Narrative:

Lots of weather cells on the west side of my sector. Most of the traffic was affected by the weather in some way; either on deviations or re-routes. The sector is a high altitude departure sector. I gave aircraft X a climb westbound from FL270 to FL400. I was then busy doing other tasks involving deviations and climbing multiple other aircraft. At some point I took the handoff (a late handoff) on aircraft Y northbound into my sector at FL390. I had just resolved a conflict with two other aircraft which had my attention; when conflict alert went off between aircraft X and aircraft Y. I quickly scanned aircraft X's data block and noticed he had slowed his climb to 100 feet a hit. My first thought was that he wouldn't be able to climb quick enough to reach FL400 since he was running out of steam; so I cleared aircraft X to descend expeditiously back down to FL360. I also asked aircraft X to report leaving FL380; which he did in time for separation with 1000 feet and 5 miles (or more).however; aircraft Y's pilot came on frequency and reported an aircraft in front of them descending through their altitude and said it was 4 miles on their TCAS. They got a traffic advisory (not an RA) on their TCAS. I was so busy I didn't even know I was talking to aircraft Y. I would have called traffic. He may have checked on; I just didn't remember. But if I had known; I could have turned him as well. With aircraft X expediting his descent and the pilot altitude report; I felt we had maintained separation.my initial reaction should have been to expedite the climb of aircraft X to FL400 and report reaching FL400. He probably could have made it easily. Also; I should have reached out in the blind and turned aircraft Y thirty degrees right of course; even though I didn't know I was talking to him. These were my mistakes that I should have known and done better on my initial reaction. I would also recommend not sending employees to team training or to safety briefings if it is going to leave us short staffed on a day with high traffic and lots of deviations. I had asked for a d-side which I did not get in time before the occurrence. It took more than 10 minutes to get help. Also; the area was left under the direction of a controller in charge and I'm not sure where the supervisor went; but that made our staffing even worse.

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Original NASA ASRS Text

Title: ZDC Controller reported a near loss of separation when a climbing aircraft unexpectedly reduced climb rate.

Narrative: Lots of weather cells on the west side of my sector. Most of the traffic was affected by the weather in some way; either on deviations or re-routes. The sector is a high altitude departure sector. I gave Aircraft X a climb westbound from FL270 to FL400. I was then busy doing other tasks involving deviations and climbing multiple other aircraft. At some point I took the handoff (a late handoff) on Aircraft Y northbound into my sector at FL390. I had just resolved a conflict with two other aircraft which had my attention; when conflict alert went off between Aircraft X and Aircraft Y. I quickly scanned Aircraft X's data block and noticed he had slowed his climb to 100 feet a hit. My first thought was that he wouldn't be able to climb quick enough to reach FL400 since he was running out of steam; so I cleared Aircraft X to descend expeditiously back down to FL360. I also asked Aircraft X to report leaving FL380; which he did in time for separation with 1000 feet and 5 miles (or more).However; Aircraft Y's pilot came on frequency and reported an aircraft in front of them descending through their altitude and said it was 4 miles on their TCAS. They got a traffic advisory (not an RA) on their TCAS. I was so busy I didn't even know I was talking to Aircraft Y. I would have called traffic. He may have checked on; I just didn't remember. But if I had known; I could have turned him as well. With Aircraft X expediting his descent and the pilot altitude report; I felt we had maintained separation.My initial reaction should have been to expedite the climb of Aircraft X to FL400 and report reaching FL400. He probably could have made it easily. Also; I should have reached out in the blind and turned Aircraft Y thirty degrees right of course; even though I didn't know I was talking to him. These were my mistakes that I should have known and done better on my initial reaction. I would also recommend not sending employees to Team Training or to Safety Briefings if it is going to leave us short staffed on a day with high traffic and lots of deviations. I had asked for a D-Side which I did not get in time before the occurrence. It took more than 10 minutes to get help. Also; the area was left under the direction of a CIC and I'm not sure where the Supervisor went; but that made our staffing even worse.

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.