I’m loving the blue skies that this summer has offered. I’ve always wondered about those lonely clouds that sometimes float by. How does a single cloud form when there are no others? I teach a bit of weather science so this would really help me.
The only thing I can think of is the temperature of the air is not as uniform as we might think. A pocket of cool air could exist quite nicely amidst some warmer air. But then I wonder, where did that cool air come from? Any help?
There are many different types of clouds, and they form in various ways. Did you have a particular type in mind?
It’s probably more often the case that a cloud is the result of locally higher moisture, rather than lower temperature. This would be the case for cumulus clouds, one very common type that can “float by”.
They are definitely cumulus clouds. These clouds are formed from vertical air movement. What would cause such localized movement? or such localized differences in moisture as you suggest?
Cumulus clouds are formed by bubbles or columns of rising air; in most cases, the air rises because it is heated by warmed ground, which itself was heated by the sun. As the air rises, it cools adiabatically (due to reduction in pressure and consequent expansion). If and when the cooling reaches the dewpoint of the rising air, water vapor becomes visible and thus a cumulus cloud forms.
If at the height where the cloud forms the air is reasonably dry, the cumulus clouds will tend to dissipate. On such days, you tend to see isolated, “lonely,” short-lived cumulus clouds. If the air aloft is relatively moist, cumulus tend to persist and even spread out into a layer of cloud.
This is exactly my question. If the ground is warm enough to allow rising air, why do we see one lonely cloud and not a flock of them. Perhaps it could be the result of air rising off a parking lot or other dark patch but then I would expect to see a series of clouds following in a trail.
On a day with the right moisture profile aloft, only the best-heated thermal bubbles (from sources such as a large, dark parking lot, as you suggest) will rise high enough to reach the condensation level. Lots of air is rising, but only a small amount of it produces clouds. Typically, cumulus clouds on such a day are short-lived.
Where was this? What was on the ground under that cloud? A tall feature on a flat ground can bump surface winds up and create its own little system. Ditto for a patch of trees on a savannah, a lake or any other feature with thermal properties sufficiently different from the ground around it.
I’ve seen it several times but most recently I was in the Canadian Shield area. Lots of trees, lots of rock, lots of water, no towns. There were no tall features around but the terrain was anything but flat.
I cannot verify that it was a short lived cloud because I did not watch it for long but I did notice that it was moving with the wind. This is definitely different than orographic clouds that form at the same rate they dissipate.