the process of retaining incoming radiant energy in a substance
Anticipated Convection - see Convective Outlook
an instrument that flies on NOAA polar orbiting satellites. It measures radiation at five different wavelengths: one visible (visible radiation), one reflective near-infrared, one middle infrared, and two thermal infrared.
a computerized system that processes data received at a NWS Forecast Office from various weather observing systems
the mixture of gases that surrounds the earth
a body of air that extends hundreds or thousands of kilometers horizontally and is relatively uniform in temperature and moisture content (see continental arctic, continental polar, continental tropical, maritime polar, and maritime tropical air masses)
a thunderstorm that forms from localized convection within an unstable air mass (e.g., not along a frontal boundary); because all thunderstorms are associated with some type of forcing mechanism, synoptic-scale or otherwise, the term is somewhat controversial and should be used with discretion
the fraction of radiation that reflects off a body
a fast-moving low pressure system that moves southeast out of the Canadian province of Alberta through the Plains, Midwest, and Great Lakes region usually during the winter. It is usually accompanied by light snow, strong winds, and colder temperatures.
a computer program (or set of programs) that is designed to systematically solve a certain kind of problem. WSR-88D radars (NEXRAD) employ algorithms to analyze radar data and automatically determine storm motion, probability of hail, VIL, accumulated rainfall, and several other parameters.
a mid-level cloud that occurs as a layer or patch with a wavy appearance and is typically white and/or gray
mid-level clouds (bases generally 8,000 to 15,000 feet), of which at least a fraction of their upper parts show cumulus-type development. These clouds often are taller than they are wide, giving them a turret-shaped appearance. ACCAS clouds are a sign of instability aloft, and may precede the rapid development of thunderstorms.
a mid-level cloud that occurs as a sheet or layer with a striated, fibrous, or uniform appearance and is gray or bluish (never white)
the surrounding undisturbed outside air
the American Meteorological Society promotes the development and distribution of information and education on the atmospheric (and related oceanic and hydrologic) sciences and the advancement of their professional applications. (External Link)
the distance from rest to crest in a wave. In other words, it is the displacement of a particle from its rest position. Let’s say that we have a rope at rest and it is lying straight on the ground. If someone comes along and wiggles the rope from side to side like a snake, we see a wave. The distance between a crest (or peak) and the original rest position is the amplitude. The amplitude can also be measured from the trough to the rest position.
see Air Mass
an instrument for measuring the speed of the wind
the angle at which a ray of light (or radiation) strikes a surface. It is measured between the incoming ray and a perpendicular to the surface at the point of incidence (i.e., where the ray strikes).
the angle at which a reflected ray of energy leaves a reflecting surface. It is measured between the outgoing ray and a perpendicular to the surface at the point of incidence (i.e., where the ray strikes).
the angle at which a refracted ray of energy leaves the interface at which the refraction occurred. It is measured between the direction of the refracted ray and a perpendicular to the interface at the point of refraction.
the departure or deviation from normal. For example, let’s say that the normal temperature for a month is 50 °F. If the actual temperature average for the month is 55 °F, the monthly temperature is 5 °F above normal, which is a positive anomaly of 5 °F. A negative anomaly occurs when a temperature is below the normal value.
an atmospheric circulation that rotates clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere, which usually has a diameter of 2000 to 3000 kilometers
rotation 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
a lightning discharge that occurs in the anvil of a thunderstorm and is characterized by one or more channels that appear to crawl along the underside of the anvil. They typically appear during the weakening or dissipating stage of a parent thunderstorm, or during an active MCS.
the point on the annual orbit of a body (about the sun) that is farthest from the sun; at present, the earth reaches this point (152 million kilometer from the sun) on about 5 July. Opposite of perihelion.
the point on the orbit of the moon (or any other earth satellite) that is farthest from the earth. Opposite of perigee.
an imaginary force. Newton’s First Law of Motion needs a coordinate system that does not move (inertial motion). However, the earth moves underneath us, so we use apparent forces to explain what we observe. Apparent forces include Coriolis Force and Centrifugal Force.
a net upward or buoyant force, equal in magnitude to the weight of the displaced fluid, acts upon a body either partly or wholly submerged in a fluid at rest under the influence of gravity. Named for Archimedes (287-212 BC), a Greek mathematician who discovered the principle.
a pattern in which pressure at polar and middle latitudes fluctuates, leading to a difference in storm paths in the Northern Hemisphere. For example, in the "negative phase", cold air plunges into the Midwestern United States and western Europe, and storms bring rain to the Mediterranean. In the "positive phase", the opposite is true, so storms follow a more northern path, leaving areas such as California, Spain, and the Middle East drier.
the air surrounding and bound to the earth
Infrared radiation (energy in the wavelength interval of 3 to 80 micrometer) emitted by or being propagated through the atmosphere. It consists of both upwelling and downwelling components. Compare with terrestrial radiation.
the amount of resistance of a layer of air to vertical motion (How likely is it that a parcel will rise or sink?). It is also the condition of equilibrium. Stable equilibrium occurs when a parcel or object will return to its original position, while unstable equilibrium occurs when a parcel moves away from its original position. For example, if one pushes a rock at the bottom of a valley up a hill, the rock will keep rolling back down the hill. This is stable equilibrium. If a rock is at the top of the mountain and gets nudged, it will roll down and away from its original position. This is unstable equilibrium.
the wavelength range between 8 and 11 micrometers in which little absorption of infrared radiation takes place. These windows allow certain types of radiation to easily pass through the atmosphere to Earth’s surface and from the surface to space.
any decrease in amplitude, density, or energy as a result of an effect such as scattering, absorption, or friction. In physical meteorology, a reduction in radiation flow, especially solar radiation by atmospheric gases and aerosols. In radar meteorology, the decrease in the magnitude of current, voltage, power, or intensity of a signal in transmission between points. Attenuation may be caused by interference such as rain or clouds.
a system designed to provide automated meteorological measurements of several parameters at selected airports and other locations. The system is operated and controlled by the Federal Aviation Administration (FAA), NWS, and Department of Defense (DOD). In addition to the parameters measured by AWOS, ASOS can also report present weather, icing, lightning, sea level pressure, and precipitation accumulation.
operated and controlled by the Federal Aviation Administration (FAA), these weather stations observe temperature, dew point, wind speed and wind direction, visibility, sky cover and ceiling up to twelve thousand feet, and altimeter setting.
the equinox at which the sun approaches the Southern Hemispheres, marking the start of astronomical autumn in the Northern Hemisphere. The time of this occurrence is approximately 22 September. On that day, daylight is 12 hours everywhere. Compare with vernal equinox, offset by six months.
Anticyclonic Vorticity Advection. See Negative Vorticity Advection.
the "middle" of a data set. For example, if your test scores are 75, 92, 90, 83, and 89, your average score is 85.8 [(75 + 92 + 90 + 83 + 89) / 5]. An average is also known as a mean.
the number of molecules in one mole of gas (6.0221415 X 1023 per mole). According to Avogadro’s law, this number is a constant for permanent gases under normal conditions - that is, pressure of one standard atmosphere and temperature of 0°C (32°F) - the volume occupied by one mole of gas is the same for all permanent gases (22,421 cubic centimeters or 22.42 liters). Named for Amedeo Avogadro (1776 -1856), an Italian chemist who identified this relationship.
the length of arc measured clockwise along the astronomical horizon (in degrees of arc) from the adopted reference direction, usually true north, to that point on the horizon where the particular object or its projection is located; north is defined as 0° (or 360°), east is 90°, south is 180° and west is 270°.