Atmospheric Radiation Measurement Program Facilities Newsletter, June 1999. Page: 4 of 5
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A thunderstorm has a three-phase life cycle. The first stage, the towering cumulus stage, consists
of an updraft. As the warm air rises, it travels through cooler air above, which causes water
vapor to condense into tiny droplets that form a cloud. As the droplets collide, they combine to
form larger drops.
When the drops become too large to be held up in the cloud by the updrafts, they fall downward
through the cloud and to the ground as rain. As the drops fall downward, they drag cold air with
them, causing a downdraft. This is the second or mature stage of the thunderstorm, which
consists of both an updraft and a downdraft. As raindrops encounter drier air, evaporation takes
place, which cools the air more and enhances the downdraft. The cool air spreads out
horizontally as it reaches the ground, producing a cold air outflow or gust front that we generally
experience as the cold winds preceding thunderstorms.
The third or dissipating stage of a thunderstorm occurs when the cold downdraft winds begin to
erode the warm updraft and eventually cause the storm to weaken and dissipate as the warm,
moist air supplied by the updraft is no longer available. Typical thunderstorm cells have life
cycles of 55 to 75 minutes and horizontal widths of 3 to 40 square miles.
Several single-cell thunderstorms can cluster together to form a multi-cell thunderstorm. The
cold outflows from each cell combine to form a stronger gust front, which in turn can trigger new
storms as the rush of cold air pushes warmer air upward, inducing more convection. Multi-cell
storms can become severe.
When updrafts are strong enough, hail can form within these storms. As the raindrops encounter
freezing temperatures in the tops of the thunderstorm clouds, they freeze. As the small frozen
drops move about within the cloud, they gather liquid droplets on their surface. This causes
them to become heavy and to begin falling downward through the cloud. The updrafts push the
small hailstones upward into the freezing temperatures again, freezing their liquid surfaces and
enlarging them. This process is repeated until the hailstone becomes too heavy to be held aloft
by the updraft or until the stone is diverted out of the updraft's path and falls to the ground.
Taller thunderstorm clouds with the strongest updrafts produce the largest hailstones.
As a thunderstorm cloud grows, it usually reaches the jet stream winds at the top of the
troposphere. When this occurs, the top of the thunderstorm cloud gets caught in the winds,
blowing the top to the side in what meteorologists call an "anvil."
Supercell thunderstorms, the most dangerous of the convective-type storms, can produce high
winds, large hail, and long-lived tornadoes. A supercell storm gains a large scale organization so
that it behaves like a single entity rather than a multi-celled storm. The supercell storm's initial
development is very similar to that of a single-cell, air-mass thunderstorm, but supercells
matures to exhibit a rotating updraft and continuous propagation. Supercell storms can reach
maturity within 90 minutes and stay intact for several hours. These were the types of storms that
produced the deadly twisters on May 3, 1999, in Oklahoma and Kansas.
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Atmospheric Radiation Measurement Program (U.S.). Atmospheric Radiation Measurement Program Facilities Newsletter, June 1999., periodical, July 15, 1999; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc618576/m1/4/: accessed May 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.