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Mesoscale Convective System
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A shelf cloud such as this one can be a sign that a squall is imminent
A mesoscale convective system (MCS) is a complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. Mesoscale convective systems may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and Mesoscale Convective Complexes (MCCs), among others, and form near weather fronts. They have been noted across North America and Europe, with a maximum in activity during the late afternoon and evening hours during the warm season (i.e. late spring and summer) on both continents. Mesoscale convective systems over the Plains of the United States bring the region about half of their annual warm season rainfall.
Definition
Mesoscale convective systems may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and Mesoscale Convective Complexes (MCCs), among others. MCS often is used to describe a cluster of thunderstorms that does not satisfy the size, shape, or duration criteria of an MCC. They tend to form near weather fronts and move into areas of 1000-500 mb thickness diffluence. Their formation has been noted worldwide, from the Mei-Yu front in the far East to the deep tropics.[1]
Great Plains of the United States
Typical evolution of thunderstorms (a) into a bow echo (b, c) and into a comma echo (d). Dashed line indicates axis of greatest potential for downbursts. Arrows indicate wind flow relative to the storm. Area C is most prone to supporting tornado development.
The convective season for the Plains ranges between May and September. Mesoscale convective systems develop over the region during this time frame, with a bulk of the activity occurring between 6 and 9 p.m. local time. Mesoscale convective systems bring 30 to 70 percent of the annual warm season rainfall to the Plains.[2] A subset of these systems known as mesoscale convective complexes lead to up to 10% of the annual rainfall across the Plains and Midwest.[3] Squall lines account for 30% of the large thunderstorm complexes which move through the region.[4]
Europe
While most form over the continent, some MCSs form during the second half of August and September over the western Mediterranean Sea. MCS triggering over Europe is strongly tied to mountain ranges. On average, a European MCS moves east-northeast, forming near 3 p.m. local solar time, lasts 5.5 hours, dissipating near 9 p.m. LST. Around 20% of the MCSs over Europe do not form during maximum heating. Their average maximum extent is around 9000 km[2].[5]
See also
References
External links
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