WordNet (r) 3.0 (2006):

downdraft
    n 1: a strong downward air current

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "downdraft":
   air current, crosscurrent, current, current of air, draft,
   fall wind, flow of air, following wind, head wind, indraft, inflow,
   inhalation, inrush, inspiration, jetstream, katabatic wind,
   monsoon, movement of air, stream, stream of air, tail wind,
   undercurrent, updraft, wind