I had something similar to this from treeplanting this summer. I stretched/minorly tore my MCL right before planting so I ended closing all my trees with one foot while compensating for the injured knee (upwards of 50000 trees over the season) and developed a pain right behind my knee cap. Doctor said it was "patellofemoral syndrome." I don't have the same problems with cold weather though and it has gotten much better over time. Try googling Patellofemoral syndrome and read up on it. Might be the same thing but I'm not sure. Hope this helps.