Thanks @korina. I am using Safari, the same browser I have always used. I cleared the cache as suggested, but it's still the same:

Any other suggestions please?
Thanks,

Andy

@andy-oxford
Here is another example. The winds appear to be blowing from opposite directions on either side of the line..

For the past 2-3 days, Windy.com has had strange straight lines running through it, with vastly different predictions on each side. See example below..

Is this something in my settings, or is this a problem for other users too?