What happened
On August 8, 2015, a Delta Air Lines Airbus A320-211, registration N332NW, was operating a scheduled passenger flight from Boston, Massachusetts, to Salt Lake City, Utah. While cruising at flight level 340 over Max, Nebraska, the flight crew encountered a line of thunderstorms.
During the flight, the Minneapolis Air Route Traffic Control Center (ZMP) notified the crew of moderate-to-extreme precipitation ahead and suggested a deviation. The company dispatcher also suggested an amended routing to fly south of the weather. Upon entering Denver Air Route Traffic Control Center (ZDV) airspace, the captain queried the controller about the weather. The controller advised that a "hole" or gap existed in the weather at a specific heading.
While the aircraft was approximately 50 to 60 miles from the weather, the crew noted a temperature increase, a rough ride, and static discharge that briefly interfered with radio communications. At approximately 0154 UTC, an eastbound Southwest Airlines flight reported to the controller that the weather gap was closing and advised against following them through the area. The ZDV controller did not relay this pilot weather report (PIREP) to the Delta crew.
At approximately 0202 UTC, as the crew attempted to maneuver the aircraft, the weather radar indicated heavy returns. The crew turned the aircraft, but subsequently encountered large hail. The hail shattered the exterior panes of both forward windows and caused surface damage to the aircraft's nose cone, engine cowlings, and wing leading edges. The captain declared an emergency and diverted the aircraft to Denver International Airport, where it landed without 0 injuries to the 119 passengers or 5 crew members.
Findings
Investigation of the flight's weather data showed that the gap between thunderstorm cells was rapidly narrowing. While the gap was 30 miles wide when the flight entered ZDV airspace, it had reduced to 7 miles by the time the aircraft encountered the weather.
Additionally, the investigation found that the company dispatcher failed to provide the crew with complete weather information, specifically omitting several severe thunderstorm warnings and turbulence plots that were available. The ZDV controller also failed to provide the crew with significant PIREP information regarding the closing weather gap and the temperature changes reported by other aircraft.