DCA25LA156

An encounter with an area of moderate clear air turbulence associated with the jet stream during cruise.

During cruise at FL345, Southwest Airlines flight 1425 enroute to San Diego International Airport (SAN) encountered turbulence, causing hot coffee to spill into a flight attendant’s boot. The incident occurred during cabin service in the aft galley, resulting in second-degree burns. The flight crew stated that before departure, they reviewed the forecasted weather conditions using Weather Services International (WSI) and SkyPath electronic flight bag (EFB) applications. Based on this assessment, the captain conducted a preflight briefing with the flight attendants, during which he informed them that no turbulence was expected during the flight. During the flight, both the captain and the first officer monitored their WSI and SkyPath EFB applications for potential weather and turbulence. They also queried other aircraft operating along similar routes and altitudes. No significant weather concerns were identified, with only occasional light turbulence reported along portions of the route. The captain did advise the FAs to secure the cabin early for arrival into SAN due to the breezy conditions reported on the automatic terminal information service (ATIS) at the time. Part of the weather document issued to the flight crew consisted of the National Weather Service (NWS) High-Level Significant Weather Prognostic Chart valid for 18Z and 00Z. The charts depicted a jet stream moving north-to-south across the track in the vicinity of the ETEOC waypoint at FL350 at 120 to 150 knots, with the tropopause lowering to FL350 in the vicinity of the event.  The NWS chart depicted the potential for moderate-to-severe turbulence between FL300 and FL460 in the vicinity of the turbulence encounter.  The winds aloft charts also indicated a defined upper-level trough and a deformation zone in the vicinity of the turbulence location and showed strong horizontal wind shears in the vicinity east of the jetstream location.  The Southwest Airlines Enhanced Weather Information System (EWINS) provider, WSI graphics, had a current advisory over the location for light to occasional moderate turbulence between FL280 to FL380.  The flight crew’s weather document provided information which depicted the route crossing the jet stream which showed moderate to occasional severe clear air turbulence (CAT) over the route.  In addition, the company issued weather advisories that warned of occasional light to moderate turbulence over the area where the event took place.  The flight attendant assigned to the “B” position reported that while performing beverage service in the aft galley, the aircraft encountered turbulence. During this time, she was pouring hot coffee, which spilled into her boot. She immediately removed the boot and applied cold water to the affected area. The flight attendant reported the onset of blistering and described the pain as severe. Despite the injury, she continued working until the flight’s final leg to Denver. Following the flight, the injured flight attendant sought medical attention and was diagnosed with second-degree burns. Eddy dissipation rate (EDR) is a measure for the intensity of turbulence in the atmosphere. It ranges from 0 to 1, where 0 indicates no turbulence and 1 indicates extreme turbulence. According to the flight data downloaded from the IATA Turbulence Aware platform, a peak EDR of 0.254 was recorded at approximately 2215 UTC at flight level FL350. Given the Boeing 737’s classification as a medium weight category aircraft, the recorded EDR value is consistent with moderate turbulence intensity.   At the time of the turbulence, the aircraft encountered winds from 338° at 64 knots and an outside air temperature of -51°C, indicative of its position on the cold (polar) side of the jet stream core and near or above the tropopause. As the flight progressed eastward, the outside air temperature further decreased to -53°C.   The approach and landing were uneventful, and the flight crew did not receive any report of the injury during the flight.