Jet Stream over lay?
I'd find a jet stream overlay cool since it is a significant contribution to the weather. Something like this: http://www.stormsurfing.com/cgi/display_alt.cgi?a=glob_250
You have it already on Windy !
What is jet stream? High speed winds which are observed at 300hPa or 250hPa altitude. So just use the Altitude slider with the Wind layer at one of these level. .
It's actually better than using a jetstream overlay with simple lines in my opinion :)