Narrative:

Due to winter weather conditions in sea the takeoff time in order to get to ZZZ prior to runway closure was exceeded. The crew's focus on winter weather ground operations; distracted our attention away from dispatch destination requirements. Upon arriving to our gate of departure for ZZZ; a recent sea ground stop due to heavy snow and reduced visibility had just been lifted. Thus; our passengers and crew were not delayed boarding. During the final minutes of the boarding process; I made a PA to let the passengers know what to expect for our taxi out plan; and although we were still waiting on a de-ice plan; we knew we would need to de-ice either at gate or remotely. That done; we ran our checklists while waiting to hear back from sea iceman as to our de-ice plan. We eventually got the word that we were in queue for remote operations.upon contacting ramp for push; it seemed to us that our clearance would be granted after the aircraft to our right was clear. Watching them attempt to push; multiple times in the snow with slick conditions under the tug; gave us a good understanding of what we might be in for as well. Also [air carrier] had a plane to their right-rear that was stuck and impeding the flow of traffic. All of this is to say that ground operations were slow going. When I had made the PA to the passengers; we had not assumed being in this lengthy of a delay. I thus made an additional PA re what was happening around and affecting us. We got a message from dispatch reference ZZZ runway closure. This being prior to our physically getting pushed out from the gate area; I called dispatch and received the message to continue operations going to ZZZ. The time frame for getting out and off with a plausible appropriate ZZZ runway time was still thought to be very doable. Also; and although; during my phone conversation with dispatch the fact that he stated that ZZZ will not extend their hours of operation did not sink into my takeoff calculations! I basically deflected that data; assuming that the company could make something happen. Although the heavy snow and snow in general had ended; we had previously looked at a holdover time of down to six minutes. If the snow was to begin again after our de-ice; that would be a holdover time we would have to contend with. With this in the background of our minds and upon clearing de-ice; tower commented that our flight plan dropped out of system. We were issued a new beacon code and cleared for takeoff. Dispatchers should emphasize the current status of operational limit intent in non normal situations. Pilots should insist on a defined plan of action in non normal situations. In this situation; the message that was received of 'continue ops for kzzz ... Push; de-ice; etc...will get paperwork to you soon'. Could have been stated 'will get paperwork prior to departure' or 'do not depart until paperwork received'.pilots should ask more questions along the lines of when can I expect the new paperwork. Not time based but rather operationally based. Push; taxi; de-ice; takeoff. The tower should not clear an aircraft for takeoff when the flight plan dropped out.

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Original NASA ASRS Text

Title: Air Carrier flight crew reported departing without knowledge the release was to an alternate destination instead of the planned destination.

Narrative: Due to winter weather conditions in SEA the Takeoff time in order to get to ZZZ prior to runway closure was exceeded. The crew's focus on winter weather ground operations; distracted our attention away from Dispatch destination requirements. Upon arriving to our gate of departure for ZZZ; a recent SEA ground stop due to heavy snow and reduced visibility had just been lifted. Thus; our passengers and crew were not delayed boarding. During the final minutes of the boarding process; I made a PA to let the passengers know what to expect for our taxi out plan; and although we were still waiting on a de-ice plan; we knew we would need to de-ice either at gate or remotely. That done; we ran our checklists while waiting to hear back from SEA Iceman as to our de-ice plan. We eventually got the word that we were in queue for remote operations.Upon contacting Ramp for push; it seemed to us that our clearance would be granted after the aircraft to our right was clear. Watching them attempt to push; multiple times in the snow with slick conditions under the tug; gave us a good understanding of what we might be in for as well. Also [Air Carrier] had a plane to their right-rear that was stuck and impeding the flow of traffic. All of this is to say that ground operations were slow going. When I had made the PA to the passengers; we had not assumed being in this lengthy of a delay. I thus made an additional PA re what was happening around and affecting us. We got a message from Dispatch reference ZZZ runway closure. This being prior to our physically getting pushed out from the gate area; I called Dispatch and received the message to continue operations going to ZZZ. The time frame for getting out and off with a plausible appropriate ZZZ runway time was still thought to be very doable. Also; and although; during my phone conversation with Dispatch the fact that he stated that ZZZ will not extend their hours of operation did not sink into my takeoff calculations! I basically deflected that data; assuming that the company could make something happen. Although the heavy snow and snow in general had ended; we had previously looked at a holdover time of down to six minutes. If the snow was to begin again after our de-ice; that would be a holdover time we would have to contend with. With this in the background of our minds and upon clearing de-ice; Tower commented that our flight plan dropped out of system. We were issued a new beacon code and cleared for takeoff. Dispatchers should emphasize the current status of operational limit intent in non normal situations. Pilots should insist on a defined plan of action in non normal situations. In this situation; the message that was received of 'continue ops for KZZZ ... push; de-ice; etc...will get paperwork to you soon'. Could have been stated 'will get paperwork prior to departure' or 'do not depart until paperwork received'.Pilots should ask more questions along the lines of when can I expect the new paperwork. Not time based but rather operationally based. Push; Taxi; De-Ice; Takeoff. The Tower should not clear an aircraft for Takeoff when the flight plan dropped out.

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.