As the others said, your ignition probably got wet. Physically remove the distributor cap & wipe the moisture out of the cap, rotor, and that general area with a cotton towell. Some rinse it out with WD-40 which displaces water.
Then if your ignition wiring is old & cracked, the spark might be leaking through the cracks & shorting to ground through the moisture on top of them. Wipe the ignition wiring off too.
I'd be very surprised if there was anything more seriously wrong than moisture simply got into the wrong area of the ignition system. Worst case it will dry out on its own & the engine will return to normal, or best case drying it out with a towel/WD-40 may fix it right away. Wipe the ignition coil down too, that is what the center wire from the distributor cap is connected to.