An Analysis of the 22 May 2004 Furnas County, Nebraska Tornadic Supercell

On May 22, 2004, a storm that formed near McCook, Nebraska near the “triple-point” of two synoptic scale boundaries (cold and quasi-stationary fronts) and a surging dry line, moved into a region of rich low and deep layer shear. This storm rapidly developed a low-level mesocyclone as it moved into Furnas County, Nebraska and then underwent at least three reorganization cycles, producing a tornado during each. An interesting facet of this event is that there were no obvious boundary interactions as the Furnas County storm underwent cyclic reorganization and tornado production. NCEP reanalyses and subjective examination of the sounding, hodograph and observational data showed that (a) 0-6 km deep layer shear was great and of a magnitude that consistent with supercell development in southern Nebraska; (b) background 0-1 km shear values in southern Nebraska were exceedingly great, and consistent with those documented across strong boundaries; (c) instability as measured by surface based CAPE values was moderate to strong in a corridor south of the stationary front along the Interstate 80 corridor; and, (d) convective inhibition was strong all over southern Nebraska and northern Kansas in the morning, but was removed by mid afternoon over a region extending from the convective initiation area eastward across all of southern Nebraska. The authors believe that this case represents a relatively unusual example in which the synoptic scale features not only provided the general thermodynamic and shear environment in which the Furnas County storm developed, but also produced the essential low level shear normally found in association with mesoscale or smaller features in cyclic tornadic supercell outbreaks. Proximity hodographs, soundings and high resolution radar imagery are presented to support these contentions and findings.