...which moderates the airflow to represent Met weather reports from the web.
The Yahoo API for weather (http://developer.yahoo.com/weather/
) can give you the info you need. Your request includes a code for your location (or at least the one you're interested in) and there are two tags in the response relevant to wind
<yweather:units temperature="F" distance="mi" pressure="in" speed="mph"/>
<yweather:wind chill="50" direction="0" speed="0" />
For your project everything else in the response can be discarded.
With some kind of network shield your Arduino could take care of this request as well as the control of the fan without the need for a computer in the mix at all.
Interesting concept you've come up with!