Most weather sites show you the current radar image, and maybe a loop of the last hour's worth of data. But what of where the severe weather is expected to be in a half-hour? We've been creating such short-term forecasts for several years now but you could look at them only with Google Earth or a custom weather display.
Some folks in Wisconsin have incorporated our algorithm product into their site which provides high-resolution images for PDAs -- all you need is a phone or PDA with a web browser. That site is not limited to the US; it carries data for all over the world. To see the forecast radar image loop, go to http://www.ssec.wisc.edu/data/paw/usus_usa_frad_anim_none.html
Remember though that our forecast product and the web application from Wisconsin are research experiments. For an operational (i.e. somewhat guaranteed) product, see the NWS web pages. But, naturally, those are not as cutting-edge (there is no radar forecast, for example).