PCG
Continue to build back your aerobic base, but also start at the basics of speed as well to wake up that system. i would have at least two of your shorter run days end with drills and strides for the summer and early fall, and then start working in a quick 3x200m after runs....literally start at 36-34-32, and slowly move your way down to 30-28-26 while you are in base phase. high knees, buttkicks, kick-outs all musts ---4x50m twice per week. By the time you get to Dec-Jan you should see the 400m speed return.