land hurricane or derecho?
you decide.
Satellite image from Weather Channel April 2006
Windstorms may last for just a few minutes when caused by downbursts from thunderstorms, or they may last for hours (and even several days) when they result from large-scale weather systems. A windstorm that travels in a straight line and is caused by the gust front (the boundary between descending cold air and warm air at the surface) of an approaching thunderstorm is called a derecho. Gustavus Hinrichs, a physics professor from the University of Iowa and the founder of the Iowa Weather Service, applied the term derecho—a Spanish word that means “straight” or “right”—to straight-line winds in 1888. Derechos are capable of causing widespread damage and landscape devastation. For example, the winds of a derecho occurring in northern Minnesota, U.S., on July 4, 1999, peaked at or near 160 km (100 miles) per hour and blew down tens of millions of trees.
Longer-period windstorms have two main causes: (1) large differences in atmospheric pressure across a region and (2) strong jet streams and winds overhead. Horizontal pressure differences may accelerate the surface winds substantially as air travels from a region of higher atmospheric pressure to one of lower. In addition, the vertical turbulent mixing of stronger jet-stream winds aloft can produce strong gusty winds at ground level.
SOURCES:
britannica online
www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm
Coniglio, M. C., and D. J. Stensrud, 2004: Interpreting the climatology of derechos. Wea. Forecasting, 19, 595-605.
sciencedaily.com
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