Subj : Wx Terms (L)(2)
To : All
From : Daryl Stout
Date : Wed Sep 13 2017 12:06 am
Lee
The side or part that is sheltered or turned away from the wind, such
as with a mountain.
Lee Wave
The 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 steep front of a mountain range. Compare mountain wave.
Leeside Low
Extratropical cyclones that form on the downwind (lee) side of a
mountain chain. In the United States, they frequently form on the
eastern side of the Rockies and Sierra Nevadas.
Leeward
The side away from the wind. Compare windward.
Left Exit Region
Used 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 direction of flow). Upward motion and severe thunderstorm
potential sometimes are increased in this area relative to the wind
speed maximum. See also entrance region, right rear quadrant.
Left Front Quadrant
Used 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 direction of flow). Upward motion and severe thunderstorm potential
sometimes are increased in this area relative to the wind speed maximum.
See also entrance region, right rear quadrant.
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.
Length
In hydrologic terms, the distance in the direction of flow between two
specific points along a river, stream, or channel.
Lentic System
In hydrologic terms, a nonflowing or standing body of fresh water, such
as a lake or pond.
Lenticular Cloud
A 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.
Levee
(Dike) In hydrologic terms, a long, narrow embankment usually built to
protect land from flooding. If built of concrete or masonary the
structure is usually referred to as a flood wall. Levees and floodwalls
confine streamflow within a specified area to prevent flooding. The
term "dike" is used to describe an embankment that blocks an area on a
reservoir or lake rim that is lower than the top of the dam.
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. This occurs most readily
in a conditionally unstable atmosphere.
LEWP
Line Echo Wave Pattern. A bulge in a thunderstorm line producing a
wave-shaped "kink" in the line. The potential for strong outflow and
damaging straight-line winds increases near the bulge, which often
resembles a bow echo. Severe weather potential also is increased with
storms near the crest of a LEWP.
LFC
An 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. This occurs most readily in a conditionally unstable atmosphere.
LFT
Lift
LGT
Light
LGWV
Long Wave
LI
Lifted Index. 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 more negative, the more
unstable the air is, and the stronger the updrafts are likely to be with
any developing thunderstorms. However there are no "magic numbers" or
threshold LI values below which severe weather becomes imminent.
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 its ascent. This tends to inhibit the development of convection
until some physical mechanism can lift a parcel to its LFC. The intensity
of the cap is measured by its convective inhibition. The term capping
inversion is sometimes used, but an inversion is not necessary for the
conditions producing convective inhibition to exist.
LIFR
Low Instrument Flight Rules
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 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 more negative, the more
unstable the air is, and the stronger the updrafts are likely to be with
any developing thunderstorms. However there are no "magic numbers" or
threshold LI values below which severe weather becomes imminent.
Lifting Condensation Level
(LCL) - The level at which a parcel of moist air becomes saturated when
it is lifted dry adiabatically.
Light Bridge
In solar-terrestrial terms, it is observed in white light, a bright
tongue or streaks penetrating or crossing sunspot umbrae. The appearance
of a light bridge is frequently a sign of impending region division or
dissolution.
Lightning
(abbrev. LTNG) A visible electrical discharge produced by a thunderstorm.
The discharge may occur within or between clouds, between the cloud and
air, between a cloud and the ground or between the ground and a cloud.
Lightning Channel
The 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 composite flash which is composed of several sequential
lightning strokes, each of which is initiated by a leader and terminated
by a return streamer.
Lightning Discharge
The series of electrical processes by which charge is transferred along
a channel of high ion density between electrical charge centers of
opposite sign. This can be between a cloud and the Earth's surface of
a cloud-to-ground discharge.
Lightning Stroke
Any of a series of repeated electrical discharges comprising a single
lightning discharge (strike). Specifically, in the case of a
cloud-to-ground discharge, a leader plus its subsequent return streamer.
Likely
(abbrev. LKLY) In probability of precipitation statements, the equivalent
of a 60 or 70 percent chance.
Limb
In solar-terrestrial terms, the edge of the solar disk.
Limb Flare
In solar-terrestrial terms, a solar flare seen at the edge (Limb) of the
sun.
Limnology
In hydrologic terms, the branch of hydrology that pertains to the study
of lakes.
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 Source
An 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. Example: the sum of emissions from individual cars traveling
down a highway can be treated as a line source. Compare area source and
point source.
Liquid Water Equivalent
Same as Water Equivalent; the liquid content of solid precipitation that
has accumulated on the ground (snow depth). The accumulation may consist
of snow, ice formed by freezing precipitation, freezing liquid
precipitation, or ice formed by the refreezing of melted snow.
Lithometeor
Atmospheric phenomena which affect the state of the atmosphere. They
constitute dry particles that hang suspended in the atmosphere, such as
dust, smoke, sand, and haze.
Lithosphere
In hydrologic terms, that part of the earth which is composed
predominantly of rocks (either coherent or incoherent, and including the
disintegrated rock materials known as soils and subsoils), together with
everything in this rocky crust.
Littoral Zone
In hydrologic terms, the area on, or near the shore of a body water.
Live Capacity
In hydrologic terms, the 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 surface level. Does not include surcharge,
or dead storage, but does include inactive storage, active conservation
storage and exclusive flood control storage.
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