If you lived in New England, our bodies weren't ready for the day. We've had windy/chilly/cloudy/rainy days for the last few months. Monday was direct (and strong) sunlight, minimal breeze, and temperatures at least 15-20 above what most trained through. The temperatures were at least 5-7 degrees above the forecast.
For those who started Elite or first wave, the challenge created by warmer conditions really hit at halfway and beyond (~10:30-11am). But for those who were starting further back, the conditions were already uncomfortable at the start. This reminds me much of the 2016 year. Forecasts called for warm, but not too bad temps (like this year). Then, when standing and waiting for the gun, you could tell the forecasts underestimated the day's high by a significant margin and you had to adjust immediately or face a blowup in the second half of the race.
Starting out at say 5% slower than your time goal would have been the ideal way to begin the race, and focusing on hydration early so that you have something in your legs after Heartbreak was key.
My compliments to everyone who ran. This was a sneaky tough day to race.