Shenandoah storm

A storm southwest of Shenandoah National Park (Viginia) has developed outside of the SPC's Marginal Risk polygon (Figure 1).

Figure 1: 20150511 2000Z outlook

Despite weakish MUCAPE and effective shear, and the satellite growth rates of ProbSevere being several hours old, and thus expired (see Figure 2), the probability of severe was still 82% at 20:34Z, 10 min before NWS in Washington D.C./Baltimore, MD issued a severe thunderstorm warning. The MESH at this point was 1.62". Multiple forecasters have mentioned today how ProbSevere can help focus their attention to developing "pulse" convection, or areas where severe weather may not be initially expected. This is the benefit of a "fused" product: where one observation platform isn't signaling severe potential, often another one can. Large trees were reported down from this storm at 20:48Z, 4 min after the NWS warning.

ProbSevere contour with VIS and radar reflectivity, near Shenandoah National Park in Virginia.

John Cintineo
UW-CIMSS