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General Discussion >> Hurricane Ask/Tell

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Weather Master

Reged: Thu
Posts: 468
Loc: Palm Coast, Florida
Barry Gone, Quiet Again
      #75403 - Tue Jun 05 2007 04:49 PM

Barry brought us some good rains saturday and the weather turned good in the afternoon. I heard it was pretty bad when it moved up north as an extra-tropical system. Today, I see a nice feature off the coast of Texas but shear looks to be too high for it to develop.. but if shear wasn't high, it would be interesting how this little disturbance would turn out. Though look closely on the satellite, a circulation seems to be on the southwest side of the blow up.....

(Post moved to this location since the Texas convective complex was not mentioned in the Main Page leadoff article. Remember, on the Main Page you should only respond to topics mentioned in the Main Page lead article and/or updates to that leadoff article. Please try to help us with this special point of interest this year. Thanks.)

Edited by Ed Dunham (Wed Jun 06 2007 04:49 PM)

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Rich B
British Meteorologist

Reged: Sat
Posts: 498
Loc: Gloucestershire, England, UK
Re: Barry Gone, Quiet Again [Re: allan]
      #75404 - Tue Jun 05 2007 05:33 PM

yh, i noticed the texas feature earlier. Radar imagery showed there was a circulation which moved off shore near Corpus Christi, but the convection has weakend somewhat in the past few hours. We seem to see these sort of features move off the coast in this region occasionally each season. If conditions were right, then we would be keeping a close eye on it, but its just too hostile at the moment i think.

Rich B

SkyWarn UK

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Storm Tracker

Reged: Sat
Posts: 278
Loc: Southeast, FL
Re: Barry Gone, Quiet Again [Re: allan]
      #75405 - Tue Jun 05 2007 10:18 PM

Im slightly more interested in what is happening out at 27n 65 w nice blow up of convection

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Posts: 573
Re: Barry Gone, Quiet Again [Re: allan]
      #75406 - Wed Jun 06 2007 12:04 AM

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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Weather Watcher

Reged: Fri
Posts: 32
Loc: Palm Beach County, FLA
Re: Barry Gone, Quiet Again [Re: allan]
      #75409 - Wed Jun 06 2007 04:30 PM

I am just curious to what is going on in the Eastern Gulf, it looks like a large blow up of convection

(Note that this is the same convective activity that is discussed above - it has just moved eastward.)

Edited by Ed Dunham (Wed Jun 06 2007 04:51 PM)

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Re: Barry Gone, Quiet Again [Re: flanewscameraman]
      #75411 - Wed Jun 06 2007 04:54 PM

It is interesting to look at, but other than being in a tropical latitude it is non-tropical in nature.

My immediate impression of it was that it was being produced by an old frontal drape in the vicinity but there is no such feature in any analysis that I can find.

Be that as it may, the outflow from the heavy convection is pooling stable, slightly denser air in the NE and E Gulf, a process detectable by observing satellite. From visible imagery, one can discern S/SE low level winds (CU streets) moving into this complex and the leading edge of the outflow boundary is lifting this tropical air flow up to its conditional instability. This is erupting thunderstorms and then the mid level momentum (strong winds moving west to east through the vicinity) is carrying the rain and associated dynamically cooling air back east and away from the zone of lifting. This whole set up appears to be perpetuating its self because there is a steady source of warm humid air streaming into a convective system that is displacing the outflow away from choking off that source. It is likely this is a remnant MCC that moved off into the Gulf, and now is taking on different processes (non-tropical) in sustaining its self.


I would not expect any trouble beyond immediate mariner's concerns as the deep layer is very hostile to tropical development in that vicinity, at this time. From middle troposphere all the way up to upper levels there are strong westerlies (as described above) shearing across the area.


Edited by typhoon_tip (Wed Jun 06 2007 04:57 PM)

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