Chloe has a weather-related super power and unleashes a tornado to destroy Arcadia at some point. As "evidence," Max flash-forwards to the tornado soon after Chloe says that sometimes she wants to blow Arcadia up (or something like that). Also, when Chloe starts comforting Max at the end it starts snowing, so the power is linked to her emotions.
My best guess is that they discover that someone has hurt or killed Amber, and Chloe summons a tornado because she is angry. Now Max has to go back and change stuff to prevent the tornado.
That does sound like a longshot, but I figured the snowing thing was a plot-reason for Chloe to believe Max. Massive storms are what happens when hot and cold cyclones clash, so when Chloe says that it's like 80 degrees and then it starts snowing literally seconds after Max has made a crazy prediction about an impending super storm, suddenly Chloe might be more inclined to listen to her crazy-weird time travel shit.
Also, I might be leaning on the scientific reasoning pretty heavily because I really don't like the idea of this particular story ending with Weather Girl vs Time Girl. I'm hoping the whole thing remains a little more low-key than all that.