Animate css weather icons from http://forecastfont.iconvau.lt/

We have a weather widget (see attachment for a base template app with the widget on the main page) using the css weather icons from [login to view URL] We would like to animate the weather icons (clouds, sun shine, rain, etc... not the windmill or wind direction which are already animated). For example, for a cloudy day the clouds could be floating by; when it rains the rain drops could be falling from the cloud. Need to be creative enough to figure out what animation will look good. Once you visit the application app, enter a city into the box at the top (enter the full city name instead of using auto complete) and press enter and the widget should update. It uses the openweatherapi API. The application itself is just a basic php script with a website template and the weather widget itself on the main page.