In the past couple years, I have begun actively trying to embrace the 2-4 weeks in both fall and spring in which the weather is flat out beautiful.
In North Carolina, we're not guaranteed more than that span and the weather is liable to swing from glorious, 65-70 degrees and sunny to oppressive cold or heat within a couple days. There will be some nice days sprinkled in throughout the season, but they're rarely strung together in the same way. As fall officially began a couple days ago, the weather has been fantastic and I've remembered what it's like to run during the day time without dealing with 85 degree, humid as hell conditions.
In the spirit of fall, get out and run!
Walk, bike, hike, whatever it is you like to do outside, go do it. Within a few weeks, I'm sure we'll be bundled up and bracing against the cold so take this opportunity to embrace the seasonal change. Set a new PR, set a new goal, just get outside!
On a more pragmatic note, this is a great time to get yourself into the routine of running or exercising outside in general. While the weather is agreeable, I find it far easier to get into a rhythm for training rather than waiting until the 20 degree weather sets in to start trying to train for that early spring race. Running in the cold isn't that bad, but it's a lot harder to get out of bed at 6:00am for a 6 miler when it's 25 degrees out as opposed to 65.