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Dew point depression and cloud formation

Discussion in 'Introductory weather & chasing' started by Steven Scott, Jan 7, 2019.

  1. Steven Scott

    Steven Scott Lurker

    Sep 12, 2018
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    Does the environmental and dew point temperatures have to coincide before saturation is reached and clouds form, or can the dew point depression be non-zero and allow clouds to form?
  2. rdale

    rdale EF5

    Mar 1, 2004
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  3. Jeff Duda

    Jeff Duda Resident meteorological expert
    Staff Member

    Oct 7, 2008
    Likes Received:
    This question is a bit ill-posed given the use of the term "environmental". It depends on how you define it. In most of the science, "environmental" in this context refers to "ambient" or "large-scale". In that context, we see this happen all the time with cumulus clouds and thunderstorms forming in large-scale environments that are not saturated.

    Keep in mind the fundamentals here - what is a cloud? it is nothing but condensed water (whether liquid or solid). Therefore you CANNOT get a cloud without condensation. While condensation can occur in the absence of saturation, it happens only on a microscopic scale, and you will never visibly see condensed water with RH < 100%. You *must* have RH > 100% for condensation to occur, but supersaturations are typically quite local. Here "local" means "occurring only very nearby".

    All clouds form in areas with local supersaturations. So in this broader sense, the answer to your question is an unconditional "yes".
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