July 16, 2021 – Very few days come and go without a cloud in the sky. Clouds can be very close to the ground (fog), a few thousand feet above Earth or very high above the Earth’s surface at 20,000 feet in the air. Commercial airplanes reach their cruising altitude around 35,000 feet in the air.

In 1803, Luke Howard, a British pharmacist who was fascinated with cloud formations, named three basic cloud types: cirrus, cumulus and stratus. He also named combinations of those three basic types, such as cirrocumulus. He named the clouds in his 1803 Essay of the Modifications of Clouds.

According to the National Weather Service (NWS), there are four basic cloud types. Those are: 1) cirrus 2) cumulus 3) stratus and 4) nimbus. The NWS also classifies clouds based on height or altitude.

The official worldwide standard for cloud types can be found in the International Cloud Atlas by the World Meteorological Organization (WMO). See link to the right.

Definitions of the four basic cloud types, according to the National Weather Service (NWS), are:

1) Cirro-form: The following definition of cirro-form clouds is from the National Weather Service:

The Latin word ‘cirro’ means curl of hair. Composed of ice crystals, cirro-form clouds are whitish and hair-like. There are the high, wispy clouds to first appear in advance of a low-pressure area such as a mid-latitude storm system or a tropical system such as a hurricane.

 2) Cumulo-form

Generally detached clouds, they look like white fluffy cotton balls. They show vertical motion or thermal uplift of air taking place in the atmosphere. They are usually dense in appearance with sharp outlines. The base of cumulus clouds are generally flat and occurs at the altitude where the moisture in rising air condenses.
 

3. Strato-form

From the Latin word for ‘layer’ these clouds are usually broad and fairly wide spread appearing like a blanket. They result f

4. Nimbo-form

Howard also designated a special rainy cloud category which combined the three forms Cumulo + Cirro + Stratus. He called this cloud, ‘Nimbus’, the Latin word for rain. The vast majority of precipitation occurs from nimbo-form clouds and therefore these clouds have the greatest vertical height.

REVIEW QUESTIONS

INQUIRY QUESTIONS

1. When Luke Howard published his essay on clouds, what was happening in the United States at the time?

2. Read the headline again. Discuss its figurative meaning.