Narrative:

Following a 1 hour 40 minute tarmac delay due to thunderstorms in the departure corridor; flight gate returned and deplaned at the request of operations. After the weather cleared the area the flight was boarded and departed without much further delay.the departure was uneventful with occasional light chop in the climb behind the weather system along with being in and out of IMC. Just prior to reaching 36;000 feet the cabin altitude warning horn sounded along with the red warning light. The immediate action items were run promptly. At this point in the flight the seat belt sign was still on. I was the pilot monitoring and the captain was the pilot flying. After crew communication was established we immediately coordinated a decent to 10;000 feet with air traffic control. The captain executed this while I continued monitoring duties.the QRH was continued beyond the immediate action items and it was determined the pressurization was not controllable even in manual mode. The QRH was finished during the emergency descent at which point flight attendants were contacted and a stable situation was reported from the back with oxygen generators deployed. This led to a decision to divert. Airport ZZZ was ahead and had favorable weather. The destination was changed and a diversion message was sent to dispatch with a brief description of the situation. Dispatch coordinated with ZZZ operations and a gate; medical personnel; and fire crews were waiting for us upon arrival. Once at a safe altitude a briefing was completed along with the appropriate checklists for the arrival.the landing was under max structural landing weight and the flight landed without incident or injuries to anyone onboard. Mechanics met us at the gate and began to diagnose the problem.

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Original NASA ASRS Text

Title: Just prior to cruise level-off; B737 First Officer reported an aural cabin altitude warning horn along with the red warning light. Crew diverted to a nearby airport.

Narrative: Following a 1 hour 40 minute tarmac delay due to thunderstorms in the departure corridor; flight gate returned and deplaned at the request of operations. After the weather cleared the area the flight was boarded and departed without much further delay.The departure was uneventful with occasional light chop in the climb behind the weather system along with being in and out of IMC. Just prior to reaching 36;000 feet the cabin altitude warning horn sounded along with the red warning light. The immediate action items were run promptly. At this point in the flight the seat belt sign was still on. I was the pilot monitoring and the Captain was the pilot flying. After crew communication was established we immediately coordinated a decent to 10;000 feet with air traffic control. The Captain executed this while I continued monitoring duties.The QRH was continued beyond the immediate action items and it was determined the pressurization was not controllable even in manual mode. The QRH was finished during the emergency descent at which point flight attendants were contacted and a stable situation was reported from the back with oxygen generators deployed. This led to a decision to divert. Airport ZZZ was ahead and had favorable weather. The destination was changed and a diversion message was sent to Dispatch with a brief description of the situation. Dispatch coordinated with ZZZ operations and a gate; medical personnel; and fire crews were waiting for us upon arrival. Once at a safe altitude a briefing was completed along with the appropriate checklists for the arrival.The landing was under max structural landing weight and the flight landed without incident or injuries to anyone onboard. Mechanics met us at the gate and began to diagnose the problem.

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.