Just had a flashback to a near death accident in Louisiana on the highway at about 70mph this way. Cloudy no rain, pavement dry, then almost instantly a torrential downpour dumped what looked like a standing half inch of water on the road. The tires lost traction and I slid off into the median. Thankfully I the median was wide and grass and I coasted to a stop (sideways) about a yard from a tree. If you've driven I-10 through Louisiana you know what I mean.

Not sure what an autonomous car could have done in such a situation but anticipate that maybe we should preemptively pull over for a bit before it starts raining.