I don't see how you'd be able to study abroad during the core of every year for any major and especially for CS. Even if it was possible you'd be negating the reason for going to a highly ranked program like UIUC's in the first place.
If weather's important to you then I agree with the above posters to consider other colleges with highly ranked CS programs that are in warmer climates - UCSD, UCLA, UCB, USC, etc. You could also try for Harvey Mudd or CalTech but I think those would be tough reaches with your stats (UCB, UCLA, and possibly UCSD should not be considered safeties either). Other UCs to consider are UCI, UCD, UCSB, and the others.