Joint implementationAgreements made between two or more nations under the auspices of the United Nations Framework Convention on Climate Change to help reduce greenhouse gas…
JokulhlaupAn Icelandic term meaning glacier dammed lake outburst flood.
JouleA metric unit of energy or work; the energy produced by a force of one Newton operating through a distance of one meter; 1 Joule per second equals 1 Watt…
JSTRJet Stream - Relatively strong winds concentrated in a narrow stream in the atmosphere, normally referring to horizontal, high-altitude winds.
Juvenile WaterWater formed chemically within the earth and brought to the surface in intrusive rock.
KSmoke- Smoke in various concentrations can cause significant problems for people with respiratory ailments.
K CoronaIn solar-terrestrial terms, of the white-light corona (that is, the corona seen by the eye at a total solar eclipse), that portion which is caused by…
K-IndexA measure of the thunderstorm potential based on vertical temperature lapse rate, moisture content of the lower atmosphere, and the vertical extent of the…
Katabatic WindA wind that is created by air flowing downhill.
KatafrontA front where the warm air descends the frontal surface (except in the low layers of the atmosphere).
Kelvin Temperature ScaleAn absolute temperature scale in which a change of 1 Kelvin equals a change of 1 degree Celsius; 0°K is the lowest temperature on the Kelvin scale.
Kelvin WavesFluctuations in wind speed at the ocean surface at the Equator result in eastward propagating waves, known as Kelvin Waves.
Kelvin-Helmholtz WavesVertical waves in the air associated with wind shear across statically-stable regions.
Kelvin-Helmoltz wavesVertical waves in the air associated with wind shear across statically stable regions.
KerogenSolid, waxy mixture of rock is heated to high temperatures, the kerogen is vaporized.
KeroseneA type of heating fuel derived by refining crude oil that has a boiling range at atmospheric pressure from 400 degrees to 550 degrees F.
KilopascalThe internationally recognized unit used by the Atmospheric Environment Service for measuring atmospheric pressure. Abbreviated kPa.
Kinetic EnergyEnergy available as a result of motion that varies directly in proportion to an object's mass and the square of its velocity.
KlystronAn electron tube used as a low-power oscillator or a high-power amplifier at ultrahigh frequencies.
Knot(abbrev. Kt) Unit of speed used in navigation, equal to 1 nautical mile (the length of 1 minute latitude) per hour or about 1.
KnucklesSlang for lumpy protrusions on the edges, and sometimes the underside, of a thunderstorm anvil.
Kp IndexA 3-hourly planetary geomagnetic index of activity generated in Gottingen, Germany, based on the K Index from 12 or 13 stations distributed around the…
KT(Knot)- Unit of speed used in navigation, equal to 1 nautical mile (the length of 1 minute latitude) per hour or about 1.15 statue miles per hour, or 0.
Kyoto ProtocolThis is an international agreement struck by 159 nations attending the Third Conference of Parties (COP) to the United Nations Framework Convention on…
La NiñaLa Niña, a phase of ENSO, is a periodic cooling of surface ocean waters in the eastern tropical Pacific along with a shift in convection in the western…
LagRefers to slow game response times. The cause can be graphical based (weak graphics card), internet based (ping), system based (lack of memory, virtual…
Lake BreezeA thermally produced wind blowing during the day from the surface of a large lake to the shore, caused by the difference in the rates of heating of the…
Lake Effect SnowSnow 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.
Lake Effect Snow AdvisoryThis product is issued by the National Weather Service when pure lake effect snow (this is where the snow is a direct result of lake effect snow and not…
Lake Effect Snow SquallA local, intense, narrow band of moderate to heavy snow squall that can extend long distances inland. It may persist for many hours.
Lake Effect Snow WarningThis product is issued by the National Weather Service when pure lake effect snow (this is where the snow is a direct result of lake effect snow and not…
Lake Effect StormA fall or winter storm that produces heavy but localized precipitation as a result of temperature differences between the air over snow-covered ground and…
LALs(L)ightning (A)ctivity (L)evels. LAL 1 - No thunderstorms. LAL 2 - Few building cumulus with isolated thunderstorms.
LaminarSmooth, 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.
Laminar FlowFlow in which the head loss is proportional to the first power of the velocity.
Land BreezeA coastal breeze at night blowing from land to sea, caused by the difference in the rates of cooling of their respective surfaces.
Land skyLand sky The relatively dark appearance of the underside of a cloud layer when it is over land that is not snow covered.
LandfallThe intersection of the surface center of a tropical cyclone with a coastline. Because the strongest winds in a tropical cyclone are not located precisely…
LandfillAn open area where trash is buried. Facility in which solid waste from municipal and/or industrial sources is disposed; sanitary landfills are those that…
Landspout[Slang], a tornado that does not arise from organized storm-scale rotation and therefore is not associated with a wall cloud (visually) or a mesocyclone…
Lapse RateThe rate of change of an atmospheric variable, usually temperature, with height.
Large Scale(Synoptic Scale) Size scale referring generally to weather systems with horizontal dimensions of several hundred miles or more.
Large-scale atmospheric processesLarge-scale atmospheric processes (circulation) Atmospheric processes with a representative scale (large-scale) of 10 000 km.
Last UpdateThe time and date in which the forecast was issued or updated. The forecast may be updated at any time as weather conditions warrant.
LATLatitude- The location north or south in reference to the equator, which is designated at zero (0) degrees.
Latent HeatThe change in heat content that occurs with a change in phase and without change in temperature.
Latent Heat FluxThe flux of heat from the earth's surface to the atmosphere that is associated with evaporation or condensation of water vapor at the surface; a component…
Latitude(abbrev. LAT) The location north or south in reference to the equator, which is designated at zero (0) degrees.
Laurentide ice sheetthe ice sheet that grew over a large part of North America during the last glacial period.
LAWEB(Great Lakes Weather Broadcast) - A National Weather Service product containing an observation summary prepared to provide Great Lakes mariners with a…
Layer Composite Reflectivity AverageThis WSR-88D radar product displays the average reflectivities for a layer. Data is taken from all elevation angles contained in a given layer for each…
Layer Composite Reflectivity MaximumThis WSR-88D radar product displays the maximum reflectivities for a layer. Data is taken from all elevation angles contained in a given layer for each…
Layered HazeHaze produced when air pollution from multiple line, area or point sources is transported long distances to form distinguishable layers of discoloration…
LCD (Local Climatological Data)This National Climatic Data Center (NCDC) publication is produced monthly and annually for some 270 United States cities and it's territories.
LCL1. Abbreviation for "local" or "locally" 2. Lifting Condensation Level - the level at which a parcel of moist air becomes saturated when it is lifted dry…
LeaderThe streamer which initiates the first phase of each stroke of a lightning discharge.
Leader SpotIn solar-terrestrial terms, in a magnetically bipolar or multipolar sunspot group, the western part precedes and the main spot in that part is called the…
LeeThe side or part that is sheltered or turned away from the wind, such as with a mountain.
Lee WaveThe wavelike effect, characterized by severe updrafts and downdrafts, that occurs in the lee of a mountain range when rapidly flowing air is lifted up the…
Leeside LowExtratropical cyclones that form on the downwind (lee) side of a mountain chain.
LeewardThe side away from the wind. Compare windward.
Left Exit RegionUsed interchangably with Left Front Quadrant; the area downstream from and to the left of an upper-level jet max (as would be viewed looking along the…
Left Front QuadrantUsed interchangably with Left Exit Region; the area downstream from and to the left of an upper-level jet max (as would be viewed looking along the…
Left MoverA thunderstorm which moves to the left relative to the steering winds, and to other nearby thunderstorms; often the northern part of a splitting storm.
LengthThe distance in the direction of flow between two specific points along a river, stream, or channel.
Lentic SystemA nonflowing or standing body of fresh water, such as a lake or pond. Compare lotic system.
Lenticular CloudA very smooth, round or oval, lens-shaped cloud that is often seen, singly or stacked in groups, near or in the lee of a mountain ridge.
LeveeA natural or man-made barrier that helps keep rivers from overflowing their banks. See dike.
Level of Free Convection(LFC) - The level at which a parcel of saturated air becomes warmer than the surrounding air and begins to rise freely.
LEWPLine Echo Wave Pattern. A bulge in a thunderstorm line producing a wave-shaped "kink" in the line.
LFCAn acronym for Level of Free Convection- the level at which a parcel of saturated air becomes warmer than the surrounding air and begins to rise freely.
LILifted Index. A common measure of atmospheric instability. Its value is obtained by computing the temperature that air near the ground would have if it…
Lid(Also called cap.) A region of negative buoyancy below an existing level of free convection (LFC) where energy must be supplied to the parcel to maintain…
LIDARAn instrument similar to a radar but uses a laser to generate light pulses rather than radio waves, generally used to measure aerosol content and particle…
Lifetime (Atmospheric)The lifetime of a greenhouse gas refers to the approximate amount of time it would take for the anthropogenic increment to an atmospheric pollutant…
Lifted Index(abbrev. LI)- A common measure of atmospheric instability. Its value is obtained by computing the temperature that air near the ground would have if it…
Lifting Condensation Level(LCL) - The level at which a parcel of moist air becomes saturated when it is lifted dry adiabatically.
Light BridgeIn solar-terrestrial terms, it is observed in white light, a bright tongue or streaks penetra- ting or crossing sunspot umbrae.
Lightning(abbrev. LTNG) A visible electrical discharge produced by a thunderstorm. The discharge may occur within or between clouds, between the cloud and air…
Lightning ChannelThe irregular path through the air along which a lightning discharge occurs. A typical discharge of flash between the ground and the cloud is actually a…
Lightning DischargeThe series of electrical processes by which charge is transferred along a channel of high ion density between electrical charge centers of opposite sign.
Lightning StrokeAny of a series of repeated electrical discharges comprising a single lightning discharge (strike).
LigniteA brownish-black coal of low rank with high inherent moisture and volatile matter content, used almost exclusively for electric power generation.
Likely(abbrev. LKLY) In probability of precipitation statements, the equivalent of a 60 or 70 percent chance.
LimbIn solar-terrestrial terms, the edge of the solar disk.
Limb FlareIn solar-terrestrial terms, a solar flare seen at the edge (Limb) of the sun.