Back in my younger days, we ran a few head of cattle. Horses were kept outside 24/7 pretty much right alongside the cattle. Had a really wet late winter and spring one year and there was a lot of flooding. Had one storm come up that dropped a lot of rain all at once. We had cattle on the wrong side of a creek and needed to get them moved fast, before it was too late and they were stranded...or worse.
Stupid truck wouldn't start, wouldn't have done us any good any way as it turned out. Hubby and I called up the horses (they were in the pasture closer to the house with some of the cattle.) Horses were soaking wet, but we had no choice. Toweled their backs off as best we could, saddled up and rode to the back pasture.
The rain had let up while we were saddling up, but there was a LOT more on the way. Had to ride down the red clay bank of the creek, across the creek and up the other side. Let me tell you, slick doesn't BEGIN to describe that Oklahoma red clay! I don't know how my mare kept her feet, but she took good care of me. We moved all of the cattle across the creek, except for one really young calf. It got swept off its feet by the current, and we had to rope the poor thing and drag it up the bank. Better than letting it drown, I guess.
That bank was really treacherous after all those cattle had torn it up, but we didn't have any real trouble, but I was terrified, and could only cling to the saddle horn and my mare's mane as she scrambled up the creek bank.
That was the first time I had ever ridden in the rain. After that, the only thing that stopped me from riding in the rain was lightening.