Medium Large Transport
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance; Ground Event / Encounter Other / Unknown
Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Weather; Human Factors
After pushback during the after takeoff flow and checklist the Captain questioned the flap setting I had selected. We reviewed the takeoff and landing report and determined that; due to in flight icing conditions below acceleration height we needed to use icing performance data. The performance data we had in our Thrust Lever Resolver (TLR) did not provide a configuration that allowed takeoff at our weight. The Captain called Dispatch and the Dispatcher confirmed that the maximum takeoff weight for current conditions was well below our current takeoff weight. We notified the station that we needed to return to the gate. The station called back and said '[load planning] says you're not overweight and you need to call them right away.' We continued into the gate. Five passengers volunteered to take a later flight and the flight was re-released and operated uneventfully.The reason the airplane was pushed back and started without the correct performance numbers is because it was the first time I have encountered the situation of having icing conditions prior to acceleration height. If I had remembered this I would have told the Captain we needed new numbers and we would have caught the problem sooner.The real problem was the fact that it had been low ceilings; precipitation and cold temperatures in Reno and no one saw these conditions and the problem it was going to cause at our planned takeoff weight.The most serious issue was the attempt from [load planning] to override the Captain and Dispatcher's decision to return to the gate by telling the station to tell us that we weren't in fact overweight. We weren't over our structural max weight; but we were limited by climb performance in the current conditions. This is an operational control issue. [Load planning] as far as I know are not licensed Dispatchers or Airline Transport Pilots and should not be interfering with pilot or dispatcher decisions.
Q400 FO reported departing the gate overweight for the weather conditions. Flight returned to gate to offload some passengers.