Agreed with the previous posts: Find yourself a heated wand wash car wash, and take it there very early in the morning or late at night when it's not busy. Take the time to do a good two bucket wash job, including door jambs etc, and then dry it off with some high quality MF cloths. As for the wax/sealant; you'll either need a heated garage, or get it professionally done until you can lay hands on it yourself in the spring.
2011 E90 M3 Alpine White on Fox Red
2007 E90 335I Graphite on Terra
2005 E83 3.0I Mocha on Black (Gone and forgotten)