Forecast.io is a new Web app that works flawlessly on Web as well as on your mobile devices. Simply point your browser to http://forecast.io to use. On the mobile devices, after visiting the site, you can save it as bookmark on your homescreen. The Web app can keep your locations across launches and does a very good job of scaling different screen sizes and generating animation without hogging much your computing resources.
The app gives fairly similar intuitive UI across the Web and mobile devices. The Web version has a time machine function that covers more date than mobile Web version.
Forecast.io automatically determines your location at launch, but you can add more location as needed. On the mobile interface, just hit the icon located on top left.
From the main page, you will find real time weather as well as the next hour; next 24 hours and next week. Maps with animated radar imagery can be selected between local, regional and global.
Head over Forecast.io and give it a try!