I hesitate to mention this because I have some concerns about the
idea of displaying a _forecast_ in a PDA during flight, but since I
know
you're into PDA flight software I will mention that the XCSoar PDA
program is capable of displaying BLIPMAP data (loaded on the ground
from the net) as a background map. So you could just load it up and
fly to your convergence line! (but I don't really think things are
quite that easy)

Jack Glendening