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Anomalous propagation: this refers to the non-standard propagation of a beam of energy, radio or radar, under certain atmospheric conditions, appearing as false (non-precipitation) echoes. may be referred to as a.p. convection: motions in a fluid that transport and mix the properties of the fluid. these properties could be heat and/or moisture. when used to imply only upward vertical motion, it is then the opposite of subsidence. cumulonimbus: a vertically developed cumulus cloud, often capped by an anvil-shaped cirriform cloud. also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail, tornadoes or strong, gusty winds. doldrums: located between 30 degrees north and 30 degrees south latitudes in the vicinity of the equator, this area typically has calm or light and variable winds. also a nautical term for the equatorial trough. downburst: a severe localized downdraft from a thunderstorm or shower. this outward burst of cool or colder air creates damaging winds at or near the surface. sometimes the damage resembles tornadic damage. : an extratropical storm is a cyclone that no longer derives its energy source from the processes involved in sustaining a tropical cyclone, but thrives on baroclinic processes; i.e., the temperature contrast between warm and cold air masses. the term extratropical is typically used when a tropical cyclone moves away from the tropics and moves poleward into cooler waters thus losing its tropical characteristics. hydrologic cycle: often called the water cycle, it is the vertical and horizontal transport of water in all its states between the earth, the atmosphere, and the seas. katabatic wind: a wind that is created by air flowing downhill. when this air is warm, it may be called a foehn wind, and regionally it may be known as a chinook or santa ana. when this air is cold or cool, it is called a drainage wind, and regionally it may be known as a mountain breeze or glacier wind. the opposite of an anabatic wind. latitude: the location north or south in reference to the equator, which is designated at zero (0) degrees. parallel lines that circle the globe both north and south of the equator. the poles are at 90° north and south latitude. line echo wave pattern (lewp): a wave-shaped bulge in a line of thunderstorms. it may often be seen as a "s"-shaped radar echo signature and is often associated with severe weather. lithosphere: the solid, outer portion of the earth's crust coupled to the rigid upper mantle. part of the geosphere. low pressure system: an area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth. this is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. also known as an cyclone, it is the opposite of an area of high pressure, or a anticyclone. sea surface temperature (sst): the temperature of the water's surface. it is measured using buoy and ship data, infrared satellite imagery, and coastal observations. storm winds: on the beaufort wind scale, a wind with speeds from 56 to 63 knots (64 to 72 miles per hour). thaw: a warm spell of weather when ice and snow melt. to free something from the binding action of ice by warming it to a temperature above the melting point of ice. zulu time: one of several names for the twenty-four hour time which is used throughout the scientific and military communities..

Barrier winds: refers to the westerly flow of air along the northern slope of the brooks range in northern alaska that precedes the arrival of colder air from the north. cloud bank: a well-defined cloud mass that can be observed at a distance. it covers the horizon, but is not directly overhead. coriolis effect: a force per unit mass that arises solely from the earth's rotation, acting as a deflecting force. it is dependent on the latitude and the speed of the moving object. in the northern hemisphere, air is deflected to the right of its path, while in the southern hemisphere, air is deflected to the left of its path. it is greatest at the poles, north and south, and almost nonexistent at the equator. debris cloud: considered a rotating cloud of debris or dust that is on the ground or near the ground. the debris cloud appearing beneath a thunderstorm will most likely confirm the presence of a tornado. dry bulb thermometer: a thermometer used to measure the ambient temperature. the temperature recorded is considered identical to air temperature. one of the two thermometers that make up a psychrometer. equator: the geographic circle at 0 degrees latitude on the earth's surface. it is equal distance from the north and south poles and divides the northern hemisphere from the southern. fair: this is a subjective description. considered as pleasant weather conditions with regard to the time of year and the physical location. fogbow: a whitish semicircular arc seen opposite the sun in fog. the outer margin has a reddish tinge, its inner margin has a bluish tinge, and the middle of the band is white. an additional bow with reversed colors sometimes appears inside the first. freezing rain: rain that falls as liquid and freezes upon impact to form a coating of glaze on the colder ground or other exposed surfaces. it is reported as "fzra" in an observation and on the metar. gust front: the leading edge of the cool, gusty surface winds produced by thunderstorm downdrafts. sometimes confused with an outflow boundary. gustnado: a weak, and usually short-lived, tornado that forms along the gust front of a thunderstorm, appearing as a temporary dust whirl or debris cloud. light waves: that part of the electromagnetic spectrum that contains visible light. the colors, from longest wave length to shortest, are red, orange, yellow, green, blue, indigo, and violet (roy g. biv). maximum: the greatest value attained by a function, for example, temperature, pressure, or wind speed. the opposite of minimum. mesoscale: the scale of meteorological phenomena that range in size from several kilometers to around 100 kilometers. this includes mccs, mcss, and squall lines. smaller phenomena are classified as microscale while larger are classified as synoptic-scale. perihelion: the point of the earth's orbit that is nearest to the sun. although the position is part of a 21,000 year cycle, currently it occurs around january, when the earth is about 3 million miles closer to the sun than at aphelion. this term can be applied to any other celestial body in orbit around the sun. it is the opposite of aphelion. rainfall: the amount of precipitation of any type, primarily liquid. it is usually the amount that is measured by a rain gauge. severe thunderstorm: a thunderstorm with winds measuring 50 knots (58 mph) or greater, 3/4 inch hail or larger, or tornadoes. severe thunderstorms may also produce torrential rain and frequent lightning. short wave: a progressive wave of smaller amplitude, wave length, and duration than a long wave. it moves in the same direction as the basic current in which it is embedded and may induce upward vertical motion ahead of it. they are more numerous than long waves and often disappear with height in the atmosphere. snow: frozen precipitation in the form of white or translucent ice crystals in complex branched hexagonal form. it most often falls from stratiform clouds, but can fall as snow showers from cumuliform ones. it usually appears clustered into snowflakes. it is reported as "sn" in an observation and on the metar. snow creep: a continuous, extremely slow, downhill movement of a layer of snow. straight-line winds: any surface wind that is not associated with rotation. an example is the first gust from a thunderstorm, as opposed to tornadic winds. water vapor (h2o): water in gaseous form. it is one of the most import constituents of the atmosphere. due to its molecular content, air containing water vapor is lighter than dry air. this contributes to the reason why moist air has a tendency to rise. wind: air that flows in relation to the earth's surface, generally horizontally. there are four areas of wind that are measured: direction, speed, character (gusts and squalls), and shifts. surface winds are measured by wind vanes and anemometers, while upper level winds are detected through pilot balloons, rawin, or aircraft reports..

Absolute humidity: a type of humidity that considers the mass of water vapor present per unit volume of space. also considered as the density of the water vapor. it is usually expressed in grams per cubic meter. barometric pressure: the pressure exerted by the atmosphere at a given point. its measurement can be expressed in several ways. one is in millibars. another is in inches or millimeters of mercury (hg). cloudburst: a sudden, heavy rainfall of a showery nature. fujita-pearson scale: a scale that classifies the severity of wind damage intensity based on the degree of destruction as it relates to the wind speed as well as path length and path width of the event. it is normally used to identify the most intense damage exhibited by a tornado. developed by t. theodore fujita and allen pearson. hydrometeor: any any form of atmospheric water vapor, including those blown by the wind off the earth's surface. liquid or solid water formation that is suspended in the air includes clouds, fog, ice fog, and mist.: drizzle and rain are example of liquid precipitation, while freezing drizzle and freezing rain are examples of freezing precipitation.: solid or frozen precipitation includes ice pellets, hail, snow, snow pellets, snow grains, and ice crystals.: water vapor that evaporates before reaching the ground is virga.: examples of liquid or solid water particles that are lifted off the earth's surface by the wind includes drifting and blowing snow and blowing spray.: dew, frost, rime, and glaze are examples of liquid or solid water deposits on exposed objects. nitrogen (n2): a colorless, tasteless, odorless gas that is the most abundant constituent of dry air. it comprises 78.09%. perihelion: the point of the earth's orbit that is nearest to the sun. although the position is part of a 21,000 year cycle, currently it occurs around january, when the earth is about 3 million miles closer to the sun than at aphelion. this term can be applied to any other celestial body in orbit around the sun. it is the opposite of aphelion. plow/plough wind: the spreading downdraft and strong straight-line winds preceding a thunderstorm. so named in the american midwest because of its ability to flatten tall grasses as it passes. polar jet: marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the polar air and the subtropical air. it often divides into two branches, the north and the south, and marks the high speed core of the prevailing westerlies. it is associated with the location and motion of the high and low pressure areas of the middle latitudes, and therefore, is variable in position, elevation, and wind speed. its position tends to migrate south in the northern hemispheric winter and north in the summer, and its core winds increase during the winter and become less strong in the summer. radiosonde: an instrument attached to a weather balloon used to measure pressure, temperature, humidity, and winds aloft. observations are made when the radiosonde is aloft and emits radio signals as it ascends. may be referred to as a raob, an acronym for radiosonde observation. rain gauge: an instrument used to measure the amount of rain that has fallen. measurement is done in hundredths of inches (0.01"). steam fog: a type of advection fog that is produced by evaporation when cool air passes over a warm wet surface and the fog rises, giving the appearance of steam. also called sea smoke when it occurs over the ocean. supercell: a severe thunderstorm characterized by a rotating, long-lived, intense updraft. although not very common, they produce a relatively large amount of severe weather, in particular, extremely large hail, damaging straight-line winds, and practically all violent tornadoes. tsunami: an ocean wave with a long period that is formed by an underwater earthquake or landslide, or volcanic eruption. it may travel unnoticed across the ocean for thousands of miles from its point of origin and builds up to great heights over shallower water. also known as a seismic sea wave, and incorrectly, as a tidal wave..

Absolute humidity: a type of humidity that considers the mass of water vapor present per unit volume of space. also considered as the density of the water vapor. it is usually expressed in grams per cubic meter. atmospheric pressure: the pressure exerted by the atmosphere at a given point. its measurement can be expressed in several ways. one is in millibars. another is in inches or millimeters of mercury (hg). fathom: the common unit of depth in the ocean for countries using the english system of measurement. it is six feet or 1.83 meters. it can also be used in expressing horizontal distance, since 120 fathoms is equal to one cable or nearly on tenth of a nautical mile. horizon: one of several lines or planes used as reference for observation and measurement relative to a given location on the surface of the earth. the geographic horizon, also called the apparent horizon, is the distant line along which earth and sky appear to meet. this is the usual concept of horizon and is used in weather observing. the local horizon is the actual lower boundary of the observed sky or the upper outline of terrestrial objects including nearby natural obstructions, such as mountains. monsoon: the seasonal shift of winds created by the great annual temperature variation that occurs over large land areas in contrast with associated ocean surfaces. the monsoon is associated primarily with the moisture and copious rains that arrive with the southwest flow across southern india. the name is derived from the word mausim, arabic for season. this pattern is most evident on the southern and eastern sides of asia, although it does occur elsewhere, such as in the southwestern united states. polar-orbiting satellite: a satellite whose orbit passes over both of the earth's between poles. radiation fog: fog that is created when radiational cooling at the earth's surface lowers the temperature of the air near the ground to or below its dew point. formation is best when there is a shallow surface layer of relatively moist air beneath a drier layer, clear skies, and light surface winds. this primarily occurs during the night or early morning. rainbow: a luminous arc featuring all colors of the visible light spectrum (red, orange, yellow, green, blue, indigo, and violet). it is created by refraction, total reflection, and the dispersion of light. it is visible when the sun is shining through air containing water spray or raindrops, which occurs during or immediately after a rain shower. the bow is always observed in the opposite side of the sky from the sun. snowpack: the amount of annual accumulation of snow at higher elevations. wind wave: an ocean or lake wave resulting from the action of wind on the water's surface. after it leaves its fetch area, it is considered a swell..

Alaskan winds: the downslope air flow that blows through the alaskan valleys. it is usually given local names, such as knik, matanuska, pruga, stikine, taku, take, turnagain, or williwaw. atmospheric pressure: the pressure exerted by the atmosphere at a given point. its measurement can be expressed in several ways. one is in millibars. another is in inches or millimeters of mercury (hg). blocking high: the development of a warm ridge or cutoff high aloft at high latitudes which becomes associated with a cold high at the surface, causing a split in the westerly winds. such a high will move very slowly, tending to move westward during intensification and eastward during dissipation. it prevents the movement of migratory cyclones across its latitudes. cape: acronym for convective available potential energy. the amount of energy available to create convection, with higher values increasing the possibility for severe weather. cape verde islands: a group of volcanic islands in the eastern atlantic ocean off the coast of west africa. a cape verde hurricane originates near here. corona: a pastel halo around the moon or sun created by the diffraction of water droplets. the droplets in the cloud, such as cirrostratus, and the cloud layer itself must be almost perfectly uniform in order for this phenomena to occur. the color display sometimes appears to be iridescent. doppler radar: weather radar that measures direction and speed of a moving object, such as drops of precipitation, by determining whether atmospheric motion is horizontally toward or away from the radar. using the doppler effect, it measures the velocity of particles. named for j. christian doppler, an austrian physicist, who in 1842 explained why the whistle of an approaching train had a higher pitch than the same whistle when the train was going away. downpour: a heavy rain. drizzle: slowly falling precipitation in the form of tiny water droplets with diameters less than 0.02 inches or 0.5 millimeters. it falls from stratus clouds and is often associated with low visibility and fog. it is reported as "dz" in an observation and on the metar. : an extratropical storm is a cyclone that no longer derives its energy source from the processes involved in sustaining a tropical cyclone, but thrives on baroclinic processes; i.e., the temperature contrast between warm and cold air masses. the term extratropical is typically used when a tropical cyclone moves away from the tropics and moves poleward into cooler waters thus losing its tropical characteristics. gradient wind: a steady horizontal air motion along curved parallel isobars or contours in an unchanging pressure or contour field, assuming there is no friction and no divergence or convergence. inches of mercury (hg): the name comes from the use of mercurial barometers which equate the height of a column of mercury with air pressure. one inch of mercury is equivalent to 33.86 millibars or 25.40 millimeters. first devised in 1644 by evangelista torricelli (1608-1647), an italian physicist and mathematician, to explain the fundamental principles of hydromechanics. isohyet: the line drawn through geographic points recording equal amounts of rainfall during a given time or for a given of storm. landfall: the point at which a tropical cyclone's eye first crosses a land mass. level of free convection (lfc): the level at which a parcel of saturated air becomes warmer than the surrounding air and begins to rise freely. this occurs most readily in a conditionally unstable atmosphere. mist: a collection of microscopic water droplets suspended in the atmosphere. it does not reduce visibility as much as fog and is often confused with drizzle. national centers for environmental prediction (ncep): as part of the national weather service, the centers provide timely, accurate, and continually improving worldwide forecast guidance products. some of the centers include the aviation weather center, the climate prediction center, the storm prediction center, and the tropical prediction center. formerly known as nmc. : for further information, contact the ncep, with central offices located in silver spring, maryland. perihelion: the point of the earth's orbit that is nearest to the sun. although the position is part of a 21,000 year cycle, currently it occurs around january, when the earth is about 3 million miles closer to the sun than at aphelion. this term can be applied to any other celestial body in orbit around the sun. it is the opposite of aphelion. poles/polar: the poles are the geographic point at 90 degrees latitude north and south on the earth's surface. they are equal distance from the equator. the polar region is considered to be that area between 60° and 90° latitude, both north and south. polar jet: marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the polar air and the subtropical air. it often divides into two branches, the north and the south, and marks the high speed core of the prevailing westerlies. it is associated with the location and motion of the high and low pressure areas of the middle latitudes, and therefore, is variable in position, elevation, and wind speed. its position tends to migrate south in the northern hemispheric winter and north in the summer, and its core winds increase during the winter and become less strong in the summer. radiosonde: an instrument attached to a weather balloon used to measure pressure, temperature, humidity, and winds aloft. observations are made when the radiosonde is aloft and emits radio signals as it ascends. may be referred to as a raob, an acronym for radiosonde observation. sky: the vault-like apparent surface against which all aerial objects are seen from the earth. solar day: the complete rotation of the earth in relation to the sun. although it varies, an average has determined a mean solar day of 24 hours. it is universally used for civil purposes. teleconnections: information used by forecasters to determine what the weather might be elsewhere when compared with past weather conditions at the same degree of longitude. tornado alley: a geographic corridor in the united states which stretches north from texas to nebraska and iowa. in terms of sheer numbers, this section of the united states receives more tornadoes than any other. vorticity maximum: a center of vorticity, or the maximum of the vorticity field of a fluid. : :.