As a Brit; take away thirty, divide by two. Really you'd only hear Fahrenheit temperatures on film or on TV programmes, so the accuracy loss is unimportant, and which can be mapped as:

• under 60 - coat weather
• 70s - t-shirt weather
• 80s - t-shirt and shorts weather
• 90s - dangerous heatwave that will make the news, have lots of fruity newspaper articles with pictures of people in their swims outside in the rivers, etc.