National Weather Service Weather Forecast Office

The graph above shows that 2010 is indeed running above average for the number of 90 degree days to date and way ahead of the past 2 summers, but is also far, far below the total for 1988. The summer of 1988 set the record in Chicago for number of days above 90 degrees and during 1988 there were even 7 days with highs above 100 degrees. So while the summer of 2010 has certainly been hot so far, the graph above really puts it into perspective that it hasn't been quite as hot as it seems. The recent cool summers are likely contributing to the impression that this summer is hotter than what the numbers stack up to...

Here's a Public Information Statement with more statistics on this summer's heat.