Australian Severe Weather Forum

Hi Jimmy,

The two cells in question were no doubt supercellular in my opinion. No#1 Cell once breaking the cap, had tops well over 40,000ft, and at the base of the updraft were two bell dome features, related to the classic type supercell. Cell No#2 did not sustain supercellular features unlike Cell No#1 and became slightly outflow dominant as you can probably see in my daytime CG shot. Michael Manning has some better contrasted photos of Cell No#1's features clearly showing that of a classic supercell. I was not aware that the BOM confirm supercells in their STWs? I have never come across the actual word being mentioned. The only way the BOM would have been able to confirm it would have been through a phone-through report from a spotter out in the field anyway.

Cheers,

Julian

Julian,

Thanks for your reply. Interesting to say that you are suggestign "without doubt". In my opinion, your pictures show separated updrafts which to me indicate that it was multicellular at least during the time you took your pictures. Nice updrafts of course but the heights of 40,000ft by no means define supercells. A supercell is a thunderstorm that has an updraft with persistent deep rotation (typically rotating for 20 minutes or more).

In terms of Michael Manning, the following photograph is the best I can refer to that you may be suggesting:

http://jeff.bsch.au.com/gallery2/main.php?g2_itemId=1058

The lower level structure is quite nice. Perhaps this was an interaction with a boundary. Nevertheless, it looks more like an LP. Very little precipitation is falling from the base of the main updraft. And then it seems to enter into a collapse mode rather quickly with rain falling through the base and cutting off the inflow. Perhaps the storm crossed a boundary to develop some nice features.

Regards,

Jimmy Deguara

The BoM do in fact issue warnings with enhanced wording to the effect "this is a dangerous storm" and I would think that this is used only when a mesocyclone is detected on doppler radar (and to that end is only used in detailed warnings for capital cities and surrounds). Since a mesocyclone cannot be seen by the human eye, BoM are unlikely to upgrade a warning on that basis as it is becomes far too subjective and, utimately, unreliable.

Hi Jimmy,

To better explain what I was referring to you before, I think you are a little confused with storm days. I am referring to the 3rd of December, not the 6th of December. Here is a picture taken from Michael Manning which clearly shows the structure in question:-



That feature is on the base of this updraft here:-



There was some time to develop in between both pictures, but you can see clearly in the first picture the feature which I have been trying to explain.

Cheers,

Julian

They often make that statement for Sydney and they don't have a doppler radar here yet (unless it is a secret one). I would say they can usually predict from the behaviour we look for - movement different from other storms in the area, the intensity in the centre. And of course storm spotter observations when you see the text "5cm hail reported at xxx".

The dangerous storm text does not necessarily infer a supercell, it has also been used for multicells....its purely when they have a spotter report or get such a radar signal that it recieves this statement....usually the prior.

The picture you show there presents in my mind no doubt that this particular storm was a supercell...structure is too well defined to be anything else. I tend to agree with Jimmy's suggestion of LP tendencies though.

As for your 'supercell 2', im a fraction skeptical without seeing any better defined imagery...ive seen bases like that on Multicells...and pulse/air mass thunderies. While it may have sustained supercell like characteristics for a short time period this does not indicate a supercell...rather the development of a short lived mesocyclone.

Only way I know of to obtain better clarification without calling the bureau is to ask yourself the following questions:

1) Relative to the movement of all other isolated storms on that day did this storm move in a different direction without a known wind change? This is usually present on radar imagery (with obvious left/right moving tendencies)

2) Was the storm long lived and isolated, or the northernmost member of a line which sustained for longer than the regular convective cycle (60 mins)?

3) If doppler is available is a mesocyclone discernable (may also be detectable on normal radar in particularly well defined storms)?

4) Is rotation occuring within the cell? (discernable from inflow bands, structural characteristics, production of a clear mesocyclonic tornado etc).

Basically to come out and say a particular storm is a supercell I would expect at least 1,2,4, 1,2,3 or 3,4 to have substantial evidence.

While this is not a be all or end all I do believe its a reasonable method for identifying these storms rather than New South Welshman or Queenslanders for example saying...that is definitely an SC (due to location and conditions), whereas they might not agree in Vic (where the conditions maybe werent as favourable, but a supercell happened).

Nice captures there though.

Julian,

Can you please indicate the orientation of this structure - which direction are we looking?

Can any radar of this storm event be placed online?

Regards,

Jimmy Deguara

I've saved millions of radar images over the past few weeks, so I need to know the dates/times and locations to put up the correct ones.   Julian - can you please advise date and time ranges and I'll do up some loops

MB

Sydney was the second Australian city to have Doppler radar. Darwin was first -- it was used in some of the many studies up there. During Sydney 2000, we had two Dopplers covering Sydney I believe (having borrowed Darwin's) -- all from memory, correct me if I am wrong.

Who told you this?

So everyone knows who reads this topic. The Kurnell Radar is in fact a Doppler Radar.

What is with the orange coluration in that image? Were you using a coloured ND grad?

Hi John,

Your comments about the VDS not just being used for supercells is interesting.  I'm wondering if this changes from state to state?  I've only seen the VDS comment for Sydney and Brisbane regions, and anytime it's been used it's always been a supercell (and a well structured one at that).  From my observations, a 'VDS' is used for supercells, but not all supercells are given a 'VDS.'

There are many times when the warnings have listed a spotter (or public) report but no VDS has been given.

I'll go one step further to say, from observations, the 'VDS' is used when significant low level rotation is being detected in the storm by doppler (ie, it's the Bureau way of saying 'this storm may produce a tornado').  But I know of two storms this year to buck this trend a little...

And yep...the Kurnell radar is a doppler (implemented for the Olympic games).

AC

I was aware that Kurnell was a doppler radar, but it isn't easy to find on the BoM site except through a google search and doesn't have the windfinding features available online. Not sure why as Brisbane and Adelaide both have links to their new dopplers and the original ones. However we seem to be digressing into what makes the bureau issue a "this is a severe storm" message.

Which is fine, but probably easier to ask someone there than speculate.

OK I just worked out how to send pics to my mailbox. Here are 2 pics of the frount of the storm from Ipswich QLD on the 3.12.08 in the arvo.

This storm has come up previously in this thread date of storm 6th of December 2008. Fairly long lived cell, that showed up some mesocyclone rotation on the Brisbane Doppler :- http://www.theweatherchaser.com/radar-loop/IDR66I-brisbane/2008-12-06-06/2008-12-06-09
I've attached a few pics that show storms structure from over the location of Kilcoy through to Beerwah app.
Paul