Location and Frequency of Surface Lows and Lower-Tropospheric Jets for U.S. Violent Tornadoes

The Violent Tornado Webpage from the Storm Prediction Center has been used to obtain data for 182 events in which a violent tornado (F4-F5 or EF4-EF5) occurred in the United States from 1950 to 2014. The positions for the surface low, 850 mb jet, 700 mb jet and 500 mb jet have been recorded on a United States map for each three-hour period in which a violent tornado was observed. The position for each meteorological feature was determined using the North American Regional Reanalysis (NARR) from 1979 to 2014 and NCEP/NCAR Reanalysis from 1950 to 1978. After the positions were recorded, frequencies were calculated using a 170 statute mile grid on a U.S. map. Contours were drawn showing the frequency of occurrence for each meteorological feature. Surface lows were most frequent along a corridor from the central High Plains east-northeastward into the Upper Midwest. For the 850 mb jet, two maxima were identified in the Great Plains with one in northeast Kansas and another in eastern Oklahoma. Other maxima for the 850 mb jet were located in western Kentucky and northeast North Carolina. For the 700 mb jet, the corridor of highest incidence was located from southeast Kansas across northeast Oklahoma into north-central Arkansas and far western Tennessee. For the 500 mb jet, the highest incidence was located from the far northeastern Texas Panhandle eastward across northern Oklahoma into far northwest Arkansas.