DENVER — In a flashback to last year’s trip to the Mile High City, the Mets were again hit with snowy and frosty weather that shelved their series opener against the Rockies. The Mets’ game against the Rockies, scheduled for 8:40 p.m. ET at Coors Field, was postponed due to heavy snow in the forecast, the home team announced on Friday afternoon. The matchup will be made up as part of a split doubleheader on Saturday, with Game 1 starting at 3:10 p.m. ET and Game 2 beginning at 8:40 p.m. ET. It will be the Mets’ fifth doubleheader of the season. The city of Denver issued a winter storm and free…