L

La Niña

Significant decrease in sea surface temperature in the central and eastern equatorial Pacific, together with a significantly increased sea level pressure in the eastern side of the Pacific and lower than normal pressures in the western side of it. It is a “cold event”, counterpart of the “warm event” known as El Niño, but La Niña events tend to be more irregular in their behavior and duration.

LAL (Lightning Activity Level)

Common parameter used for wildfire prediction, consisting of a numerical rating (from 1 to 6) that represents observed or forecasted frequency and characteristics of cloud-to-ground lightning for a fire zone.

Land breeze

Coastal region breeze, blowing from land to sea at night, as a result of the nocturnal temperature difference when the land surface cools and the sea surface results comparatively warmer. Then, it usually alternates with sea breezes which blow in the opposite direction during the day.

Landfall

Time at which a storm passes over shore.

Landslide

Geological phenomenon which includes a wide range of abrupt movement of soil and bedrock downhill. This occurs in response to gravity acting on an over steep slope, but it can be triggered by earthquakes, erosion, snowmelt, heavy rains, volcanic eruptions, shallow soils or other natural or anthropogenic causes. Undersea landslides can cause tsunamis.

Latent heat

Amount of energy (heat) released or absorbed during a change of phase of a substance. In the atmosphere, when water changes its state from vapor to liquid to solid, energy is being released to the surrounding air. On the contrary, when water changes from a solid to liquid to gaseous phase, energy is absorbed from the air.

Latitude

Angular distance along the meridian from a given point to the equator.

Light air

Beaufort scale wind Force 1, that is a wind of 1 to 3 knots (1 to 3.5 MPH/ 1.5 to 5.5 KPH).

Lightning

Luminous manifestation accompanying a sudden electrical discharge that takes place within one second between electric charge centers of opposite sign within a thundercloud, between a cloud and the Earth’s surface, between two different clouds or between a cloud charged and the air.

Lithosphere

Solid portion of the earth, as compared to atmosphere and hydrosphere. Layer located on top of the asthenosphere, it includes the crust and the upper mantle of our planet, with a thickness of 100 km approximately.

Little Ice Age

Period within the Holocene, between approximately A.D. 1400-1550 and 1850, in which mountain glaciers advanced in many parts of Earth, after previous shrinkage or disappearance. In Europe and North America, it was characterized by a marked decrease in temperatures, being noticeably colder than nowadays.

Local wind

Wind blowing in a small area, due to local conditions. Wind that acquires particular characteristic for a time, owing to local conditions.

Long-range forecast

Forecast with a period of validity beyond ten days.

Low cloud

Low-level cloud. Cloud of the low cloud étage, typically stratus and stratocumulus.

Low Depression

An area of low pressure, referring to a minimum of atmospheric pressure, always associated with a cyclonic circulation.