Squall line

quasi-linear convective systemrain bandbandingbanding featurescold front squall linesquall linessquallsthunderstorms
A squall line or quasi-linear convective system (QLCS) is a line of thunderstorms forming along or ahead of a cold front.wikipedia
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Thunderstorm

thunderstormssevere thunderstormelectrical storm
A squall line or quasi-linear convective system (QLCS) is a line of thunderstorms forming along or ahead of a cold front.
Thunderstorms may line up in a series or become a rainband, known as a squall line.

Cold front

cold frontscoldfrontal
A squall line or quasi-linear convective system (QLCS) is a line of thunderstorms forming along or ahead of a cold front.

Derecho

blowdownprogressive derechosevere weather
Some bow echoes which develop within the summer season are known as derechos, and they move quite fast through large sections of territory.
In many cases, convection-induced winds take on a bow echo (backward "C") form of squall line, often forming in an area of wind divergence in upper levels of the troposphere, within a region of low-level warm air advection and rich low-level moisture.

Wake low

On the back edge of the rainband associated with mature squall lines, a wake low can be present, sometimes associated with a heat burst.
A wake low, or wake depression, is a mesoscale low-pressure area which trails the mesoscale high following a squall line.

Precipitation

rainfallhydrometeorannual precipitation
It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts.
In mid-latitudes, convective precipitation is intermittent and often associated with baroclinic boundaries such as cold fronts, squall lines, and warm fronts.

Bow echo

Book end vorticesbow'' or ''spearhead radar echobowing
Strong straight-line winds can occur where the squall line is in the shape of a bow echo.
A bow echo is associated with squall lines or lines of convective thunderstorms.

Rainband

banding featuresouter bandsrainbands
On the back edge of the rainband associated with mature squall lines, a wake low can be present, sometimes associated with a heat burst.
Rainbands spawned near and ahead of cold fronts can be squall lines which are able to produce tornadoes.

Line echo wave pattern

Tornadoes can occur along waves within a line echo wave pattern (LEWP), where mesoscale low-pressure areas are present.
A LEWP, according to the NWAS, is defined as "a squall line that has developed into a wave-like pattern due to acceleration at one end of the line and deceleration along the portion immediately adjacent."

Cyclone

cyclonescycloniccyclonic storm
This theory proposed that the main inflow into a cyclone was concentrated along two lines of convergence, one ahead of the low and another trailing behind the low.
Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines.

Synoptic scale meteorology

synoptic scalesynopticsynoptic-scale
The leading area of a squall line is composed primarily of multiple updrafts, or singular regions of an updraft, rising from ground level to the highest extensions of the troposphere, condensing water and building a dark, ominous cloud to one with a noticeable overshooting top and anvil (thanks to synoptic scale winds).
Mesoscale systems and boundaries such as tropical cyclones, outflow boundaries and squall lines also are analyzed on surface weather analyses.

Wind shear

windshearvertical wind shearshear
Wind shear is an important aspect of a squall line.
Cold fronts feature narrow bands of thunderstorms and severe weather, and may be preceded by squall lines and dry lines.

Outflow (meteorology)

outflowinflowoutflow channel
The cold air outflow leaves the trailing area of the squall line to the mid-level jet, which aids in downdraft processes.
Squall lines typically bow out the most, or bend the most convex outward, at the leading edge of low level outflow due to the formation of a mesoscale high-pressure area which forms within the stratiform rain area behind the initial line.

Downburst

straight-line windsstraight-line windmacroburst
It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts. Severe squall lines typically bow out due to the formation of a stronger mesoscale high-pressure system (a mesohigh) within the convective area due to strong descending motion behind the squall line, and could come in the form of a downburst.
Another variety, the heat burst, is created by vertical currents on the backside of old outflow boundaries and squall lines where rainfall is lacking.

Mesoscale convective system

Mesoscale convective systemsconvection-induceddisturbance
The resultant mesoscale convective system (MCS) forms at the point of the upper level split in the wind pattern in the area of best low level inflow.
A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape, and include weather systems such as tropical cyclones, squall lines, lake-effect snow events, polar lows, and Mesoscale Convective Complexes (MCCs), and generally form near weather fronts.

Mesohigh

Severe squall lines typically bow out due to the formation of a stronger mesoscale high-pressure system (a mesohigh) within the convective area due to strong descending motion behind the squall line, and could come in the form of a downburst.
A mesohigh forms underneath the downdraft in a squall line and is associated with the cold pool of a thunderstorm.

Squall

squallsmesolowrainbands
Squall
Usually, this sudden violent wind is associated with briefly heavy precipitation as squall line.

Mesocyclone

tornadocyclonelow-level mesocyclonemesoanticyclone
In high shear environments created by opposing low level jet winds and synoptic winds, updrafts and consequential downdrafts can be much more intense (common in supercell mesocyclones).
A mesovortex is a similar but typically smaller and weaker rotational feature associated with squall lines.

Outflow boundary

gust frontoutflow boundariesoutflow
As supercells and multi-cell thunderstorms dissipate due to a weak shear force or poor lifting mechanisms, (e.g. considerable terrain or lack of daytime heating) the gust front associated with them may outrun the squall line itself and the synoptic scale area of low pressure may then infill, leading to a weakening of the cold front; essentially, the thunderstorm has exhausted its updrafts, becoming purely a downdraft dominated system.
When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise which is normally just ahead of its radar signature.

Convective storm detection

mesocyclone detections
Convective storm detection
In multicellular storms and squall lines, the mid-level jet stream is often intersecting the line and its dry air introduced into the cloud is negatively unstable.

Hail

hailstormhailstoneshailstone
It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts.

Lightning

lightning boltlightning strikelightning strikes
It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts.

Tornado

tornadoestornadicCyclone
It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts. Tornadoes can occur along waves within a line echo wave pattern (LEWP), where mesoscale low-pressure areas are present.

Waterspout

waterspoutswater spouttornadic waterspout
It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts.

Low-pressure area

area of low pressurelow pressure arealow pressure
Tornadoes can occur along waves within a line echo wave pattern (LEWP), where mesoscale low-pressure areas are present.

Summer

austral summersummer seasonsummers
Some bow echoes which develop within the summer season are known as derechos, and they move quite fast through large sections of territory.