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   Caju Rains - Light showers in northeast Brazil during the month of October.

   Calina - Local name in Spain of a summer haze which consists of dust particles.

   Canterbury Northwester - A strong, warm and gusty northwest foehn wind which comes down the New Zealand Alps and blows out onto the Canterbury Plains of South Island,  New Zealand.

   Canyon Wind - A wind which blows down the canyon at night due to the cooling of the canyon's walls.  It is a mountain wind.  

   Cap - Cap, which stands for capping inversion, is a layer of comparatively warm air several thousand feet above the ground. A cap either delays or suppresses thunderstorm development.



                                Cap cloud over Mt. Hood by Dennis Stilwell 

   Cap Cloud - A nearly stationary cloud on or just above an isolated mountain peak.

   CAPE - The abbreviation for Convective Available Potential Energy which is a measure of the amount of energy available for convection with higher values indicating greater potential for severe weather.

   Cape Doctor - On the south coast of South Africa, the Cape Doctor is a strong, refreshing southeast wind which results in the formation of the "tablecloth" - a sheet of hill cloud which covers Table Mountain.

Stratocumulus Castellanus cloud

   Castellanus - A species of cloud whose upper part exhibits marked vertical development in the form of turrets or towers which are often taller than they are wide.

   Cavaburd - A thick fall of snow in the Shetland Islands.

   Ceiling - In the practice of U.S. weather observing, the height of the lowest layer of clouds.

   Ceiling Balloon - A small balloon which is used to obtain the height of the cloud base.

   Laser Beam Ceilometer - photo from Flickr  

   Ceilometer - A remote-sensing, automatic instrument which detects the presence of clouds overhead and determines their height.

   Celsius  Temperature  Scale  -  Formerly  known  as  the  centigrade  scale,  this temperature scale has the boiling point of water at 100 degrees and the freezing point at 0 degrees.

   Center Jump - The formation of a second low pressure center which, as it deepens, saps the strength of the original low so that the center of the low seems to jump from the first to the second low pressure center.

   Challiho - Southerly and sometimes violent winds which result in blinding duststorms in India

   Chanduy - At Guayaquil, Ecuador, a cool, descending wind which blows during the dry season from July to November.

   Chili - In Tunisia, a warm and dry descending wind.

   Chinook - The name given to the foehn which blows on the eastern side of the Rocky Mountains in the United States and Canada.  It is often strong and gusty and is warm and dry due to subsidence.

Chinook Arch Cloud

   Chinook Arch - A form of mountain-wave cloud which occasionally forms along the eastern slopes of the Rocky Mountains and may extend in a north-south direction for a couple hundred miles.

   Chou lao hu - This phrase, meaning "autumn tiger", is a term used in northern China for a hot spell after the beginning of autumn.

   Chubasco - On the western coast of Nicaragua and Costa Rica, a severe thunderstorm coming from the land accompanied by violent wind and vivid lightning often most comn in May and October.



              Circumhorizontal Arc by Jeff Medkeff - photo from Flickr.

   Circumhorizontal Arc - A colored arc located at least 46 degrees below the sun or moon and parallel to the horizon.           



Circumscribed Halo (note inner colored halo of 22 degrees

And outer white circumscribed halo).  Photo from Flickr.


   Circumscribed Halo - The name given to the 22 degree tangent arcs when they are fully developed which may occur when the elevation angles of the light source are between 30 degrees and 75 degrees.  At these angles, the lower and upper 22 degree tangent arcs merge and form a halo which is shaped somewhat like a kidney bean and circumscribe (form a circle around) the halo of 22 degrees.




                                  Circumzenithal Arc - Flickr photo.  


   Circumzenithal Arc - a colored arc at least 46 degrees above the sun and centered on the zenith.





   Cirrocumulus - A main cloud genus which appears as a thin, white patch of clouds with no shadows and whose individual elements are like little grains or ripples.



              Sun shining through cirrostratus clouds - photo from Flickr.


   Cirrostratus - A principal cloud genus which looks like a white veil which may be either smooth or fibrous and may cover the entire sky.  It often causes halo phenomena.





   Cirrus - A principal cloud genus composed of ice crystals and usually seen as detached white filaments, narrow bands, or mostly white patches.

   Clear - Condition of the sky when there is less than .1 sky cover.

   Climate - The long-term variation in the weather (including the historical record of average daily and seasonal weather events) at any given location.

   Closed High - An area of high atmospheric pressure (a high) which is completely encircled by at least one isobar.

   Closed Low - An area of low atmospheric pressure (a low) which is completely encircled by at least one isobar.  This term is usually used to refer to a low pressure area aloft and distinguish it from a low pressure trough.

   Cloud - The visible mass of tiny water droplets or ice crystals in the air above the surface of the earth.



                                    Cloudbow, also called a fogbow.                                                                    Photo by  Adrian Brain from Flickr.


   Cloudbow - Sometimes also called a fogbow, is a fairly large and faintly colored arc formed by light (usually sunlight) falling on fog or cloud.

   Cloud Condensation Nuclei  -  Aerosol  particles  which are hygro-scopic (particles around which water readily condenses) and thus serve as the centers (nuclei) of cloud droplets.

   Cloud Flash - A lightning discharge which occurs between a positive charge center and a negative charge center within the same cloud.  This is also called an intracloud flash.

   Cloud Genus - The ten main groups of clouds as defined by the World Meteorological Organization.



                                 Cloud-to-ground Lightning Flash


   Cloud-to-ground Flash - A lightning flash which occurs between a charge center within a cloud and the ground and which begins with a leader coming down toward the ground from the cloud.

   Cloudy - The state of the sky when .7 or more is covered by clouds.

   Cold Front - The boundary between an advancing cold air mass and a retreating relatively warmer air mass.

   Cold High - An anticyclone (high) which has colder air at its center than  it does around its edges. 

   Cold Low - A cyclone (low) which is colder at its center than aound its edges at any given level in the atmosphere.

   Cold Pool - A region of relatively cold air ("pool" of cold air) surrounded by relatively warmer air.

   Cold Wave - A rapid fall of temperature within a period of 24 hours to temperatures which require considerably increased protection to agriculture, commerce, industry, and other activities.

   Colla - A rather strong south or southwest wind accompanied by heavy rain and violent squalls in the Philippines.

   Collada - A north to northwest wind of between 35 and 50 mph in the upper part of the Gulf of California and from the northeast in the lower part.



                                   Wall Cloud with Collar Cloud


   Collar Cloud - A cloud ring sometimes seen at the top of a wall cloud where it is attached to the updraft base above it.

   Colorado Low - A low which first appears on the eastern slopes of the Rocky Mountains in or near Colorado.

   Condensation - The process by which water vapor in the air changes into water droplets in the form of dew, fog, or clouds.

   Confluence - A wind flow pattern in which air flows inward toward an axis which is oriented parallel to the general direction of flow.

   Convection - Vertical transport of heat and moisture with special reference to updrafts and downdrafts in an atmosphere which is unstable.

   Convergence - A condition in the atmosphere which exists when winds cause a net horizontal inflow of air toward a specific region.

   Cooling Degree Day - One cooling degree day is recorded for each degree that the daily mean temperature is above 65 degrees Fahrenheit.  Cooling degree days are used to estimate the energy needed for cooling.

   Coriolis Force - The apparent force due to the earth?s rotation which deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.



                              Moon Corona by Jerry Xiaojin Zhu.


   Corona - A set of one or more colored rings around the sun, moon, or other light source when a veil of thin clouds covers the light source.

   Corona Discharge - A glowing and sometimes audible electrical discharge which occurs from various objects, especially pointed ones, when the electric field strength reaches high values.



        Daytime Crepuscular Rays                  Twilight Crepuscular Rays

                                    Both above photos from Flickr.

   Crepuscular Rays - Crepuscular literally means "twilight" and, thus, crepuscular rays are "twilight rays" of alternating light and dark bands coming from the sun's position at twilight, but the term crepuscular rays has come to be applied to similar rays produced when the sun shines through openings in the clouds at any time of day.                           

   Crest Cloud - A variety of standing cloud which forms either on or above a mountain range or just to the lee of it.




   Cumulonimbus - Frequently called a thunderhead, this "heaped up rain cloud", forms as a result of convection into a tall, billowing mass which is frequently topped by an anvil-shaped cloud.  It usually produces lightning, thunder, heavy rain, and sometimes hail and high winds.



                            Cumulus Cloud by Jeff Kubina from Flickr.


   Cumulus - A principal cloud genus which has a flat base and develops a cauliflower top but to a much lesser extent than the cumulonimbus.



                                             Cumulus Congestus 


   Cumulus Congestus - Literally, a "congested heap".  A cumulus cloud which develops to a sometimes great vertical extent and which, if it continues to develop, often becomes a cumulonimbus 



                                              Cumulus Humilis


   Cumulus Humilis - A "humble heap".  This is the fair weather cumulus which has a small vertical development and a flat base.

   Cut-off High - A warm high (anticyclone) which has become displaced from the main westerly wind flow, lies poleward of this flow, and often becomes a blocking high.  

   Cut-off Low - A cold low (cyclone) which has become cut off from the main westerly flow, lies southward from this flow, and usually is quite slow-moving.

   Cyclogenesis - The development or intensification of a low pressure area.

   Cyclolysis - The weakening of a low pressure area.

   Cyclone - An area of low pressure (a low) around which winds spiral counterclockwise in the Northern hemisphere and clockwise in the Southern Hemisphere.  Cyclone is also the word used for a hurricane in the Indian Ocean and Western Pacific Ocean.

   Cyclonic Circulation - Rotation,  or  circulation  which  is counter-clockwise in the Northern hemisphere and clockwise in the Southern Hemisphere. 

   Darling Shower - In the area of the River Darling in Australia, a duststorm caused by cyclonic winds.

   Dart Leader - After the first stroke in a multiple stroke lightning flash, each succeeding stroke is begun by a continuous leader known as a dart leader.

   Dendritic Crystal - A six-sided (hexagonal) ice crystal, also called a dendrite, which has intricate fern-like or tree-like branching.



                              Minnesota Derecho of July 4, 1999

                            infrared satellite image 5:15 a.m. CDT


   Derecho - A term specifically applied to any family of downburst clusters (thunderstorm clusters producing downburst winds) which are produced by a mesoscale convective complex, or MCC.

   Dew - Moisture which condenses on objects near the ground when the temperature of those objects falls to or below the dew point due to radiational cooling.

   Dew Point - The temperature to which the air needs to be cooled in order for saturation to occur.

   Diamond Dust - Tiny ice crystals falling from what seems to be a cloudless sky.

   Diffluence - Air flowing outward in a fan-like pattern away from a central axis which is oriented parallel to the general wind flow direction.  It is the opposite of confluence.

   Diffraction - A process by which the direction of light rays is changed when passing through the edges of opaque bodies so that the rays seem to be deflected  and thus produce fringes of parallel light and dark or colored bands such as in a corona.

   Dimmerfoehn - A strong but rare south foehn of the Alps in which the strong foehn winds only reach ground level in the plain and lower parts of the valleys.

   Disdrometer - An instrument which measures and records raindrop sizes. 

   Divergence - The spreading out of horizontal winds.

   Doctor - A dry harmattan on the Guinea coast of western Africa which brings relief from the hot and humid onshore winds.

   Dog Days - The period of greatest heat in summer beginning about July 3 and continuing for 40 days.  This period was named for Sirius, the Dog Star, whose spiral rising was believed to be the cause of the hot and humid weather.

    Doister - A severe storm from the sea in Scotland.

   Doppler Effect - Named for Christian Doppler, this is the change in frequency and wavelength of a wave which is "seen" by an observer who is moving relative to the source of the wave. 

   Doppler Radar - A type of radar which uses the Doppler effect to determine the velocity of particles, such as raindrops and hailstones, suspended in the air.  By measuring the frequency shift of the sound waves returning to it compared to the original transmitted frequency, this type of radar can determine whether raindrops, for instance, in a storm are moving toward or away from the radar and at what speed they are traveling toward or away from the radar.

   Downburst - A severe and often damaging localized (between about one-half and 6 miles horizontally) downdraft from a thunderstorm.

   Downdraft  - A usually cool downward-moving air column in a thunderstorm.

   Downslope Wind - A wind which descends a slope and experiences warming and drying as a result of subsidence.

   Downvalley Wind - A nighttime wind which is caused by the nighttime cooling of the valley air due both to cold air draining off the mountain slopes in the early evening and to upward motion with upward cold air advection from convergence of the downslope winds in the valley center.  

   Drizzle - Very small (from about .008 to .02 inch diameter), numerous and slowly falling water droplets.





   Dropsonde - A radiosonde with attached parachute dropped from an airplane and used for taking upper-air soundings.

   Drosometer - An instrument which is used to measure the amount of dew which has formed on a certain surface.

   Drought - A period of abnormally dry weather lasting long enough to cause a serious water imbalance.

   Droxtal - A very tiny ice particle approximately .0004-.0008 inch in diameter formed by direct freezing of supercooled water droplets directly from the vapor form at temperatures below -22 degrees Fahrenheit.

    Dry Adiabatic Lapse Rate - The rate at which dry air cools as it rises.  This rate is 5.5 degrees per 1000 feet.

    Dry Air - In general terms, dry air is air with a low moisture content.

    Dry  Fog  Fog  which  does  not  deposit  any  moisture  on exposed surfaces.

    Dry Freeze - The freezing of vegetation and soil when the air does not contain enough moisture for hoarfrost formation.

    Dry Haze - Haze which occurs when the relative humidity is low.

   Dry Line - A line, or boundary, separating hot and dry air to the west from very warm and moist air to the east.

   Dry Slot - An area of dry and usually fairly cloud free air which wraps into the southern and eastern sections of a synoptic scale or mesoscale low pressure system.

   Dry Tongue - A protrusion of relatively dry air, often associated with the jet stream, into an area of higher moisture content.



                                    Dust Devil - photo from Flickr.


   Dust Devil - A small, well-developed, rapidly rotating wind made visible by dust and other debris it picks up and usually forming on clear, hot, dry afternoons.



                    Leading Edge (Dust Wall) of Dust Storm in Australia


   Dust Storm - An event which arises suddenly and is characterized by strong winds and dust-filled air over a large area.  The leading edge of a dust storm is seen as an advancing dust wall which can be several miles long and nearly a mile deep, and the air ahead of it is hot with light wind.

   Dust Wall - The leading edge of a dust storm appearing as a convex or vertical knobby wall when seen from the clear air ahead of it.




















                                                         Copyright 2006 Ronald Hahn. All Rights Reserved