I also have the same problem with my La Crosse ws-2305... I read the topic a little bit, but it is very hard to understand for me in Italian. I was taught Latin for a couple of years, so I understood something ;-)
I think that you guys were saying: the bad record from the anemometer (WSW, everyday between 16-20 hours, only on sunny days) comes from the sun shining into the anemometer. Am I correct? How can I solve this problem?
Segnalibri