I've noticed several posts from other writers about the difficulty of writing during the summer. For me, my writing picks up during the summer because the sport that I cover picks up. There are more places to go, more things happening to report on...
But yes, the writing becomes more difficult. My house gets warmer and I feel myself slowing down... Not only does my backyard garden call, but soccer practice, swimming lessons and the local theme park all want a piece of my time.
It becomes a lesson in procrastination.
I use a reward system. If I get one thing done, I reward myself with something. If I accomplish a specific set of goals before the due date, I take the next day 'off' of writing. (I don't think I'm ever truly off, but I do not set a daily goal on that particular day.)