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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]
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]
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 ...
A snow squall is a brief period of intense snowfall and wind that leads to whiteout conditions which could trigger dangerous traffic accidents. Snow squalls are most common in the northern United ...
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]
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.
Squall lines typically "bow out" due to the formation of a mesoscale high-pressure system which forms within the stratiform rain area behind the initial convective line. This high-pressure area is formed due to strong descending air currents behind the squall line, and could come in the form of a downburst. [10]