Smoking mountain


A smoking mountain might seem an odd topic during a wet spring. However, the title does not refer to a wildfire, but to the name of a weather phenomenon.

Sometimes a cloud streaming off the lee of a mountain has the appearance of smoke from a wildfire. This is most likely to be seen when: the mountain has a fairly sharp ridge line; there is a brisk wind flowing across the mountaintop; the valley on the lee is deep and the air in it is moist.

The wind flowing across the mountain top does not follow the terrain. The sharp mountaintop causes air to separate from the surface and carry on high above the valley. However, this wind drags air in the valley with it causing it to flow in the same direction. This, in turn, causes air to flow up the lee of the mountain. As the moist air is lifted, a cloud forms, giving the impression of smoke pouring off the mountainside.

Streamlines have been added to the picture to illustrate the wind: the air above the mountain top is flowing from right to left; on the lee side of the mountain, a cloud forms as the moist air is lifted. The cloud has the appearance of smoke from a wildfire. To see the picture without the streamlines, roll the cursor over the image (computer), or tap on the image (mobile device).

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4 Responses to Smoking mountain

  1. Carlo says:

    Not just a well-illustrated and clearly-described fascinating event – also such a neat trick with the blue lines. Atmo physicist, photographer, and graphics artist – what will you have for us next, Alistair?

  2. Nancy Van Allen says:

    Glad to see your latest entry. I was worried when I didn’t see anything for quite some time.

  3. Hi Alistair

    Another great post. Many thanks.

    Extrapolating a bit, am I right in thinking that those banner clouds that sometimes extend past a sharp mountain ridge are a product of adiabatically cooled air on the windward side coming into contact with warmer (non adiabatic) air on the leeward side?

    No need to respond if I’ve garbled the terminology, which is likely.

    • Alistair says:

      Trevor, banner cloud, flag cloud, and (the cloud of the) smoking mountain are merely different names for the same thing. The cloud, itself, is on the lee, not windward, and it does form as a result of adiabatic ascent. The air flowing across the mountain merely serves to induce the ascent of air on the lee.

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