Accessory CloudA cloud which is dependent on a larger cloud system for development and continuance. Roll clouds, shelf clouds, and wall clouds are examples of accessory clouds.ACLDAbove Cloud LevelAlberta ClipperA fast moving low pressure system that moves southeast out of Canadian Province of Alberta (southwest Canada) through the Plains, Midwest, and Great Lakes region usually during the winter. This low pressure area is usually accompanied by light snow, strong winds, and colder temperatures. Another variation of the same system is called a "Saskatchewan Screamer".AnticyclogenesisThe formation or intensification of an anticyclone or high pressure center.AnticycloneA large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern HemisphereAnticyclonic RotationRotation in the opposite sense as the Earth's rotation, i.e., clockwise in the Northern Hemisphere as would be seen from above. The opposite of cyclonic rotation.AquicludeIn hydrologic terms, a formation which contains water but cannot transmit it rapidly enough to furnish a significant supply to a well or spring.Banner CloudA cloud plume often observed to extend downwind behind isolated mountain peaks, even on otherwise cloud-free days.Baroclinic leaf shieldA cloud pattern on satellite images - frequently
noted in advance of formation of a low pressure center.Baroclinic ZoneA region in which a temperature gradient exists on a constant pressure surface. Baroclinic zones are favored areas for strengthening and weakening systems; barotropic systems, on the other hand, do not exhibit significant changes in intensity. Also, wind shear is characteristic of a baroclinic zone.BaroclinityA measure of the state of stratification in a fluid in which surfaces of constant pressure (isobaric) intersect surfaces of constant density (isosteric).Billow CloudA cloud consisting of broad parallel bands oriented perpendicular to the wind.Cap CloudA stationary cloud directly above an isolated mountain peak, with cloud base below the elevation of the peak.CCLConvective Condensation Level- The level in the atmosphere to which an air parcel, if heated from below, will rise dry adiabatically, without
becoming colder than its environment just before the parcel becomes saturated. See Lifted Condensation Level
(LCL).CLAn abbreviation used on climate outlook maps issued by CPC to indicate areas where equal chances of experiencing below-normal, normal, and above-normal conditions are possible.Class I AreasGeographic areas designated by the Clean Air Act where only a small amount or increment of air quality deterioration is permissible.CLDCloud- A visible aggregate of minute water droplets or ice particles in the atmosphere above the Earth's surface.Clear Air Turbulence(CAT) - In aviation, sudden severe turbulence occurring in cloudless regions that causes violent buffeting of aircraft.Clear IceA thin coating of ice on terrestrial objects, caused by rain that freezes on impact. The ice is relatively transparent, as opposed to rime ice, because of large drop size, rapid accretion of liquid water, or slow dissipation of latent heat of fusion.Clear SlotWith respect to severe thunderstorms, a local region of clearing skies or reduced cloud cover, indicating an intrusion of drier
air; often seen as a bright area with higher cloud bases on the west or southwest side of a wall
cloud. A clear slot is believed to be a visual indication of a rear flank downdraft.Client AgencyAs used in connection with reimbursable National Weather Service (NWS) fire
weather services, a public fire service or wildlands management agency, Federal or non-Federal,
which requires and uses NWS fire and forestry meteorological servicesClimateThe composite or generally prevailing weather conditions of a region, throughout the year, averaged over a series of years.Climate ChangeA non-random change in climate that is measured over several decades or longer. The change may be due to natural or human-induced causes.Climate Diagnostics Bulletin(CDB) - The monthly CPC Bulletin reports on the previous months' status of the ocean-atmosphere climate system and provides various seasonal ENSO-related outlooks. It is issued by the fifteenth of the month.Climate Diagnostics Center(CDC) - The mission of NOAA's Climate Diagnostics Center is to identify the nature and causes for climate variations on time scales ranging from a month to centuries.Climate ModelMathematical model for quantitatively describing, simulating, and analyzing the interactions between the atmosphere and underlying surface (e.g., ocean, land, and ice).Climate OutlookA climate outlook issued by the CPC gives probabilities that conditions, averaged over a specified period, will be below-normal, normal, or above-normal.Climate Prediction CenterThis Center is one of several centers under the National Centers for Environmental Prediction (NCEP) part of the National Weather Service (NWS) in the National Oceanic and Atmospheric Administration (NOAA). The Center serves the public by assessing and forecasting the impacts of short-term climate variability, emphasizing enhanced risks of weather-related extreme events, for use in mitigating losses and maximizing economic gains.Climate SystemThe system consisting of the atmosphere (gases), hydrosphere (water), lithosphere (solid rocky part of the Earth), and biosphere (living) that determine the Earth's climate.Climatological OutlookAn outlook based upon climatological statistics for a region, abbreviated as CL on seasonal outlook maps. CL indicates that the climate outlook has an equal chance of being above normal, normal, or below normal.ClimatologyThe science that deals with the phenomena of climates or climatic conditions.CLIMOClimatology/ClimatologicalClimometerAn instrument that measures angles of inclination; used to measure cloud ceiling heights.Closed BasinA basin draining to some depression or pond within its area, from which water is lost only by evaporation or percolation. A basin without a surface outlet for precipitation falling precipitation.Closed Basin Lake FloodingFlooding that occurs on lakes with either no outlet or a relatively small one. Seasonal increases in rainfall cause the lake level to rise faster than it can drain. The water may stay at flood stage for weeks, months, or years.Closed LowA low pressure area with a distinct center of cyclonic circulation which can be completely encircled by one or more isobars or height contour lines. The term usually is used to distinguish a low pressure area aloft from a low-pressure trough. Closed lows aloft typically are partially or completely detached from the main westerly current, and thus move relatively slowly (see Cutoff Low).Cloud(abbrev. CLD) A visible aggregate of minute water droplets or ice particles in the atmosphere above the Earth's surface.Cloud CeilingSame as Ceiling; the height of the cloud base for the lowest broken or overcast cloud layer. Cloud Condensation NucleiSmall particles in the air on which water vapor condenses and forms cloud droplets.Cloud LayerAn array of clouds whose bases are at approximately the same level.Cloud MovementThe direction toward which a cloud is movingCloud StreetsRows of cumulus or cumulus-type clouds aligned parallel to the low-level flow. Cloud streets sometimes can be seen from the ground, but are seen best on satellite photographs.Cloud TagsRagged, detached cloud fragments; fractus or scud.CloudyWhen 7/8ths or more of the sky is covered by clouds.CLRClearCLRGClearingClutterRadar echoes that interfere with observation of desired signals on the radar display.Cold OcclusionA frontal zone formed when a cold front overtakes a warm front and, being colder than the air ahead of the warm front, slides under the warm front, lifting it aloft. Compare with warm occlusion.Collar CloudA generally circular ring of cloud that may be observed on rare occasions surrounding the
upper part of a wall cloud.
This term sometimes is used (incorrectly) as a synonym for wall cloud. Comma CloudA synoptic scale cloud pattern with a characteristic comma-like shape, often seen on satellite photographs associated with large and intense low-pressure systems.Convective CloudsThe vertically developed family of clouds are cumulus and cumulonimbus. The height of their bases range from as low as 1,000 feet to a bit more than 10,000 feet.
Clouds with extensive vertical development are positive indications of unstable air. Strong upward currents in vertically developed clouds can carry high concentrations of supercooled
water to high levels where temperatures are quite cold. Upper portions of these clouds may be composed of water and ice.CYCLGNCyclogenesis - The formation or intensification of a cyclone or low-pressure storm system.Cyclic StormA thunderstorm that undergoes cycles of intensification and weakening (pulses)
while maintaining its individuality. Cyclic supercells are capable of producing multiple tornadoes (i.e.,
a tornado family) and/or several bursts of severe weather.Cyclogenesis(Abbrev. CYCLGN) - The formation or intensification of a cyclone or low-pressure storm system.Cyclone(abbrev. CYC) - A large-scale circulation of winds around a central region of low atmospheric pressure, counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.Cyclonic CirculationCirculation (or rotation) which is in the same sense as the
Earth's rotation, i.e., counterclockwise (in the Northern Hemisphere) as would be seen from above. Nearly
all mesocyclones and strong or violent tornadoes exhibit cyclonic rotation, but some smaller vortices, such as
gustnadoes, occasionally rotate anticyclonically (clockwise). Compare with anticyclonic rotation.Daily Climatological ReportAs the name indicates, this climatological product is issued daily by each National Weather Service office. Most of the climatological data in this report are
presented in a tabular form; however, some narrative statements may also be used in the product. The report is organized so that similar items are grouped together (i.e., temperature,
precipitation, wind, sunrise and sunset times, etc.).Debris CloudA rotating "cloud" of dust or debris, near or on the ground, often appearing
beneath a condensation funnel and surrounding the base of a tornado.
This term is similar to dust whirl, although the latter typically refers to a circulation which contains
dust but not necessarily any debris. A dust plume, on the other hand, does not rotate. Note that a
debris cloud appearing beneath a thunderstorm will confirm the presence of a tornado, even in the
absence of a condensation funnel.DeclinationThe latitude that the sun is directly over at a given time. The declination is ~23°N at the summer solstice, ~23°S at the winter solstice, and 0° (over the equator) at the spring and autumn equinoxes.Diurnal CyclesVariations in meteorological parameters such as temperature and relative humidity over the course of a day which result from the rotation of the
Earth about its axis and the resultant change in incoming and outgoing radiation.EXCLDExcludeExclusive Flood Control Storage CapacityIn hydrologic terms, the space in a reservoir reserved for the sole purpose of regulating flood inflows to abate flood damageExtratropical CycloneA cyclone in the middle and high latitudes often being 2000 kilometers in diameter and usually containing a cold front that extends toward the equator for hundreds of kilometers.Few CloudsAn official sky cover classification for aviation weather observations, descriptive of a sky cover of 1/8 to 2/8. This is applied only when obscuring phenomenon aloft are
present--that is, not when obscuring phenomenon are surface-based, such as fog.Funnel CloudA condensation funnel extending from the base of a towering cumulus or Cb, associated with a rotating column of air that is not in contact with the ground (and hence different from a tornado). A condensation funnel is a tornado, not a funnel cloud, if either a) it is in contact with the ground or b) a debris cloud or dust whirl is visible beneath it.Gravity Recovery and Climate Experiment (GRACE)NASA satellites that detect small changes in the Earth’s gravitational field caused by the redistribution of water on and beneath the land surface.Great Circle TrackA great-circle track is the shortest distance between two points on a sphere, and when viewed on a 2-dimensional map the track will appear curved. Swell waves travel along routes that mark out great circles. Ground ClutterA pattern of radar echoes from fixed ground targets (buildings, hills, etc.) near
the radar. Ground clutter may hide or confuse precipitation echoes near the radar antenna.High CloudsThese clouds have bases between 16,500 and 45,000 feet in the mid latitudes. At this
level they are composed of primarily of ice crystals. Some clouds at this level are cirrus,
cirrocumulus, and cirrostratusHydrologic CycleThe description of the transport of water substance between the earth, the atmosphere, and the seas.
In hydrologic terms, the natural pathway water follows as it changes between liquid, solid, and gaseous states.Ice NucleusAny particle that serves as a nucleus in the formation of ice crystals in the atmosphere.In-Cloud Lightning(abbrev. IC) Lightning that takes place within the cloud.Iridescent CloudsClouds that exhibit brilliant bright spots, bands, or borders of colors, usually red and green, observed up to about 30 degrees from the sun. The coloration is due to the diffraction with small cloud particles producing the effect. It is usually seen in thin cirrostratus, cirrocumulus, and altocumulus clouds.LCD (Local Climatological Data)This National Climatic Data Center (NCDC) publication is produced monthly and annually for some 270 United States cities and it's territories. The
LCD summarizes temperature, relative humidity, precipitation, cloudiness, wind speed and direction observation. LCL1. Abbreviation for "local" or "locally"
2. Lifting Condensation Level - the level at which a parcel of moist air becomes saturated when it is lifted dry adiabatically.Lenticular CloudA very smooth, round or oval, lens-shaped cloud that is often seen, singly or stacked in groups, near or in the lee of a mountain ridge.Mammatus CloudsRounded, smooth, sack-like protrusions hanging from the underside of a cloud (usually a thunderstorm anvil). Mammatus clouds often accompany severe thunderstorms, but do not produce severe weather; they may accompany non-severe storms as well.MesoclimateThe climate of a small area of the earth's surface which may differ from the general climate of the district.Mesocyclone(abbrev. MESO)- A storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often on the eastern, or front, flank of an HP storm). The circulation of a mesocyclone covers an area much larger than the tornado that may develop within it. Properly used, mesocyclone is a radar term; it is defined as a rotation signature appearing on Doppler radar that meets specific criteria for magnitude, vertical depth, and duration. It will appear as a yellow solid circle on the Doppler velocity products. Therefore, a mesocyclone should not be considered a visually-observable phenomenon (although visual evidence of rotation, such as curved inflow bands, may imply the presence of a mesocyclone).MicroclimateThe climate of a small area such as a cave, house, city or valley that may be different from that in the general region.Middle Clouds(or Mid-Level Clouds) - A term used to signify clouds with bases between 6,500 and 23,000 feet. At the higher altitudes, they may also have some ice crystals, but they are composed mainly of water droplets. Altocumulus, altostratus, and nimbostratus are the main types of middle clouds. This altitude applies to the temperate zone. In the polar regions, these clouds may be found at lower altitudes. In the tropics, the defining altitudes for cloud types are generally higher. Monthly Climatological ReportThis climatological product is issued once a month by each
National Weather Service office. It is a mix of tabular and narrative information. It is organized so
that similar items are grouped together (i.e., temperature, precipitation, wind, heating/cooling
degree information, etc.). Mostly ClearWhen the 1/8th to 2/8ths of the sky is covered by with opaque (not transparent) clouds. Sometimes referred to as Mostly Sunny if this condition is present during daylight hours.Mostly CloudyWhen the 6/8th to 7/8ths of the sky is covered by with opaque (not transparent) clouds. Same as Considerable Cloudiness. Mount Wilson Magnetic ClassificationsIn solar-terrestrial terms, a classification system for sunspots:
Nacreous CloudsClouds of unknown composition that have a soft, pearly luster and that form at altitudes about 25 to 30 km above the Earth's surface. They are also called "mother-of-the-pearl clouds."National Climatic Data CenterThe agency that archives climatic data from the National Oceanic and Atmospheric Administration, as well as other climatological organizations.Noctilucent CloudsWavy, thin, bluish-white clouds that are best seen at twilight in polar latitudes. They form at altitudes about 80 to 90 km above the Earth's surface.Occluded FrontA composite of two fronts, formed as a cold front overtakes a warm or quasi-stationary front. Two types of occlusions can form depending on the relative coldness of the air behind the cold front to the air ahead of the warm or stationary front. A cold occlusion results when the coldest air is behind the cold front and a warm occlusion results when the coldest air is ahead of the warm front.Occluded MesocycloneA mesocyclone in which air from the rear-flank downdraft has completely enveloped the circulation at low levels, cutting off the inflow of warm unstable low-level air.Particle Trajectory ModelA computer sub-model that tracks the trajectories of multiple particles that are released into an atmospheric flow model.Partly CloudyBetween 3/8 and 5/8 of the sky is covered by clouds.Positive Cloud to Ground LightningA CG flash that delivers positive charge to the ground, as opposed to the more common negative charge. Positive CGs have been found to occur more frequently in some severe thunderstorms. Their occurrence is detectable by most lightning detection networks, but visually it is not considered possible to distinguish between a positive CG and a negative CG. (Some claim to have observed a relationship between staccato lightning and positive CGs, but this relationship is as yet unproven.)Probability of Tropical Cyclone ConditioThe probability, in percent, that the cyclone center will pass within 50 miles to the
right or 75 miles to the left of the listed location within the indicated time period
when looking at the coast in the direction of the cyclone's movement.PTCLDYPartly CloudyRoll CloudA low, horizontal tube-shaped arcus cloud associated with a thunderstorm gust front (or sometimes with a cold front). Roll clouds are relatively rare; they are completely detached from the thunderstorm base or other cloud features, thus differentiating them from the more familiar shelf clouds. Roll clouds usually appear to be "rolling" about a horizontal axis, but should not be confused with funnel clouds.Rope CloudIn satellite meteorology, a narrow, rope-like band of clouds sometimes seen on satellite images along a front or other boundary. The term sometimes is used synonymously with rope or rope funnel.Rotor CloudA turbulent altocumulus cloud formation found in the lee of some mountain barriers when winds cross the barrier at high speed. The air in the cloud rotates around an axis parallel to the range. Also called a roll cloud.Shelf CloudA low, horizontal wedge-shaped arcus cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). Unlike the roll cloud, the shelf cloud is attached to the base of the parent cloud above it (usually a thunderstorm). Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn.Solar CycleIn solar-terrestrial terms, the approximately 11-year quasi-periodic variation in frequency or number of solar active events.SPCLYEspeciallySubtropical CycloneA non-frontal low pressure system that has characteristics of both tropical and extratropical cyclones. This system is typically an upper-level cold low with circulation extending to the surface layer and maximum sustained winds generally occurring at a radius of about 100 miles or more from the center. In comparison to tropical cyclones, such systems have a relatively broad zone of maximum winds that is located farther from the center, and typically have a less symmetric wind field and distribution of convection.Sunspot Group Classification
- Alpha: Denotes a unipolar sunspot group.
- Beta: A sunspot group having both positive and negative magnetic polarities, with a simple and distinct division between the polarities.
- Beta-Gamma: A sunspot group that is bipolar but in which no continuous line can be drawn separating spots of opposite polarities.
- Delta: A complex magnetic configuration of a solar sunspot group consisting of opposite polarity umbrae within the same penumbra.
- Gamma: A complex active region in which the positive and negative polarities are so irregularly distributed as to prevent classification as a bipolar group.
Tail CloudA horizontal, tail-shaped cloud (not a funnel cloud) at low levels extending from the precipitation cascade region of a supercell toward the wall cloud (i.e., it usually is observed extending from the wall cloud toward the north or northeast). The base of the tail cloud is about the same as that of the wall cloud. Cloud motion in the tail cloud is away from the precipitation and toward the wall cloud, with rapid upward motion often observed near the junction of the tail and wall clouds. Compare with beaver tail, which is a form of inflow band that normally attaches to the storm's main updraft (not to the wall cloud) and has a base at about the same level as the updraft base (not the wall cloud).ThermoclineAs one descends from the surface of the ocean, the temperature remains nearly the same as it was at the surface, but at a certain depth temperature starts decreasing rapidly with depth. This boundary is called the thermocline. In studying the tropical Pacific Ocean, the depth of 20ºC water ("the 20ºC isotherm") is often used as a proxy for the depth of the thermocline. Along the equator, the 20ºC isotherm is typically located at about 50 m depth in the eastern Pacific, sloping downwards to about 150 m in the western Pacific.Tidal CycleThe periodic changes in the intensity of tides caused primarily by the varying relations between the earth, moon, and sun.Tropical CycloneA warm-core, non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters with organized deep convection and a closed surface wind circulation about a well-defined center.Tropical Cyclone Plan of the DayA coordinated mission plan that tasks operational weather reconnaissance requirements during the next 1100 to 1100 UTC day or as required, describes reconnaissance flights committed to satisfy both operational and research requirements, and identifies possible reconnaissance requirements for the succeeding 24-hour period.Tropical Cyclone Position EstimateThe National Hurricane Center issues a position estimate between scheduled advisories whenever the storm center is within 200 nautical miles of U.S. land-based weather radar and if sufficient and regular radar reports are available to the hurricane center. As far as is possible, the position estimate is issued hourly near the beginning of the hour. The location of the eye or storm center is given in map coordinates and distance and direction from a well-known point. Tropical Cyclone UpdateThis brief statement is issued by the National Hurricane Center in lieu of or preceding special advisories to inform of significant changes in a tropical cyclone or the posting or cancellation of watches and warnings.TRPCLTropicalWall CloudA localized, persistent, often abrupt lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation.
- A: A small single unipolar sunspot or very small group of spots without penumbra.
- B: Bipolar sunspot group with no penumbra.
- C: An elongated bipolar sunspot group. One sunspot must have penumbra.
- D: An elongated bipolar sunspot group with penumbra on both ends of the group.
- E: An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 10 deg. but not 15 deg.
- F: An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 15 deg.
- H: A unipolar sunspot group with penumbra.
However, not all wall clouds rotate. Rotating wall clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour. Wall clouds should be monitored visually for signs of persistent, sustained rotation and/or rapid vertical motion.
"Wall cloud" also is used occasionally in tropical meteorology to describe the inner cloud wall surrounding the eye of a tropical cyclone, but the proper term for this feature is eyewall.Warm OcclusionA frontal zone formed when a cold front overtakes a warm front and, finding colder air ahead of the warm front, leaves the ground and rises up and over this denser air. Compare with cold occlusion.X-Ray Flare ClassIn solar-terrestrial terms, rank of a flare based on its X-ray energy output. Flares are classified by the order of magnitude of the peak burst intensity (I) measured at the earth in the 1 to 8 angstrom band as follows:
Zurich Sunspot ClassificationIn solar-terrestrial terms, a sunspot classification system that has been
modified for SESC use.
|Class||Intensity (in Watts/m2)|
|B||I < 10-6|
|C||10-6 <= I < 10-5
|M||10-5 <= I < 10-4|
|X||I >= 10-4|
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