Edge effects in LightningCast

One forecaster in Birmingham, AL noted how LightningCast probabilities were much higher in an overlapping region of the GOES-16 mesoscale sectors. In Figure 1, the region of interest is over Atlanta, GA. LightningCast probabilities in Meso1 (left) are quite a bit higher in this stratiform region than those of Meso2 (right). This is most likely due the region being on the edge of the Meso1 sector. LightningCast makes its most accurate predictions when it can "see" a larger neighborhood of data around it. We think that this portion of Meso1 is not seeing the complete picture of the scene like Meso2 is. This is something for forecasters to keep in mind when they are using LightningCast, particularly at the edges of GOES-R sectors.

Figure 1: Left: LightningCast for GOES-16 Meso1 sector. Right: LightningCast for GOES-16 Meso2 sector, over Atlanta, GA.

Lone severe storm in Georgia

A single severe thunderstorm formed in an environment with marginal effective shear (~35 kts) and MUCAPE (~1200 J/kg) yesterday afternoon in northern Georgia, traveling southward through the eastern suburbs of Atlanta. The storm produced between quarter-sized and golf-ball-sized hailstones and downed multiple trees and power lines. 

Figure 1: ProbSevere contours (pink is > 70%; gray is < 5%), MRMS MergedReflectivity, and GOES-16 visible reflectance.

In the absence of strong environmental forcing, the ProbHail model is largely influenced by the MRMS MESH and ENI total lightning flash rate. The low wet-bulb 0C height (8500 ft) also contributed positively to ProbHail. Even in marginal environments with few storms, ProbSevere can still highlight potential threats. 

The ProbWind model remained fairly low (≤ 40%), owing mainly to a weak 1-3 km mean wind and low-to-moderate MRMS AzShear values. Work is ongoing to improve ProbWind predictions in both wet and dry microburst environments. 

Figure 2: Time series of ProbSevere models for this storm, with corresponding severe reports and NWS warnings. 

Figure 3: Time series of select predictors and the maximum hazard probability (thick red line), with corresponding severe reports and NWS warnings.