For northbounders leaving in late March, the first several weeks on the AT can be brutally cold. You might think that Georgia and North Carolina in spring would be nice, but the trail runs around 2500' above sea level with several peaks well above 5000'. Snow and overnight lows in the low teens and below are common.
We're looking at two sleep systems - One for the "shoulder" seasons of spring and fall on either end of the trail, and another for the dog days of summer. The shoulder system needs greater insulation - both from the air, and from the ground. Sleeping bags, rated for 15 degrees, with insulated sleeping pads are prescribed. We'll dedicate a pair of dry socks to sleep in. On colder nights, we'll wear any clothing required to supplement the bag!