With Chicago looking to at least get close to 100 if not make it later this week and weekend, here are some stats.
Officially, Chicago has reached 100+ a total of 65 times, with the last occurrence on July 6, 2012. On average, that is almost 1 day every 2 years, but it is a bit misleading. The 65 days of 100+ have occurred in just 33 years, suggesting that it is not all that rare to get multiple such days in a year when it does happen. Several year gaps between 100 degree days are not uncommon.
43 out of 65 days have been 100 or 101, so roughly 2/3 of the time. It is much more unusual to get to 103+
To weave some cold talk into this and throw beavis a bone... the largest spread in temperatures in the same year is 126 degrees, which happened in 1985 (-27 for lowest temp, 99 for highest temp). Chicago reached -23 at the end of January, so in order to achieve a 126 degree spread, Chicago would have to hit 103. Might be tough to do but may at least get kind of close.