Convective initiation has once again lined up pretty well with the instability depicted on the theta-e difference graphic in the nearcast. I have now seen this in a couple of cases. The nearcast forecast brings some instability north into Oklahoma later this evening. It will be interesting to see how this lines up with the convection at that time, as the HRRR model has shown some decent development across portions of North Central Texas and Southwestern Oklahoma.
Late Monday evening more thunderstorms developed over portions of southeastern Virginia. The environment was marginal; ~600 J/kg of MUCAPE and ~35 kts of effective bulk shear. By 0216 UTC 6 May 2014, the developing storm near Sussex county, VA had moderate MRMS MESH values (~0.85 inches). The moderate MESH and environmental fields yielded a 31% ProbSevere probability (Figure 1). Four minutes later, at 0220 UTC, the GOES scan from 0215 UTC captured both strong normalized vertical growth rate and strong glaciation rates associated with this storm, which caused the ProbSevere output to jump to 79%–demonstrating the value of satellite growth rates! The probabilities continued to increase as the radar storm intensity increased. The NWS issued a severe thunderstorm warning for this storm at 0241 UTC (21 minutes after the first ProbSevere value in excess of 50%) and first severe hail report was received at 0238 UTC (18 minutes after the first ProbSevere > 50%).
|Figure 1. Animation of NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 0216 – 0242 6 May 2014.
Additionally there were storms further east from the storm described above. These storms also exhibited ProbSevere values in excess of 50%. These storms had similar GOES inferred vertical growth rates and glaciation rates and similar MRMS MESH values, however these storms were not warned nor were associated with severe reports. This example demonstrates key points made in the NOAA/CIMSS ProbSevere training–the model skill is comparable, yet lower than an experienced forecaster, but often provides additional lead-time. One also wonders given the late evening timing of these additional storms if severe hail occurred but was never reported.