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![]() September 27, 2004 MIDWEST THUNDERSTORM STUDY POINTS TOWARD BETTER FORECASTSA set of newly documented small-scale circulations embedded in thunderstorm squall lines not only spews destructive straight-line winds, but may spawn up to 20% of all U.S. tornadoes. And the remnant circulations from large thunderstorm clusters can survive for days, triggering new storm cells. Over warm oceans, similar remnant circulations provide seed for hurricane development. Scientists expect these and other findings to help improve forecasts of damaging winds and heavy rain. The new results emerge from three-dimensional portraits of thunderstorms collected across the storm-tossed Midwest in a field study coordinated by the National Center for Atmospheric Research (NCAR) in 2003. A summary will be presented on October 5 in Hyannis, Massachusetts at the American Meteorological Society’s 22nd Conference on Severe Local Storms. Based just east of St. Louis, the Bow Echo and MCV Experiment (BAMEX) employed aircraft and ground-based storm chasers to document a wide range of
storm types that prowled the Midwest from May to July 2003. Over a dozen colleges and universities joined NCAR and the National Oceanic and
Atmospheric Administration (NOAA) for BAMEX. Key funding for the $4 million study was provided by the National Science Foundation, NCAR’s
primary sponsor.
Up to now, forecasters haven’t been able to tell in advance just when an intense thunderstorm might morph into a destructive bow echo. The process appears to hinge on small-scale factors that everyday weather observations can’t trace and radar operators can’t easily spot. BAMEX captured this near-storm environment in detail with Doppler radars aboard P-3 aircraft from NOAA and the Naval Research Laboratory. Ground crews launched more than 200 radiosondes (weather balloons), while a Lear Jet dropped more than 400 parachute-based dropsondes. The result is a set of three-dimensional portraits that will help scientists unravel the processes driving the high winds and heavy rains of bow
echoes. For instance, about two hours after damaging winds struck eastern Nebraska on the night of June 9, 2003, BAMEX aircraft showed winds of over
90 miles an hour howling less than a mile and a half above ground level, even as the surface winds had decreased. Whether over land or sea, thunderstorm complexes can generate broad areas of low pressure, from about 30 to 200 miles in width that survive after
the storms die off. Once formed, one of these mesoscale convective vortices (MCVs) can merge with a cold front, grow to become a larger center of low
pressure, and/or generate new thunderstorms for one or more days. It may even become the seed of a tropical or subtropical cyclone if it passes over
warm ocean water. “The output was used daily by forecasters across most of the central United States,” says Weisman. “They’ve told us this new information is really valuable to their outlooks.” ### Anatta This text derived from http://www.ucar.edu/news/releases/2004/bamex.shtml Recommend this Article to a Friend Back to: News |
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