Several years since, when travelling by night in the mail coach, in the depth of winter and during the absence of the moon, I was surprised to observe, that, though dense clouds covered every part of the horizon, and not a single star could be seen, yet the night was far from being dark, and large objects near the road were easily discerned. On expressing my surprise to the driver, he replied, ‘The wind is very high, and during a great many years that I have been upon the road, I never knew it to be dark on a windy night.’ The observation was at that time new to me; but subsequent experience has convinced me that it was true.

— B. Hampstead, in The Magazine of Natural History, May 1831

Anecdotally, I’ve noticed that this seems to be true — the darkest nights are calm, regardless of cloud cover. Why?