Python and Perl scripts glean this data from several sources using screen-scraper parsing, and XML and JSON feed-reader techniques. Links to these scripts are in the data-source topic of the FAQs. Check out the "forecast" for Waconia or install it now on your local network.
Since its start, Waconia has been sponsored by Pacific Northwest National Laboratory in Richland, Washington and later by the Physics department at Gustavus Adolphus College in Saint Peter, Minnesota. Its current host is timetocode.org.
About the technology behind the chart...