Severe Weather Watches
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Severe Weather Watches


The majesty of a looming thunderhead (colloquial for a thunderstorm cloud, technically identified as cumulonimbus), highlighted in bright white and tinged with shades of red and orange by a setting sun, belies the truly violent and potentially deadly nature of the beast. Viewed more closely, from beneath its base, the same storm takes on a truly frightening aspect, cutting off sunlight to appear dirty grey or black, with roiling, petulent fragments of cloud at its edges being ripped apart by strong wind shear. Seen at night, this monster puts on a dazzling light show, with high energy bolts of lightning crackling through the air to shake the very earth with reverberation caused by the nearly instantaneous heating of air molecules to temperatures hotter than the surface of the sun.

Very strong and well-developed thunderstorms (referred to by meteorologists as cells or, in the case of certain severe thunderstorms, supercells) can achieve heights in excess of 60,000 feet (18,000 meters). This pushes their tops well above the maximum altitudes attainable by today’s commercial airliners. It is fortunate that, except under the most extreme conditions, very few cells in an advancing line of thunderstorms (known as a squall line) can achieve such heights, leaving aircraft a means of navigating, albeit with an often bumpy ride for passengers, through the breach.

Thunderstorms are capable of producing a variety of intense and severe weather, including heavy rain, lightning, high straight-line winds, hail, and tornadoes. Of special concern to aircraft, particularly during takeoff and landing, are microbursts — strong downrush winds which often radiate outward from intense thunderstorms. Major airports have been outfitted with special instruments to warn of such winds. The difference in air density between cold air plunging earthward behind a gust front and the warmer, lighter (less dense) surface air may become visible to weather radar as a thin arc advancing ahead of a thunderstorm cell.

Thunderstorms can sometimes cause death, injury and destruction far from their boundaries. Flash flooding, particularly in narrow river canyons and arroyos such as are plentiful in the Western U.S., has claimed many lives. Often the parent cloud has long since dissipated; unwary hikers and travelers may be caught totally off guard under a cloudless sky by a sudden mad rush of water. Gust fronts formed by strong downburst winds can fan out miles ahead and to the sides of a strong storm or squall line. Hail can be ejected from the top of a thunderstorm cloud, striking aircraft in clear air miles away from the storm. Finally, lightning can strike as far as ten miles beyond the perimeter of a thunderstorm; people have actually been struck by lightning that seemingly appeared out of nowhere, with no thunderstorm cloud visible.

Thunderstorms are truly awe-inspiring creations of Nature. They are enjoyed and photographed by many as a consequence of their beauty, their constantly-changing appearance, and the raw power they unleash. While they should not be feared, they should be granted a healthy respect due to the potential destruction and death they are capable of producing. Since thunderstorms can strike anywhere in the U.S. and throughout most areas of the world, everyone should know how to recognize an approaching storm and what to do when thunderstorms are present or expected.

The National Weather Service is tasked with the responsibility for determining thunderstorm and severe weather threat within the U.S. Severe weather information is typically disseminated by local and national broadcast media. Special weather bulletins and severe weather warnings may be dispatched through civil defense avenues such as the Emergency Broadcast System. Many communities, particularly in the Midwest, have siren warning systems that can be activated by civil defense authorities in the event of a tornado warning. When the potential for severe weather exists, being aware of weather safeguards and how to respond to them will help you keep yourself and your family safe.


Authored by Kenneth L. Anderson.   Original article published 4 June 2003, updated 22 June 2005.


Follow links to the right to learn more about severe weather watches and severe weather forecasting. At the left margin, Related Links address topics of interest pertaining to weather warnings and other topics relating to severe weather and meteorology. View the Weather & Meteorology SiteMap for a complete list of meteorology and weather-related topics.


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