Was that thunder and lightning when McClusky got out of his car to confront Mike at the hosptal? If so, that is a very rare occurence to have lightning and thunder in the winter in the Northeast.
While its certainly not a frequent occurence its not all that rare to have thunder in December. The article you quoted is stating the rarity of thunder with snow. It wasn't snowing when Mike visited the hospital.
Besides, that thunder adds so much to that scene, just as the noise of the subway does when Mike exacts his revenge and kills McCluskey later on.
