This looks like a great idea!
Granted, I haven't played very much competitive battling this year yet (too much schoolwork, argh!), and I've never been much of an expert at it or anything, but...
1. It seems to me that there's so many pokemon not in Ubers/OU now that having three or more tiers under them may be the best idea to give a decent percentage of pokemon a chance to actually fight. Also...
2. If the last auto-weather-starter is in this tier, then that will leave NU with no auto-weather starters, giving people who don't want a metagame centered around weather a tier to play, whereas if Snover were simply placed in NU, that could potentially make all tiers' metagames be centered around some sort of weather or another.