Upper Midwest storms and NOAA/CIMSS Prob Severe Model Demonstration

The GOES-R PG CIMSS/MKX shift focused on the Upper Mississippi Valley on Thursday, September 4.  Ongoing convection existed over far northern Wisconsin early in the morning on Tuesday.  The storms were discrete, elevated supercells that eventually congealed into a linear convective system.  While the NOAA/CIMSS ProbSevere model is designed to increase lead-time to the initial severe warning/hazards, this case demonstrates what others have noted during the spring and summer this year, that the ProbSevere model performs well with discrete mature convection.  Figure 1 below is shows the Green Bay 0.5 degree reflectivity with NOAA/CIMSS ProbSevere model output in the shaded contours around storm cells valid at 1452 UTC 4 September 2014.  These two storms with high ProbSevere values (> 90%) produced golf ball sized hail around this time.

Figure 1.  KGRB 0.5 degree reflectivity and NOAA/CIMSS ProbSevere output valid at 1452 UTC 4 September 2014.

Not shown was the progression of these storms across northern Wisconsin in the morning hours on Thursday.  During this time the ProbSevere values were consistently high (> 85%) with sporadic severe reports across the rural Northwoods.

Additional elevated storms developed over western and southwestern Wisconsin during the early afternoon hours, fueled by warm air advection.  These storms struggled to develop as the atmosphere was strongly capped.  The ProbSevere values associated with these storms remained (correctly) quite low over southwestern Wisconsin.  The storms over west-central Wisconsin did exhibit higher probabilities, as much as ~60% (largely due to much higher values of effective bulk shear and MRMS MESH values approaching 0.75"), but as of this writing have yet to produce severe weather.

The strong cap in place is likely to inhibit surfaced based convection along the cold front in Minnesota through the duration of the shift.

-Justin Sieglaff (UW/CIMSS)
-Ben Herzog (NWS MKX)