18 results. (Showing 1 - 18)
1.
La Niņa
La Niņa, 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 Niņa is a phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal (for the 1971-2000 base period), averaged over three months, greater than or equal in magnitude to 0.5oC in a region defined by 150oW-160oE and 5oN-5oS (commonly referred to as Niņo 4).
2.
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.
3.
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.
4.
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.
5.
Large-scale
6.
Left Front Quadrant (or 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.
Related Term :
Entrance Region
7.
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.
Related Term :
Right Mover
8.
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 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.
9.
lightning
An electrical discharge from a thunderstorm.
10.
Line Echo Wave Pattern
(LEWP )
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.
11.
Loaded Gun (Sounding)
[Slang], a sounding characterized by extreme instability but containing a cap, such that explosive thunderstorm development can be expected if the cap can be weakened or the air below it heated sufficiently to overcome it.
12.
local storm report
(LSR )
Used to distribute severe weather reports to the media, emergency managers, and other NWS offices. It is issued as reports are received, and may also be issued as a collection of all reports received after an event is over. Delayed reports are disseminated after an event is over as well.
13.
Long Wave (or Planetary Wave)
In meteorology, a long wave in atmospheric circulation in the major belt of westerlies has different characteristics than rapidly moving storms nearer the Earth's surface
14.
Longwave Trough
A trough in the prevailing westerly flow aloft which is characterized by large length and (usually) long duration. Generally, there are no more than about five longwave troughs around the Northern Hemisphere at any given time. Their position and intensity govern general weather patterns (e.g., hot/cold, wet/dry) over periods of days, weeks, or months. Smaller disturbances (e.g., shortwave troughs) typically move more rapidly through the broader flow of a longwave trough, producing weather changes over shorter time periods (a day or less).
15.
low
The center of an area of low pressure, accompanied by cyclonic and inward wind flow in the northern hemisphere. Also known as a cyclone.
16.
Low Level Jet
A jet stream that is typically found in the lower 2-3 km, or approximately 6,000 to 9, 500 feet, of the troposphere.
17.
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).
The term also may be used to describe a narrow zone of strong winds above the boundary layer, but in this sense the more proper term would be low-level jet stream.
18.
LP Storm (or LP Supercell)
Low-Precipitation storm (or Low-Precipitation 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 often exhibit a striking visual appearance; the main tower often is bell-shaped, with a corkscrew appearance suggesting rotation. They are capable of producing tornadoes and very large hail. Radar identification often is difficult relative to other types of supercells, so visual reports are very important. LP storms almost always occur on or near the dry line, and thus are sometimes referred to as dry line storms.
