I think he just needs to get used to the outside, as it can be a big scary place. Wait a few days or so and the weather should be a bit nicer once again around here!
I think if you can try to make a game with him when you take him to the park, bring a favorite toy, or play tug of war or fetch with him, he'll get more used to the outside world and fear it a little less. When Yoda was a baby, he would get pretty scared of the outside and would shake too when he's cold. A little sweater did help him, but then we kept taking him out more and more, and he started to enjoy it. Good luck!