I can't see where either of those resources (as good as they are - especially ours) answers the question.
My guess is that it refers to cloud.
Code Low Clouds Middle Clouds High Clouds
---- --------------- --------------- ---------------
0 None None None
1 Cu (fair wx) As (thin) Ci (filaments)
2 Cu (towering) As (thick) Ci (dense)
3 Cb (no anvil) Ac (thin) Ci (often w/Cb)
4 Sc (from Cu) Ac (patchy) Ci (thickening)
5 Sc (not Cu) Ac (thickening) Ci/Cs (low in sky)
6 St or Fs (fair) Ac (from Cu) Ci/Cs (hi in sky)
7 Fc/Fs (bad wx) Ac (w/Ac,As,Ns) Cs (entire sky)
8 Cu and Sc Ac (w/turrets) Cs (partial)
9 Cb (T-storm) Ac (chaotic) Cc or Cc/Ci/CsAc-Altocumulus, As-Altostratus, Cb-Cumulonimbus,
Cc-Cirrocumulus, Ci-Cirrus, Cs-Cirrostratus, Cu-Cumulus,
Fc-Fractocumulus, Fs-Fractostratus, Ns-Nimbostratus,
Sc-Stratocumulus, St-Stratus
(wx = weather)
So, 1AC140 might mean thin Altocumulus at 14,000 feet, and 6AC160 might be Altocumulus from Cumulus at 16,000 feet.