It is great to have the LMA data still in operations at WFO Huntsville in our AWIPS II system. Although thunderstorm activity has not been particularly severe this spring and early summer, the overall pattern has been sufficiently active to provide many instances where the LMA data have been useful. Forecasters are employing it into their normal severe weather strategies once again, and such was the case this morning. A couple of waves of thunderstorms moved across the Huntsville County Warning Forecast Area during the early morning hours, producing large amounts of lightning, small hail, and strong to damaging winds. As thunderstorms passed through the Huntsville metro just after sunrise, they intensified, leading to severe thunderstorm warnings downstream in Jackson and DeKalb Counties in Alabama. The warning forecaster, using the LMA data as a decision support aid noticed a “spike” in the source density values as storms were moving through the Huntsville metro and points just downstream. The last spike was followed by increases in reflectivity values and wind speeds aloft, prompting the warning issuance. While the LMA data alone did not provide sufficient evidence that a severe thunderstorm was occurring or was in the offing, it did enhance the forecaster’s awareness of the situation and served as supplementary evidence that the storm would potentially breach severe thresholds soon.
The first image below contains KHTX radar data and North Alabama LMA (lower left) from 1156 UTC this morning, June 27, 2013.
This elevated slice, at 8.7 degrees, represented a region of graupel and hail growth this morning, at about 21kft elevation AGL. LMA data had indicated a few spikes earlier in the morning, while the storm was cycling in strength. At 1156 UTC in the image above, you’ll notice that reflectivity values (upper left) were generally low, less than 50 dBZ.
A little later, LMA began to make some small jumps, over 200 sources by 1206 UTC (image 2). Notice that reflectivities began to climb over 50 dBZ between the towns of Owens Crossroadas and Gurley.
At 1216 UTC, a significant jump in LMA data occurred near the far eastern border of Madison County, near the town of Gurley, indicating the updraft was likely strengthening in the storm. Source density values had climbed to about 400. A corresponding increase in reflectivity values was ongoing, but increased further in the next series of radar scans. Additionally, winds aloft began to increase (upper right), while a small area of relatively low CC values (lower right) appeared just northwest of Gurley.
A little later, at 1241 UTC, a more significant increase in reflectivity occurred, with values climbing over 60 dBZ at the 8.7 degree elevation scan. During the interim period, total lightning activity had decrased markedly, with values generally around or less than 100 sources in most updates.
With velocity data at this level and lower levels indicating storm organization and low-mid level winds were increasing (not shown), increasing reflectivity and the recent spike in LMA, the decision was made to issue a severe thunderstorm warning, which was disseminated at 1247 UTC.
The thunderstorm did eventually produce wind damage in the Fyffe and Powell communities further downstream around 1225-1330 UTC (the warning was extended into those areas later).