Date: 201511
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Weather elements / visibility: Thunderstorm
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center ZZZ
Aircraft component: Weather Radar
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Contributing factors: Weather
Primary problem: Weather

Narrative: Departed after a 2 hour rolling maintenance delay for several issues including the MEL placarding of the Predictive Windshear System of the onboard weather radar. We were heading to ZZZ and there was a large area of thunderstorms throughout the [area]. Once leveled enroute I decided to test the radar to make sure it was still operating and a weather radar fail annunciated on both my side and the FO's side of the NAV Display. We happened to have an FAA Inspector onboard with us that day who was a Maintenance Inspector. We tried several different things to see if we could get the radar to function; but could not. I was concerned about continuing the flight without a working weather radar into a line of weather that ran South of the ZZZ1 area; and an area with thunderstorms around the destination airport; and thought that landing at ZZZ1 might be the safe thing to do in order to have the radar repaired; or exchange the aircraft for another one. We had a large amount of fuel remaining so time was not critical. I contacted Dispatch; who briefed me on the weather conditions. I told him of my concerns; and we agreed that we would divert to ZZZ1. I discussed with him about the plan to either burn down fuel and land below max landing weight; or to land overweight and get the required inspections after that landing. He contacted me a few minutes later via ACARS and said that Maintenance and Dispatch both agreed an overweight landing would be acceptable. We took the time enroute to review the QRH; as well as the Operating Manual regarding overweight landings. I briefed the flight attendants; and then spoke to the passengers about what was going to happen; including the fact that there would be Aircraft Rescue and Fire Fighting (ARFF) there when we landed and why. We coordinated the Emergency with ATC letting them know what was wrong. We informed ATC that we would need to land on Runway 10L as it gave us the longest runway length so we had more distance for our rollout; thus reducing the brake energy we would need to slow the aircraft in an effort to reduce the likelihood of blowing tires due to excessive heat buildup. Weather was beginning to move into the area as we descended for our approach. I flew the aircraft down final to a smooth touchdown at a sink rate of less than 200 FPM. I had the auto brakes selected to 2; which decelerated at a consistent rate until we were below 100 KTS; then disengaged the auto brakes letting the aircraft roll to the end of the Runway to the XXR pad where we started the APU; had ARFF chock our wheels so we could release the brakes; and then shut down the engines so ARFF could check out our brakes with a thermal sensor for heat buildup. After getting the all clear we started engines and taxied to the gate with ARFF in trail without incident. I entered the overweight landing into the maintenance log with the info Maintenance needed for their inspection.Interesting side note: The brake temp at the end of the runway after 5 minutes was about 110 degrees. By the time we got to the gate; I asked them if they would check the temps again; and in that time the temperature had risen to over 210 degrees.Max landing weight was 154;000 LBS. Sink rate at touchdown less than 200 FPM. Touchdown was smooth to an easy deceleration to taxi speed. Even though the 'emergency' was relatively benign; the task load was high as we moved into the terminal area with weather approaching and coordinating all the final details before landing. I would like to recognize and thank my First Officer; for an outstanding job of support and professionalism. His ability to assist and anticipate was exceptional; and without a doubt contributed to safe and uneventful result at the end of the flight.




Synopsis: B737 crew experienced a weather radar failure enroute. Due to predicted thunderstorms at the destination; crew elected to divert and have the problem corrected.