I always have brides that say "What if it rains on my wedding day?". My answer is- then it does... and you will have awesome pictures! So don't worry about that part!
To me, a good attitude goes a long way. Is it ideal? No... but if you are okay with your dress getting a little wet (it can be cleaned later) then it's worth it to keep going. This wedding is a great example. Not only was it rainy, it was FREEZING. Seriously. My feet were numb well before the end of the shoot not to mention completely soaked. (I am sure poor Jenna froze more than me!)
I tell my brides to bring fun umbrellas and to tell their wedding party to do the same.

This was taken under an overhang during the rain.

This was the end of our couples pictures. Oh the cold... I cannot express. You guys are awesome Jenna! You can't even tell looking at the pictures.

Just keep having fun!