Our biggest issue when the weather turns cold is the lack of desire to drink and hydrate! It's cold, you aren't "Thirsty". You have to hydrate. Here's a short video on how to keep from dehydrating during the winter!
Did you find your base training heading into the season was good, so you hit the spring with full on passion? April and May were great then all of the sudden boom, you hit a bottom. Sleeping? Nutrition? Heart Rate? Check this video out.