I’ve always been of the mindset that if I had enough time to train everyday hiking 15-20+ miles I would have already started my trip. Considering that, I do think it’s a good idea to be in decent overall shape and get some miles in with a pack on to reduce the stress your body will feel day-one.
Regardless, you are going to be sore, your body just isn’t used to walking all day with a pack on, but you can minimize your discomfort and maximize your daily recovery speed with some degree of preparation. I also, plan to ease into the bigger miles. I have found that my muscles and stamina are often ahead of my ligaments and tendons in their recovery…so I can often walk further than my body is really ready to appreciate. Needless, to say I have planned in some forced recovery time the first couple weeks, whether it’s a half day leading into town or an extended stay when I arrive.
Training in Colorado can be hit or miss weather-wise . I had several weekends of beautiful 60-70 degree weather in the Denver area the last couple weeks then we got hit with 6-10″ of snow the other day. Snow doesn’t need to be a deterrent, especially if you bring yak-trai or micro-spikes (love these!)
I try to focus my training on gaining elevation…preferably steep (the AT is brutal like that). One of my flavorite short but steep hikes is Mt Royal in Frisco. I can walk out the garage and be at the trailhead in 10 minutes, and then it gains about 1200′ in 1.5 miles. Plus, it’s a great view on the way up!