The North Alabama Lightning Mapping Array (NALMA) data have been in and out of operations at WFO Huntsville, AL for a while now, due mainly to AWIPS II testing and related issues. After being unavailable in operations for about a week, we were able to get the data back into operations on the afternoon of Thursday, June 13th…and it couldn’t have happened at a better time. I was working the Aviation Forecast desk and was assisting in monitoring radar for severe weather operations and the data were of great benefit once again. The first image below shows a small cluster of thunderstorm cells moving southward from Tennessee across the border into Lauderdale County, Alabama…the very northwest corner of the state, at about 2000 UTC, although the various data in the image range from 1955 to 2000 UTC. NALMA data overlay the radar data and were being used to monitor for lightning activity in the cells. Notice that at this time, NALMA data indicated the cell near St. Joseph, Tennessee was electrically active (white-pinkish shading). Also, notice that the cell to the west and just north of Threet, Alabama was not electrically active yet, according to both the NALMA and NLDN data.
Image 1. KHTX radar data at 1955 UTC June 13, 2013…together with 15-min (2000 UTC) and 5-min (1955 UTC) NLDN data, NALMA source densities (1956 UTC), and METAR observations (~2000 UTC).
A little later, at about 2005 UTC, the cell had moved into Lauderdale County, now a few miles east of the town of Threet, and the NALMA indicated a sudden burst of electrical activity. At this time, NLDN were not indicating any cloud-to-ground (CG) strikes. Perhaps more importantly, this developing thunderstorm was moving towards the Muscle Shoals airport, which is located at the observation site (KMSL) in the northeastern section of Colbert County, directly to the south.
Image 2. KHTX radar data at 2004 UTC June 13, 2013…together with 15-min (2000 UTC) and 5-min (2005 UTC) NLDN data, NALMA source densities (2004 UTC), and METAR observations (~2000 UTC).
The next image (Image 3), valid at about 2015 UTC shows the subsequent CG strikes in the NLDN data (horizontal blue lines). Given the albeit small, but steady lightning production in this storm and increasing confidence that lightning was possible within 5 miles of the KMSL airport, a lightning warning was issued at 2015 UTC.
Image 3. KHTX radar data at 2014 UTC June 13, 2013…together with 15-min and 5-min NLDN data (2015 UTC), NALMA source densities (2014 UTC), and METAR observations (~2000 UTC).
The next image shows a CG strike within 5 miles of the KMSL airport at 2025 UTC, as noted by the small blue horizontal line north of KMSL and east of Florence.
Image 4. KHTX radar data at 2024 UTC June 13, 2013…together with 5-min NLDN data (2025 UTC), and METAR observations (~2000 UTC).
In this case, the LMA data alerted me that the cluster of cells had become electrically active, allowing me to shift my focus on when they might enter a 5-mile radius of the KMSL airport. With a continuation of electrical activity as observed in the LMA data, my confidence was raised sufficiently, and the warning was issued for the airport. The LMA data can be a great tool in situations like this, letting a forecaster know when a storm is electrically active and helping him/her to shift situational awareness appropriately, especially when CGs may not be initially present. The LMA proved to be very beneficial in this case, allowing for some extra lead time with the airport weather warning for this cell.
Interestingly, the cell that entered eastern Lauderdale County was producing intra-cloud lightning throughout this time, but no CGs were reported by the NLDN. Nevetheless, a forecaster would want some confirmation that a thunderstorm is in progress, particularly if he/she was involved in real-time weather watches for outdoor events, or for the possibility of lighting that could affect airport operations, as in the example above.