Winter and snow is hard for a lot of reasons. But we did some testing with safety drivers in NYC last year and will be in Buffalo this year: https://twitter.com/Waymo/status/1721629316625093035 (and others historically).
[1] https://www.americanrallyassociation.org/
I've always said that self-crashing cars will win my stamp of approval when they can compete in stage rally. It'd likely push the Waymo team to evolve even further by getting involved in something like that, even with just the basics.
Edit to add this link to some footage: https://twitter.com/dmitri_dolgov/status/1489318507342807041