Thunderstorm Wind in Fillmore County, Nebraska

Wind gusts were estimated to be near 90 MPH, with damage generally confined to southern portions of Fillmore County. Along this path, multiple irrigation pivots were overturned, power poles were broken and trees were damaged. A number of grain bins were damaged or destroyed, outbuildings were damaged and one home suffered damage, mainly broken glass.

This Monday, also Memorial Day, was one of the more widespread severe weather events of spring 2013 over South Central Nebraska. The first storms developed over Phelps and Harlan counties around 4:30 pm CDT, and they formed as a short line segment of supercells that exhibited multicell characteristics. Several cell splits occurred during the following two hours, each of which headed north of Interstate 80 and then weakened. The storms that comprised the original line segment continued to advance eastward, remaining south of Interstate 80. After about 7 pm CDT, they transitioned to a dominant multicell mode in the form of a large cluster. The initial storms produced the most hail, including the strongest of the left split supercells of this event, which produced hail as far north as Buffalo county. The largest hail reported was the size of golf balls. As the thunderstorm mode transitioned to multicellular, damaging winds became the primary severe weather threat. Several locations, from Kearney county east to Fillmore county, measured winds in excess of 70 mph. The highest wind measured was 78 mph near Davenport. However, damage surveys suggested winds were as high as 90 mph. Trees and power lines were knocked down, several grain bins were damaged or destroyed and irrigation pivots were overturned. An EF-2 tornado was confirmed in southern Clay County, affecting the town of Edgar. This non-supercellular tornado formed at the leading edge of the line, just after a strong surge of downdraft winds within the line.

With the 8 am CDT Severe Weather Outlook, the Storm Prediction Center upgraded South Central Nebraska, south of Highway 6, to a moderate risk for severe thunderstorms. A weak short-wave trough was approaching the region, embedded within a broad upper-level trough, over the western United States. A quasi-stationary front, oriented in an east-west fashion, extended across Nebraska. During the early morning hours, a mesoscale convective system tracked through eastern Nebraska southeastward into Missouri. This MCS laid down an outflow boundary that extended across northern Kansas, to a lee-side low. It was to the north of this outflow boundary that storms initiated. At the time of initial thunderstorm development, temperatures were in the lower to middle 80s south of the front, with dewpoints in the middle 60s. This resulted in a moderately unstable atmosphere, with MLCAPE between 2000 and 3000 J/kg. Deep layer shear was 40 to 50 knots, which was more that strong enough for supercell storm structures.