Geography 101 Online











  1. What are the five basic cloud classification words and what do they mean?
  2. Describe ten basic cloud types shown in the diagram.
  3. What name is given to mid-altitude puffy clouds? A high altitude layer of clouds? A deep thunderstorm cloud producing rain?
  4. Describe how the four types of fog form and give examples.

Cloud watching, from children looking for animals in cloud shapes to the meteorologist studying weather patterns in satellite images, is an international pastime. Both observations, the whimsical and the analytical, try to interpret one of nature's most complex phenomena.

Even a basic classification of these continuously shifting shapes eluded humanity for millennia until about 200 years ago when amateur meteorologist Luke Howard proposed one. His basic cloud designations are still in use.

Cloud Types

Most clouds can be classified combinations of just five words: cirrus (referring to high-altitude, and sometimes wispy), alto (referring to mid-altitude), cumulus (individual puffy), stratus (continuous layer), and nimbus (meaning precipitating). Look at the chart below and see how these words are used by themselves and in combination to describe ten basic cloud types. Notice the difference in the Sun's appearance seen though cirrostratus and altostratus clouds: cirrostratus often produces a circular halo. You may see this halo at night around a full moon when cirrostratus clouds are present. Also note that the huge, thunderstorm-producing cumulonimbus clouds can fill the entire depth of the troposphere and range from liquid water at the bottom to ice crystals at the top.

ten basic cloud types

mackerel skyThe altitude designations represent the different states of water in the atmosphere. Below about 2 km (1.2 mi), clouds consist mostly of liquid water droplets. Above about 6 km (4 mi), cirrus clouds consist mostly of ice crystals, and in between alto clouds are a mixture of both ice and liquid water.

lenticular cloud over Mauna KeaAltocumulus (mid-altitude puffy) clouds sometimes form a fish-scale pattern called a mackerel sky, shown at left. And if you see a flying saucer floating over a tall Hawaiian mountain, don't be alarmed; it's just a lenticular cloud, such as this one over Mauna Kea. These form at mountain tops under very stable conditions with high winds. Air squeezes over the summit and creates these eerily distinct clouds.


Fog is simply a cloud that touches the ground. Fog forms in many ways, including:

Radiant Cooling

In cool climates, the ground may become extremely cold under clear skies at night when heat is lost through radiation cooling. The cold ground cools the air above it and a shallow layer of fog may form. In mountainous areas, cool air may collect in valleys and produce a "puddle" of fog.

Advection Cooling

Think San Francisco. The water by the shore is very cold, so when warmer air from farther out to sea is drawn toward land, it cools to the dew point and fog rolls into the Bay.

Orographic Cooling

When wind blows into a mountain, air is forced to rise. If it cools to the dew point, fog forms along windward slopes. This is the most common type of fog in Hawai'i, but it is often referred to as cloud, as in the expression "cloud forest."

Evaporation Fog

This is equivalent to a steaming cup of coffee. If cold air overlies warm water, evaporation from the warm water greatly increases the vapor pressure. When the vapor pressure increases to the saturation vapor pressure of the cooler air, fog forms.

fog in San Francisco Bay


ToC | CLOUDS | Evap | Humidity | Stability | Condense | Clouds

Dennis Nullet
Kapiolani Community College Geography