Thanks for your help igor_chubin and teddyh!

According to The Fine Manual: watch --color (-c for short) , should render color correctly, eg.

    watch --color ls --color  

but

    watch --color curl -s v2.wttr.in  

doesn't quite play ball.

In the end I went with something like your solution. I didn't need to put the sleep 60 as the first operation though.

    #!/bin/bash
    while true; do
      clear 
      curl -s v2.wttr.in
      sleep 100
    done

^C breaks out of this loop just fine on my system.