Multicell Line Storms
Introduction:
Also known as squall lines, multicell line storms consist of a line of storms with a continuous, well developed gust front at the leading edge of the line. An approaching multicell line often appears as a dark bank of clouds covering the western horizon. The great number of closely-spaced updraft/downdraft couplets qualifies this complex as multicellular, although storm structure is quite different from that of the multicell cluster storm. Covered topic-Weather associated with multicell line storms.
Squall lines most frequently produce severe weather near the updraft/downdraft interface at the storm's leading edge. Downburst winds are the main threat, although hail as large as golf balls small tornadoes can occur. Flash floods occasionally occur when the squall line decelerates or even becomes stationary, with thunderstorms moving parallel to the line and repeatedly across the same area. Squall lines with a confirmed severe weather history allow for the issuance of reliable warnings. Pilots should be extremely cautious, as they should for all thunderstorms, particularly near the squall line's leading updraft/downdraft interface.
Squall lines are common, especially in vertically sheared environments where the mid-level winds are moderate to strong. The most common sever weather element in squall lines, by far, is the downburst, with damaging winds possible from the time of gust front passage, into the period of heavy precipitation. Hail may occur with the rain, with the heaviest rain and largest hail adjacent to the updraft. Dissipating elements at the rear of the squall line often result in a period of light rain before cessation of precipitation.
Intense storms, in rare cases even tornadic supercells, periodically occur in squall lines. The most likely locations for these more powerful storms are at an eastward bend, on the south end, or north of a significant break in the line. Note that all these positions allow a storm to compete better with its neighbors for the low-level inflow of air.
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