This sky– portending a quiet evening– is our model sky for understanding the explanations in Instant Weather Forecasting by Alan Watts (1968). (Also available in its 4th, 2012, edition.)

[Has it really been 10 days since I’ve looked at a Quiet Evening? My! How time does fly when one is busy.]

I have to confess, this photograph confused me at first. Why is that fire with its smoke getting in the way of the sky?

Same photo but with the white balance adjusted to highlight the low fog.

The Major Inference of this sky is a calm night with patchy fog and mist, especially in “industrial areas and in hollows.”

The Major Clues are– for ease of reading I’m quoting/paraphrasing without worrying about proper quotations (see page 42)– (i) lack of wind at surface and aloft; (ii) strongly stabilizing air near the ground causing mist and smoke decks (the reason for the fire); (iii) little or no low or medium cloud to prevent radiation from the ground.

So no wind– see the tree. Low fog just above the horizontal of the fence. High, wispy clouds. And note the rise of the smoke (from a burn pile, no doubt) and then its fall– almost as if it were being pushed down from above. Here at the Farm this could be an early Spring or Fall evening.

Here’s the Explanation:

The smoke deck shows how rapidly the earth is cooling and so stratifying the air layers over it.

Oh wow. Am I supposed to understand that the hot smoke is cooling so quickly as it rises that it falls again?

The smoke is trapped in an ‘inversion’ where cool air changes to warmer above it.

Hummm…

This inversion layer will move upward with the night and trap water vapour and smoke near the ground so leading to mist and fog.

Okay. So don’t forget the earth is cooling.

If the ground falls below freezing then the fog risk is less as some of the moisture is now held in suspension as solid ice crystals on grass, etc.

But what about the sky?

The upper cloud is largely spread-out vapour trails, but they are dense and persistent. There seems, however, to be no organized wind direct at their level and tis points to a continuation of the present quiet weather.

I don’t know if these clues are visible to City Mice, but we Country Mice know this scene well. It’s quite pleasant.