Strong satellite growth lends great lead-time in southern Nebraska

Convection was erupting along a cold front over portions of Nebraska and Kansas Thursday afternoon.  A storm along the Nebraska/Kansas border caught our attention.  The NOAA/CIMSS ProbSevere model had a probability of 10% at 1932 UTC 07 May 2015 (Figure 1).  At 1934 UTC the latest GOES-dervied growth rates (both strong vertical growth and glaciation rates) made it into the ProbSevere model and the probability increased to 43%.  Four minutes later at 1938 UTC, the radar observed intensity continued to increase (MRMS MESH of 0.57") and the ProbSevere output jumped to 69%.  At 1940 UTC, the MESH sized continued to increase (just over 1.00") and the ProbSevere probability jumped to 96%.

Figure 1.  NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 1932 - 1940 UTC 07 May 2015 centered on the Nebraska/Kansas border.

This storm went on produce severe hail (1.25") at 2004 UTC--24 minutes after the ProbSevere output jumped to 96%!  This example showcases how the different ingredients of the ProbSevere model work together to produce a skillful forecast with good lead-time.   At 1934 UTC, the strong derived vertical growth rates and glaciation rates caused a significant jump probabilities, but the radar estimated hail size of only just over 0.50" acted as a restraint--keeping the probabilities from being too large too quickly.  As soon as the radar estimated hail sized increased closer to severe thresholds, combined with environmental information and the GOES-dervied growth rates the probabilities jumped into a very confident range (in the 90% range).

-Sieglaff