Glossary
La Niña
a cooling of the ocean current along the coasts of Peru and Ecuador. See El Niño for the opposite effect.
Land Breeze
a wind blowing from land to sea, caused by the temperature difference when the sea surface is warmer than the adjacent land
Landspout
a tornado that does not form in an organized storm-scale rotation; a non-supercell tornado. Landspouts are typically observed under cumulonimbus or towering cumulus clouds and are the land-based equivalents of waterspouts, which are also tornadoes.
Latitude
the location north or south in reference to the equator (0°). 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.
Leader
the streamer that starts the first phase of each stroke of a lightning discharge. A stepped leader leads the first stroke, while all subsequent strokes begin with a dart leader.
Lee Wave
the wavelike effect, characterized by severe updrafts and downdrafts, that occurs in the lee of a mountain range (downwind) when rapidly flowing air is lifted up the steep front of a mountain range.
Left Mover
a thunderstorm that moves to the left relative to the steering winds, and to other nearby thunderstorms; often the northern part of a splitting storm
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.
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.
Lifted Index (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 computed temperature to the actual temperature at that level. Negative values indicate instability; the more negative the LI value, the more unstable the air is and the stronger the updrafts are likely to be with any developing thunderstorms.
Lifting Condensation Level (LCL)
the level in the atmosphere at which an unsaturated air parcel lifted dry adiabatically would become saturated. See Convective Condensation Level (CCL).
Light Detection and Ranging (LIDAR)
sends a light beam (usually in the form of a laser) out and detects the reflected signal. Similar to a radar, but uses light instead of radiowaves. LIDAR may be used to measure the speed of winds and to obtain turbulence and wind shear data.
Lightning Stroke
a series of repeated electrical discharges that make up a single lightning discharge (or strike). For example, a cloud-to-ground discharge is composed of a leader plus a subsequent return streamer.
Line Echo Wave Pattern (LEWP)
a bulge in a thunderstorm line that produces 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.
Liquid
one of the basic three phases of matter; characterized by free movement of the constituent molecules among themselves but without the tendency to separate
Liquid Water Equivalent
the amount of water estimated from a reflectivity signature on a radar. The liquid water equivalent is computed using an empirical mathematical equation.
Loaded Gun (Sounding)
a sounding characterized by extreme instability, but containing a cap. If the cap can be weakened or if the air below is heated sufficiently to overcome the cap, explosive thunderstorm development can be expected.
Local Storm Report (LSR)
a product issued by local NWS offices to inform users of reports of severe and/or significant weather-related events
Local Winds
winds that blow over a small area at a speed or in a direction generally different from those that are appropriate to the general pressure distribution of the region (the general wind flow). Examples include sea and land breeze, Santa Ana wind, foehn winds, outflow from thunderstorms, etc.
Longitude
the location east or west in reference to the Prime Meridian, which is designated as 0° 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 marked by longitude lines.
Longwave Radiation (LW Radiation)
in meteorology, radiation having a wavelength greater than that of visible light
Longwave Trough (LGWV)
a trough in the prevailing westerly flow aloft that is characterized by a large length and (usually) long duration. The longwave trough may stay fairly stationary over an area as shortwave troughs rotate through it.
Low-Level Jet (LLJ)
a region of relatively strong winds in the lower part of the atmosphere. Specifically, it often refers to a southerly wind maximum in the boundary layer, common over the Plains states at night during the warm season (spring and summer).
Low-Precipitation Supercell (LP Supercell)
a supercell thunderstorm characterized by a relative lack of visible precipitation; visually similar to a classic supercell, except without the heavy precipitation core. LP storms almost always occur on or near the dry line, and thus are sometimes referred to as dry line storms.
