I'm sure everybody is tired of hearing about how my tempo runs suck, but what can I do?

On Wednesday, in cold (33 F), light snow, I ran my worst tempo since the LSC half. 4 miles fast with splits of 6:22, 6:31, 6:27, 6:36. As you can see, by mile 4, I was done for. Average of 6:29/mile. It's time to admit that I can't run 6:20 paced tempos just now. So next week, I'll slow it down to run the first two miles at 6:30, and only accelerate if I can in the last two miles.

There are many plausible explanations why I'm slowing. For one, I'm increasing mileage. Also, it is getting colder, darker, and it is hard to run in the winter due to seasonal changes in human metabolism. It could also be partly mental. I can run mile 1 in 6:20 and feel fine, but then when fatigue starts to take over, I may lack the mental strength to push through it. Anyway, considering that a year ago I had trouble running sub-7 miles at this phase of my training, I think I'm OK.