I would suspect in any one of the Northernmost outdoor stadiums excluding Seattle, most likely in Green Bay but maybe Chicago, Cleveland, New England, Buffalo or Cincinnati. Kansas City an outside shot as well as mentioned, Denver.
Green Bay, Chicago, Cleveland, all on the lakes can get colder than a witches’ er, they can freeze the brass er, no wait a second. Cincy famously has one of the coldest games on record and it was the windchill that did it, so they’d be a candidate too.