Weather Underground Content Usability
Site is optimized for advanced mobile browsers that make it easy to scroll through long pages like the iPhone, Palm Blazer, Pocket IE, Opera (including Mini). This site gives you a great deal of information beyond a simple forecast including dew point, barometer, visibility, marine forecast and sun and moon rise and set.
Page size is under 15KB so most mainstream phones will be able to load the page. The low usability rating reflects the excessive scrolling required to reach the most important information - the weather forecast.