In the late evening of April 24, a strong storm was approaching Marion County in southeast Tennessee. I evaluated the storm to be just below severe levels. In the 4-panel image below, the LMA source density is in the lower left panel. 5 minute lightning and Hail Index are also in that panel. The POSH on this storm at this time was 40%, and source density values were around 80.
At this point, I was on the fence about issuing a warning for Marion County, but leaning against it. Then the next LMA image came in:
Source density values jumped up over 200. Other radar products did not indicate significant intensification – other than the POSH rising to 60%, just about everything else stayed the same. But based on the big jump in source density values and the slight jump in POSH (and the favorable storm environment), I decided to issue a SVR.
The storm produced damaging winds near Jasper around 0410Z (1110 am CDT). The jump in LMA source density values gave about a 20 minute lead time.
As shown in this example, the LMA source density product can be useful along side other radar products and help “tip the scales” on a storm that may be borderline severe.