Subj : Wx Terms (L)(1)
To : All
From : Daryl Stout
Date : Wed Sep 13 2017 12:06 am
La Ni�a
La Ni�a, 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 Pacific further west than the climatological average. These
conditions affect weather patterns around the world. The preliminary CPC
definition of La Ni�a is a phenomenon in the equatorial Pacific Ocean
characterized by a negative sea surface temperature departure from normal.
Lag
1) The measure of the time between the center of mass of precipitation to
the center of mass of runoff (on the hydrograph); basin lag is a function
of not only basin characteristics, but also of storm intensity and
movement. Some hydrologic texts define lag from the center of mass of
rainfall to the hydrograph peak.
2) The time it takes a flood wave to move downstream.
Lake Breeze
A 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 surfaces of the lake and of the land.
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.
Lake Effect Snow Advisory
This 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 because of a low pressure system) may pose a hazard or it
is life threatening. The criteria for this advisory varies from area to
area.
Lake Effect Snow Squall
A local, intense, narrow band of moderate to heavy snow squall that can
extend long distances inland. It may persist for many hours. It may also
be accompanied by strong, gusty, surface winds and possibly lightning.
Accumulations can be 6 inches or more in 12 hours.
Lake Effect Snow Warning
This 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 because of a synoptic storm or low pressure system) may pose
a hazard or it is life threatening.
Lake Effect Storm
A fall or winter storm that produces heavy but localized precipitation as
a result of temperature differences between the air over snow-covered
ground and the air over the open waters of a lake.
Lakeshore Flood Advisory
Lakeshore Flood Watch
Lakeshore Flooding
LALs
(L)ightning (A)ctivity (L)evels.
LAL 1 - No thunderstorms.
LAL 2 - Few building cumulus with isolated thunderstorms.
LAL 3 - Much building cumulus with scattered thunderstorms. Light to
moderate rain.
LAL 4 - Thunderstorms common. Moderate to heavy rain reaching the ground.
LAL 5 - Numerous thunderstorms. Moderate to heavy rain reaching the
ground.
LAL 6 - Dry lightning (same as LAL 3 but without the rain).
Laminar
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.
Laminar Flow
Streamline flow in which successive flow particles follow similar path
lines and head loss varies with velocity to the first power.
Land Breeze
A coastal breeze at night blowing from land to sea, caused by the
difference in the rates of cooling of their respective surfaces.
Landfall
The intersection of the surface center of a tropical cyclone with a
coastline. Because the strongest winds in a tropical cyclone are not
located precisely at the center, it is possible for a cyclone's
strongest winds to be experienced over land even if landfall does not
occur. Similarly, it is possible for a tropical cyclone to make
landfall and have its strongest winds remain over the water. Compare
direct hit, indirect hit, and strike.
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 (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 rate of change of an atmospheric variable, usually temperature,
with height. A steep lapse rate implies a rapid decrease in temperature
with height (a sign of instability) and a steepening lapse rate implies
that destabilization is occurring.
Large Scale
(Synoptic Scale) Size scale referring generally to weather systems with
horizontal dimensions of several hundred miles or more. Most high and
low pressure areas seen on weather maps are synoptic-scale systems.
Last Update
The time and date in which the forecast was issued or updated. The
forecast may be updated at any time as weather conditions warrant.
LAT
Latitude- The location north or south in reference to the equator,
which is designated at zero (0) degrees. Lines of latitude are parallel
to the equator and circle the globe. The North and South poles are at 90
degrees North and South latitude.
Latent Heat
Heat absorbed or released during a change of phase at constant
temperature and pressure.
Latent Heat Flux
The 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 of the surface energy budget.
Latitude
(abbrev. LAT) The location north or south in reference to the equator,
which is designated at zero (0) degrees. Lines of latitude are parallel
to the equator and circle the globe. The North and South poles are at
90 degrees North and South latitude.
LAWEB
(Great Lakes Weather Broadcast) - A National Weather Service product
containing an observation summary prepared to provide Great Lakes
mariners with a listing of weather observations along or on the Lakes.
Layer Composite Reflectivity Average
This 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 grid box. It is available for 3 layers (low, mid, high).
It is used to aid in determining storm intensity trends by comparing
mid level layer composite products with a low level elevation angle
base reflectivity product and aid in routing air traffic.
Layer Composite Reflectivity Maximum
This 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 grid box. It is available for 3 layers (low, mid, high).
Currently, the low layer extends from the surface to 24,000 feet, the
mid layer extends from 24,000 feet to 33,000 feet, and high layer
extends above 33,000 feet. It is used to aid in determining storm
intensity trends by comparing mid level layer composite products with
a low level elevation angle base reflectivity product and aid in
routing air traffic.
Layered Haze
Haze produced when air pollution from multiple line, area or point
sources is transported long distances to form distinguishable layers
of discoloration in a stable atmosphere.
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. The LCD summarizes temperature, relative humidity,
precipitation, cloudiness, wind speed and direction observation.
LCL
1. 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 adiabatically.
LDS
Lightning Detection System
LDT
Local Daylight Time.
Leader
The streamer which initiates the first phase of each stroke of a
lightning discharge. The first stroke is led by a steeped leader, which
may be preceded by a pilot streamer. All subsequent strokes begin with
a dart leader.
Leader Spot
In 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 leader.
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