A very cool trip planner can be found at the link below.

Put in your proposed dates of travel, and for the destination put our zip code 62928.  It will tell you the average temperature, humidity, cloud cover, wind, and what are the chances of having a rain day during your stay.  Notice the historical highs and lows.  Even if the average high is, say, 70, be prepared for highly variable weather if the historical highs range from 37 to 97 !!!

http://www.wunderground.com/travel/index.asp