They ingest raw data from the National Weather Service (which you could access directly) and display it on their own graphics, maps and backgrounds.
For a much better commercial weather site, try intellicast.com. It's all free and it's good stuff.
I use Automated Weather Service(AWS), myself. It uses local automated weather stations for local data, and the NWS for forecasts. It also has a link to Homeland Security.
Here's a link. For your local weather, just type in your zip code in the box to the right of the page.
http://www.aws.com/aws_2001/asp/obsForecast.asp?zipcode=97402&x=0&y=0
I also use the NWS web page for more detailed weather information, radar maps and historical information. Is this free service what the Accuweather folks are trying to take away from me?