In the large room after the armory, you need to use a duck-jump to get onto a light fixture on the right wall (right of the room when you enter) and then jump from there onto the higher area. There is a series of diagonal beams. Walk up one near to the end of it and use it to duck-jump onto one of the rails. You can fall between the rails, so be careful. Once on the rail, walk down it until you can jump onto the highest platform. Then bash the trashcan. It says Thunderstorm when you pick it up.