It was humid, and the sun was poking out of the clouds above Citi Field when the Mets announced that due to severe weather forecast for later in the evening, their series opener against the Cardinals on Monday was postponed. The matchup was rescheduled as part of a single-admission doubleheader on Tuesday, beginning at 3:10 p.m. The gates at Citi Field will open one hour before first pitch, at 2:10 p.m. Game two will begin 30-40 minutes following the conclusion of game one. “With severe weather in the area, we are thinking about everyone’s safety, so tonight’s game has been postponed,” the Met…