I'm glad some folk made the point about the weather, something folk "down south" really don't realize
May is NOT summer in that country.
We almost always go camping that weekend, in the mountains of Montana and Idaho we have seen snow on numerous trips, it was deeper and colder north of us.
Although we have have seen temps rising to near 90(F)
Along the same line, while Labor Day is often nice, I can recall a trip near Banff where it went below freezing very night, the only reason it didn't snow was because it was clear.