- Squall line
Cyclonic vortexover Pennsylvania with a trailing squall line.] A squall line is a line of severe thunderstorms that can form along and/or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes and waterspouts. Severe weatheralong squall lines can be expected if it displays a line echo wave pattern (LEWP) or if the line is in the shape of a bow echo.
Original use of the term
Polar front theory was developed by
Jacob Bjerknes, derived from a dense network of observation sites in Scandinaviaduring World War I. This theory proposed that the main inflow into a cyclonewas concentrated along two lines of convergence, one ahead of the low and another trailing behind the low. The trailing convergence zone was referred to as the squall line or cold front. Areas of clouds and rainfall appeared to be focused along this convergence zone. The concept of frontal zones led to the concept of air masses. The nature of the three dimensional structure of the cyclone was conceptualized after the development of the upper air network during the 1940s.University of Oklahoma. [http://weather.ou.edu/~metr4424/Files/Norwegian_Cyclone_Model.pdf The Norwegian Cyclone Model.] Retrieved on 2007-05-17.]
Development and movement
Organized areas of thunderstorm activity reinforce pre-existing frontal zones, and they can outrun cold fronts. This outrunning occurs in a pattern where the upper level jet splits into two streams. 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. The convection then moves east and toward the
equatorinto the warm sector, parallel to low-level thickness lines. 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. [Office of the Federal Coordinator for Meteorology. [http://www.ofcm.gov/slso/pdf/slsochp2.pdf Chapter 2: Definitions.] Retrieved on 2006-10-22.] This feature is commonly depicted in the warm season across the United Stateson surface analyses, as they lie within sharp surface troughs. If squall lines form over arid regions, a duststorm known as a haboobmay result from the high winds in their wake picking up dust from the desert floor. [Western Region Climate Center. [http://www.wrcc.dri.edu/ams/glossary.html#H H.] Retrieved on 2006-10-22.] Squall lines are depicted on National Weather Servicesurface analyses as an alternating pattern of two red dots and a dash labelled "SQLN" or "SQUALL LINE".
Line echo wave pattern
The best indication of the presence of severe weather along a squall line is its morphing into a line echo wave pattern, or LEWP. A LEWP is a special configuration in a line of convective storms that indicates the presence of a low pressure area and the possibility of damaging winds, large hail, and tornadoes. At each kink along the LEWP is a mesoscale low pressure area. In response to very strong outflow southwest of the mesoscale low, a portion of the line bulges outward forming a bow echo. Behind this bulge lies the mesoscale high pressure area. [Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=line-echo-wave-pattern1 Line echo wave pattern.] Retrieved on
Surface weather analysis
Mesoscale convective system
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Look at other dictionaries:
squall line — noun a cold front along which squalls or thunderstorms are likely • Hypernyms: ↑cold front, ↑polar front * * * noun 1. : an intersection or boundary between the cold and the warm winds of an extratropical cyclone or between the cold air of an… … Useful english dictionary
squall line — A narrow zone of meteorological activity usually parallel or nearly parallel to a cold frontal surface, occurring some distance away. Squall line activity, or a line squall, is characterized by thunderstorms, heavy rain, brief wind shifts, gusty… … Aviation dictionary
squall line — Meteorol. a line or extended narrow region within which squalls or thunderstorms occur, often several hundred miles long. * * * … Universalium
squall line — noun A line of thunderstorms, hundreds of miles long, with squalls at the advancing edge … Wiktionary
squall line — A line of severe thunderstorms that can form along and/or ahead of a cold front … Geography glossary
squall line — noun Meteorology a narrow band of high winds and storms associated with a cold front … English new terms dictionary
Squall — A squall is a sudden, sharp increase in wind speed which is usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. [The Weather Channel. [http://www.weather.com/glossary/s.html Weather Glossary: S.] Retrieved… … Wikipedia
line squall — noun a squall advancing along a front that forms a definite line • Hypernyms: ↑squall * * * noun : a squall or thunderstorm occurring along a squall line; also : a line of squalls or thunderstorms * * * a squall advancing along a front that forms … Useful english dictionary
squall — Synonyms and related words: altercation, bark, battle cry, bawl, bay, beef, bell, bellow, bickering, black squall, blare, blast, blat, blate, bleat, blizzard, blow, blow a hurricane, blow great guns, blow over, blow up, blubber, bluster, boom,… … Moby Thesaurus
line squall — A squall or series of squalls extending along a squall line or instability line. The word squall is used to describe a strong wind that rises and dies away quickly. A line squall is a squall advancing on a wide front, sometimes hundreds of miles… … Aviation dictionary