Can a cloud block rain?

When I was a young teenager at school I remember sitting in class and staring out the window onto a miserable wet day. It was a craft and design class in a cheap temporary building so you could hear every drop striking the wooden roof or battering the thin windows. It was one of those overcast days where a huge single rain cloud hung from horizon to horizon giving an unrelenting spell of rain from morning to night. Then I noticed a black cloud. Not grey, black. I was astounded, this thing was the blackest cloud I’ve ever seen. It was quite small, perhaps the size of my fist held out at arms length. And it was heading right for me. I prepared for a rain storm of biblical proportions within this already rainy day.

As it rolled over my position the rain which had been falling all day… well it just stopped. The black cloud appeared to be blocking the rain!

Now I think back on this as an adult, every semblance of logic I possess tells me this must be nonsense. That my memory has played tricks on me. But it is a very vivid memory. And I remember puzzling over it for a few days afterwards and telling friends.

However, as I say, I was a youngster, so it’s more than possible my memory has warped some aspect of it. Or perhaps coincidentally the rain stopped or eased at that exact moment.

The question I have is: can such a phenomena even be possible?

A cloud in and of itself cannot block rain; it is no more substantial than the ground-level fog you might see from time to time in your neighborhood. However the violent air currents associated with severe thunderstorms can push rain to the side or even force it back upwards.

Yes that sounds more logical. Could a cloud of the type I witnessed have had such an effect?

Rain has three general causes,

  • “oragraphic” air being pushed up the slope.
  • cold front - the humid air is going to get cold. (the cold air is more dense and pushes warmer air up, which cools the warm air…)
  • convection - on a warm day thermals take warm humid air up, and when it goes up it cools.
    The singleton cloud represents a front.

Not all fronts cause rain. There’s cold fronts, warm fronts, occluded fronts, so the small wind change or the front that moves over can stop rain - eg stopped the air moving up the slope, stopped the cold air pushing humid air up… (its unlikely to be a thermal given the “all day of rain from a stable cloud layer”. Thermals create moving thunderstorms. )