I'm a Minnesota girl, but wherever I have lived (Minnesota, Virginia, or London) I have noticed that everyone has a different threshold at which they transition from boots to sandals.  

For me....

40 degrees: Put away the UGGS.  It's time for bare legs + boots (see the rules on this below). 

50 degrees: Bring out the peep-toe shoes, open-toe heels, and running shoes (it's running weather).  Heck, if the snow was melted I would wear flip-flops and sandals. 

60 degrees: Every type of shoe is acceptable as long as it's not meant to be worn in Alaska. 

70+ degrees: If you don't want stinky toesies, put those boots away asap.  There is nothing worse than seeing someone's feet trapped in boots when its a hot day. 

90+ degrees:  It's officially gross to wear cowboy boots, EVEN at country concerts.  People will assume you're stomping around in puddles of your own sweat.   In fact, you probably would be!

XOXO,

Dylan