Originally Posted by AaronM

I've changed lenses outdoors in a number of situations including standing in a river in the pouring down rain. The key is to take your time and BE CAREFUL.

That being said.....

Knowing what you are shooting I would suggest you consider this as an option:

http://www.bhphotovideo.com/c/produc...50_f_3_5_.html

I could show you additional options offered by Canon with faster lenses but you don't really need them for what you are doing and they come with a stiffer price tag.