Narrative:

Flight attendants were briefed of weather conditions east and in the vicinity of the airport prior to takeoff; necessitating an early cabin cleanup. Cruising at FL400 approximately 70 NM east and painting no weather returns on the radar; the captain and I simultaneously noticed rapidly building convective activity at our 12 o'clock position. The captain began an immediate left turn in an attempt to avoid the area and seated the flight attendants via a public address. I notified ATC we were deviating left of course for weather. Soon after; the aircraft entered moderate turbulence; during which the aircraft experienced intermittent low speed stick shaker two different times and bank angle exceeded 45 degrees once. The captain disconnected autopilot and autothrottles [and] used appropriate pitch and roll inputs while adding power to recover from the stall indications.it was evident a descent was necessary to gain flying airspeed; so I informed ATC we were descending to FL380 and that we encountered moderate turbulence from convective activity that was not painting on the weather radar. The aircraft recovered at FL380 and ATC gave us pilot discretion descent to FL350. The captain checked on the flight attendants after the event to get the status of all passengers and crew while I flew the aircraft and talked to ATC. It was discovered that one of the flight attendants hit her head; was emotionally distraught; but did not need immediate medical attention. We were told that no passengers sustained any injuries. The fasten seatbelt sign remained on during the remainder of the flight; and landing was uneventful.after landing and just prior to all passengers deplaning; I discovered that a passenger who was in the aft lavatory hit [their] head during the turbulence event. I gathered information on the passenger and passed it on to an operations supervisor. The operations supervisor called EMS and an assessment was performed. After the assessment with EMS; the passenger chose to not receive further treatment and exited the aircraft; as this was [their] final destination. The captain called dispatch to work any and all issues with maintenance and scheduling. The B and C flight attendants were pulled from the next leg; and after getting two new flight attendants; we continued on.

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Original NASA ASRS Text

Title: B737-700 First Officer reported that they encountered moderate turbulence causing momentary loss of control.

Narrative: Flight Attendants were briefed of weather conditions east and in the vicinity of the airport prior to takeoff; necessitating an early cabin cleanup. Cruising at FL400 approximately 70 NM east and painting no weather returns on the radar; the Captain and I simultaneously noticed rapidly building convective activity at our 12 o'clock position. The Captain began an immediate left turn in an attempt to avoid the area and seated the Flight Attendants via a public address. I notified ATC we were deviating left of course for weather. Soon after; the aircraft entered moderate turbulence; during which the aircraft experienced intermittent low speed stick shaker two different times and bank angle exceeded 45 degrees once. The Captain disconnected autopilot and autothrottles [and] used appropriate pitch and roll inputs while adding power to recover from the stall indications.It was evident a descent was necessary to gain flying airspeed; so I informed ATC we were descending to FL380 and that we encountered moderate turbulence from convective activity that was not painting on the weather radar. The aircraft recovered at FL380 and ATC gave us pilot discretion descent to FL350. The Captain checked on the Flight Attendants after the event to get the status of all Passengers and Crew while I flew the aircraft and talked to ATC. It was discovered that one of the Flight Attendants hit her head; was emotionally distraught; but did not need immediate medical attention. We were told that no Passengers sustained any injuries. The fasten seatbelt sign remained on during the remainder of the flight; and landing was uneventful.After landing and just prior to all Passengers deplaning; I discovered that a Passenger who was in the aft lavatory hit [their] head during the turbulence event. I gathered information on the Passenger and passed it on to an Operations Supervisor. The Operations Supervisor called EMS and an assessment was performed. After the assessment with EMS; the Passenger chose to not receive further treatment and exited the aircraft; as this was [their] final destination. The Captain called Dispatch to work any and all issues with Maintenance and Scheduling. The B and C Flight Attendants were pulled from the next leg; and after getting two new Flight Attendants; we continued on.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.