The Birth of MESOSCALE FORECASTING

摘要

Before June 29 and 30, 2012, most people other than meteorologists and dedicated weather watchers had never heard of something called a "derecho." They certainly had no idea that a derecho-whatever that is-could bring extremely dangerous weather.On those two June days in 2012 a derecho ripped a 240-mile-wide path of destruction from the Midwest to the mid-Atlantic Coast, killing 27 people, leaving millions without power, and forcing thousands to cope with serious damage from fallen trees.The NWS defines a derecho as a squall line of thunderstorms that produces 57 mph or stronger winds along a path at least 240 miles over a period of hours. It is "a line of active deep moist convection frequently associated with thunder, either continuous or with breaks, including contiguous precipitation areas." Most derechos are at least 50 miles wide.