Zenith City Weekly
Most of us have looked for shapes in the passing clouds, but cloud watching is also a great way to try your hand at amateur meteorology. Upcoming weather conditions are virtually always indicated by the many different types of clouds (or lack thereof).
Cirrus. Visible year-round, these form at least three miles aboveground, at altitudes with very cold temperatures. They are composed of ice crystals and are frequently the first sign of an approaching storm. But they can also indicate the dissipation of a storm, when cloud particles are blown off the top of a storm by strong winds.
Stratus. Also visible year-round, these are par for the course on dreary days. They generally form in large, flat layers close to the ground. They frequently block out the sun and can be made up of either water droplets or ice crystals, depending on the temperature.
Contrails. Short for condensation trail, these are man-made clouds that form high in the atmosphere when water vapor from a jet’s exhaust condenses into ice crystals. They begin as thin, bright lines in the sky and then spread out over time. Gusty winds break them up faster, in what is known as diffusion. They are visible year-round and are most common near heavy air traffic.
Contrails are the subject of a conspiracy theory that the water vapor is really “chemtrails,” from planes dousing us with a chemical agent. Conspiracists cite as evidence that contrails sometimes last a long time—which is true in humid conditions.
Contrails form at altitudes too high for chemical spraying to be effective. For example, planes spraying aerial pesticides fly only about 10 to 15 feet off the ground; contrails form at 26,000 feet and higher. Chemicals released at that height would dissipate before reaching the ground.
Altocumulus. Visible year-round, these middle altitude clouds indicate rising warm air and increasing water vapor in the atmosphere, frequently in advance of an approaching storm. They form one to three miles above the earth, comprised mostly of water droplets, making their presence at sunrise or sunset a beautiful sight.
Fog. Yes, fog is a cloud. It’s a ground-level cloud that forms when there’s less than four degrees’ difference between the air temperature and the dew point. It can form at any time of year, but we most often see it in the spring when cool, moist air blows in off Lake Superior. Made up entirely of water droplets, it can also form from ice crystals in very cold conditions, thus being called “ice fog.”
Cumulus. The best type for seeing shapes, these classic clouds are common on beautiful, fair weather days. They form at low altitudes, most commonly in the summer, but they can be seen year-round. The upper portions of taller clouds are made up of ice crystals.
Cumulonimbus. Only seen during the warmer months, these are the tallest clouds of all, often rising to 70,000 feet. They originate when a towering cumulus cloud keeps growing until it flattens out at the top into an anvil shape as the cloud pushes up against the stratosphere, the second layer of the earth’s atmosphere. The stable air of the stratosphere resists the encroaching cloud, causing the shape. These clouds can turn into severe thunderstorms with heavy rain, flash flooding, large hail, cloud-to-ground lightning, destructive straight-line winds, and tornadoes.
Mammatus. Seen during the warmer months, these resemble the udders of a cow hanging down towards the earth. The air that makes cumulonimbus clouds so tall can also push clouds downward into such shapes. They often form from well-developed thunderstorms, but can also be seen when severe weather is not imminent.
Shelf. Shelf clouds are formed when rain at the front of a storm pushes out cooler air. Thus, these broad clouds function as the leading edge of thunderstorms.
Mesocyclones. All thunderstorms rotate, but mesocyclones are the rotating updraft of a supercell thunderstorm. They’re not a cloud, but typically originate within clouds and stretch down towards the ground.
Scud. Scud clouds tend to exist below most of the clouds of a thunderstorm, hanging down closer to the earth. They develop when humid air is lifted into cooler air. They are generally seen below shelf clouds or wall clouds and can look very threatening. They are often mistaken for funnel clouds, but do not pose a hazard.
Wall. Seen most often at the back end (southwest corner) of severe thunderstorms, wall clouds result when a rotating mesocyclone drops beneath the base of a cumulonimbus cloud. A wall cloud is the portion of the cloud base that appears to drop closer towards the earth. Most funnel clouds and tornadoes come from wall clouds, but many wall clouds produce neither. The sight of a wall cloud may be cause for taking shelter, and persistent wall clouds are even more dangerous.
There is a wide range of clouds not covered here, but these are some we may see next month. Look for a toasty, dry August (five degrees above average and one inch below average), with thunderstorms. You might be able to identify some of the above-mentioned cloud formations, but when the thunder roars, get indoors.