Success in Mitigating a Bad Situation: Intense, Long-Lived Thunderstorms Over the Atlanta Airport on 24 June 2015

The Center Weather Service Unit's (CWSU's) across the country strive to provide timely, thorough, and effective decision support directly to the aviation customers who will benefit most from these services. In the Atlanta CWSU, these services are most effectively delivered in the form of briefings to decision makers at the Atlanta and Charlotte air traffic control facilities, and their respective airline partners. Summertime thunderstorms provide the most difficult of challenges to the controllers of the airspace. Services become enhanced by NWS employees at the Atlanta Center, during the convective season, by real-time evaluation of the evolution of weather patterns on the synoptic scale, mesoscale, and storm scale, all in real time. Internal collaboration between the CWSU meteorologists and the Peachtree City, GA and Greer, SC Weather Forecast Offices (WFO's), becomes critical in these types of situations. The primary mission of this collaboration is to ensure internal consistency is maintained, and all aviation-based forecast services are provided with a clear, unified, and concise message.

On June 24th, 2015, a rapidly evolving complex of thunderstorms necessitated a prolonged period of holding, when the Atlanta Airport was closed to incoming arrivals. The most deleterious impacts from these thunderstorms were the repeated rounds of radar-indicated microbursts in or around the Atlanta Aerodrome and TRACON airspaces. The peak ASOS wind was measured as 39 kts, although other sensors measured as high as 57 knots at the Airport. Proximal storm surveys estimated wind gusts over 85 knots.

Several keys to the success of this operation included recognition of subtle changes in daily weather patterns from previous days with little to no activity. In addition, use of rawinsonde soundings and other meteorological observations, rather than model output alone, increased confidence in forecasts. Finally, hourly evaluation of the HRRR model for strengths and weaknesses of model initialization fields prevented a situation where controllers were warned prematurely of impending storms. Services were further enhanced by the dispatch of additional personnel to the Atlanta TRACON facility and continuous communication between the CWSU and remote facility personnel.

The outcome of the situation was over 70 diverted airplanes due to the rapid evolution of the thunderstorms. Despite these unfortunate steps, what was most encouraging was that all aircraft ended up eventually resuming their travel to Atlanta by the end of the night. This meant that stranded travelers were more ready to complete their travels promptly the next morning. Follow-up conversations with core partners came in the form of praise by airlines for the center Controllers, and Traffic Management Unit for in their mitigation of a bad scenario to the best of their ability. Respectively, this praise was conveyed to the CWSU and WFO Meteorologists, for their contribution to the operation in the form of rapid forecast updates and timely briefings.