LAKE EFFECT SNOW
Snow 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.
LAND BREEZE
A diurnal coastal breeze that blows offshore, from the land to the sea. It is
caused by the temperature difference when the sea surface is warmer
than the adjacent land. Predominate during the night, it reaches its
maximum about dawn. It blows in the opposite direction of a sea
breeze.
LANDFALL
The point at which a tropical cyclone's eye first crosses a land mass.
LANDSPOUT
A small, weak
tornado, which is not formed by a storm-scale rotation. It is generally
weaker than a supercell tornado and is not associated with a wall cloud
or mesocyclone. It may be observed beneath cumulonimbus
or towering cumulus clouds and is the land equivalent of a waterspout.
LAPSE RATE
The change of an atmospheric variable, usually temperature, with height. A steep lapse
rate implies a rapid decrease in temperature with height and is
a sign of instability. Related
term: absolute instability
LATENT HEAT
The energy released or absorbed during a change of state. Related terms: condensation
and sublimation
LATITUDE
The location north
or south in reference to the equator, which is designated at zero (0)
degrees. Parallel lines that circle the globe both north and south of
the equator. The poles are at
90 degrees North and South latitude. Related term: Longitude
LEE/LEESIDE/LEEWARD
The side of an object or obstacle, such as a ship's sail, a mountain,
or a hill, furthest away from the wind, and therefore, protected from
the direct force of the wind. The
opposite of windward.
LENTICULAR CLOUD
A cloud species which has elements
resembling smooth lenses or almonds and more or less isolated. These
clouds are caused by a wave wind
pattern created by the mountains. They are also indicative of down-stream
turbulence on the leeward side
of a barrier.
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.
LIFTED INDEX (LI)
A measure of atmospheric instability
that is obtained by computing the temperature that the air near the
ground would have if it were lifted to a higher level and comparing
it to the actual temperature
at that altitude. Positive values
indicate more stable air and negative values indicate instability.
LIFTING CONDENSATION LEVEL (LCL)
The height at which a parcel of moist air
becomes saturated when it is lifted dry
adiabatically.
LIGHTNING
A sudden and visible discharge of electricity produced in response to the build up
of electrical potential between cloud and ground, between clouds, within
a single cloud, or between a cloud
and surrounding air. Related terms: ball
lightning and heat lightning
LIGHT WAVES
That part of the electromagnetic spectrum
that contains visible light. The colors, from longest wave length to
shortest, are red, orange, yellow, green, blue, indigo, and violet (ROY
G. BIV). Related term: visible
light
LINE ECHO WAVE PATTERN (LEWP)
A wave-shaped bulge
in a line of thunderstorms. It may often be seen as a "S"-shaped radar
echo signature and is often associated with severe weather.
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
The solid, outer portion of the earth's crust coupled to the rigid upper mantle.
Part of the geosphere.
LONGITUDE
The location east or west in reference to the Prime Meridian, which is designated
as zero (0) degrees longitude. The distance between lines of longitude
are greater at the equator and smaller at the higher latitudes, intersecting
at the earth's North and South Poles. Time zones are correlated to longitude.
Related term: Greenwich
Mean Time
LONG WAVE TROUGH
A wave in the prevailing westerly
flow aloft which is characterized by a large length and amplitude.
A long wave moves slowly and is persistent. Its position and intensity
govern weather patterns over a period of days or weeks.
LOW CLOUDS
A term used to signify clouds with bases below
6,000 feet and are of a stratiform or a cumuliform variety. Stratiform
clouds include stratus and stratocumulus. Cumuliform clouds include
cumulus and cumulonimbus.
This altitude applies to the
temperate zone. In the polar regions, these clouds may be found at lower
altitudes. In the tropics, the defining altitudes for cloud types are
generally higher.
LOW LATITUDES
The latitude belt between 30 and 0 degrees North and South of the equator.
Also referred to as the tropical or torrid region.
LOW LEVEL JET (LLJ)
Strong winds that are concentrated in relatively narrow bands in the lower
part of the atmosphere. It is often amplified at night. The southerly
wind over the US Plains states during
spring and summer is a notable example. Related term: jet
stream
LOW PRESSURE SYSTEM
An area of a relative pressure minimum
that has converging winds and rotates in the same direction as the earth. This is counterclockwise
in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Also known as an cyclone, it is the opposite of an area of high
pressure, or a anticyclone. Related terms: closed low, cold
low, and cut-off low
LUNAR ECLIPSE
An eclipse of the moon occurs when the earth is in a direct line between the sun
and the moon. The moon does not have any light of its own, instead,
it reflects the sun's light. During a lunar eclipse, the moon is in
the earth's shadow. It will often look dim and sometimes copper or orange
in color.
