30 results. (Showing 1 - 20)

1. A
Used on climate outlooks to indicate areas that are likely to be above normal.

2. Accessory Cloud
A cloud which is dependent on a larger cloud system for development and continuance. Roll clouds, shelf clouds, and wall clouds are examples of accessory clouds.

3. acid rain
Rainwater that has an acidity content greater than the postulated natural pH of about 5.6. It is formed when sulfur dioxides and nitrogen oxides, as gases or fine particles in the atmosphere, combine with water vapor and precipitate as sulfuric acid or nitric acid in rain, snow, or fog. The dry forms are acidic gases or particulates.

4. advection
The horizontal transport of air or atmospheric properties. Commonly used with temperatures, i.e., "warm air advection", or moisture, i.e., "moisture advection".

5. advisory
Official information issued by Tropical Cyclone Centers, such as the National Hurricane Center near Miami, FL. Describes all tropical cyclone watches and warnings in effect along with details concerning locations, intensity, movement, and precautions that should be taken. Advisories are also issued to describe tropical cyclones prior to the issuance of watches and warnings and subtropical cyclones.

6. advisory
Issued for weather situations that cause significant inconveniences but do not meet warning criteria and, if caution is not exercised, could lead to life-threatening situations.

7. air mass
A large body of air having similar horizontal temperature and moisture characteristics.

8. Air-mass Thunderstorm
Generally, a thunderstorm not associated with a front or other type of synoptic-scale forcing mechanism. Air mass thunderstorms typically are associated with warm, humid air in the summer months; they develop during the afternoon in response to insolation, and dissipate rather quickly after sunset. They generally are less likely to be severe than other types of thunderstorms, but they still are capable of producing downbursts, brief heavy rain, and (in extreme cases) hail over 3/4 inch in diameter. Since all thunderstorms are associated with some type of forcing mechanism, synoptic-scale or otherwise, the existence of true air-mass thunderstorms is debatable. Therefore the term is somewhat controversial and should be used with discretion.

9. Algorithm
A computer program (or set of programs) which is designed to systematically solve a certain kind of problem. WSR-88D radars (NEXRAD) employ algorithms to analyze radar data and automatically determine storm motion, probability of hail, VIL, accumulated rainfall, and several other parameters.

10. altocumulus
Mid-altitude clouds with a cumuliform shape.

11. AltoCumulus CAStellanus (ACCAS )
Mid-level clouds (bases generally 8 to 15 thousand feet), of which at least a fraction of their upper parts show cumulus-type development. These clouds often are taller than they are wide, giving them a turret-shaped appearance. ACCAS clouds are a sign of instability aloft, and may precede the rapid development of thunderstorms.

12. altostratus
Mid-altitude clouds with a flat sheet-like shape.

13. anemometer
An instrument for measuring the force or velocity of wind; a wind gauge.

14. Anomalous Propagation (AP )
Radar term for false (non-precipitation) echoes resulting from nonstandard propagation of the radar beam under certain atmospheric conditions.

15. Anomaly
The deviation of a measurable unit, (e.g., temperature or precipitation) in a given region over a specified period from the long-term average, often the thirty year mean, for the same region.

16. Anticipated Convection (AC )
Convective outlook issued by the SPC. The term originates from the header coding [ACUS1] of the transmitted product.

17. anticyclone
A large area of high pressure around which the winds blow clockwise in the Northern Hemisphere.

18. Anticyclonic Rotation
Rotation in the opposite sense as the Earth's rotation, i.e., clockwise in the Northern Hemisphere as would be seen from above. The opposite of cyclonic rotation.

19. Anvil
The flat, spreading top of a Cb (cumulonimbus), often shaped like an anvil. Thunderstorm anvils may spread hundreds of miles downwind from the thunderstorm itself, and sometimes may spread upwind.

20. Anvil Crawler
[Slang], a lightning discharge occurring within the anvil of a thunderstorm, characterized by one or more channels that appear to crawl along the underside of the anvil. They typically appear during the weakening or dissipating stage of the parent thunderstorm, or during an active MCS.