I also like to fitness walk a 5 mile loop on days I'd like to exercise but when there is a possibility of rain.

If i get caught in the rain on my bike 15 miles from home it's no fun....my brakes don't work as well, I have to slow down on curves so as not to skid, my bike gets filthy, and cars splash me with wet muddy water.
Walking in the rain is no big deal however- just change my clothes when I get home.