The feasability study for developing a turbine calls for wind measurements for at least 3 months to determine the information needed to make a decision on location. However, the local community High School is 4 miles down the road and did extensive monitoring for thier site. Would thier data be relavant enough to use?

You can certainly use nearby data to get an estimate for your site. If the two sites are very similar in terrain and elevation the error is small. If you are just doing prefeasibility work, I could provide an estimate that would likely be +/- 5-10%. If you are farther along and need the more professionally confirmed number, there are several professional meteorological firms that do work in MN and could do the correlation and estimates you require. One is called AWSTrueWind and Mike Markus is a contact, call
+1-518-437-8660 (phone).
Another local firm is Windlogics, they'll charge more I believe and mostly like to do wind estimates without using the local data nearby (they charge more to incorporate it)Typically quoting $3,000 for a quick estimate, and more to incorporate nearby data (and AWS might charge less than $3,000 and use the local data)
Windlogics claims to have accuracy within 2.5%, so you can go with them as you see fit. Contact Larry Sinesio Tel: 651.556.4200
If you are doing a one turbine project in MN, it'd probably be fine to just use that nearby data for an estimate. There are many generators operating in your area and loking at their yearly production will give you a very good level of confidence in your expected output.

Wes Slaymaker, P.E.
Windustry