22nd Conference on Severe Local Storms


Non-convective windstorms in the Midwest United States: surface and satellite climatologies

John A. Knox, University of Georgia, Athens, GA

Every year, the Midwest United States experiences windstorms with damaging gusts (at least 58 mph) not associated with severe convection. A single windstorm of this type can cause tens of millions of dollars in damage and several deaths. Furthermore, since 2000, non-convective windstorms have killed more Americans than thunderstorm winds, and they have caused more injuries than tropical cyclones. This is due perhaps in part because the risk to life and property is underestimated when conventional hallmarks of severe weather are not involved. In addition, forecasts of these extreme wind events are inexact and often underestimate the peak gusts involved. The risks to the aviation community in such circumstances are considerable.

Surface wind data from the upper Midwest and GOES satellite imagery have been juxtaposed to create climatologies of non-convective wind events in the Midwest. Surface wind data from the 1940s through 1995 have been used to create two regional climatologies, one of non-convective winds and another of November 12Z winds. The results of the first climatology reveal a fall-season spatial trend in the month of most frequent non-convective winds from northwest to southeast, from Minnesota in October to Ohio in December. The second climatology reveals a pronounced southwest quadrant preference for the strongest winds in the Midwest on November mornings, a preference that becomes very dominant for the highest winds. Both of these results imply that the windstorms are closely related to mid-latitude cyclones and are not strongly influenced by geography, counter to some published research on the subject.

The possibility that stratospheric intrusions in mid-latitude cyclones are dynamically related to these windstorms in the upper Midwest has been explored using water vapor and ozone products from GOES. Dry slot development in satellite imagery and high surface wind reports have been used to identify case-study candidates, in order to develop nowcasting techniques using advanced satellite products. Results of this work will be presented at the meeting.

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Tuesday, 5 October 2004, 3:00 PM-4:30 PM

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