Weather and Climate

Clouds
Over Mount Shasta

You will often hear the expression, "Mount Shasta makes its own weather." How can a mountain make its own weather? The main answer is that Mount Shasta's presence causes air to be uplifted.

All precipitation comes from clouds. Clouds are formed through the process known as condensation, which is typically caused by cooling. Cooling, in turn, is often caused by the uplifting of air. There are four major processes by which air is uplifted: convective lifting, frontal lifting, convergent lifting, and orographic lifting. Convective summertime thunderstorms produce massive thunderheads on Mount Eddy and Mount Shasta. Wintertime extratropical cyclones produce most of the precipitation formed by frontal lifting in our region. It is the process of orographic lifting that results in Mount Shasta "producing its own weather."

The term orographic comes from the Greek word oros, meaning mountain. Orographic lifting is caused when moving air (wind) encounters a mountain and is forced upwards in the process. The layer of air replaced at the surface causes the air above it to be lifted and cooled. If there is enough moisture in the air, the cooling will cause it to condense and form clouds. If further condensation occurs then orographic precipitation can be produced.

Mount Shasta is known for its beautiful clouds. The lenticular clouds, often called "flying saucers," are probably the most well-known type of cloud in the region. However, there are many types of clouds that can be seen around Mount Shasta.

Photo of Lenticular cloud courtesy of Barrie Rokeach
Lenticular Cloud over Mount Shasta
Photo © 1989 Barrie Rokeach

Clouds are the visible expression of the process known as condensation. We can learn to "read" what the weather holds for us in the near future by examining clouds. But clouds are more than the result of a scientific process. Clouds also bring beauty to our lives. The next time you say to yourself, "Mount Shasta is so beautiful today," look closely at the sky and you will probably find that the clouds that clothe Mount Shasta add to its beauty.

Shasta looms majestically in the pure ether,
capped with a cloud,
against whose bosses the early sungold is beating...
John Muir, 1877

Lenticular cloud over Mount Shasta, reflected in Siskiyou Lake
Photo © 2001 Jane English

Clouds are constantly changing shape and so it is sometimes difficult to categorize them. Two of the first to classify clouds were Jean Baptiste Lamarck from France in 1802 and Luke Howard from England in 1803. Howard was heavily influenced by Linneaus' binomial classification system. Howard named clouds using Latin names and divided clouds into three groups, or shapes, of clouds, which he named heap, layers, and layers and heaps. In addition, Howard also separated clouds into three elevational tiers that he called low, middle, and high. This system, with a few modifications, is still commonly used today.

Rather than having what Howard called groups, clouds today are often categorized into forms. Puffy clouds are called cumuliform clouds. Layered clouds are called stratiform clouds. Thin, wispy clouds composed of ice crystals rather than water droplets are called cirriform clouds. Clouds are still separated into high, middle, and low clouds.

Ten common cloud types, all named and recognized by Howard, are described below. Howard realized, however, that unusual clouds also existed. Mount Shasta, too, has had some unusual cloud formations. Some of the more unusual formations will be described last.

Cirrus

Cirrus clouds are the thin, wispy clouds high up in the sky. The root cirrus is Latin for "curl of hair." Cirrus clouds are made of ice crystals, which is what causes them to be so delicate in appearance.

Scattered cirrus clouds often indicate that fair weather lies ahead. However, in our region most of our precipitation falls in the late fall, winter, and early spring from storms coming from the west. If you see mares' tails followed by clouds that gradually become lower and thicker, then a storm may be heading our way.

Photo of Cirrus cloud courtesy of Carl Wozniak

Mares' Tails
Photo © 2001 Carl Wozniak

Cirrocumulus

Cirrocumulus clouds are small, puffy clouds high up in the sky that are composed of supercooled water droplets or ice crystals. They usually occur in groups. This type of cloud formation is commonly called a "mackerel sky" due to its resemblance to fish scales. These little puffs of clouds are formed by very small convective currents. Cirrocumulus are frequently seen as harbingers of rain later in the day. In a typical extratropical cyclone the first clouds to be seen are cirrus followed by cirrocumulus and altocumulus. Knowing this, the following proverb makes sense if the ship is sailing in the midlatitudes.

Mackerel skies and mares' tails
Make tall ships carry low sails.

Image of mackerel skies and mares' tails © 2001 Rutgers Cooperative Extension
Cirrocumulus Clouds
Photo by Keith G. Diem, Ph.D. © 2001 Rutgers Cooperative Extension

Cirrostratus

Cirrostratus Clouds
Photo by Keith G. Diem, Ph.D.
© 2001 Rutgers Cooperative Extension

Cirrostratus are sheet-like or layered clouds in the upper atmosphere. Sometimes they are so thin that they are hardly noticeable. This is the type of cloud that helps form the right conditions for halos around the sun or moon.

Halo in cirrostratus behind Black Oak leaves © 1997 Linda Freeman

Halo in Cirrostratus Clouds
Photo © 1997 Linda Freeman

Altocumulus

Altocumulus clouds are very similar to cirrocumulus clouds and they, too, can produce "mackerel skies." Generally the convection cells of altocumulus are a little larger than cirrocumulus and the clouds are frequently said to resemble flocks of sheep. Convection cells indicate unstable conditions and so mackerel skies are often seen as harbingers of rain later in the day, as this proverb suggests:

Mackerel clouds in sky,
Expect more wet than dry.

Image of Altocumulus clouds © 2001 Rutgers Cooperative Extension
Altocumulus Clouds
Photo by Keith G. Diem, Ph.D. © 2001 Rutgers Cooperative Extension

Altostratus

Altostratus clouds are layered, mid-level clouds that are typically gray because the water droplets are relatively large. These clouds are close to becoming nimbostratus, or rainclouds.

Photo of Altostratus clouds over Shasta Valley by Linda Freeman
Altostratus clouds over Shasta Valley
Photo © 2001 Linda Freeman

Cumulus

Cumulus clouds are often called "fair weather" clouds--this especially holds true if the clouds become smaller throughout the day. These isolated, puffy clouds look rather like cauliflower or cottonballs.

Cumulus clouds above Mount Shasta,
Photo © 2001 Jane English

If cumulus clouds have a flattened base then they are more likely to produce rain later in the day, as the following proverb indicates.

A round-topped cloud and flattened base,
Carries rainfall in its face.

Stratocumulus

Stratocumulus are somewhat puffy, layered clouds. Sometimes they occur in rows of rolls with patches of blue sky in the background. Stratocumulus clouds generally do not lead to precipitation.

Photo of Stratocumulus cloud by Linda Freeman
Stratocumulus clouds over Mount Shasta
Photo © 2001 Linda Freeman

Stratus

Stratus clouds are low, layered clouds that are generally gray because the drops of water are relatively large. They can fill the sky and make for a gray day. Stratus clouds are commonly found in coastal regions where the air is humid and temperatures are relatively cool. Stratus clouds occur in the Mount Shasta region usually in conjunction with the warm front of wintertime extratropical cyclones.

Stratus clouds over Brewer Creek on Mount Shasta
Photo © 2001 Marc Hoshovsky

Nimbostratus

When the root nimb occurs in a cloud's name it indicates that the cloud produces precipitation. Nimbostratus clouds are associated with warm fronts and drizzly rain.

Nimbostratus clouds and rainbow over Mount Shasta
Photo © 2001 Jane English

Cumulonimbus

The towering puffy clouds that produce precipitation are called cumulonimbus. Their bases are down with the low clouds, but their tops often reach the zone of high clouds. This type of cloud is associated with convective summer thunderstorms or wintertime cold fronts. How can the same kind of cloud appear under such differing circumstances? You can find out more by reading about summer thunderstorms and extratropical cyclones.

Unusual Clouds

Mount Shasta attracts a large following of New Agers. Some of our special clouds and atmospheric phenomenon have helped convince believers of supernatural essences that Mount Shasta is, indeed, one of Earth's major power centers.

Abraham's Tree

Abraham is considered the patriarch of Jews, Christians, and Muslims. The appearance of Abraham's Tree above Mount Shasta is, no doubt, seen as a sign of Mount Shasta's sacredness to some people.

This cloud formation is composed of cirrus clouds fanning out in plumes from a central point. In weather lore, if there appears to be a lake at the base of the fan, then it is a sign of a storm brewing.

Contrails

The term contrail is a contraction of "condensation trail." It typically forms after a jet has sped by, contributing heat, moisture, and particulate matter to the atmosphere. This results in a cloud forming in the trail the jet left behind, making their paths visible. The Shasta Valley provides a natural flight path for aircraft, and so contrails are a common site in the skies above Shasta Valley.

Lenticular Clouds

Mount Shasta is part of the mold that helps shape its clouds. Because Mount Shasta pokes up into the sky above, air is forced to rise above it. Mount Shasta is over 11,000 feet above the valley floor, and so the air is cooled significantly. The height where clouds begin to form indicates where the water vapor has cooled sufficiently to begin condensing out of the air. The lenticular or cap clouds seen above Mount Shasta are formed in this way. Sometimes there are several "saucers" in the air at one time. These clouds form in the "crests" of the wave of air caused by the peaks below or from undulating winds.

Wave Clouds

Kelvin-Helmholtz wave clouds are formed when there are two parallel layers of air that are usually moving at different speeds and in opposite directions. The upper layer of air usually moves faster than the lower layer because there is less friction. In order for us to see this shear layer, there must be enough water vapor in the air for a cloud to form. Even if clouds are not present to reveal the shear layer, pilots need to be aware of invisible atmospheric phenomenon.

Photo of Kelvin-Helmholtz cloud © 2001 Brooks Martner

This special cloud, in conjunction with Mount Shasta, is discussed in the article "Billow Talk" in the November-December 1999 issue of Weatherwise; the Fall 1998 Siskiyou County Scene; and an article entitled "That mysterious cloud" in the Winter 1998/1999 Siskiyou County Scene. A more detailed explanation of wind flow around Mount Shasta is described in "Airborne Doppler Lidar Wind Field Measurements of Waves in the Lee of Mount Shasta" in the May 1988 issue of the Journal of the Atmospheric Sciences. The Kelvin-Helmholtz wave cloud does not last very long because the upper layer of air is usually drier than the lower layer, which results in evaporation of the cloud. Beverly really did "Catch the Wave" when she photographed this spectacular formation over Mount Shasta.

Photo of Kelvin-Helmholtz cloud © 1999 Beverly Shannon

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