In the Northern Hemisphere, circulation or rotation which is counter-clockwise. In the Southern Hemisphere, clock-wise.
A measure of atmospheric moisture, specifically the temperature to which the air must be cooled to reach saturation, assuming constant moisture and pressure. When the air reaches dewpoint, visible drops of water form.
The changing of wind direction with height.
To split and move out in different directions from a single point, usually said of horizontal winds. Divergence at upper levels of the atmosphere enhances upward motion, and hence the potential for thunderstorm development.
A powerful downdraft often associated with an intense thunderstorm that strikes the ground and deflects in all directions. A downburst may produce damaging surface winds.
A small-scale column of air that rapidly sinks toward the ground, usually accompanied by precipitation as in a shower or thunderstorm. A downburst is the result of a strong downdraft.
The height above ground of the center of the radar beam using the tilt, or scan, that contains the highest elevation where reflectivities greater than 18 dBZ can be detected.
See Elevated Convection
Convection occurring within an elevated layer, i.e., a layer in which the lowest portion is based above the earth's surface. Elevated convection often occurs when air near the ground is relatively cool and stable and an unstable layer of air is present aloft.
A rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event
Issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.
Issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent.
Any high flow, overflow, or inundation by water which causes or threatens damage.
A statement of prediction
The main region of downdraft in the forward, or leading, part of a supercell, where most of the heavy precipitation is.
The altitude at which the air temperature first drops below freezing.
A condensation funnel extending from the base of a towering cumulus or cumulonimbus, associated with a rotating column of air that is not in contact with the ground.
Precipitation falling from a cumulonimbus cloud in the form of pellets or balls of ice greater than 5mm in diameter. Hailstones are usually composed of concentric layers of clear ice and compact snow.
A narrative statement produced by the National Weather Service, frequently issued on a routine basis by a local weather forecast office (WFO), to provide information regarding the potential of significant weather expected during the next 1 to 5 days.
A property of a moving fluid which represents the potential for helical flow (i.e. flow which follows the pattern of a corkscrew) to evolve. Helicity is proportional to the strength of the flow, the amount of vertical wind shear, and the amount of turning in the flow (vorticity). Atmospheric helicity is computed from the vertical [...]