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freshet | Space and Astronomy | 1 | 1. A springtime thaw of snow and ice that produces a significant local inundation of rivers, streams, small watercourses, and floodplains as the snowpack melts within a watershed. |
front | Space and Astronomy | 1 | A boundary separating two masses of air of different densities and usually also of different temperatures and humidities. Weather fronts are the principal cause of meteorological phenomena outside the tropics, often bringing with them clouds, precipitation, and changes in wind speed and direction as they move. Types of fronts include cold fronts, warm fronts, and occluded fronts. |
frontogenesis | Space and Astronomy | 1 | The meteorological process by which a weather front is created, usually as a result of the narrowing of one or more horizontal temperature gradients across the boundary between two adjacent air masses. Contrast frontolysis. |
frontolysis | Space and Astronomy | 1 | The dissipation or weakening of an atmospheric weather front. Contrast frontogenesis. |
frost | Space and Astronomy | 1 | A very thin layer of ice crystals on a solid surface, typically restricted to that which forms when water vapor in an atmosphere whose temperature is above freezing comes into contact with a surface whose temperature is below freezing. Frost may exhibit a great variety of forms. |
funnel cloud | Space and Astronomy | 1 | A funnel-shaped cloud associated with a rotating column of air and protruding from the base of a parent cloud but not reaching the ground or a water surface. Funnel clouds form most frequently in association with supercell thunderstorms and often develop into tornadoes. |
gale | Space and Astronomy | 1 | 1. A strong surface wind, typically used as a descriptor in nautical contexts and variously defined based on speed. In the modern Beaufort scale, a gale is any sustained wind of Beaufort number 7 or greater, corresponding to near gale at 28–33 kn (52–61 km/h; 32–38 mph); gale at 34–40 kn (63–74 km/h); strong gale at 41–47 kn (76–87 km/h); and storm at 48–55 kn (89–102 km/h). |
gap wind | Space and Astronomy | 1 | A local, low-level wind that blows along a valley or through a col between mountains, often at speeds as high as 20–40 knots (37–74 km/h; 23–46 mph). |
geopotential height | Space and Astronomy | 1 | A measure of the vertical distance or altitude above mean sea level that accounts for variations in gravitational potential as altitude and latitude change. In meteorology and atmospheric science, geopotential height is often used in place of ordinary altitude when calculating the primitive equations in numerical weather prediction and when creating atmospheric models. |
geostrophic wind | Space and Astronomy | 1 | The theoretical wind that would result from an exact balance between the Coriolis force and the pressure gradient force (known as geostrophic balance). The true wind almost always differs from the geostrophic wind due to the influence of other forces such as friction from the ground. |
glaze | Space and Astronomy | 1 | A coating of smooth, clear ice, sometimes of considerable thickness, that forms when supercooled water, usually precipitated as freezing rain or freezing drizzle, freezes upon contact with the ground or other exposed surfaces where the temperature (and that of the lower atmosphere) is at or below 0 °C (32 °F). Glaze is denser, harder, and more transparent than rime and hoarfrost. |
gps meteorology | Space and Astronomy | 1 | A type of observational meteorology that interprets the effects of atmospheric properties such as total precipitable water vapor on the propagation of Global Positioning System (GPS) radio signals to derive information about the state of the local atmosphere. |
graupel | Space and Astronomy | 1 | A type of precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming balls of rime 2–5 mm (0.079–0.197 in) in diameter. Graupel is distinct from hail, small hail, and ice pellets. |
great salt lake effect | Space and Astronomy | 1 | A lake-effect snow that occurs in the lee of Utah's Great Salt Lake. |
green flash | Space and Astronomy | 1 | An optical phenomenon consisting of a momentary glimmer of green light occasionally observed near the upper limb of the Sun's apparent disk just as it disappears from view at sunset or just as it appears at sunrise. It is most likely to be seen where there is a low, clear, distant horizon, such as over the ocean. |
ground blizzard | Space and Astronomy | 1 | A weather condition that occurs when loose snow or ice on the ground is lifted and blown into the air by strong winds. This can create low-visibility conditions even in the absence of precipitation. |
ground truth | Space and Astronomy | 1 | Information, such as local weather conditions, provided by direct observation (i.e. empirical evidence) as opposed to information provided by inference. |
gust | Space and Astronomy | 1 | A brief, sudden increase in the speed of the wind, usually lasting less than 20 seconds. Gusts are more transient than squalls and are followed by a lull or slowing of the wind speed. They are generally only reported by weather stations when the maximum wind speed exceeds the average wind speed by at least 10–15 knots (12–17 mph). |
gust front | Space and Astronomy | 1 | See outflow boundary. |
gustnado | Space and Astronomy | 1 | A relatively weak tornado associated with the outflow at the leading edge of a thunderstorm cell, and often occurring along a gust front. A debris cloud or dust whirl may indicate the presence of a gustnado. |
hail | Space and Astronomy | 1 | A type of solid precipitation that consists of balls or irregular lumps of ice, usually 5–150 mm (0.20–5.91 in) in diameter, each of which is called a hailstone. Hail formation requires environments with strong, upward motion of air and low altitudes at which water freezes, which makes it possible within most thunderstorms. It is distinct from graupel and sleet or ice pellets. |
hailstorm | Space and Astronomy | 1 | Any storm, usually a strong thunderstorm, which precipitates hail. |
haines index | Space and Astronomy | 1 | A weather index that measures the potential for dry, unstable air to contribute to the development of large or erratic wildland fires. The index derives from data on the stability and moisture content of the lower atmosphere and is calculated over three ranges of atmospheric pressure. |
hard rime | Space and Astronomy | 1 | A type of rime consisting of opaque, granular masses of ice deposited primarily on vertical surfaces by freezing fog. Hard rime is more compact and amorphous than soft rime and usually develops on windward surfaces exposed to high wind speeds and air temperatures between −2 and −8 °C (28 and 18 °F). |
haze | Space and Astronomy | 1 | Any suspension in the atmosphere of very small, dry particulate matter, including natural aerosols (e.g. dust, salt, or smoke) as well as man-made pollutants (e.g. smog), the individual particles of which are invisible to the naked eye but collectively produce a milky, often opalescent sky with reduced visibility at long distances. Haze usually indicates sub-saturated air, whereas fog or mist indicates full saturation. |
heat dome | Space and Astronomy | 1 | The effect created by Earth's atmosphere trapping hot ocean air like a lid or cap. |
heat burst | Space and Astronomy | 1 | A rare phenomenon involving a sudden, localized increase in surface temperature (sometimes 10 °C (18 °F) or more within just a few minutes) associated with a decaying thunderstorm or other mesoscale convective system and possibly accompanied by gusty winds and a rapid decrease in humidity. |
heat index | Space and Astronomy | 1 | A meteorological index that posits the apparent temperature perceived by the average human being who is exposed to a given combination of air temperature and relative humidity in a shaded area. For example, when the air temperature is 32 °C (90 °F) with 70% relative humidity, the heat index is 41 °C (106 °F). |
hi | Space and Astronomy | 1 | A meteorological index that posits the apparent temperature perceived by the average human being who is exposed to a given combination of air temperature and relative humidity in a shaded area. For example, when the air temperature is 32 °C (90 °F) with 70% relative humidity, the heat index is 41 °C (106 °F). |
heat wave | Space and Astronomy | 1 | A period of weather characterized by excessively high temperatures, which may or may not be accompanied by high humidity or by drought. Very hot weather is often only referred to as a heat wave if the temperature is abnormal relative to the typical climate for a given location during a given season. Contrast cold wave. |
heavy snow warning | Space and Astronomy | 1 | A type of weather warning formerly issued by the U.S. National Weather Service to alert areas in which a high rate of snowfall (generally 6 in (15 cm) or more in 12 hours) was occurring or was forecast. The warning was replaced by the Winter Storm Warning for Heavy Snow beginning with the 2008–09 winter storm season. |
hodograph | Space and Astronomy | 1 | A vectorial visual representation of the movement of a body or a fluid, with the position of any data plotted on it proportional to the velocity of the moving particle. In the context of meteorology, hodographs are used to plot winds from atmospheric soundings: for a given vector, wind direction is indicated by the angle from the center axis and wind speed by the distance from the center. |
humidity | Space and Astronomy | 1 | A measure of the amount of water vapor present in a parcel of air. By quantifying the saturation of the air with moisture, humidity indicates the likelihood of precipitation, dew, or fog occurring. The amount of water vapor needed to achieve full saturation increases as the air temperature increases. Three primary measurements of humidity are widely employed in meteorology: absolute, relative, and specific. |
humilis | Space and Astronomy | 1 | See cumulus humilis. |
hurricane | Space and Astronomy | 1 | The local name for a tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean and achieves one-minute maximum sustained winds exceeding 74 mph (119 km/h; 64 kn). |
huaico | Space and Astronomy | 1 | A mudslide or flash flood caused by torrential rainfall occurring high in the Andes mountains of South America, especially during the weather phenomenon known as El Niño. |
hydrometeor | Space and Astronomy | 1 | Any particulate of liquid or solid water within the atmosphere, encompassing all types of precipitation, formations due to condensation such as clouds and haze, and particles blown from the Earth's surface by wind such as blowing snow and sea spray. |
hydrometeorology | Space and Astronomy | 1 | A branch of meteorology and hydrology that studies the transfer of water and energy between land surfaces and the lower atmosphere. |
hydrosphere | Space and Astronomy | 1 | The combined mass of all solid, liquid, and gaseous forms of water found on, beneath, or above the surface of the Earth, including all oceans, lakes, streams, groundwater, atmospheric water vapor, snow, ice caps, and glaciers. |
hygrometer | Space and Astronomy | 1 | A scientific instrument used to measure humidity. |
hygroscopy | Space and Astronomy | 1 | The phenomenon by which a substance attracts and retains water molecules via either absorption or adsorption from the surrounding environment. |
hypsometer | Space and Astronomy | 1 | A scientific instrument used to measure height or elevation, either by trigonometry or by the principle that atmospheric pressure influences the boiling point of liquids. |
ice | Space and Astronomy | 1 | Water frozen into a solid state. Ice is abundant on Earth's surface and in the atmosphere and plays a major role in Earth's water cycle and climate. Its natural occurrence in weather phenomena takes many forms, including snowflakes, hail, frost, icicles, and ice spikes. |
ice crystal | Space and Astronomy | 1 | 1. A minute spicule of ice that forms from water in the atmosphere at temperatures below the freezing point of 0 °C (32 °F). Ice crystals may take on any of a number of macroscopic, crystalline forms depending on the temperature at their formation, including needles, hexagonal prisms, and stars. Their growth occurs by the diffusion of water vapor onto them, and they may collide with other ice crystals to form snowflakes. |
ice fog | Space and Astronomy | 1 | A type of fog consisting of a sufficient concentration of tiny ice crystals suspended in the atmosphere to reduce visibility to less than 1 kilometre (0.62 mi). Ice fog forms at very low ambient air temperatures, typically −30 °C (−22 °F) or below, usually in calm conditions at high latitudes but sometimes also as the result of mild maritime air blowing across ice- or snow-covered surfaces. |
ice spike | Space and Astronomy | 1 | A rare ice formation that consists of a long, slender projection of ice extending upward from the surface of a frozen body of water, often in the shape of an inverted icicle. |
ice storm | Space and Astronomy | 1 | A type of winter storm characterized by freezing rain which results in the accumulation of at least 6.4 millimetres (0.25 in) of ice on exposed surfaces. |
icicle | Space and Astronomy | 1 | A long, slender spike of ice formed when water dripping or falling from an object freezes. |
inflow | Space and Astronomy | 1 | The influx of heat and moisture into a storm system from the surrounding environment. The inflow of parcels of warm, moist air drives and sustains most types of storms, including thunderstorms and tropical cyclones. Contrast outflow. |
international standard atmosphere | Space and Astronomy | 1 | A static atmospheric model of the variations in temperature, pressure, density, and viscosity over a wide range of altitudes within the Earth's atmosphere, established as an international standard by the International Organization for Standardization in order to provide a common reference for atmospheric variables relevant to meteorology and atmospheric science. |
isa | Space and Astronomy | 1 | A static atmospheric model of the variations in temperature, pressure, density, and viscosity over a wide range of altitudes within the Earth's atmosphere, established as an international standard by the International Organization for Standardization in order to provide a common reference for atmospheric variables relevant to meteorology and atmospheric science. |
irisation | Space and Astronomy | 1 | See cloud iridescence. |
jet-effect wind | Space and Astronomy | 1 | See canyon wind. |
jet stream | Space and Astronomy | 1 | A narrow, fast-flowing, meandering air current primarily occurring in the upper part of the troposphere, at altitudes above 9 km (30,000 ft), and usually flowing from west to east. The Northern and Southern Hemispheres each have a predictable though discontinuous polar jet and subtropical jet; low-level jets and other types of jet streams can form under certain conditions. |
jet streak | Space and Astronomy | 1 | The region of maximum wind speed that runs along the elongated axis of a jet stream. In the local winter, the maximum speed in the polar-front jet stream can reach upwards of 200 knots (370 km/h; 230 mph). |
k-index | Space and Astronomy | 1 | An operational atmospheric stability index indicating the potential for thunderstorms, based on temperature lapse rate, moisture content of the lower troposphere, and the vertical extent of the moist layer. K-index values of 36 and above suggest a high likelihood of thunderstorm development. |
kata-front | Space and Astronomy | 1 | A warm front or cold front that is overrun by drier air, or in which the warm air subsides, so that any clouds and precipitation tend to be suppressed, making them generally inactive fronts. Contrast ana-front. |
katabatic wind | Space and Astronomy | 1 | A local wind that carries cold, high-density air from a higher elevation downslope under the force of gravity as a result of the radiative cooling of the upland ground surface at night, usually at speeds on the order of 10 kn (19 km/h) or less but occasionally at much higher speeds. Contrast anabatic wind. |
kelvin–helmholtz instability | Space and Astronomy | 1 | A phenomenon of instability that occurs occasionally in an atmospheric layer within which wind speed increases rapidly with altitude. Kelvin–Helmholtz waves form in this layer of strong vertical wind shear, and are often marked by a distinct train of clouds that resemble breaking ocean waves. |
khamsin | Space and Astronomy | 1 | The local name for a dry, hot, seasonal wind, often carrying large quantities of dust or sand, that occurs in the deserts of Egypt, Israel, Palestine, and Jordan. Compare haboob, harmattan, sirocco, and simoom. |
kinematics | Space and Astronomy | 1 | A branch of classical mechanics that describes the motion of points, bodies, and systems of bodies without considering the forces that caused the motion. |
knot | Space and Astronomy | 1 | A unit of speed commonly used in maritime and aviation disciplines, equivalent to one nautical mile per hour (1.1508 miles per hour or 0.5145 metres per second). It is often used in meteorology for measuring wind speed. |
kn | Space and Astronomy | 1 | A unit of speed commonly used in maritime and aviation disciplines, equivalent to one nautical mile per hour (1.1508 miles per hour or 0.5145 metres per second). It is often used in meteorology for measuring wind speed. |
lake-effect snow | Space and Astronomy | 1 | A weather phenomenon produced when a cold air mass moves across long expanses of warmer lake water, which causes the lowest layers of air to pick up warm water vapor from the lake, rise through the upper layers, freeze and then precipitate on the lake's leeward shores. In combination with orographic lift, the effect produces narrow but very intense bands of precipitation, especially snow, which can deposit at very high rates and result in very large amounts of snowfall over a region. The same effect can also occur over bodies of salt water, when it is termed ocean-effect or bay-effect snow. |
laminar flow | Space and Astronomy | 1 | A flow in which the particles of a fluid moves smoothly in parallel layers or sheets, i.e. without turbulence. |
land breeze | Space and Astronomy | 1 | An offshore local wind that blows from land to sea, usually at night, a result of the more rapid cooling of the land surface relative to the sea after sunset. It blows in the opposite direction of a sea breeze, its daytime counterpart in a diurnal cycle of coastal winds caused by lateral differences in surface temperature between land and sea. |
landfall | Space and Astronomy | 1 | The movement of a storm or other weather phenomenon over land after being over water. |
landspout | Space and Astronomy | 1 | A type of tornado emerging from a parent cloud that does not contain a pre-existing mid-level mesocyclone or other rotation. Landspouts share a development process and resemblance with waterspouts. They are generally smaller and weaker than supercell tornadoes and are rarely detected by Doppler weather radar. |
lapse rate | Space and Astronomy | 1 | The rate at which an atmospheric variable, most commonly temperature or pressure, decreases with increasing altitude. |
latent heat | Space and Astronomy | 1 | The amount of heat absorbed or released per unit mass during a change of phase of a substance at constant temperature and pressure. In meteorology, the term usually refers to the amount absorbed or released in the various transformations between the three physical states of water: ice, liquid water, and water vapor. For instance, the latent heat of vaporization requires about 2.4 × 106 Joules per kilogram at 0 °C. Contrast sensible heat. |
latent heat flux | Space and Astronomy | 1 | The movement of water vapor (a major transporter of latent heat) from one location to another, e.g. from the tropics toward the poles, where there is a persistent energy deficit relative to lower latitudes. Poleward latent heat flux reaches its global maximum of 1.5 × 1015 watts at latitudes 38 °N and 40 °S. |
law of storms | Space and Astronomy | 1 | A general statement of the manner in which the winds of a cyclone rotate about the cyclone's center, and the way in which the entire disturbance moves across the Earth's surface. The development by meteorologists of a "law" describing the general behavior of storms proved important in historical times to sailors navigating during storms at sea. |
layer cloud | Space and Astronomy | 1 | See stratiform. |
lee trough | Space and Astronomy | 1 | A trough of low atmospheric pressure that forms preferentially to the lee or downwind side of a mountain barrier when air currents flow in directions perpendicular to the barrier and become vertically "squashed" as they cross it. As the column resumes its original depth on the other side of the barrier, it tends to develop a strong spin about its vertical axis, which manifests as a low-pressure center. |
lemon technique | Space and Astronomy | 1 | A method used by meteorologists which focuses on updrafts and uses weather radar to determine the relative strength of thunderstorm cells in a vertically sheared environment. |
length of record | Space and Astronomy | 1 | The time interval during which a particular observation or observations in general have been maintained without interruption at a meteorological station, and which therefore serves as the frame of reference for climatic data at that station. |
lenticular cloud | Space and Astronomy | 1 | A type of stationary cloud with a distinct lens or saucer shape which typically forms in an arrangement perpendicular to the wind direction and at altitudes less than 12 kilometres (39,000 ft) above sea level, most commonly above or near very large natural obstructions in the atmosphere, such as mountains and hills. |
level of free convection | Space and Astronomy | 1 | The altitude in the atmosphere at which the temperature of the environment decreases faster than the moist adiabatic lapse rate of a saturated air parcel at the same level. Air masses with one or many LFCs are potentially unstable and may develop convective clouds such as cumulonimbus. |
lfc | Space and Astronomy | 1 | The altitude in the atmosphere at which the temperature of the environment decreases faster than the moist adiabatic lapse rate of a saturated air parcel at the same level. Air masses with one or many LFCs are potentially unstable and may develop convective clouds such as cumulonimbus. |
lidar | Space and Astronomy | 1 | A surveying method that measures the distance to a target by illuminating the target with pulsed laser light and measuring the reflected pulses with a sensor; differences in laser return times and wavelengths can then be used to create digital three-dimensional representations of the target. The name is now used as an acronym of light detection and ranging. |
lifted index | Space and Astronomy | 1 | The difference in temperature between the ambient environment and an air parcel that is lifted adiabatically at a given pressure height within the troposphere, typically 500 hectopascals (0.49 atm). When the value of the lifted index is positive, the atmosphere at the given height is stable; when it is negative, the atmosphere is unstable. |
li | Space and Astronomy | 1 | The difference in temperature between the ambient environment and an air parcel that is lifted adiabatically at a given pressure height within the troposphere, typically 500 hectopascals (0.49 atm). When the value of the lifted index is positive, the atmosphere at the given height is stable; when it is negative, the atmosphere is unstable. |
lightning | Space and Astronomy | 1 | A naturally occurring electrostatic discharge during which two electrically charged regions of the atmosphere or ground temporarily equalize themselves, instantaneously releasing about a billion joules of energy across a wide range of the electromagnetic spectrum, from very hot plasma to brilliant flashes of light visible in the atmosphere. Lightning is often followed by its audible consequence, thunder, and is one of the distinguishing features of thunderstorms. Lightning phenomena are generally separated into three classes based on where they occur – either inside a single cloud, between two different clouds, or between a cloud and the ground – but many other observational variants have been recognized. |
lightning strike | Space and Astronomy | 1 | Any lightning discharge that occurs between the atmosphere and an object (rather than between different parts of the atmosphere). Most lightning strikes are cloud-to-ground, meaning they terminate on the Earth's surface or on an object attached to it, but lightning can also strike airborne objects or travel from ground-to-cloud. The primary electron-conducting channel in such discharges, visible for a fraction of a second as a very bright, "zigzagging" path of light, is sometimes called a lightning bolt. |
lysimeter | Space and Astronomy | 1 | An instrument used to measure the total amount of evapotranspiration that occurs within a certain area of the Earth's surface, usually by recording the amount of precipitation received by the area and the amount of moisture subsequently lost through the soil. |
mackerel sky | Space and Astronomy | 1 | A sky that is partially or fully covered by high altocumulus or cirrocumulus clouds with a regular pattern of ripples and patches separated by small areas of blue sky, resembling the scales on a mackerel. |
macroburst | Space and Astronomy | 1 | A strong downburst that affects a path longer than 4 kilometres (2.5 mi) and persists for up to 30 minutes, with surface winds reaching as high as 210 kilometres per hour (130 mph). |
macrometeorology | Space and Astronomy | 1 | The study of the largest-scale meteorological processes, i.e. those occurring over very large regions, oceans, continents, or the entire Earth, such as the general circulation, as opposed to mesometeorology and micrometeorology. See also synoptic-scale meteorology. |
mafor | Space and Astronomy | 1 | A North American system used in the transmission of marine weather forecasts to compress large amounts of information about meteorological and marine conditions, including visibility, expected future wind speed and direction, the "state of sea", and the period of validity of the forecast, into shorter code for convenience during radio broadcasting. MAFOR is an abbreviation of MArine FORecast. |
manometer | Space and Astronomy | 1 | A scientific instrument consisting of a liquid column gauge used to measure differences in the pressures of gases, as with a mercury barometer. |
marine climate | Space and Astronomy | 1 | A regional climate that is strongly influenced by its location in relation to a sea or ocean, characterized by relatively small diurnal and seasonal temperature variations and high atmospheric moisture content, which contributes to high precipitation and humidity. Contrast continental climate. |
mass flow | Space and Astronomy | 1 | The movement of a fluid, such as an air mass, down a pressure or temperature gradient. |
meridional circulation | Space and Astronomy | 1 | The component of the large-scale atmospheric general circulation that is oriented parallel to a meridian or line of longitude, and thus shows large north–south movement. |
mesosphere | Space and Astronomy | 1 | The third major layer of the Earth's atmosphere, above the stratosphere and below the thermosphere. The lower boundary of the mesosphere varies between 50 and 65 km (31 and 40 mi) above the Earth's surface, depending on latitude and time of year. |
météo-france | Space and Astronomy | 1 | The national meteorological agency of France. |
meteorology | Space and Astronomy | 1 | A branch of the atmospheric sciences which seeks to understand and explain observable weather events, with a major focus on weather prediction. Meteorology uses variables familiar in chemistry and physics to describe and quantify meteorological phenomena, including temperature, pressure, water vapor, mass flow, and how these properties interact and change over time. |
micronet | Space and Astronomy | 1 | A weather observation network even denser than a mesonet, such as the Oklahoma City Micronet. |
microscale meteorology | Space and Astronomy | 1 | Meteorological phenomena that occur on a scale of 40 m to 4 km. |
mini-supercell | Space and Astronomy | 1 | A distinct kind of supercell that is smaller than a typical supercell. |
mini-tornado | Space and Astronomy | 1 | A fallacious term often used in news media to refer to damaging winds accompanying a thunderstorm, indifferently caused by tornadoes or microbursts, on a small area. |
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