Looks like someone forgot to pay the domain renewal fee at Weather Underground:
update
The Weather Underground issued the following statement:
Hello Wunderground users. We first want to apologize for the connectivity issues that many of you are or have been experiencing. The problems were caused when someone at our domain name registrar inadvertently made a change to our domain name record. This essentially means that in the yellow pages of the Internet, they got our address wrong. Most people were left unable to the find our site and were instead presented with our registrar’s default page.
We’ve been working frantically here trying to do anything we could to minimize the damage. We’ve just received word that in about 2 hours most of the connectivity should be restored thanks to some quick work by our registrar. In the meantime if you’re in contact with individuals who cannot access the site through the wunderground.com domain name, please let them know that they can still access the site through weatherunderground.com.
Amazing how vulnerable we are to a slip in the DNS, eh?