LimnologyScientific study of the physical characteristics and biology of lakes, ponds, and streams.
Line Echo Wave Pattern(abbrev. LEWP) A radar echo pattern formed when a segment of a line of thunderstorms surges forward at an accelerated rate.
line of sightUsually refers to contributions of radiation from the atmosphere along the line-of-sight (path) that an instrument receives.
Line SourceAn array of pollutant sources along a defined path that can be treated in dispersion models as an aggregate uniform release of pollutants along a line.
Liquefied natural gas (LNG)(LNG)Reducing the temperature of natural gas to -259 degrees Fahrenheit at atmospheric pressure will convert the gas into a liquid, with a volume about 1/600…
Liquefied petroleum gas (LPG)Ethane, ethylene, propane, propylene, normal butane, butylene, and isobutane produced at refineries or natural gas processing plants, including plants…
Liquid Water EquivalentSame as Water Equivalent; the liquid content of solid precipitation that has accumulated on the ground (snow depth).
liquid water path (gm/m^2)(gm/m^2)A measure of the weight of the liquid water droplets in the atmosphere above a unit surface area on the earth, given in units of kg m-2.
LithometeorAtmospheric phenomena which affect the state of the atmosphere. They constitute dry particles that hang suspended in the atmosphere, such as dust, smoke…
LithosphereThat part of the earth which is composed predominantly of rocks (either coherent or incoherent, and including the disintegrated rock materials known as…
LitterUndecomposed plant residues on the soil surface. See decomposition.
Littoral ZoneThe zone or strip of land along the shoreline between the high and low water marks.
Live CapacityThe total amount of storage capacity available in a reservoir for all purposes, from the dead storage level to the normal water or normal pool level…
Loaded Gun (Sounding)[Slang], a sounding characterized by extreme instability but containing a cap, such that explosive thunderstorm development can be expected if the cap can…
Local Convective WindIn fire weather terminology, local thermally driven winds arising over a comparatively small area and influenced by local terrain.
LoessA group of windblown soils, largely comprising silt, weakly cemented by calcite.
LoftingA pattern of plume dispersion in a stable boundary layer topped by a neutral layer, in which the upper part of the plume disperses upward while the lower…
Long Term RetentionRetention of data for 5 years to satisfy requirements for local studies and to support litigation.
LongitudeThe location east or west in reference to the Prime Meridian, which is designated as zero (0) degrees longitude.
longwave net radiationThe difference between upwelling and downwelling broadband longwave radiation.
longwave radianceThe rate at which light energy in the longwave portion of the spectrum is emitted in a particular direction per unit of projected surface area…
Longwave RadiationA term used to describe the infrared energy emitted by the earth and atmosphere at wavelengths between about 5 and 25 micrometers.
Longwave TroughA trough in the prevailing westerly flow aloft which is characterized by large length and (usually) long duration.
Loop Prominence System(abbrev. LPS) In solar-terrestrial terms, a system of loop prominences associated with major flares.
LoopingA pattern of plume dispersion in an unstable atmosphere, in which the plume undergoes marked vertical oscillations as it is alternately affected by rising…
LoranLong Range Navigation, a system of long range navigation whereby latitude and longitude are determined from the time displacement of radio signals from…
Lotic SystemA flowing body of fresh water, such as a river or stream. Compare lentic system.
LowA region of low pressure, marked as "L" on a weather map. A low center is usually accompanied by precipitation, extensive cloudiness, and moderate winds.
Low Frequency(abbrev. LF) The portion of the radio frequency spectrum from 30 to 300 kHz.
Low Level Jet(abbrev. LLJ)- A region of relatively strong winds in the lower part of the atmosphere.
Low Pressure SystemAn area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth.
Low-level cloudsLow-level clouds (St, Sc, Ns) Stratus, Stratocumulus, and in some degree, Nimbostratus are low clouds.
Lower heating valueQuantity of heat liberated by the complete combustion of a unit volume or weight of a fuel assuming that the produced water remains as a vapor and the…
Lowland FloodingInundation of low areas near the river, often rural, but may also occur in urban areas.
LP StormLow-Precipitation storm (or Low-Precipitation supercell). A supercell thunderstorm characterized by a relative lack of visible precipitation.
LTNGLightning- A visible electrical discharge produced by a thunderstorm. The discharge may occur within or between clouds, between the cloud and air, between…
LysimeterAn isolated block of soil, usually undisturbed and in situ, for measuring the quantity, quality, or rate of water movement through or from the soil.
M 3000In solar-terrestrial terms, the optimum high frequency radio wave with a 3000 km range, which reflects only once from the ionosphere (single hop…
M2/S2m2/s2 (meters squared per second squared), unit of measure equivalent to J/kg (joules per kilogram).
Mackeral SkyThe name given to cirrocumulus clouds with small vertical extent and composed of ice crystals. The rippled effect gives the appearance of fish scales.
MacroburstA convective downdraft with an affected outflow area of at least 2½ miles wide and peak winds lasting between 5 and 20 minutes.
MacroscaleLarge scale, characteristic of weather systems several hundred to several thousand kilometers in diameter.
Madden-Julian Oscillation(abbrev. MJO)- Tropical rainfall exhibits strong variability on time scales shorter than the seasonal El Niño-Southern Oscillation (ENSO).
MAFOR(Great Lakes Marine Forecast) - A National Weather Service coded summary appended to each of the Great Lakes Open Lakes forecasts.
MagflareIn solar-terrestrial terms, a geomagnetic and/or cosmic storm has been associated with this flare
Magnetic BayIn solar-terrestrial terms, a relatively smooth excursion of the H (horizontal) component of the geomagnetic field away from and returning to quiet levels.
Magnetic poleMagnetic Pole Either of the two points on the Earth's surface at which magnetic meridians converge.
MagnetogramA magnetogram is an image of the Sun's magnetic flux. They are derived by using emission lines which are magnetically sensitive, which allows the magnetic…
MagnetopauseIn solar-terrestrial terms, the boundary layer between the solar wind and the magnetosphere.
MagnetosphereAn area around a planet in which the planet’s magnetic field is stronger than the magnetic field carried by the solar wind.
Main StemThe reach of a river/stream formed by the tributaries that flow into it.
Main Synoptic TimesThe times of 0000, 0600, 1200, and 1800 UTC. Also known as the standard synoptic times.
Major FlareIn solar-terrestrial terms, this flare is the basis for the forecast of geomagstorm, cosmic storm and/or protons in the earth's vicinity
Major FloodingA general term including extensive inundation and property damage. (Usually characterized by the evacuation of people and livestock and the closure of…
Major HurricaneA hurricane which reaches Category 3 (sustained winds greater than 110 mph) on the Saffir/Simpson Hurricane Scale.
MALRMoist Adiabatic Lapse Rate- The rate at which the temperature of a parcel of saturated air decreases as the parcel is lifted in the atmosphere.
Mammatus CloudsRounded, smooth, sack-like protrusions hanging from the underside of a cloud (usually a thunderstorm anvil).
ManureDung and urine of animals that can be used as a form of organic fertilizer. See fertilizer, organic fertilizer.
MAP1. verb: to determine the relative positions of loci (genes or DNA sequences) on a chromosome.
Mare's TrailThe name given to thin, wispy cirrus clouds composed of ice crystals that appear as veil patches or strands, often resembling a horse's tail.
MAREP(MArine REPort) A voluntary marine observation program of the National Weather Service whose goal is to solicit meteorological and oceanographic…
Marginal Visual Flight Rules(Abbrev. MVFR) - In an aviation product, refers to the general weather conditions pilots can expect at the surface.
Marine climateMarine (maritime or oceanic) climate A climate dominated by the ocean. Because of the moderating effect of water, sites having this climate are considered…
Marine InversionTemperature inversion produced when cold marine air underlies warmer air.
Marine PushA replacement of the current air mass with air from off the ocean. Temperatures are much cooler and relative humidities much higher.
Marine Small Craft Thunderstorm AdvisoryA marine warning issued by Environment Canada Atmospheric Environment Branch when the possibility of thunderstorms is greater than 40 percent.
Marine Small Craft Wind WarningA marine warning issued by Environment Canada Atmospheric Environment Branch for winds which are forecasted to be in the 20-33 knot range inclusive.
Marine Weather StatementA National Weather Service product to provide mariners with details on significant or potentially hazardous conditions not otherwise covered in existing…
Marine ZoneSpecific, defined over-water areas contained in the various NWS marine forecasts. These are the equivalent of "zones" in the public forecast program.
Maritime Air MassAn air mass influenced by the sea. It is a secondary characteristic of an air mass classification, signified by the small "m" before the primary…
MAROBA voluntary marine observation program of the National Weather Service in the early stages of development whose goal is to solicit meteorological and…