Get the CSV report off a page from http://www.spc.noaa.gov. One such page with a CSV report is here. From there, paste whatever storms you want converted to wiki format, enter the date, and click the button.
This script runs entirely on your web browser. I apologize for the roundabout method, but there are various security implications not too easy to dodge with this implementation. This would be trivial to port to a perl CGI script which could fetch the data directly if I but had a place to host it.
See also [[:en:User:Ke4roh/Storm Wikifier]].