Working the threshold

Today I tested my heart rate monitor for the first time on a tempo run. The goal was to get up to 85% of my maximum heart rate reserve (160) as fast as possible and not let myself get over 90% (167) for the remainder of the workout. The weather conditions were decent for January -- about 40F when I started but the winds were pretty strong, pushing 20mph give or take in some spots. Of course that allowed me to get some nice tailwinds in other sections, but made it difficult to get my pace down. The paths were mostly clear but there were still some slick spots with packed snow and ice. That said, I ended up nailing the workout quite well.  I started out a little more aggressively than I normally do in these types of workouts and it took about a mile to get my HR to 85%, splitting 6:12. I maintained pace in the second mile, staying comfortably at 165/167, and splitting 12:24 (another 6:12). I stayed in the same HR in the third mile and the effort actually felt easier -- I had to keep slowing down a notch to stay at 167 or under (the old me would have gunned the last mile). I ended up finishing at 18:36 for 3 miles. Really happy with that. During the warm up I was expecting more like 19:00 based on the conditions. What this tells me is that pre-heart rate training I was probably going over threshold in the final mile of tempos, while also, starting the workouts  too slowly. Today the first mile felt quick, the second just about right, and the third slow, yet the splits were exactly the same: 6:12 x 3. I'm guessing I could have run 6:00 pace in better weather at the same HR, but for Jan. 16, I'll definitely take this. My overall average HR was 160 (factoring in the time it took to build up to there), but I'd say for the last 2 miles, I was easily 165, so pretty much exactly what I was hoping for.