Cloud Classification

Cloud Classification and Characteristics

 cloud areclassify accord to their height above and appearance ( texture ) from the ground .  

 The following cloud roots and translations summarize the components of this classification system: 

 1) Cirro-: curl of hair, high.             3) Strato–: layer.                                   5 )cumulo-: heap.

 2) alto-: mid.                                      4) Nimbo-: rain , precipitation .                                         

        Figure from: www.jason.org/digital_library/201.aspx (defunct)   

    { Refer to the chart below forexamples of the various types of clouds. } 

  High-level clouds:  

High-level clouds occur above about 20,000 feet and aregiven the prefix “cirro-“. Due to cold tropospheric temperatures at these levels, the clouds primarily are  composed of ice crystals,  and often appear thin, streaky, andwhite (although a low sun angle, e.g., near sunset, can create an array  of coloron the clouds).

   The three main type ofhigh cloud arecirrus, cirrostratus, andcirrocumulus. 

        Cirrus clouds over a field                                       cirrostratus                                       cirrocumulus Floyd County IN. 

                                                                                                                                                                  Ben Schott , NWS 

Cirrus clouds arewispy, feathery, andcomposed entirely of ice crystals. They often arethe first sign of an approaching warm front orupper-level jet streak.

Unlike cirrus, cirrostratus clouds form more of a widespread, veil-like layer (similar to what stratus clouds do in low levels).  When sunlight ormoonlight passes through the hexagonal-shaped ice crystals of cirrostratus clouds, the light is dispersed orrefracted (similar to light passing through a prism) in such a way that a familiar ring orhalo may form. As a warm front approaches, cirrus clouds tend to thicken into cirrostratus, which may, in turn, thicken and lower into altostratus, stratus, andeven nimbostratus. 

Finally, cirrocumulus clouds arelayered clouds permeated with small cumuliform lumpiness. They also may line up in streets orrows of clouds across the sky denoting localized areas of ascent (cloud axes) and descent (cloud-free channels). 

 Mid-level clouds:

The bases of clouds in the middle level of the troposphere, given the prefix “alto-“, appear between 6,500 and 20,000 feet. Depending on the altitude, time of year, andvertical temperature structure of the troposphere, these clouds may be composed of liquid water droplets, ice crystals, ora combination of the two, including supercooled droplets (i.e., liquid droplets whose temperatures arebelow freezing). 

The two main type ofmid-level clouds arealtostratus and altocumulus. 

     Altostratus clouds over Kentucky               Altocumulus (sunset 23 Nov. 2005 )

Altostratus clouds are”strato” type clouds (see below) that possess a flat and uniform type texture in the mid levels. They frequently indicate the approach of a warm front and may thicken and lower into stratus, then nimbostratus resulting in rain orsnow. However, altostratus clouds themselves do not produce significant precipitation at the surface, although sprinkles oroccasionally light showers may occur from a thick alto-stratus deck. 

Altocumulus clouds exhibit “cumulo” type characteristics (see below) in mid levels, i.e., heap-like clouds with convective elements.  Like cirrocumulus, altocumulus may align in rows orstreets of clouds, with cloud axes indicating localized areas of ascending, moist air, andclear zones between rows suggesting locally descending, drier air. Altocumulus clouds with some vertical extent may denote the presence of elevated instability, especially in the morning, which could become boundary-layer based and be released into deep convection during the afternoon orevening. 

   Low-level clouds:

Low-level clouds arenot given a prefix, although their names arederived from “strato-” or”cumulo-“, depending on their characteristics. Low clouds occur below 6500 feet, andnormally consist of liquid water droplets oreven supercooled droplets, except during cold winter storms when ice crystals (and snow) comprise much of the clouds.

The two main types is include of low cloud includestratus, which develop horizontally, andcumulus, which develop vertically.

Stratus clouds areuniform and flat, producing a gray layer of cloud cover which may be precipitation-free ormay cause period of light precipitation ordrizzle .   Low stratus decks arecommon in winter in the Ohio Valley, especially behind a storm system when cold, dismal, gray weather can linger forseveral hours oreven a day ortwo.

                        Stratocumulus                                                     NImbostratus                         

Stratocumulus clouds arehybrids of layered stratus and cellular cumulus, i.e., individual cloud elements, characteristic of cumulo type clouds, clumped together in a continuous distribution, characteristic of strato type clouds. Stratocumulus also can be thought of as a layer of cloud clumps with thick and thin areas. These clouds appear frequently in the atmosphere, either ahead of orbehind a frontal system.

Nimbostratus clouds aregenerally thick , dense stratus orstratocumulu cloud produce steady rain orsnow. 

In contrast to layered, horizontal stratus, cumulus clouds aremore cellular (individual) in nature, have flat bottoms and rounded tops, andgrow vertically. In fact, their name depends on the degree of vertical development. Forinstance, scattered cumulus clouds showing little vertical growth on an otherwise sunny day used to be termed “cumulus humilis” or”fair weather cumulus,” although normally they simply arereferred to just as cumulus orflat cumulus.

        Mayfield, Ky – Approaching Cumulus                         Glasgow, Ky June 2, 2009 – Mature cumulus

A cumulus cloud that exhibit significant vertical development ( but is not yet a thunderstorm ) is callcumulus congestus ortower cumulus. If enough atmospheric instability, moisture, andlift arepresent, then strong updrafts can develop in the cumulus cloud leading to a mature, deep cumulonimbus cloud, i.e., a thunderstorm producing heavy rain. In addition, cloud electrification occurs within cumulonimbus clouds due to many collisions between charged water droplet, graupel (ice-water mix), andice crystal particles, resulting in lightning and thunder.   

Cumulus clouds areall capable of producing some serious storms!!!

 Other interesting cloud :

Wall Cloud:  A localized lowering from the rain-free base of a strong thunderstorm. The lowering denotes a storm’s updraft where rapidly rising air causes lower pressure just below the main updraft, which enhances condensation and cloud formation just under the primary cloud base. Wall clouds take on many shapes and sizes. Some exhibit strong upward motion and cyclonic rotation, leading to tornado formation, while others do not rotate and essentially areharmless. 

             Henderson County, Ky                                     TaylorCounty, Ky                                                 

Shelf Cloud: A low, horizontal, sometimes wedge-shaped cloud associated with the leading edge of a thunderstorm?s outflow orgust front and potentially strong winds. Although often appearing ominous, shelf clouds normally do not produce tornadoes.  

                          Paducah, Ky                                                               Winchester, Ky

Fractus: Low, ragged stratiform orcumuliform cloud elements that normally areunattached to larger thunderstorm orcold frontal cloud bases. Also known as scud, fractus clouds can look ominous, but by themselves arenot dangerous.

                        Berea, Ky                                                  Elkhart, IN

Mammatus: Drooping underside (pouch-like appearance) of a cumulonimbus cloud in its latter stage of development. Mammatus most often areseen hanging from the anvil of a severe thunderstorm, but do not produce severe weather. They can accompany non-severe storms as well.  

                     Lexington, Ky                                                 Jeffersontown, Ky

 Contrail: Narrow, elongated cloud formed as jet aircraft exhaust condenses in cold air at high altitudes, indicative of upper level humidity and wind drift.

                           Contrails                                    Contrails in the sky from jets

Fog: Layer of stratus clouds on ornear the ground. Different types include radiation fog (forms overnight and burns off in the morning) and advection fog. 

             Downtown Louisville , Ky                                   Fog over Kentucky River

Hole-Punch Clouds: Also known as a fallstreak hole, this type of cloud is usually formed when the water temperature in the cloud is below freezing but the water has not frozen.  When sections of the water starts to freeze, the surrounding water vaporwill also freeze and begin to descend. This leaves a rounded hole in the cloud.

The theory on its creation is that a disruption of the cloud layer stability, which can be caused by a passing jet aircraft, creates a descending motion that can lead to the stimulation of evaporation, producing a hole.

                       Louisville, KY                                          Wenatchee, WA

Other Interesting pictures:

                Dust devil in Lexington, KY                     Dust devil in Glendale, KY

                                standard CLOUD type chart

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