Mustang just couldn't believe it.
He stood, soaking wet from the snowstorm, in the center of the little shack that he and Fullmetal had found. It was a lucky thing, too - when the snow was falling too hard for Edward Elric to see to transmute, you knew you were in trouble. So here he stood, still freezing (the air in the cabin was not warm by any means), watching as Fullmetal slammed the rickety door shut behind him. He looked up at Mustang, frustrated. "This," he said authoritatively, "is bullshit." He strode across the room, dropping snow and slush from the folds of his coat as he went, and picked up the sole item in the shack - a ratty old blanket. He looked from the blanket to Mustang, and then back.
"You can use it," he finally said, wadding it up and throwing it at the Flame Alchemist. He clapped his hands together and pressed them to his coat, instantly drying his clothes, and smirked up at Mustang.
Had Roy been a lesser man, he might have rolled his eyes, but two could play at that game. After all, he wasn't without alchemy himself, despite being soaked - his gloves helped him manipulate air to make fire, yes, but he knew more arrays. He crossed the shed in two strides and bent down to draw in the dusting of snow on the ground that was blowing in under the shed door. When he activated the array, the whole room warmed up instantly - and Mustang was grateful it saved him from shivering. Unfortunately, he did not have the option of instantly drying his own clothes.
Fullmetal could be unforgiving, but when Mustang looked up he merely snorted. "Nice trick," he observed. "But you probably still need the blanket."
As it turned out, he didn't need it for long - stripping out of his trenchcoat, military jacket, and flyaway was enough to leave him in relatively dry clothes, and Edward had mercy and instantly dried the outer layers (he grumbled that he couldn't let Mustang die on his watch, and Mustang supposed that was the closest thing to an acknowledgement that he was useful that he would get).
They slept on opposite sides of the cabin, Mustang waking up to redraw and reactivate the circle whenever the room grew too cold again, and in the morning they pressed on, returning to the military camp without incident.