typhoon_tip
Meteorologist
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Re: Barry Gone, Quiet Again
Wed Jun 06 2007 12:04 AM
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It was an MCC (Mesoscale Convective Complex). They are typical in the warmer month east of the Rockies in Canada, and the conterminous U.S. They usually get their start during the late afternoon or evening hours from diurnal destablization, combined with a trigger. That trigger is usually outflow boundaries separating slightly differential airmass, or oriographic lift (winds moving over higher terrain). When you have high CAPE (Convective Available Potential Energy), you do not need much of a trigger to spark off heavy convection.
MCCs are not typically associated with frontal mid-latitude cyclone related boundaries; the frontal boundary driven convective process is somewhat different.
The way they work is, a strong thunderstorm will develop do to either oriographics or as said, a residual outflow boundary from a previous days convective traffic. That thunderstorm then produces an outflow, which rushes out and lifts the higher CAPE air, producing new updrafts and thunderstorms. This initially keeps the cluster of thunderstorms going until the other process, a little more obscure , can take over. It has to do with radiative cloud top cooling. Basically, the tops of the convective cloud masses radiate energy to space faster than the deeper parts of the cloud or the surrounding atmosphere, and this causes the temperature in the upper parts of the cloud to actually cool additionally; this adds instability to the columns of rising air, allowing the whole system to perpetuate. That is why when you look out in the Plains, at an overnight satellite loop, you may see a bright red/orange blob meandering from NW to SE, with very little attending frontal systems. This was a self-propogating convective process, referred to as an MCC.
MCCs do not typically run out into the Gulf and spawn tropical entities. The physics that drive these different systems are just non-transferable. Although, radiative cloud top cooling is part of the nocturnal tropical upward intensification process, with MCCs the convection is no longer surface based instability once the process is being heavily guided by RCTC. Convective systems inherently are surface based; in fact, tropical model assume a near oceanic-atmospheric coupled environment.
What typically happens to MCCs is the sun rises over them and stops the radiative process; the cloud top is heated faster than it radiates and the destrablization process ends -- that is why MCCs often die a rather quick death before noon of the next day. In some rare cases they may morph into other events, such as Derechos and so forth, but in general, the MCC is primarily a nocturnal system.
John (Typhoon_Tip)
Edited by typhoon_tip (Wed Jun 06 2007 12:38 AM)
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