| You
wouldn't leave the house without first checking the local weather
forecast. You can get weather information from the FAA (800-WX-BRIEF), TV,
radio, your VHF radio and on the Internet. Even so, at certain times of
the year weather can change rapidly and you should continually keep a
"weather eye" out, especially to the west, in order to foresee
changes which might be impending.
Clouds
are a tool you can use to predict or forecast weather. The type of cloud
and direction of movement can warn you of weather changes that are
imminent. Clouds are categorized by the altitude at which they appear and
the shape that they take.
Note: This is not an in-depth study of clouds,
but an attempt to cover the most important information for use by Powered
Paraglider Pilots.
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Cloud
Group
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Cloud
Height
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Cloud
Types
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High Clouds = Cirrus
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Above 18,000 feet
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Cirrus
Cirrostratus
Cirrocumulus
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Middle Clouds = Alto
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6,500 feet to 18,000 feet
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Altostratus
Altocumulus
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Low Clouds = Stratus
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Up to 6,500 feet
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Stratus
Stratocumulus
Nimbostratus
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Clouds with vertical growth
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Cumulus
Cumulonimbus
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It is
helpful to remember the following definitions of cloud shapes:
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Cumulus meaning "heap, a pile, an accumulation"
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Stratus meaning "spread out, flatten, cover with a
layer"
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Nimbus meaning "rainy cloud"
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Variations
of cloud types are created by combining the cloud's shape/description with
the altitudinal names as a prefix or suffix.
Cirros
(high) or Cirro can be used with cumulus (heap) to indicate
a cirrocumulus or high, lumpy cloud. Cirrocumulus clouds, sometime
called "mackerel skies", can indicate the approach of a
hurricane in the tropics. It can also be used with stratus (flat,
layered) as in cirrostratus to indicate a high, flat or
layered cloud.
Alto
can also be used with cumulus and stratus to indicate altocumulus
and altostratus which are middle altitude lumpy clouds and middle
altitude layered clouds respectively.
Nimbo
or nimbus might be used with cumulus or stratus to
indicate a cloud formation that is producing precipitation. These clouds
could be either cumulonimbus which would be a lumpy,
vertically-rising rain cloud or nimbostratus which would be a sheet
or flat-looking rain cloud.
High
clouds exist above 18,000 feet and are cirrus clouds.
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Cirrus clouds are the most common of the high clouds. They are
composed of ice and consist of long, thin, wispy streamers. Cirrus
clouds are usually white and predict fair weather. Sometimes
called mares tails, they stream with the wind. By watching the
movement of cirrus clouds you can tell from which direction
weather is approaching. The appearance of cirrus clouds usually
indicates that a change in weather will occur within 24 hours.
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Cirrostratus are sheetlike, thin clouds that usually
cover the entire sky. The sun or moon can shine through
Cirrostratus clouds. Cirrostratus clouds usually come 12-24 hours
before a rain or snow storm.
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Cirrocumulus are small, rounded puffs that usually appear
in long rows. They are usually white, but sometimes appear gray.
Cirrocumulus are usually seen in the winter and indicate fair, but
cold, weather. In the tropics, they may indicate an approaching
hurricane.
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Medium
high clouds occupy altitudes of 6,500 feet to 18,000 feet.
These clouds are called alto clouds. Alto clouds are used to
predict weather changes in 6 to 12 hours.
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An Altostratus
cloud usually covers the whole sky. The cloud looks gray or
blue-gray. The sun or moon may shine through an Altostratus cloud,
but will appear hazy. An altostratus cloud usually forms ahead of
storms with continuous rain or snow.
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Altocumulus clouds are grayish-white with one part of
the cloud darker than the other. Altocumulus clouds usually form
in groups. If you see Altocumulus clouds on a warm, sticky
morning, be prepared for thunderstorms by late afternoon.
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Low
clouds, called stratus clouds, are at altitudes up to 6,500 feet.
These clouds form a solid sheet or layer of cloud mass.
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Stratus clouds are uniform gray in color and almost cover the
entire sky. Light mist or drizzle is sometimes associated with
Stratus clouds.
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Stratocumulus clouds are low, lumpy and gray. Most form in
rows with blue sky visible in between. Precipitation rarely occurs
with Stratocumulus clouds, however, in frontal weather they may
turn to Nimbostratus.
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Nimbostratus clouds are dark gray with a ragged base.
Rain or snow is associated with Nimbostratus clouds.
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Clouds
with vertical growth
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Vertically developing clouds are the Cumulus
type. These small, lumpy clouds are low "fair weather"
clouds. However, as they develop vertically (by rising hot air)
they may go from small, fair weather clouds to large, boiling,
vertically-growing monsters called cumulonimbus.
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Cumulonimbus are generally known as thunderstorm clouds.
High winds will flatten the top of the cloud into an anvil-like
shape. Cumulonimbus are associated with heavy rain, snow, hail,
lightning, and tornadoes. The anvil usually points in the
direction the storm is moving.
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If you
still can't remember all of the cloud names and formations, you can always
watch the clouds for two specific weather situations that indicate a high
probability of a storm:
- A "lowering ceiling": This means that
the height of cloud formations continues to get lower and lower,
usually caused by a warm front. As the ceiling lowers you will see
clouds in the following order:
- Cirrus
- Cirrostratus
- Altostratus
- Stratus
- Nimbostratus - storm clouds!
- On the other hand, watch for cumulus (puffy)
clouds that start to rapidly develop vertically to become cumulonimbus
thunderstorm clouds. On hot and humid days, these storms occur over
water as the radiant heat from the land absorbs moisture from nearby
water and rises to produce thunderheads. These storms can also
indicate a cold front and may be preceded by squall lines, a row of
black storm clouds. Wind shifts unpredictably and accelerates
dramatically. Lightning can occur for miles in front of a storm and
after the storm appears to have passed.
Other
things to look for that indicate an approaching weather change:
- Weather changes generally come from the west so
scan the sky with your weather eye, especially to the west.
- A sudden drop in temperature and change in the
wind (increasing winds and/or seas) often means that a storm is near.
- If you have a barometer check it every two to
three hours. A rapid drop in pressure means a storm is approaching.
About
John: "I have been flying ultralights for some time, but I did not have a great understanding of weather. I was always in search of something related to weather that was easy to
understand. I went on the Internet looking for weather related material. With lots of research and no luck I called a meteorologist that pointed me in the right direction. What I came up with is weather
101. Flying powered paragliders and knowing what type of weather you should fly in will not only insure a enjoyable flight but a safe flight as well."
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