You could replace "webcam.wunderground.com" with an IP address, provided your software/camera will accept IP addresses.
However in general that would not be advised, but would work as a temporary band-aid.
Here is the problem by doing that. Once you change to that IP, you are stuck with only that one server. As long as that one is online and working properly, all is good. If that one goes down, your down until you change the IP, or until that server comes back up operational again. In general using the URL webcam.wunderground.com will normally get you connected to a working server in the "pool". In this case now, it doesn't because the one server that is broke, is online and appears to be working. (until you go an use it.)
So at the moment, if your camera/software will accept a IP address, you could do that. After it's fixed (I'm hoping here), you would want to change it back to the URL webcam.wunderground.com to take advantage of any available server .