I was planning for 20 miles today and all ready to go. My training buddy even came out and ran for about 90 minutes with me.
Problem was, it was 100% humidity. Literally. It sucked the life out of me. When I got home after quitting at 10 miles it had dropped to 99% humidity. I drank four 24-ounce bottles of water in 2 hours, plus 9 Endurolytes, ate a bagel with cheese and several Clif Bloks and still lost over a pound.
Revising pace plans downward. . . .
Let's see, the median time last year in the Marine Corps Marathon for women in my age group, 50-54 years old, was 5:19:40. A 12:00 min/mile average pace would be 5:14:24. That's a more realistic range that I'm thinking of aiming for now than that sub-5 I was previously thinking of. But everything hinges on the weather on race day.
In 99-100% humidity, I'm a goner for sure.