A radar reflectivity echo which is linear, but bent outward into the shape of an archer's bow. The strongest straight-line winds often occur near the "crest" or apex of the bow.

A region of relatively cold air surrounded by warmer air. It isrepresented on a weather map analysis as a relative minimum in temperature surrounded by closed isotherms. Cold pools aloft represent regions of relatively low stability, while surface-based cold pools are regions of relatively stable air.

A widespread convectively induced straight-line windstorm.

An area of strong, often damaging winds produced by one or more convective downdrafts over an area from less than 1 to 400 km in horizontal dimensions.

Small-scale downward moving air current, most often forced by negative buoyancy processes, in a cumulonimbus cloud.

In the same direction as the shear vector within a specified layer.

In the same direction as the wind flow, or toward the direction in which the wind is moving.

In radar, a general term for the appearance, on a radar display, of the radio signal scattered or reflected from a target. The characteristics of a radar echo are determined by 1) the waveform, frequency, and power of the incident wave; 2) the

range and velocity of the target with respect to the radar; and 3) the size, shape, and composition of the target.

Convection whose ascending air parcels are rooted within an atmospheric layer above the boundary layer.

In meteorology, the mixing of environmental air into a preexisting organized air current so that the environmental air becomes part of the current; the opposite of detrainment

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 (e.g., intense rainfall, dam failure, ice jam).

The leading edge of a mesoscale pressure dome separating the outflow air in a convective storm from the environmental air. This boundary, which is marked by upward motion along it and downward motion behind it, is followed by a surge of gusty winds on or near the ground. A gust front is often associated with a pressure jump, wind shift, temperature drop, and sometimes with heavy precipitation. Gust fronts are often marked by arcus clouds.

A radar signature characterized by a curve-shaped band of

reflectivity echo caused when precipitation is drawn into the spiral of a mesocyclone.

The level at which a parcel of moist air lifted dry-adiabatically

would become saturated.

Relatively strong winds concentrated within a narrow band found in the lowest 2–3 km of the troposphere.

A mesoscale area of high atmospheric pressure that typically forms beneath a multicell thunderstorm. It is usually associated

with a mesoscale convective system (MCS) or its

remnants.

A mesoscale low pressure center.

Mesolow should not be confused with mesocyclone, which is a storm-scale phenomenon.

A subset of mesoscale convective systems (MCS) that exhibits a large, circular (as observed by satellite), long-lived, cold cloud

shield with the following physical characteristics: Size: A - Cloud shield with continuously low infrared (IR) temperature ≤ -32°C

must have an area ≥ 105 km2; and B - Interior cold cloud region with temperature ≤ -52°C must have an area ≥ 0.5 X 105 km2.

Initiate: Size definitions A and B are first satisfied Duration: Size

definitions A and B must be met for a period ≥ 6 h. Maximum

extent: Contiguous cold cloud shield (IR temperature ≤ -33°C)

reaches maximum size. Shape: Eccentricity (minor axis/major

axis) ≥ 0.7 at time of maximum extent. Terminate: Size

definitions A and B no longer satisfied.MCCs typically form during

the afternoon and evening in the form of several isolated

thunderstorms, during which time the potential for severe weather

is greatest. During peak intensity (usually at night), the primary

threat shifts toward heavy rain and flooding.

A complex of thunderstorms which becomes organized on a scale

larger than the individual thunderstorms, produces a contiguous

precipitation area on the order of 100 km or more in horizontal

scale in at least one direction, and normally persists for several

hours or more. An MCS exhibits deep, moist convective

overturning contiguous with or embedded within a mesoscale

vertical circulation that is at least partially driven by the convective

overturning. MCSs may be round or linear in shape, and include

systems such as tropical cyclones, squall lines, and MCCs

(among others). MCS often is used to describe a cluster of

thunderstorms that does not satisfy the criteria of a mesoscale

convective complex (MCC).

A quasi-steady, mesoscale, cyclonic circulation that forms in the

mid-troposphere within the stratiform region of a mesoscale

convective system (MCS) often persisting after its parent MCS

has dissipated. With a core of only 50-100 km wide and 1500-

4500 m deep, and MCV is often overlooked in standard weather

analyses. And MCV can persist for more than 12 hours upon

achieving a balance between pressure gradient and Coriolis

forces, sometimes becoming the seed of the next thunderstorm

outbreak or, upon reaching tropical waters, serving as the nucleus for a tropical cyclone.

A downburst that covers an area less than 4 km (2.5 nm) along a side with peak winds that last 2–5 minutes.

A mesoscale surface boundary separating thunderstorm-cooled air (outflow) from the surrounding air.

1. The component of convective storm motion that does not lie

along the passive steering layer flow. It is the result of new cell

development and old cell dissipation.

2. The transmission of electromagnetic energy as waves through or along a medium.

A linear mesoscale convective system (MCS) that has taken the

form of a squall line or bow echo.

Variation in wind speed (speed shear) and/or direction (directional

shear) over a short distance within the atmosphere. Shear usually refers to vertical wind shear, i.e., the change in wind with height, but the term also is used in Doppler radar to describe changes in radial velocity over short horizontal distances.

A line of active thunderstorms, either continuous or with breaks,

including contiguous precipitation areas resulting from the

existence of the thunderstorms.

The speed and direction at which a thunderstorm travels.

Measured relative to a moving thunderstorm, usually referring to winds, wind shear, or helicity.

An often dangerous convective storm that consists primarily of a single, quasi-steady rotating updraft (i.e., a mesocyclone), which persists for a period of time much longer than it takes an air parcel to rise from the base of the updraft to its summit (often much longer than 10–20 min).

Convection occurring within a surface-based layer, i.e., a layer in which the lowest portion is based at or very near the earth's

surface

A small-scale current of rising air. If the air is sufficiently moist, then the moisture condenses to become a cumulus cloud or an individual tower of a towering cumulus or Cumulonimbus.

In the opposite direction as shear vector within a specified layer.

In the opposite direction as the wind flow, or opposite the direction in which the wind is moving.

The rate at which wind velocity changes from point to point in a

given direction (as, vertically). The shear can be speed shear

(where speed changes between the two points, but not direction), direction shear (where direction changes between the two points, but not speed) or a combination of the two.