Lenticular Clouds over Plymouth, NH
Plymouth State University Meteorology Program Cloud Boutique
The Plymouth State Meteorology Program has developed this
server to provide explanations of and access to detailed pictures of some
basic cloud forms. The cloud images are relatively large (640x480) in order
to show detailed structure and features. All of these pictures were taken
in the local area around Plymouth, New Hampshire and most from the weather
observation deck on the roof of the Boyd Science Center on the
Plymouth State campus. Clouds
can move and change shape quickly as indicated in this 30 minute time-lapse
mpeg video loop. The purpose of this "boutique"
is to provide a general cloud reference and is not intended to provide
an all-inclusive list. Images will be added to or changed as opportunities
permit.
Cloud Classification
Clouds are generally classified based on characteristics, such as, altitude,
appearance, or origin. Altitude distinctions apply to those clouds that
fit in various layers of the atmosphere as follows:
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high clouds - have bases above 18,000 feet
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middle clouds - have bases between 7,000 and 18,000 feet
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low clouds - have bases below 7,000 feet
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fog - cloud in contact with the ground
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multi-level clouds... vertically thick spanning multiple layers
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orographic clouds - distinct clouds that form via interaction between wind
and mountainous terrain features
In appearance, clouds may be thick or thin, have well defined edges or
be very diffuse, appear hairlike, cellular, towering, or in sheets, and
be associated with fair weather or precipitation. Most clouds owe their
existence to upward vertical motion of air, hence they are often associated
with weather producing phenomena, such as fronts, troughs, and low pressure
systems. However, topography can also help move air upwards and produce
clouds.
Cloud Descriptions and Pictures
This section provides verbal descriptions and pictures of clouds that have
been observed in this area. Because of their size, these images have been
stored in JPG format. To view a picture, click on the appropriate cloud
name or other highlighted text.
High Clouds are primarily composed of ice crystals and include the following:
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Cirrus are high altitude wispy clouds. They are usually
quite thin and often have a hairlike or filament type of appearance. The
curled up ends as depicted in this picture are very common features.
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Cirrocumulus are high clouds that have a distinct patchy and/or wavelike
appearance, such as, in our patchwork cirrocumulus photo,
composed of many individual cloud elements, or in our wavy
cirrocumulus photo with its banded linear structure. These features
are common to all types of cumuloform clouds.
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Cirrostratus are high clouds that usually blanket
the sky in ill-defined sheets. These clouds are usually optically thin
and the sun and moon can usually shine some light through. Like other stratiform
clouds, one usually can't detect distinct cells or sharp features. This
picture shows the sun shining through a gray, diffuse cirrostratus overcast.
Middle clouds have many similarities to the cumuloform and stratiform
high clouds. Since they are closer to a groundbased observer, the cumuloform
elements in particular appear larger than their high cloud counterparts.
They can contain ice crystals and/or water droplets and may occasionally
be associated with some light precipitation.
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Altocumulus have distinct cloud elements and are
either in a patchy, scattered distribution or can appear in linear bands.
The altocumulus in this photo by Jay Shafer consists of a number of individual cloud
elements. Jay also took this beautiful sunset
photo of altocumulus clouds.
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Altostratus have a more uniform and diffuse coverage
where it is difficult to detect individual elements or features. In this
picture, a few altocumulus clouds in the foreground precede a more uniform
deck (see arrow) of altostratus.
Low clouds are most often composed of water droplets, but can have
ice crystals in colder climates. Some of these clouds can develop into
the multi-level clouds and can go through various phases, such as, a morning
stratus deck turning into late morning stratocumulus, then early afternoon
cumulus, and vertical development into cumulonimbus which can produce heavy
rain and possible lightning and thunder.
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Cumulus are usually puffy and often have very distinct
edges and usually a noticeable vertical development. They often have a
popcorn-like appearance. Cells can be rather isolated or they can be grouped
together in clusters as shown in this photo. The
main cumulus cloud pictured in this view was nearly
overhead, so the vertical extent is hidden from view. However, since the
sun is on the other side of the cloud, its thickness is evident from the
negligible amount of light passing through its center.
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Stratocumulus can be widely scattered (as depicted in this
photo, but are usually concentrated closer together in clusters or layers
and have very little vertical development. This photo of a stratocumulus layer
from above was taken by Jay Shafer, a Plymouth State meteorology graduate, from Mt. Washington. Jay also
went down to a lower elevation and took another photo providing a closeup, side view
of a stratocumulus cloud in this deck. These relatively flat clouds usually lack
the sharp edges and "popcorn" appearance of most normal cumulus clouds.
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Stratus are usually the lowest of the low clouds.
Stratus often appear as an overcast deck (as shown), but can be scattered.
The individual cloud elements have very ill-defined edges compared to most
low cumuloform clouds (e.g. cumulus and stratocumulus).
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Fog can be considered as a low stratus cloud in contact
with the ground. When the fog lifts, it usually becomes true stratus. This
photo shows fog over the Pemigewasset River basin with clear skies elsewhere.
Multi-layer clouds are the heavy precipitation producers. The depth
of these clouds give precipitation hydrometeors a better environment to
develop and grow.
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Nimbostratus are often included in many texts as
low clouds, but here they are considered multi-layer clouds because their
vertical extent often goes well into the middle cloud region and these
clouds often have even taller cumulonimbus clouds embedded within them.
The clouds are very dark, usually overcast, and are associated with large
areas of continuous precipitation. If it's a gray and rainy day as shown
in this photo, the sky most will most likely be filled with nimbostratus
clouds.
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Cumulonimbus, as shown in this photo (with cumulus
in the foreground), are the clouds that can produce lightning, thunder,
heavy rains, hail, strong winds, and tornadoes. They are the tallest of
all clouds that can span all cloud layers and extend above 60,000 feet.
They usually have large anvil-shaped tops (as shown) which form because
of the stronger winds at those higher levels of the atmosphere. This first
"cb" picture was taken by Plymouth State student Bill Schmitz from an airplane outside
of the New York City area--note the three smaller turrets developing.
Another picture shows a view from the ground of a cumulonimbus
with a base at around 3,000 feet and vertical development upward to
around 30,000 feet - small compared to most thunderstorms which are
associated with really severe weather. Sometimes, strong cumulonimbus
clouds can have appendages protruding from the base of the cloud, which
are called "mammatus" clouds because they
resemble the mammary glands of mammals. They indicate that the atmosphere
is quite unstable and can also be an indicator of impending severe weather.
The picture of mammatus clouds, shown here, was taken by Mark Gibbas, a Plymouth State
meteorology alumnus, at Acadia National Park. Additional mammatus photos have also
been submitted by Cindy Shannon (image) and Robert Himes (image)
Orographic clouds, as the name implies, are produced by the flow
of air interacting with mountainous terrain.
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Cap clouds form when air containing water vapor is uplifted
on the windward slide of the slope and reaches saturation producing liquid
water cloud droplets and a cloud which can "cap" the summit. The spectacular picture
was provided by Michael Nahmias and shows the cap cloud shrouded summit of Mt. Rainier.
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Lenticular clouds are lens-shaped clouds that can
result from strong wind flow over rugged terrain. At the time of this photo,
the winds were blowing around 30-40 mph from right to left, forming several
lenticular clouds. Sometimes they stack up like pancakes in multiple layers
as are several depicted in this first photo. The strong flow produces a
distinct up and down wavelike pattern on the lee side of the mountain or
large hill and the lenticular clouds tend to form at the peaks of these
waves. They sometimes are very round and the edges are so well defined
that they resemble flying saucers. This close
up sequence shows a large lenticular cloud at various stages of illumination
as the sun moved lower on the horizon and lit the cloud from below. Another
lenticular cloud can be seen in the background of the last frame of the
sequence. These photos were taken on January 25, 1999 in Plymouth, NH,
by James D. Rufo, a Plymouth State meteorology graduate. Mrs. Lorraine Brown of Bristol
NH captured this same cloud formation from about 20-25 miles further away
in these pictures. Lenticular clouds
are often placed into the middle cloud category since they are most common
at those altitudes. Plymouth State meteorology graduate, Jay Shafer, has also provided
some stunning additional lenticular pictures taken around
the White Mountain region of New Hampshire.
Another "specialty" cloud is one that can develop due to Kelvin-Helmholtz
(K-H) instability waves and subharmonic resonance with other waves in the
atmosphere. This can result in an intertwined or spiral cloud pattern as
shown in this picture, which was also taken
by James D. Rufo. H-H instability is the result of strong wind shear. K-H
clouds that form in early stages can resemble well-organized waves that
appear to be breaking like ocean waves.
Another type of cloud can be formed from the vapor contained in the
exhaust of a jet engine of an airplane when they are flying at high enough
altitudes where cold temperatures cause the vapor to turn into ice crystals
like cirrus clouds. These clouds are called "contrails"
(short for "condensation trails") and look like lines in the sky. The photo
shows two contrails. The one on the lower right was formed by a jet that
flew a few minutes ahead of the jet which formed the contrail in the center.
The newer contrail is narrower and hasn't had the chance to diffuse like
the older one.
Return to Plymouth State Weather Center
Another useful cloud information resource is the U
of Illinois Cloud Catalog.
For more information or comments, contact Jim
Koermer at koermer@mail.plymouth.edu.