Severe Storms in Northwestern Arkansas

As the CIMSS/MKX GOES-R Proving Ground shift wound down Tuesday afternoon, severe thunderstorms rapidly developed over northwestern Arkansas.  This region was supportive for strong to severe thunderstorms with MUCAPE between 2500 and 3000 J/kg and effective bulk shear 20-30 kts.  Figure 1 below shows the NOAA/CIMSS ProbSevere Model overlaid on MRMS composite reflectivity.  Of note is the rapid increase in the ProbSevere values over the course of 6 minutes between 2032 UTC and 2038 UTC 08 July 2014.  At 2032 UTC the ProbSevere value was 8%, then at 2034 UTC the ProbSevere value jumped to 56%.  This jump was attributed to more intense satellite growth rates (the normalized vertical growth rate went from 1.4%/min (strong) to 2.6%min (quite strong) and the glaciation rate increased from 0.02/min (weak) to 0.06/min (strong)) as well as a jump in the MRMS MESH associated with this storm 0.35" to 0.52".  Another four minutes later at 2038 UTC the probability jumped again to 95% as the MRMS MESH approached 1.00".

Figure 1.  NOAA/CIMSS ProbSevere Model and MRMS Composite Reflectivity over northwestern Arkansas during late afternoon of July 8 2014.

This example illustrates the increase in lead-time to severe hazards as well as severe thunderstorm warning issuance that is possible by quantitatively using satellite growth trends with environmental information and radar observations of a storm's precipitation core.  In this example, the initial severe thunderstorm warning was issued at 2059 UTC--20 to 25 minutes after the significant jumps in the NOAA/CIMSS ProbSevere output.   More storms continued to develop further west during late Tuesday afternoon, most of which became severe thunderstorm warned after reaching high levels of NOAA/CIMSS ProbSevere values.  Only one severe report was received with these thunderstorms, but one wonders if this is more related to the population of very rural northwestern Arkansas--with much of this region covered by state and national parks (Figure 2).

Figure 2.  Google maps showing the one severe hail report received with these storms (green 'H').  The very rural nature to the area inferred by this map makes one wonder if more severe weather occurred than was actually reported.

-Justin Sieglaff, UW/CIMSS
-Steve Hentz, NWS MKX

Low Topped Wisconsin Storms

The synoptic setting for Wisconsin July 7th 2014 featured a small shortwave in a mid level trough over the upper Great Lakes.  MUCAPE values ranged from 300 to 800 j/kg with 0-6 km shear around 25 to 30 kts.  Scattered thunderstorms developed by noon.  SCAN max hail values were from 0.50 inch to 0.75 inch.  The CIMSS probabilities over severe were mainly in the single digit to around 25%, but many storms did have strong vertical and strong glaciation rates.  One storm did approach severe criteria. Using FSI with the Donovan technique a narrow core of 50dbz did just reach severe criteria.  The CIMSS Probability of severe was low at 49% , with the MESH value around 0.50 inch,   giving confidence that the storm was not severe.

-Steve Hentz