Weather Definitions Ipsum

Word Lists: Weather Definitions

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Alberta clipper: a fast moving, snow-producing weather system that originates in the lee of the canadian rockies. it moves quickly across the northern united states, often bring gusty winds and cold arctic air. ceiling light: an instrument consisting of a drum and an optical system that projects a narrow vertical beam of light onto a cloud base. cooling degree day: a cooling degree day is given for each degree that the daily mean temperature departs above the baseline of 75 degrees fahrenheit. it is used to estimate the energy requirements and is an indication of fuel consumption for air conditioning or refrigeration. cut-off high: a warm high which has become displaced and is on the polarward side of the jet stream. it occurs mostly during the spring and is most frequent over northeastern siberia, alaska, and greenland. it is an example of a blocking high. duststorm: a severe weather condition characterized by strong winds and dust-filled air over a large area. visibility is reduced to between 5/8ths and 5/16ths statute mile. it is reported as "ds" in an observation and on the metar. freezing precipitation: precipitation that is liquid, but freezes upon impact with a solid surface, such as the ground or other exposed surfaces. heat balance: the equilibrium which exists on the average between the radiation received by the earth and atmosphere from the sun and that emitted by the earth and atmosphere. the balance between heat loss (long wave radiation from the earth back into the atmosphere) and heat gain (incoming solar radiation). humidity: the amount of water vapor in the air. it is often confused with relative humidity or dew point. melting level: the altitude at which ice crystals and snow flakes melt as they descend through the atmosphere. mountain breeze: a katabatic wind, it is formed at night by the radiational cooling along mountainsides. as the slopes become colder than the surrounding atmosphere, the lower levels of air cool and drain to the lowest point of the terrain. it may reach several hundred feet in depth, and extreme cases, attain speeds of 50 knots or greater. it blows in the opposite direction of a valley breeze. national meteorological center (nmc): now incorporated into the national centers for environmental prediction, it was the division of the national weather service that produced, processed, handled, and distributed meteorological and oceanographic information to users throughout the northern hemisphere, specifically u.s. governmental organizations. ozone (o3): a nearly colorless gas and a form of oxygen (o2). it is composed of an oxygen molecule made up of three oxygen atoms instead of two. 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. synoptic chart: any map or chart that depicts meteorological or atmospheric conditions over a large area at any given time. thickness: the thickness of a layer in the atmosphere is proportional to the mean temperature of that whole layer. the layer most often used in meteorology is between 1000 and 500 millibars. there can be different temperature profiles in the lowest layer of the atmosphere with the same 1000-500 millibar thickness value, depending on what is happening above that lowest layer. for example, if the lower levels are warming but higher levels are cooling, the overall mean temperature, the thickness, could remain the same. likewise, on a sunny day, the amount of incoming solar radiation, affects the temperature right at the earth's surface, without necessarily having much effect on the thickness of the whole layer. tropical storm: a tropical cyclone in which the maximum sustained surface winds are from 39 miles per hour (34 knots) to 73 miles per hour (63 knots). at this point, the system is given a name to identify and track it. weathering: the decay and breakup of rocks on the earth's surface by natural chemical and mechanical processes. the mechanical action includes large changes of temperature, extreme temperatures, frost, or the impact of wind borne sand or water. chemical action includes the chemical reactions between atmospheric constituents in a moist environments or in rain water. biological agents are mainly fungi which attack organic material. winter: astronomically, this is the period between the winter solstice and the vernal equinox. it is characterized as having the coldest temperatures of the year, when the sun is primarily over the opposite hemisphere. customarily, this refers to the months of december, january, and february in the north hemisphere, and the months of june, july, and august in the southern hemisphere..

Altocumulus castellanus: a middle cloud with vertical development that forms from altocumulus clouds. it is composed primarily of ice crystals in its higher portions and characterized by its turrets, protuberances, or crenelated tops. its formation indicates instability and turbulence at the altitudes of occurrence. altostratus: this middle cloud genus is composed of water droplets, and sometimes ice crystals, in the mid-latitudes, cloud bases are generally found between 15,000 and 20,000 feet. white to gray in color, it can create a fibrous veil or sheet, sometimes obscuring the sun or moon. it is a good indicator of precipitation, as it often precedes a storm system. virga often falls from these clouds. blizzard: a severe weather condition characterized by low temperatures, winds 35 mph or greater, and sufficient falling and/or blowing snow in the air to frequently reduce visibility to 1/4 mile or less for a duration of at least 3 hours. a severe blizzard is characterized by temperatures near or below 10°f, winds exceeding 45 mph, and visibility reduced by snow to near zero. ceiling light: an instrument consisting of a drum and an optical system that projects a narrow vertical beam of light onto a cloud base. 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. diablo winds: dry winds in the diablo mountain range in central california that can exceed 60 miles per hour. similar to the santa ana winds, they develop as the wind flows from high pressure over nevada to lower pressure along the central california coast. downdraft: a sudden descent of cool or cold air to the ground, usually with precipitation, and associated with a thunderstorm or shower. dry line: the boundary between the dry desert air mass of the southwest u.s. and the moist air mass from the gulf of mexico. it usually lies north-south across the central and southern high plains states during spring and summer. the passage of a dry line results in a sharp decrease in humidity, clearing skies, and a wind shift from southeasterly or south to southwesterly or west. its presence influences severe weather development in the great plains. exosphere: this region is considered the very outer limits of the earth's atmosphere. its lower boundary is often called the critical level of escape, where gas atoms are so widely spaced that they rarely collide with one another and have individual orbits. it is estimated to be some 400 plus miles (640 kilometers) above the surface. front: the transition zone or interface between two air masses of different densities, which usually means different temperatures. for example, the area of convergence between warm, moist air and cool, dry air. isallobar: the line of equal change in atmospheric pressure during a certain time period. it marks the change in pressure tendency. jet stream: an area of strong winds that are concentrated in a relatively narrow band in the upper troposphere of the middle latitudes and subtropical regions of the northern and southern hemispheres. flowing in a semi-continuous band around the globe from west to east, it is caused by the changes in air temperature where the cold polar air moving towards the equator meets the warmer equatorial air moving polarward. it is marked by a concentration of isotherms and strong vertical shear. lake effect snow: snow showers that are created when cold dry air passes over a large warmer lake, such as one of the great lakes, and picks up moisture and heat. latent heat: the energy released or absorbed during a change of state. lee/leeside/leeward: the side of an object or obstacle, such as a ship's sail, a mountain, or a hill, furthest away from the wind, and therefore, protected from the direct force of the wind. the opposite of windward. microburst: a severe localized wind blasting down from a thunderstorm. it covers an area less than 2.5 miles (4 kilometers) in diameter and is of short duration, usually less than 5 minutes. mixed precipitation: any of the following combinations of freezing and frozen precipitation: snow and sleet, snow and freezing rain, or sleet alone. rain may also be present. mountain wave: a wave in the atmosphere caused by a barrier, such as a mountain. sometimes it is marked by lenticular clouds to the lee side of mountain barriers. may be called a standing wave or a lee wave. nocturnal thunderstorms: thunderstorms which develop after sunset. they are often associated with the strengthening of the low level jet and are most common over the plains states. they also occur over warm water and may be associated with the seaward extent of the overnight land breeze. occluded front: also known as an occlusion, it is a complex front formed when a cold front overtakes a warm front. it develops when three thermally different air masses conflict. the type of frontal boundary they create depends on the manner in which they meet. pascal: the unit of pressure produced when one newton acts on about one square meter. pressure characteristic: the pattern of the pressure change during the specified period of time, usually the three hour period preceding an observation. this is recorded in three categories: falling, rising, or steady. rotation: the spinning of a body, such as the earth, about its axis. satellite: any object that orbits a celestial body, such as a moon. however, the term is often used in reference to the manufactured objects that orbit the earth, either in a geostationary or a polar manner. some of the information that is gathered by weather satellites, such as goes9, includes upper air temperatures and humidity, recording the temperatures of cloud tops, land, and ocean, monitoring the movement of clouds to determine upper level wind speeds, tracing the movement of water vapor, monitoring the sun and solar activity, and relaying data from weather instruments around the world. snow squall: a heavy snow shower accompanied by sudden strong winds, or a squall. 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. squall: a sudden onset of strong winds with speeds increasing to at least 16 knots (18 miles per hour) and sustained at 22 or more knots (25 miles per hour) for at least one minute. the intensity and duration is longer than that of a gust. it is reported as "sq"s in an observation and on the metar. subsidence: a sinking or downward motion of air, often seen in anticyclones. it is most prevalent when there is colder, denser air aloft. it is often used to imply the opposite of atmospheric convection. sunset: the daily disappearance of the sun below the western horizon as a result of the earth's rotation. in the united states, it is considered as that instant when the upper edge of the sun just disappears below the sea level horizon. in great britain, the center of the sun's disk is used instead. time of sunset is calculated for mean sea level..

Azores high: a semi-permanent, subtropical area of high pressure in the north atlantic ocean that migrates east and west with varying central pressure. depending on the season, it has different names. in the northern hemispheric winter and early spring, when the icelandic low dominates the north atlantic, it is primarily centered near the azores islands. when it is displaced westward, during the summer and fall, the center is located in the western north atlantic, near bermuda, and is known as the bermuda high. bermuda high: a semi-permanent, subtropical area of high pressure in the north atlantic ocean that migrates east and west with varying central pressure. depending on the season, it has different names. when it is displaced westward, during the northern hemispheric summer and fall, the center is located in the western north atlantic, near bermuda. in the winter and early spring, it is primarily centered near the azores islands. continental air mass: an air mass with continental characteristics. it is a secondary characteristic of an air mass classification, signified by the small "c" before the primary characteristic, which is based on source region. for example, cp is an air mass that is continental polar in nature. 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. dust devil: a small, rapidly rotating column of wind, made visible by the dust, dirt or debris it picks up. it usually occurs in arid or semi-arid areas and is most likely to develop on clear, dry, hot afternoons in response to surface heating. easterly wave: an inverted, migratory wave-like disturbance or trough in the tropical region that moves from east to west, generally creating only a shift in winds and rain. the low level convergence and associated convective weather occur on the eastern side of the wave axis. normally, it moves slower than the atmospheric current in which it is embedded and is considered a weak trough of low pressure. it is often associated with possible tropical cyclone development and is also known as a tropical wave. heat index: the combination of air temperature and humidity that gives a description of how the temperature feels. this is not the actual air temperature. infrared: the long wave, electromagnetic radiation of radiant heat emitted by all hot objects. on the electromagnetic spectrum, it can be found between microwave radiation and visible light. water vapor, ozone, and carbon dioxide are capable of absorbing or transmitting infrared radiation. may be referred to as ir. mesocyclone: a area of rotation of storm size that may often be found on the southwest part of a supercell. its circulation can be larger than the tornado that may develop within it, but not necessarily. originally a radar term for a rotation signature that met certain criteria, it is best seen on doppler radar. middle clouds: a term used to signify clouds with bases between 6,000 and 18,000 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. nadir: the point on any given observer's celestial sphere diametrically opposite of one's zenith. pascal: the unit of pressure produced when one newton acts on about one square meter. rossby waves: the movement of ridges and troughs in the upper wind patterns, primarily the jet stream, circling the earth. named for carl-gustaf rossby, a u.s. weather bureau (nws) employee, who first theorized about the existence of the jet stream in 1939. snow banner: a plume of snow blown off a mountain crest, resembling smoke blowing from a volcano. squall: a sudden onset of strong winds with speeds increasing to at least 16 knots (18 miles per hour) and sustained at 22 or more knots (25 miles per hour) for at least one minute. the intensity and duration is longer than that of a gust. it is reported as "sq"s in an observation and on the metar. temperate climate: climates with distinct winter and summer seasons, typical of regions found between the tropics of cancer and capricorn and the arctic and antarctic circles. considered the climate of the middle latitudes. 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. walker circulation: a deep east-west overturning in the atmosphere normally confined to within about 20 degrees latitude of the equator extending from low-levels to near the tropopause. wall cloud: an abrupt lowering of a cloud from its parent cloud base, a cumulonimbus or supercell, with no visible precipitation underneath. forming in the area of a thunderstorm updraft, or inflow area, it exhibits rapid upward movement and cyclonic rotation. it often develops before strong or violent tornadoes. weather vane: originally used as a wind vane, it is an instrument that indicates the wind direction. the name developed based on observations on what kind of weather occurred with certain wind directions. creative designs often adorn the tops of barns and houses..
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