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A squall line, or quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompanied by abrupt and gusty wind shifts).
A squall line is an elongated line of severe thunderstorms that can form along and/or ahead of a cold front. [11] [12] In the early 20th century, the term was used as a synonym for cold front. [13] The squall line contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts. [14]
A summer squall line in Southern Ontario, producing lightning and distant heavy rains. Wind shear is an important aspect to measuring the potential of squall line severity and duration. In low to medium shear environments, mature thunderstorms will contribute modest amounts of downdrafts, enough to turn will aid in create a leading edge lifting ...
Rainbands in advance of warm occluded fronts and warm fronts are associated with weak upward motion, [1] and tend to be wide and stratiform in nature. [2] In an atmosphere with rich low level moisture and vertical wind shear, [3] narrow, convective rainbands known as squall lines form generally in the cyclone's warm sector, ahead of strong cold fronts associated with extratropical cyclones. [4]
When thunderstorms are able to organize into squall lines, a feature known as a rear inflow jet develops to the south of the mid-level circulation associated with its northern bookend vortex. This leads to an erosion of rain within the broad rain shield behind the squall line, and may lead to acceleration of the squall line itself. [4]
A mesovortex is a small-scale rotational feature found in a convective storm, such as a quasi-linear convective system (QLCS, i.e. squall line), a supercell, or the eyewall of a tropical cyclone. [1] [2] Mesovortices range in diameter from tens of miles to a mile or less [3] and can be immensely intense.
Conceptual airflow in a squall line with the Rear-inflow jet shown. The rear-inflow jet is a component of bow echoes in a mesoscale convective system that aids in creating a stronger cold pool and downdraft. The jet forms as a response to a convective circulation having upshear tilt and horizontal pressure gradients.
The dry line normally moves eastward during the day and westward at night. A dry line is depicted on National Weather Service (NWS) surface analyses as an orange line with scallops facing into the moist sector. Dry lines are one of the few surface fronts where the pips indicated do not necessarily reflect the direction of motion.