I just went to wunderground.com, did a search for your city, selected the Nexrad tab and displayed the main radar. The image showed the text "Radar down for maintenance" in red at the top. Doing a mouse click/drag to select a zoomed-in version also showed the text. The 'Save image' link at the bottom allows you to see just the image if you like.
The WU-radar.php script just uses the same URLs for the image as is created by the Nexrad page on WU.