Topic: What defines a Supercell ???

[Gambit]

Hi all,

I have seen recently talk about some storms being "Supercells" or just "Severe Storms" I've had a look throught the threads and can't find a definative answer so could someone, please, for the people playing at home maybe explain the difference?

(I'm not trying to start WW3 as I feel that this question may have the potential to be a "can of worms" so please put down the can opener and play nicely)   

Regards

Mat

[Jimmy Deguara]

Mat,

There is no requirement for a war but debates are fine - it helps us to learn.

Generally speaking, a supercell is a thunderstorm with updrafts that exhibits persistent deep rotation for at least 20 minutes. I welcome for anyone to introduce a documented definition from a good source.

Where my comments dwell are that supercells are relatively rare making up a small proportion of all storms or even severe storms. But they often do cause most of the insurance related damage. Statistics people - I am pretty sure that currently accepted statistics have changed over the years as to proportionality.

Regards,

Jimmy Deguara

[Gambit]

Generally speaking, a supercell is a thunderstorm with updrafts that exhibits persistent deep rotation for at least 20 minutes.

Hi Jimmy,

When you say deep rotation do you mean a large portion of the storm rotating?

[Jimmy Deguara]

Gambit,

Yes when a whole storm updraft rotates visually, you can be certain that there is a supercell around - take cover. I have seen some people show base rotation in some cases disorganised rotation. You can get 'eddies' or localised vorticity but usually these do not sustain for long periods.

I guess what we are trying to do without access to doppler radar is build supportive evidence of observed features that lead to what could be a picture. I guess I relate it to a confidence level. For instance on the 9th December 2007, we could safely say with a high level of confidence it was a supercell. Giant hail fell, the structure looked classic, the storm veered in a different directly on the day as observed on radar, a funnel was observed as well as a wall cloud, it had a nice back-sheared anvil and nuckles which suggest it has powerful updraft and it was certainly a severe storm. I am pretty sure this would have had a bounded weak echo region as well on radar but we do not have access to 3 D radar scans.

The storm also was long lived with a persistent echo core and deviation for a long period of time - beyond the defined 20 minute period.

Regards,

Jimmy Deguara

[Gambit]

Hi Jimmy,

Thank you very much for your description, I do appreciate all the help I can get...

With the storm that hit Dunoon on the 26th Oct 07, I remember seeing a definite lowering of and rotation to the base as it passed over Lismore (I work in Goonellabah). Was this an example of what you have described? ( was it a supercell? )

Regards,

Mat

[Jimmy Deguara]

Gambit,

The storm that approached Lismore on the 26th October 2007 was a supercell - no doubt. However, as it approached Lismore, the storm became messy and eventually gave rise to another storm on its northern flank. This one was the storm that developed rapidly and produced the tornado.  It seems that due to an interaction with the boundary coming from the north that this storm produced a tornado. If you watch the tornado video, the rotation of the mesocyclone and the surrounding base is violent.

This is why these are categorised and recognised separately as very serious severe storms.

Regards,

Jimmy Deguara

[Gambit]

Wanted to say a quick thank you but I need 10 words or more so

Thanks Jimmy.


Mat