I will visit chicago in may 11 and im staying for 10 days so is the weather cold ?can i wear ugg boot?

Boots happen to be in style year round right now but it depends on the boot - not a heavy suede maybe a more colorful style would be better - really it is more sandal season now. It could be 90's it could be 70's who knows? Bright summer clothes but maybe a small sweater or jacket as well.