The National Weather Service is issuing a potential risk for a progessive derecho event this evening June 3rd, 2014 until early morning on Thursday June 4th, 2014, for the Midwest United States. This potential event is associated with a low pressure system currently over the heartland, which will move eastward over the Midwest as the week progresses. This event can produce significantly strong winds, rain and even tornados in certain scenarios. These strong winds can occur within seconds without notice. Even though they move quickly they can do a significant amount of damage in a small amount of time.
Not an extremely common weather phenomena, derecho events are the product of downbursts. Downbursts are concentrated areas of strong winds produced by a convective downdraft. Convective downdrafts which is air cooled by the evaporation, melting, and/or sublimation (the direct change to vapor phase) of precipitation in thunderstorms or other convective clouds. Because the chilled air is denser than its surroundings, it becomes negatively buoyant and accelerates down toward the ground. Derechos occur when meteorological conditions support the repeated production of downbursts within the same general area.
A Derecho Event is a widespread, long-lived wind storm. Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems.
By definition, winds in a derecho must meet the National Weather Service criterion for severe wind gusts (greater than 57 mph) at most points along the derecho path. But in stronger derechos, winds may exceed 100 mph. Derecho development necessarily is tied to the formation of bow echoes. A bow echo usually arises from a cluster of thunderstorms, but also may evolve from a single strong storm.
Precautions should be taken to protect yourself against this weather event. Keep an eye out for any potential risks and seek shelter from the extreme winds, lightning and possible tornadic events.
-" http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm "
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The Forecasting Consultants Team