Storm Track http://www.stormtrack.org/
Extensive compilation of information for storm chasers, including storm chasing FAQs, a library of chase articles and accounts, message board, and storm chasing chat.
WeatherMatrix http://www.weatherwatchers.org/
Worldwide organization of amateur and professional weather enthusiasts is dedicated to the observation and documentation of weather events. Formerly known as the Central Atlantic Storm Investigators (CASI).
