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We love clouds.  Melanie is a meteorologist by education, after all.  Not only are clouds themselves fascinating, but their names are mysterious and enigmatic.  We hope to remove some of the mystery from cloud names by providing their etymologies.  Note that we will discuss only scientific names of clouds in this issue.  Folk names for clouds and weather events are "a whole nother thing" which we may discuss in a future issue.

Today's system of classifying clouds comes from a system proposed by Luke Howard in 1803. Either he was very thorough and/or foresightful, or meteorology hasn't changed much since 1803! Actually, since Howard was using morphology (form) to classify clouds, and basic cloud forms are not going to change over 200 years, his system is still applicable.  However, meteorology and especially forecasting have changed dramatically over the last 200 years.

Howard used Latin to name cloud types and characteristics.  If you have some knowledge of Latin, you may be able to figure out what some of the cloud terms mean.

First we should identify the different cloud classifications.  Clouds are classified based on the following:

1. main characteristics (genera)

2. differences in shape and internal characteristics (species)

3. special characteristics of arrangement and/or transparency (varieties)

4. supplementary features and accessory clouds.

There are ten genera:

Cirrus: Latin, "curl, fringe" - cirrus are curled, wispy or feathery high clouds.
Stratus: "layered, in a sheet" from Latin sternere/stranere "to spread out, to flatten" - stratus form low grey sheets across the sky.  In ancient Rome, the word stratum was used for many flat, layered or spread-out objects, including "a bed-covering", " a horse-blanket" and "pavement". In geology, a stratum is a layer of rock.
Cumulus: Latin, "little heap" - the white, fluffy clouds associated with summer days.  We also find the Latin cumulus in accumulate (literally "to heap up").
Cumulonimbus: nimbus with cumuliform characteristics. Nimbus is Latin for "cloud" - in meteorology, nimbus means specifically "rain cloud" - cumulonimbus are large storm clouds, often thunderclouds.
Cirrocumulus: cirrus with small globular elements (instead of being wispy or sheet-like).
Cirrostratus: stratus-like cirrus (cirrus taking on a sheet-like form).
Altocumulus: Latin alto "high" + cumulus - a high sheet of globular elements that are fairly evenly spaced and of uniform size.  Altitude, of course, is related.
Altostratus: high stratus - a fairly uniform sheet of cloud at a relatively high altitude (i.e., not extremely low like stratus).
Nimbostratus: nimbus with stratiform characteristics - in meteorology, nimbus means "rain cloud" and nimbostratus appears as a sheet covering the sky. It is also relatively thick in the vertical direction.  It often produces steady rain which obscures the cloud shape and extent. Sometimes nimbostratus produces rain that evaporates before it hits the ground (see virga, below). The ancients believed that when their gods descended to earth they were surrounded by a shining cloud of glory - nimbus in Latin. That is why the halo around a saint's head is still called a nimbus.
Stratocumulus: stratus with cumulus-like properties - this is stratus that is forming heaps or globules, versus pure stratus, which appears in a fairly uniform sheet.

There are also two other, rarer clouds, which occur mostly at very high latitudes: nacreous clouds (from Latin nacrum "mother of pearl", referring to the iridescence of the clouds); they are found at altitudes of 15-20 miles and are identifiable as remaining lit long after cirrus has gone dark (after sunset).  The other rare cloud is the noctilucent cloud, named from Latin nox "night" and lucere "to shine".  It remains brilliantly lit well after sunset, having an altitude of as much as 50 miles.  These are usually seen only in latitudes above 45°.

There are fourteen species that may be associated with the ten basic genera:

Fibratus: Latin for "fibrous", having a hair-like or filamentous shape.
Uncinus: Latin for "hooked".
Spissatus: Latin for "thickened".
Castellanus: Latin for "castle-like", referring usually to altocumulus having "turrets" or vertical formations.
Floccus: Latin for "tuft of wool, fluff", said of cirrus, cirrocumulus and altocumulus that form a patch or sheet of small tufts with ragged bases.
Stratiform: Latin for "layered"  + forma  "form".
Nebulosus: Latin for "mist-like, nebulous", a cloud showing no distinct details or margins.  In astronomy, a nebula is a cloud of interstellar gas. It was also used to mean a cloud made up of a myriad of stars, though we now tend to call these galaxies (from the Greek galactos, "milk").
Lenticularis: Latin for "little lentil", it is the diminutive form of lens "lentil".  The name implies a lens-shaped cloud, not necessarily a lentil-shaped cloud (though our word lens derives from the shape of the lentil).
Fractus: Latin "broken" (as in fracture, fraction and fractious), referring to ragged clouds.
humilis: Latin "low, of small size, insignificant", referring to fair weather (vertically short) cumulus.  Humility and humble are related.
Mediocris: Latin "of middle or medium quality", applied to cumulus that are larger than humilis but smaller than congestus.  The obvious cognate is mediocre.
Congestus: Latin "to pile up, heap up, accumulate", applied to cumulus whose tops are achieving respectable vertical height and have a cauliflower-like appearance.  English congested comes from the same Latin source and refers to an "accumulation" of phlegm (or, originally, blood).
Calvus: Latin "bald" or "bare", referring to a cumulonimbus which has reached a stage in its development such that its top is starting to lose its cumuliform (cauliflower) shape due to high-speed winds at the altitude of the cloud top.  English callow is thought to be related.  It means "immature" or "inexperienced". Considering that men tend to go bald as they age, this may seem a strange derivation, but callow was applied to baby birds who had no feathers, and the sense of "inexperienced" and "immature" developed from there.
Capillatus: Latin "having hair", referring to a cumulonimbus whose top is growing fibrous or striated, often taking the shape of an anvil.  This stage of development suggests that the cloud was or is producing rain and possibly lightning and hail.  The tiny blood vessels knows as capillaries are so named because they are as thin as a hair.

There are nine varieties which refer to cloud arrangements and transparency:

Intortus: Latin for "twisted, turned", referring to cirrus filaments that seem entangled.  Related words are distort and the legal term tort "injustice".
Vertebratus: Latin for "in the form of vertebrae", used mainly for cirrus that have a fish-skeleton appearance.
Undulatus: Latin for "having waves", said of sheets or patches of clouds that have visible undulations.  Undus, Latin for "wave", is related to the verb undare ("to flow") which gave us inundate - literally "to flood".
Radiatus: Latin for "radiating", clouds that appear to be radiating from one  or two "radiation points".  Other words deriving from radium are radial, radio (which is an abbreviation for radio-telegraphy), radioactive ("radiating ionizing radiation") and there is, of course, radium, the first known radioactive element.
Lacunosus: Latin for "having holes or furrow", a honeycombing effect in a cloud patch, sheet.  Old manuscripts sometimes have lacunae - gaps in the text.
Duplicatus: Latin for "doubled", cloud patches, sheets or layers that occur at slightly different levels, sometimes merging (and so appearing to be "doubled").  Duplicate derives from the Latin word.
Translucidus: Latin for "translucent", said of clouds that are thin enough to allow the shape of the sun or moon to be seen through them.  Translucent is related.
Perlucidus: Latin for "allowing light to pass through", for a large cloud patch or sheet that has distinct, though often very small, clear patches between the elements, allowing sky or overlying clouds to be seen.
Opacus: Latin for "shady, shadowy, dark", opaque clouds that do not allow the sun or moon to be seen at all.  Opaque, of course, comes from the same source.

Finally, there are nine supplementary features and accessory clouds:

Incus: Latin for "anvil", for the anvil-shape that cumulonimbus often acquire to their tops due to high-speed winds in the upper levels of the atmosphere.  There is a tiny anvil-shaped bone in the inner ear called the incus.
Mamma/mammatus/mammatocumulus: Latin for "udder" or "breast", these pendulous formations appear on the undersides of clouds, especially cumulonimbus, and are an indicator of turbulence.  They are sometimes an indicator of severe weather, but not always.
Virga: Latin for "rod, stick, branch", virga is a shaft or trail of precipitation which is visible coming from the base of the cloud but does not reach the ground.  In the U.S., this is most often seen in the West, where the air near the surface is very dry, allowing falling rain to evaporate when it hits the dry boundary.  A striking example of virga occasionally occurs in the Himalayas where snow falls to within a few feet of the ground and then disappears. The Tibetans call this lha'i metog ("flowers of the gods") and consider it highly auspicious.
Praecipitatio: Latin for "a fall", ultimately from prae "before" and caput "head" - "a headlong fall".  It refers, of course, to precipitation that is falling from a cloud .
Arcus: Latin for "bow, arch", a horizontal roll formation on the front of certain clouds, it can often look like an architectural arch.
Tuba: Latin for "trumpet" or "tube", this is simply the Latin term for a tornado, waterspout, or funnel cloud. The instrument called a tuba takes its name from the same Latin word.
Pileus: Latin for "cap", the pileus is a small cloud which forms a cap on the top of a cumuliform cloud.
Velum: Latin for "ship's sail" or "tent flap", a velum is a horizontal, veil-like cloud which a cumuliform cloud may pierce.  The vellum which means "parchment" is not related (and derives from vel, French for "veal").
Pannus: this is the Latin word for what we often call scud (because they scud, or move quickly), shreds of cloud moving beneath a main cloud, but sometimes also part of the main cloud.

These accessory clouds do not have Latin names but are sometimes included in the above group:

Wall cloud: this is English, of course, referring to an obvious lowering of a portion of the base of a large cumulonimbus cloud.  Rotation is often visible within the wall cloud, and wall clouds can produce tornadoes.  This feature was named by Dr. Theodore Fujita because of its appearance - a "wall of cloud". Dr. Fujita is the inventor of the Fujita Scale which measures the strength/destructive power of tornadoes on a scale of F1 (weakest) to F5 (strongest).

Flanking line: again, this is English, and refers to towers of cumulus which grow beside and as a part of a main cumulonimbus cloud.  These grow and then dissipate, and more towers build further down the line, causing the thunderstorm activity to shift down that line. 

Now that you know something about cloud classifications, the following table may be helpful in applying species and varieties to the proper genera:

Note that in meteorology, only the singular form of the Latin terms is used, for example, multiple cirrus are called cirrus and not cirri.

We've just had a fall of snow here, so we're off to find a patch to play in!

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