep it from
rising and dissipating energy by forming normal

thunderstorms.Throughout the morning of April 3, sunlight continued to heat
the
moist surface air, increasing its normal tendency for upward convection.
Eventually
in the early to mid afternoon the pent-up upward convection could
not be contained
any longer over many locations from Illinois to Ohio to
Alabama and Georgia in the
south.

In many locations over this broad
geographic area, the rising, moist air had enough
energy to punch through
the "lid" holding it down. As the energetic, moist air rapidly
rose,
friction and other perturbations led to localized rotation and tornado

development. Nearly 150 tornados developed over this region of the US. This
tornado
outbreak was relatively rare. Several factors came together at the
right time to allow
for the magnitude of this tornado outbreak. These
factors include: the location and
energy of the upper level wave
(disturbance) with respect to the surface low pressure
region; the
relatively warm Gulf region providing an abundance of warm, moist
surface
air; the extent of the upper level dry air and the resulting subsidence (lid
effect);
and the extent of the solar heating. Take away one or more of these
factors and the
enormity of the outbreak would most likely have been greatly
reduced. It is near s
peculation as to how frequently such a confluence of
factors might occur. One such
guess might be several hundred to five hundred
years.

To download the NOAA report on this day, click here.