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NOAA - Meteorology glossary
Category: Sciences > Meteorology
Date & country: 14/10/2013, US
Words: 671

Inflow Bands (or Feeder Bands)
Bands of low clouds, arranged parallel to the low-level winds and moving into or toward a thunderstorm.

Inflow Jets
Local jets of air near the ground flowing inward toward the base of a tornado.

Inflow Notch
A radar signature characterized by an indentation in the reflectivity pattern on the inflow side of the storm. The indentation often is V-shaped, but this term should not be confused with V-notch. Supercell thunderstorms often exhibit inflow notches, usually in the right quadrant of a classic supercell, but sometimes in the eastern part of an HP storm or in the rear part of a storm (rear inflow notch).

Inflow Stinger
A beaver tail cloud with a stinger-like shape.

Incoming solar radiation. Solar heating; sunshine.

A state of the atmosphere in which convection takes place spontaneously, leading to cloud formation and precipitation.

An increase in temperature with height. The reverse of the normal cooling with height in the atmosphere. Temperature inversions trap atmospheric

Also known as the thermosphere. A layer in the atmosphere above the mesosphere extending from about 80km above the Earth's surface. It can be considered a distinct layer due to a rise in air temperature with increasing height. Atmospheric densities here are very low.

Brilliant patches of green or pink sometimes seen near the edges of high

Isentropic Lift
Lifting of air that is traveling along an upward-sloping isentropic surface. Situations involving isentropic lift often are characterized by widespread

Isentropic Surface
A two-dimensional surface containing points of equal potential temperature.

A line of equal barometric pressure on a weather map.

A line of equal dew point temperature.

A line of equal precipitation amounts.

General term for a line of equal value of some quantity. Isobars, isotherms, etc. all are examples of isopleths.

A line of equal wind speed.

A line of equal temperature on a weather map.

January Thaw
A period of mild weather popularly supposed to recur each year in late January.

Jet streak
A local wind speed maximum within a jet stream.

Wind blowing down an incline, such as down a hillside; downslope wind.

A front ( usually a cold front) at which the warm air descents the frontal surface.

Kelvin Temperature Scale
A temperature scale in which 0 degrees is the point at which all molecular motion ceases (absolute zero).

Killing Frost
Frost severe enough to end the growing season. This usually occurs at temperatures below 28F.

The internationally recognized unit for measuring atmospheric pressure. It is equal to 10 millibars.

A measure of speed. It is one nautical mile per hour (1.15 mph). A nautical mile is one minute of one degree of latitude.

Lumpy protrusions on the edges, and sometimes the underside, of a thunderstorm anvil. They usually appear on the upwind side of a back-sheared anvil, and indicate rapid expansion of the anvil due to the presence of a very strong updraft. They are not mammatus clouds.

La Nina
A cooling of the equatorial waters in the Pacific Ocean.

Lake effect
The effect of a lake (usually a large one) in modifying the weather near the shore and down wind. It is often refers to the enhanced rain or snow that falls downwind from the lake. This effect can also result in enhanced snowfall along the east coast of New England in winter.

Smooth, non-turbulent. Often used to describe cloud formations which appear to be shaped by a smooth flow of air traveling in parallel layers or sheets.

Land Breeze
A wind that blows from the land towards a body of water. Also known as an offshore breeze. It occurs when the land is cooler than the water.

A tornado that does not arise from organized storm-scale rotation and therefore is not associated with a wall cloud (visually) or a mesocyclone (on radar). Landspouts typically are observed beneath Cbs or towering cumulus clouds (often as no more than a dust whirl), and essentially are the land-based equivalents of waterspouts.

Lapse Rate
The change in temperature with altitude in the atmosphere.

Latent Heat
The heat energy that must be absorbed when a substance changes from solid to liquid and liquid to gas, and which is released when a gas condenses and a liquid solidifies.

An array of clouds and/or obscurations whose bases are at approximately the same level.

Situated away from the wind; downwind

Left Mover
A thunderstorm which moves to the left relative to the steering winds, and to other nearby thunderstorms; often the northern part of a splitting storm.

Lenticular Clouds
A cloud that generally has the form of a smooth lens. They usually appear in formation as the result of orographic origin. Viewed from the ground, the clouds appear stationary as the air rushes through them.

Lifted Index (or LI)
A common measure of atmospheric instability. Its value is obtained by computing the temperature that air near the ground would have if it were lifted to some higher level (around 18,000 feet, usually) and comparing that temperature to the actual temperature at that level. Negative values indicate instability

The forcing of air in a vertical direction by an upslope in terrain or by the movement of a denser air mass.

Lifting Condensation Level
The level in the atmosphere where a lifted air parcel reaches its saturation point, and as a result, the water vapor within condenses into water droplets.

Any form of visible electrical discharges produced by thunderstorms.

In probability of precipitation statements, the equivalent of a 60 or 70 percent chance.

Loaded Gun (Sounding)
A sounding characterized by extreme instability but containing a cap, such that explosive thunderstorm development can be expected if the cap can be weakened or the air below it heated sufficiently to overcome it.

Longwave Trough
A trough in the prevailing westerly flow aloft which is characterized by large length and (usually) long duration. Generally, there are no more than about five longwave troughs around the Northern Hemisphere at any given time. Their position and intensity govern general weather patterns (e.g., hot/cold, wet/dry) over periods of days, weeks, or months.

An area of low pressure, usually accompanied by cyclonic and inward wind flow. Also known as a cyclone.

Low-level Jet
A region of relatively strong winds in the lower part of the atmosphere.

Large downburst with a 2.5 mile or greater outflow diameter and damaging winds lasting 5 to 20 minutes.

Mamma Clouds
Also called mammatus, these clouds appear as hanging, rounded protuberances or pouches on the under-surface of a cloud. With thunderstorms, mammatus are seen on the underside of the anvil. These clouds do not produce tornadoes, funnels, hail, or any other type of severe weather, although they often accompany severe thunderstorms.

Maritime Air Mass
An air mass that forms over water. It is usually humid, and may be cold or warm.

Maximum Temperature
The highest temperature during a specified time period.

Mean Sea Level (MSL)
The average height of the sea surface, based upon hourly observation of the tide height on the open coast or in adjacent waters that have free access to the sea.

Mean Temperature
The average of a series of temperatures taken over a period of time, such as a day or a month.

Medium Range
In forecasting, (generally) three to seven days in advance.

Mercury Barometer
An instrument that measures barometric pressure by measuring the level of mercury in a column.

Meridional flow
A type of atmospheric circulation pattern in which the north and south component of motion is unusually pronounced. Opposite of zonal flow.

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.

A mesoscale high pressure area, usually associated with MCSs or their remnants.

Mesolow (or Sub-synoptic Low)
A mesoscale low-pressure center. Severe weather potential often increases in the area near and just ahead of a mesolow.

A regional network of observing stations (usually surface stations) designed to diagnose mesoscale weather features and their associated processes.

Size scale referring to weather systems smaller than synoptic-scale systems but larger than single storm clouds. Horizontal dimensions generally range from around 50 miles to several hundred miles. Squall lines are an example of mesoscale weather systems.

Mesoscale Convective System (MCS)
A complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. MCSs may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and MCCs (among others). MCS often is used to describe a cluster of thunderstorms that does not satisfy the size, shape, or duration criteria of an MCC.

A layer of the atmosphere separated by the ionosphere above and the stratosphere below extending from about 50km-80km above the Earth's surface. The air temperature in mesosphere decreases with height.

The mesoscale ETA model. A mathematical model of the atmosphere run on a computer that makes forecasts out to 30 hours.

Changes in the structure and texture of snow grains which results from variations in temperature, migration of liquid water and water vapor, and pressure within the snow cover

A weather observation near ground level. It may include date and time, wind, visibility, weather and obstructions to vision, sky condition, temperature and dew point, sea level pressure, precipitation amount and other data used for aircraft operations.

A person who studies meteorology. Some examples include research meteorologist, climatologist, operational meteorologist, TV meteorologist.

The study of the physics, chemistry, and dynamics of the atmosphere and the direct effects of the atmosphere upon the Earth's surface, the oceans, and life in general.

A strong localized downdraft from a thunderstorm with peak gusts lasting 2 to 5 minutes.

A local climate that differs from the main climate around it.

The areas in the northern and southern hemispheres between the tropics and the Arctic and Antarctic circles.

A metric unit of atmospheric pressure. 1 mb = 100 Pa (pascal). Normal surface pressure is approximately 1013 millibars.

Minimum Temperature
The lowest temperature during a specified time period.

Consists of microscopic water droplets suspended in the air which produce a thin grayish veil over the landscape. It reduces visibility to a lesser extent than fog.

Air movements (usually vertical) that make the properties of the air with a parcel homogeneous. It may result in a lapse rate approaching the moist or dry adiabatic rate.

A mathematical representation of a process, system, or object developed to understand its behavior or to make predictions. The representation always involves certain simplifications and assumptions.

Moisture Advection
Transport of moisture by horizontal winds.

Moisture Convergence
A measure of the degree to which moist air is converging into a given area, taking into account the effect of converging winds and moisture advection. Areas of persistent moisture convergence are favored regions for thunderstorm development, if other factors (e.g., instability) are favorable.

A persistent seasonal wind, often responsible for seasonal precipitation regime. It is most commonly used to describe meteorological changes in

Morning Glory
An elongated cloud band, visually similar to a roll cloud, usually appearing in the morning hours, when the atmosphere is relatively stable. Morning glories result from perturbations related to gravitational waves in a stable boundary layer.

Model Output Statistics.

Mountain Breeze
System of winds that blow downhill during the night.

Medium Range Forecast model generated every 12 hours by NCEP.

Mean sea level.

Mean sea level pressure.

Colloquially descriptive of warm and especially humid weather.

Multicell Cluster Thunderstorm
A thunderstorm consisting of two or more cells, of which most or all are often visible at a given time as distinct domes or towers in various stages of development.

Multivortex Tornado
A tornado in which two or more condensation funnels or debris clouds are present at the same time, often rotating about a common center or about each other. Multiple-vortex tornadoes can be especially damaging.

A thunderstorm with a well-defined anvil rollover, and thus having a visual appearance resembling a mushroom.

Negative Tilt Trough
An upper level system which is tilted to the west with increasing latitude (i.e., with an axis from southeast to northwest). A negative-tilt trough often is a sign of a developing or intensifying system.

National Oceanic and Atmospheric Administration. A branch of the U.S. Department of Commerce, NOAA is the parent organization of the National Weather Service.

A low-pressure disturbance forming along the South Atlantic coast and moving northeast along the Middle Atlantic and New England coasts to the Atlantic Provinces of Canada. It usually causes strong northeast winds with rain or snow. Also called a Northeaster or Coastal Storm.

Northern Lights
Also known as the aurora borealis. The luminous, radiant emission from the upper atmosphere over middle and high latitudes, and centered around the earth's magnetic poles. These silent fireworks are often seen on clear winter nights in a variety of shapes and colors.

A short-term weather forecast, generally out to six hours or less.

The National Severe Storms Laboratory.

a particle of any nature upon which molecules of water or ice accumulate.

Numerical Forecasting
Forecasting the weather through digital computations carried out by supercomputers.

Numerical Weather Prediction.

National Weather Service.

Any phenomenon in the atmosphere, other than precipitation, that reduces the horizontal visibility in the atmosphere.

Occluded Front
A complex frontal system that occurs when a cold front overtakes a warm front. Also known as an occlusion.