Date: 201306
Local time of day: 0001-0600
Location: ZHU.ARTCC, TX
Flight conditions: IMC
Weather elements / visibility: Thunderstorm
Light: Night
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZHU
ATC / advisory: Center ZHU
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Human factors: Workload; Training / Qualification; Communication Breakdown
Second reporter function: Pilot Flying; Captain
Anomaly: ATC Issue All Types; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; General Maintenance Action
Contributing factors: Procedure; Weather
Primary problem: Ambiguous

Narrative: Pushed on time; taxied out uneventful and with no indication of ground delay by neither company nor ATC. Upon arriving at Spot 1 on the West Ramp; Clearance Delivery expeditiously handed us to Ground; also giving no indication of delay. Once on ground; Controller indicated ATC was going to unilaterally ground stop all flights but still had us taxi to 15L. Weather was excellent with just a cell visible to the distant northwest. This cell proved problematic for IAH airspace so even though our direction of flight and route of flight were CAVOK; ATC would not allow us to depart because all the north bound flights were already clogging the runway entrances. So we sat in line behind all the northbound flights; shut engines; and waited an hour along with everyone else. The cell passed directly overhead and as it traveled south it grew quickly. Winds shifted so ATC had everyone start engines and taxi to the RWY 33 complex. We were assigned 33L and were cleared for takeoff 90 minutes after initial on time push. But by now the storms were over our direction of flight. We were given and accepted a southwest heading by Tower. Then departure cleared us direct an enroute intersection. We accepted. We were in IMC now climbing through 10;000 feet and Captain; as PF; accelerated in ECON climb to 280 knots. Our weather RADAR showed two intense cells ahead and we saw ATC's clearance was to send us between them. We asked to deviate with discretion and ATC granted deviations and direct when able. The cells closed together as we were between them and we experienced severe turbulence for approximately 30 continuous seconds. We were configured for penetration with our harnesses on; flight attendants seated; seatbelt sign on; airspeed 280 and engine ignition continuous. After 30 seconds we were in total clear air; unlimited visibility and the turbulence immediately ended; consistent with a thunderstorm penetration. It took another 60 seconds to notify ATC as all unsecured objects in the cockpit were scattered. Headsets were blown off our heads and I reached for the hand mic; turned on speaker to full and told ATC we had severe turbulence; maintaining 16;000 feet and to standby for our report. They said roger but never passed along our PIREP to other aircraft; just as they never passed along the PIREP for those aircraft preceding us that went over our same route minutes before. After assessing any immediate damage; I assumed PF duties and Captain called the flight attendants. They were cleared to check cabin now that it was smooth. No reports of injured passenger or crew; however; the lav doors blew open and all the holding tank contents sprayed into the lavs; onto the flight attendants and up to the cabin ceiling. In the cockpit there was one cup of ice water that now covered the center console and First Officer comm panel. All flight bag contents were emptied onto the floor and charts covered the cockpit floor; dash; and cubbie holes. Captain coordinated with Operations and determined it was best to return to IAH for required inspections; clean up; and a re-crew. Did not ask for emergency handling; just an expeditious return to field; and we were at least 4000 pounds under landing weight upon touchdown.


Second narrative: [Narrative 2 contains no additional information.]


Synopsis: An Air Carrier crew encountered severe turbulence between to thunderstorm cells at 16;000 feet climbing and because of aircraft lavatory and flight station disarray returned to the departure airport as a precaution.