The fix is easy enough. They have replaced the old xml.weather.com feed with a new wxdata.weather.com version, which works exactly the same.
So all you have to do is open the skin .ini file for your weather, and find the WebParser parent measure(s) that have a URL option looking something like this:
Replace just the part in red above with:
So that xml.weather.com URL in this example would end up as:
The RegExp option used to parse the information is still the same, and the only change you should have to make is to the URL option. Save the change and restart Rainmeter and all should be well.
Note: Do NOT replace the part after "/local/", as those variables #Location# and #Unit# will likely be called something different in your skin, and the skin you are using may be getting a different number of days from the feed with &dayf=X.