Southwest Minnesota Tornadoes
March 29, 1998
A series of devastating tornados struck southwest Minnesota on Sunday, March 29, 1998. These tornados formed from severe thunderstorms that tracked across Nobles and Murray county into Cottonwood county. Most of the tornados that struck Nobles and Murray counties were rated as F2 on the Fujita scale. However the storm intensified as it moved northeast into Cottonwood county and produced an F3 tornado which started 5 miles south of Westbrook in Cottonwood County and traveled a total path length of 62 miles where it ended 4 miles east of Courtland.
The main thunderstorm complex that produced the tornado originally formed on the eastern edge of Minnehaha county but as it moved into Rock county it intensified rapidly as can be seen by the composite reflectivity and matching cell trends products from the Sioux Falls Doppler radar at 2:53 pm.
From the National Weather Service WSR-88D Doppler radar imagery it appears the F2 tornados formed on a flanking line to the south of the main thunderstorm complex across northern Nobles county between 3:23 pm and 3:35 pm. This flanking line was the interface between the rear flank downdraft and ambient southerly flow feeding moisture into the storm. In this animation you can see the flanking line, the hook echo, and gate-to-gate storm relative velocity (SRM) shear located just north of Lismore at 3:18 pm.
By 3:48 pm the storm was located in eastern Murray county and crossing over into Cottonwood county. This animation shows the reflectivity and a zoomed-in SRM product which highlights the mesocyclone and TVS signatures associated with strong rotation and gate-to-gate shear. Note in the reflectivity that since the storm is farther away from the radar, the 0.5 degree slice is cutting through the mid levels of the storm and showing the bounded weak echo region (BWER). It also appears that the TVS signature is co-located with the BWER.
At 4:08 pm the storm had moved into northeast Cottonwood county where, not surprisingly, the cell trends product continued to show high VIL values, high maximum reflectivity, and a 100 percent probability of severe hail. Note that the storm tracking algorithm was tracking the storm centroid just north of Comfrey. This would place Comfrey on the south end of the storm where earlier the radar showed a hook echo and strong gate-to-gate shear.
For more on this storm check out the Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin - Madison.
