21st Conf. on Severe Local Storms


Observations of the 27 May 2001 High-End Derecho Event in Oklahoma

Daniel J. Miller, NOAA/NWSFO, Norman, OK; and D. L. Andra, J. S. Evans, and R. H. Johns

During the late afternoon and evening hours of 27 May 2001, a derecho producing mesoscale convective weather system (MCS) developed over western Kansas and moved rapidly southeastward across most of central and western Oklahoma and into northern Texas. Both observed wind speeds and wind damage associated with this derecho event were exceptionally severe over much of the western half of Oklahoma where numerous wind gusts in excess of 40 m/s (80 knots) were observed, and total damage estimates from this event were in excess of $300 million. A rather remarkable suite of high resolution data and observations are available from this event, including 1) surface observations at 5 minute intervals from the Oklahoma Mesonet, 2) high-resolution (level 2) volumetric radar reflectivity and velocity data from the Twin Lakes (KTLX) WSR-88D, and 3) numerous photographs and eyewitness accounts of the storms from storm chasers. Thus, this event provides a unique opportunity to study the evolution of the individual, wind damage producing storm scale elements within the derecho producing MCS, and to synthesize the radar data with visual observations and high quality, high-resolution surface observations. Data analyses indicate that this particular derecho producing MCS was composed of several supercell storms with strong, deep, and persistent mesocyclones through much of its lifetime. Although wind damage was produced along the length of the common gust front, the most severe surface wind speeds were associated with the paths of the embedded supercell storm elements. We will document this event using the high-resolution observations and specifically relate the most extreme non-tornadic surface winds to their parent convective elements within the MCS. In addition, we will offer a hypothesis for reasons why supercells may enhance the likelihood for extreme non-tornadic surface winds when present within a derecho producing MCS.

Session 1, Mesoscale Convective Systems I
Monday, 12 August 2002, 10:30 AM-12:00 PM

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