Why do rain clouds appear black?

When cirrus clouds are above a deck of altocumulus clouds, occasionally a clear area or "hole" will appear in?

• When cirrus clouds are above a deck of altocumulus clouds, occasionally a clear area or "hole" will appear in the altocumulus cloud layer. What do you suppose this happens?

• Answer:

  That is what we call a hole(d) punched cloud". The hole is likely caused a an airplane that flew through the mid cloud deck. This will cause a wave to form on that moist layer and that will mixed in some drier air from the layer below and above this deck of AC. What you end up with is what this link will take you to. https://www.google.com/search?hl=en&q=hole+punch+cl&gs_sm=e&gs_upl=8224l14912l2l17589l20l9l7l2l2l3l1637l5244l0.2.2.0.1.0.3.0.1l14l0&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1210&bih=575&wrapid=tlif132029908626810&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi#um=1&hl=en&tbm=isch&sa=1&q=hole+punch+cloud&oq=hole+punch+cloud&aq=f&aqi=g1g-S1&aql=1&gs_sm=e&gs_upl=2808l3704l0l5920l3l2l0l1l1l0l224l224l2-1l1l0&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=8f0eda00b1092607&biw=1210&bih=575 http://alansealls.com/HolePunch.html http://www.youtube.com/watch?v=MhJ6QkIfVwc http://www.wired.com/wiredscience/2010/06/strange-hole-punch-clouds-explained/