how about a frozen cassette?

Today the temps changed from 36 to 26 with slushy rain/snow stuff coming down in about an hour, and about 3 miles from home I couldn't change gears. I had to stop and using my left hand I tried getting all the ice that built up around the cassette out but couldn't. The watery/slushy stuff just momentarily froze especially as the wind was picking up.

I made it back home in the low, hill-climbing gear. Anything higher, and the chain kept coming off of one cog onto the adjacent one and back and forth.

A spray bottle of RainX in my backpack for next time this happens? I do have fenders and disk brakes.