18km Run

Since just jogging felt a bit boring today, I tried a light buildup run. I ran a 2km warmup, a 15km buildup (5:00-4:20), and a 1km cooldown.
When I woke up this morning, my legs felt a bit heavy, so I wondered if I should just do a slow jog, but after warming up and running at a 5:00 pace, it didn't feel bad. I originally intended to maintain a pace of around 4:40 at most, but as I ran, my body loosened up, and I pushed through the latter half quite easily at sub-4:30. The last 1km was close to 4:15, and I felt great because I was able to maintain it without overexerting myself.
I wonder if it's because the weather has improved. The temperature has dropped significantly. The humidity is still a bit high, but it's not at sauna levels, so it's much better. It finally feels like autumn.