Horizon DH8D at Reno on Sep 29th 2013, moderate turbulence causes three injuries

A Horizon Air de Havilland Dash 8-400 on behalf of Alaska Airlines, registration N449QX performing flight QX-441/AS-2441 from Seattle,WA to Reno,NV (USA) with 57 passengers and 4 crew, was descending through about 10,000 feet towards Reno when the crew reported they had encountered moderate to severe turbulence following up a minute later, that they had a pretty bad injury in the cabin and requested medical services attend the aircraft after landing. The crew indicated they did not require priority as that wouldn't changed anything. After being handed off to tower tower advised of gains of 15 knots on short final, the crew upgraded their turbulence rating to "severe to extreme" just below 10,000 feet. The aircraft landed safely on Reno's runway 16R about 5 minutes after the turbulence encounter. A flight attendant was taken to hospital.

The NTSB have opened an investigation into the occurrence rated an accident. The aircraft encountered moderate turbulence, a flight attendant assisting a passenger into the seat received serious injuries, two passengers received minor injuries in the encounter.

ATC subsequently changed vectoring for approaching aircraft to have these aircraft avoid the turbulence area.

On Aug 15th 2014 the NTSB released their final report concluding the probable cause of the accident was:

The airplane’s encounter with known moderate-to-severe turbulence, which resulted in a serious injury to a flight attendant.

The NTSB reported that ATC alerted the flight crew of possible turbulence at or below 12,000 feet. When the aircraft levelled off at 10,000 feet the aircraft encountered a series of escalating turbulence jolts each lasting for about one second the most serious reaching category of severe turbulence.

A mountain wave was at 10,000 feet and at several layers above. SIGMETs had been forecasting the possibility of severe turbulence all day.