Of course it didn't happen that way!
First of all, to ensure that this would happen, I traveled out to Reston, VA in the morning and worked from one of our virtual offices there. I had a call that was scheduled from 11am to 11:30am, and I was hoping to pack it up then, get to the gym to change, and be on the trail by noon or a little thereafter.
The 11am meeting went long, and I wasn't out on the trail until 12:30pm. It was 84 degrees and sunny at the time...not really what I am used to with my normal 6am runs.
The first mile went well - 10:27 with an average HR of 147. I hit the mile 1 marker on the trail and kicked it up - a few notches too many. By the end of mile 2, I knew I was going to run out of steam - an 8:59 pace but my average HR was 168. UGH!
I decided to turn around when I hit the intersection of Herndon Parkway - 2.4 miles into the run. This was the first decision point of shortening my run. Partially that I did not want to wait and cross the busy intersection (i.e. wait for the traffic light) to run a half mile and then come back and cross it again - and partially because by this time I knew there was no way I was going to be able to keep up a tempo pace for 2.5 more miles.
I ended up slowing down 2.5 miles into my tempo pace and slowed down for the final mile. I called it quits after 4.5 miles - final time 44:44 (9:57/mile pace and average HR of 166).
I need to remember this on Sunday morning for Riley's Rumble - it will be hot and keep it SLOW.