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)

FROPA convection on the Plains

Strong early September convection fired on a trailing cold front in the late evening and overnight hours in northern OK, southern KS, and southwest MO. The environment near and along the front was characterized by MUCAPE ~2500-4000 J/kg and effective shear ~20-35 kts. The IR-derived satellite growth rates, as captured by the NOAA/CIMSS ProbSevere model were very strong, during this period of GOES-East rapid-scan operation.

GOES-East IR brightness temperature, 5-minute NLDN lightning plot, and METAR station plots.

 The explosive growth rates, along with strong MRMS MESH and a favorable environment, led to very high probabilities of severe (80-100%) before severe weather was reported from many of these storms.

ProbSevere contours overlaid MRMS reflectivity and NWS warnings.

 The first storm to initiate in south-central KS (shown below) went from 10% (22:30Z) to 57% (22:34Z) probability of severe as the observed satellite growth went from moderate/weak to very strong, while the MESH remained constant at 0.25". Six minutes later, the probability of severe was 79% (MESH still < 0.5"). By 22:52Z, the probability of severe exceeded 90%, as the MESH was nearly 0.75". The probability maxed-out at 100% at 23:14Z, when the MESH was 1.47" and the first 1" report was also recorded at this time. This storm would go on to produce a large tornado near the town of Cedar Vale, in Chautauqua county, as well as baseball-sized hail in Winfield, KS.

The storms in the region produced numerous severe weather reports, including hail up to the size of baseballs, wind gusts up to 80 mph, and large tornadoes. The satellite growth rates from the model may increase forecaster confidence in issuing warnings and perhaps increase lead-times to initial severe hazards.

John Cintineo
UW-CIMSS