This must be unprecedented. The only one I've heard of is Chicago 2007 and now two in the same week in the same state. Weird weather too–nice today, warm tomorrow, blazing hot on Sunday and then moderately hot (high 80s) on Monday. Wonder if we'll be seeing more and more of this due to litigious nature of our society (no argument there!) and possibly climate change–yes I said it. Sure seems warmer now than 30-40 years ago and weather data are showing it practically every year.
In the mid-90s I ran the Winnepeg Half, which was in conjunction with a full marathon. Even though we had a 7 AM start it was 88 with a strange 15-20 mph wind blowing from the south. It was like being in a convection oven. They still had the race and there were no casualties. I had hoped to place in the top 10 in the half, but threw my goal time out at the start and ran 10-15 sec/mile slower than planned. Ended up 4th, running 3 min slower than expected. They were melting.
In the full the leaders went out in low-mid 2:20s pace like it was 60 instead of 90 and just a handful finished under 3.