Yeah, you don't even need precipitation to make summer tires dangerous if it's < 50 degrees outside... The tread compound will get hard... And if you continue driving on it while the tread is hard, the tread can actually break apart in chunks, resulting in permanent damage that will not be covered under warranty. Also, when the tread is hard, you will loose A LOT of grip. You can try driving carefully all you want, but all it will take is one emergency maneuver, and you will likely total your car. I've been there before... Summer tires in 45 degree weather, with no precipitation... Just morning dew... Fishtailed all over the place no matter how lightly I pressed the gas. And throw some curves in the mix, particularly while driving down a hill... That's a recipe for disaster... That's also how my neighbor wrecked his summer tire clad Audi S4 a while back... Slid his car right over a curb into a retaining wall becuase he couldn't navigate a simple curve in the middle of the hill we live on.