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Can a cloud ever be stationary with respect to the ground surface? For some reason (experience, logic?) it seems to me such case is not possible. I read that stationary fronts are defined as two air masses such that

neither air mass is strong enough to advance into the other at least 5 knots (about 6 miles per hour or about 9 kilometers per hour) at the ground surface

But this is not referring directly to clouds' speed, nor discussing the particular case of speed equal to 0.

There are the lenticular clouds, which are defined as stationary, but it is not clear to me whether such stationarity is strict (0 knots per hour) or rather a very low speed relative to "normal" clouds.

Anyone can provide insights on this?

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    $\begingroup$ There is a difference between the air in the cloud having zero speed and the boundaries of the cloud having zero speed. Clouds form when air reaches saturation. This is impacted by pressure and height, so cloud boundaries might have zero speed even while the air is moving. The discussion of lenticular clouds in your link touches on this - the air moves over a mountain, but the location of where a cloud can exist remains steady. $\endgroup$
    – John
    Aug 28 '20 at 14:58
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    $\begingroup$ A lenticular cloud does not move, because it is caused by the geometry of the surface, though it may change shape or extent in response to things like temperature, humidity, and wind speed. $\endgroup$
    – jamesqf
    Aug 28 '20 at 20:15

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