Fourth AMS Student Conference


A statistical investigation of severe weather indices and associated severe weather in the north-central U.S.

John R. Wetenkamp Jr., Northland College, Ashland, WI; and A. J. Hamm

Severe weather indices are important tools for forecasting severe weather. This research investigates severe weather indices in the Upper Midwest, with a special focus on northern Minnesota, northern Wisconsin, and the eastern one-third of the upper peninsula of Michigan. Two sounding locations are used for this study: International Falls, MN and Green Bay, WI. Proximity soundings are used to calculate several different severe weather indices, including convective available potential energy (CAPE), convective inhibition (CIN), downdraft CAPE, vorticity generation parameter (VGP), height of the lifting condensation level, Bulk-Richardson Number, Bulk Shear, Helicity (0-1 km, 0-2 km, and 0-3 km), wet-bulb zero height, the Lifted index, the Total-Totals index, and the K index on days where severe weather occurred in the vicinity of the sounding location. The vicinity of the sounding site is defined as any location within 100 miles and within one hour before or five hours after the balloon is released. Soundings are rejected if it is determined that the atmosphere at the sounding location is significantly different than the atmosphere where the severe weather occurred (i.e., a front moved through the sounding location before the severe weather occurred).

A data set was created that contains all local storm reports from 1973 through the present and is organized by type of severe weather and severity of the severe weather. The Storm Prediction Center's definitions on significant severe weather are used to distinguish between severe weather and significant severe weather. Six categories of severe weather are used in this data set: severe hail, significant severe hail, severe wind, significant severe wind, tornado, and significant tornado. Statistical tests are used to identify threshold values for specific indices for each type of severe weather as well as identify which indices tend to better predict severe weather. Research is ongoing and results are expected within the next 15-30 days.

Poster Session 1, Student Conference Poster Session
Sunday, 9 January 2005, 5:30 PM-5:30 PM

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