Schau mal hier...

Webseiten:
http://www.a1freesoundeffects.com/weather.html
http://www.partnersinrhyme.com/soundfx/Weather.shtml

Direkte Sounds (Download):
http://www.acoustica.com/sounds/user_requests/rain.wav
http://www.acoustica.com/sounds/user...ts/thunder.wav
http://www.acoustica.com/sounds/user...ts/thunder.wav

In Google einfach mal nach "free weather sounds" suchen .