If you do encounter lousy weather in SNP when you hike in March, you can mitigate it somewhat by altering your plan to hike the A.T. end-to-end to embrace side trails. There are quite a few that provide great loops, beginning and ending back on the A.T. (tho you’ll miss parts of the A.T.).
Generally, these blue- and yellow-blazed side trails traverse lower elevations where the weather is not quite the issue it is on the ridgeline the A.T. often stays on or near. By being aware of the direction (east or west) a weather system is coming from, you can further avoid the worst by hiking and camping on the other side of the ridge.
I suggest you get the excellent three-set SNP maps produced by the Potomac Appalachian Trail Club (comes with the official SNP A.T. guidebook as item PB130). These will show the A.T. and all side trails in better detail than other maps available, plus a number of lesser-known boundary entry/exit points. Check them out at: http://www.patc.net/store/
Skyline