Storm Australian Severe Weather Forum
Severe Weather Discussion => General Weather - all topics not current severe weather. => Topic started by: Jeff Brislane on 18 November 2006, 10:55:55 AM
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Seeing as there has been some discussion recently about the validity of supercells in regards to their possible presence either alonside or within (embedded in) meso scale convective systems I thought it would be appropriate to continue the discusion in it's own thread.
From what we know from observations from the last 25+ years supercells and meso scale convective systems (MCS) are not mutually exclusive. Supercells usually form firstly as isolated storms (isolated from other supercells - except when splitting) and as they progress through the atmosphere they can easily increase in size as high precipitation (HP) type supercells and merge with surounding HP supercells to form MCS clusters. Often the supercells become linear as they merge into the systems but not always. They can still retain their meso-cyclone updraft and continue as supercells embedded in the MCS. There are 3 basic types of MCS - the squall line - the standard MCS cluster - and the derecho which is an MCS on steroids! There are also more intense MCS's that are in fact classified as MCC's or meso scale convective clusters.
Such an example of and MCS with embedded supercells is a famous one which should bring back a few fond memorys for Jimmy and Dave!
http://www.spc.noaa.gov/misc/AbtDerechos/casepages/may27-282001page.htm (http://www.spc.noaa.gov/misc/AbtDerechos/casepages/may27-282001page.htm)
Let the discussion begin.
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Are the supercells themselves remaining within the system? or are the just the intiators, present for a short amount of time before the linear motion of the MCS begins to dominate the updraft
Are you asking this generally or in relation to the test case I've presented in the link?
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Then in relation to the system in question, supercells maintained themselves within the system as it progressed south through Oklahoma. There is also evidence that supercells in fact increased in intensity during the passage of the system as evident by the Oklahoma mesonet data which shows winds speeds in southern Oklahoma sharply increased in a narrow swathe to over 100mph which would have been due to a supercell interacting with the derecho.
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Now with reference to the Squall line case: These can be intiated by a single supercell correct?
No.
Squall lines can be initiated by supercells but there has to be a merging of gust fronts from a line of supercells to form a Squall Line MCS. I mean that a single supercell can produce a storm scale squall line with it's gust front, especially during collapse of the supercell (which often causes a bow-echo, but that's another story). But an MCS squall line is produced by more than one cell, because to be classed as an MCS it has to be meso scale and not storm scale. Mesoscale Convective system
Squall lines are also more commonly formed as linear systems in the first place which is what we most commonly see in Australia. Such systems develop when the windshear is uni-directional through out the atmosphere. Cold Fronts are probably the most common causes of squall line MCS's.
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A single supercell CAN form a squall line MCS: Outflow Propagation forming normal cells which proceed to form a cold pool and hence a squall line(bow echo in some cases).
John, you are not understanding what i'm saying. I'm not saying that a supercell cannot initiate an mcs (look at my last post more carefully), I'm saying that a single supercell cannot form into a squall line mcs. A single supercell can produce a large gustfront but it's not meso scale, it's still only storm scale. We are obviously talking about two different processes.
Now does anybody else, such as those who witnessed this event, want to comment in any way?
Jeff.
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Nice debate. Jeff and John - we are getting into technicalities here.
From here on, can we come up with documentation and quotes from scientific papers or essays to back up any arguments? That would help as it seems not to begetting anywhere.
Regards,
Jimmy Deguara
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I will be honest and say I have not read any literature on Mesoscale Convective Systems (MSC) aside for a study of derecho's within the US. For these reasons I do not have a detailed understanding of what a MSC really is. However, maybe it would be nice to introduce some examples of squall lines with embedded supercells from within Australia. I think a recent event on the 16/12/06 is quite interesting. On this day it appears as if supercell formed from near Esk from a group of multicell-type thunderstorms. This supercell later crossed the coast around Rainbow Beach and produced the strongest ever record wind gust in Australia from a thunderstorm. For much of the supercell's life time it is embedded within the southern end of a squall line-
http://i60.photobucket.com/albums/h19/mmcctt/IDR662-20061216070423.gif
I would say that supercells merging with squall lines is in most cases though is accompanied by a dramatic decrease in the storms intensity. I think the 8/11/06 had a good example of this where, what appear by radar to be an extremely powerful supercell, rapidly lost its identity upon merging with the advancing squall line.
http://i60.photobucket.com/albums/h19/mmcctt/IDR233-20061108093531_Biloela.gif
1hr later-
http://i60.photobucket.com/albums/h19/mmcctt/IDR233-20061108103525.gif
Finally, I'd like to give an example of what I believe may of been a text book example of a MSC. This occured on the 13/10/05 near Alice Springs. In the radar image storms a sqaull line can seen propagating on the edge of a convectively generated cold pool. I particular like the rounded shape of the squall line in this image.
http://i60.photobucket.com/albums/h19/mmcctt/3.gif
Michael