Standing at the window I was watching the stratus clouds outside. Another term for a stratus cloud is “overcast”. Its been overcast this entire past week and I’m tired of it, but it got me to thinking about a cloud I watched develop last summer while mowing.

The small cloud was visible to the south when I started.

By the time I was finished, three hours later, it was a very large cumulonimbus “thunderhead”. It was impressive.

I’m not sure the folks that live around Arapahoe thought it was impressive given the wind and hail associated with it, but from my perspective; 60 miles away, impressive was the description.

All clouds have their origins at the surface. The water in the soil or at the surface of a lake, river, or ocean, evaporates. Even in the winter water is constantly evaporating all day long. The water, now in vapor form, rises with the air.

The sun powers the whole process as it heats the surface. The surface then heats the air. The warmed air rises taking the water vapor with it. As the air gets higher and higher it cools and the air pressure is reduced.

The two variables that control the state of water (solid, liquid, and gas) are temperature and pressure. With both the temperature and pressure dropping the water vapor condenses out as a liquid.

The water is in such small droplets that the rising air keeps it aloft. If the temperature drops enough the droplets turn to ice. The water and ice form the visible “cloud”.

There are three major kinds of clouds based upon their shape and height above the ground. The very high clouds are called cirrus clouds and are somewhat tendril-like. The middle clouds are called alto and they have more body than the cirrus clouds. The lowest clouds are either stratus or cumulous clouds. Stratus comes from the flattened shape of the cloud and cumulous comes from its puffy shape.

To confuse the issue you can have combinations. For example, stratocumulus clouds or cumulonimbus clouds.

Adding the suffix or prefix “nimbus” means get ready for rain.

As the air continues to rise and cool the water drops or ice particles get bigger and bigger as more and more water condenses around them. Eventually, they will get too heavy to remain in the air and we have rain, snow, or hail. Strong upwellings can keep the ice particles in the air long enough to grow into large hail stones.

According to the University of Nebraska, the largest hailstone in Nebraska is also the second largest ever recorded. A stone measured near Aurora in 2003 was seven inches in diameter. As a reference, a volleyball is only eight inches in diameter!

I think I’ll be satisfied with our stratus, overcast clouds instead of a cumulonimbus monster that would produce something like that.