Condensation is one of the enemies of photographers. It occurs at the most inopportune times. A lot of people associate condensation with the colder seasons, but it can also happen on your summer outing.
About 3 years ago I was all set to shoot the airshow in Atlantic City, NJ, “Thunder over the boardwalk“. I had my 20D with a 100-400 all prepared, batteries charged, I was raring to go. About 20 minutes before the show was set to begin, I got in the elevator, camera in my bag, got out on the boardwalk, walked up the hill I had scoped out, took the camera out…and waited…and waited, with the camera back in the bag, for it to come up to the ambient temperature, which was probably around 90°F.