Don't base decisions on the weather that prevailed for one day or a weekend or even a week. Berkeley has a fantastic climate. The major differences are that it is not as warm in December and January, when a student is going to be at home anyway, though the low temps are comparable, and it gets more rain. In the summer it is not as hot, again when most students are not in town. Air conditioning is rarely used.
The academic reputations of the two universities are significantly different....
http://www.arwu.org/ARWU2010.jsp
http://www.timeshighereducation.co.uk/world-university-rankings/2011-2012/reputation-rankings.html
Another issue is that Irvine along with Davis and Riverside have two hour finals that take two hours and also the lowest GPA's at graduation in the UC system while Berkeley has three hour finals that take two and a half hours and the highest GPA in the UC system. At Berkeley, students have a week to ten days from the end of classes till the time finals begin to prepare for Finals. At UCI they have one day to a weekend.
http://statfinder.ucop.edu/library/tables/table_139.aspx
Another issue is that Irvine has a very skewed diversity that is more appropriate to a university in Hong Kong than California, about 70% Asian, the highest level in the UC system. Oakland is a wonderfully diverse city with a few bad areas, West Oakland and East Oakland. These areas are not near the UC campus. Rockridge is about a mile down College Avenue from the campus and a great area of Oakland. Piedmont is nicer than any neighborhood in Orange County. On the Northside of the campus, the area called Holy Hill has the highest concentration of seminaries in the US. There is no comparison in the campus environments. It is like comparing apples and oranges. Irvine is a suburban campus where there is no meeting of town and gown whatsoever similar to Stanford, whereas Berkeley is on the traditional university model where it is often difficult to differentiate the town limits from the university similar to the Harvard or Oxford model.
Good Luck!