Oct 15th 2011 “Bellthorpe-Stony creek” storm including funnel structure

On Oct 15th I observed and filmed a couple of storms near the Sunshine Coast that developed in the afternoon.

The first was the Caboolture storm which went on to split and disappear out of sight but not before showing a bit of inflow structure after it split.

Right mover 4-20pm app

Left mover at 4-43pm app

The other storm of interest which developed further west started showing a lowered inflow area on the NW side after around 4-50pm

Bellthorpe-Stoney creek storm 4-56pmapp

I continued filming this storm which went on to produce a very interesting and  suspect "feature" at 5-01 which lasted app one minute in development.
Initially I got excited but on reviewing the footage at various contrasts it became evident what had occurred was not straight forward textbook funnel to the ground as I of course had hoped.
Here is the Bris 128 rain rate @ 5-00pm showing both a nicely developed Caboolture right mover which now appears to be a supercell with a right mover hook out over Morton Bay. Also highlighted is the developing Bellthorpe-stoney creek storm which appears to me as at best a developing / marginal supercell at this point.

Bris 128km radar image (© Australian Bureau of Meteorology -from http://www.theweatherchaser.com/radar-loop/IDR663-brisbane, with overlayed highlights for purposes of discussion only)

Bris doppler at 5-01pm

Here is the footage of the Bellthorpe-Stony Creek Storm. With the structure in question at a few different contrasts at the end.

 

Now exactly what was going on... in the footage...
(initial timelapse section of the film is run at 30x normal speed, the contrasted closeup structure sections of the film have been sped up by a factor of 2x for the first 2 and 4x for the last. The ridge top in the closeup footage is app 17km distant)
The long and the short of it is I'm still not convinced or sure.... Thanks to those (including Jimmy) who have reviewed and given there thoughts on what was happening..
I will list my thoughts and throw it open as to what happened.
couple of other things of interest-
1:55-2:27 "neck" of bell lowering seems to be rotating in an anti-cycloninc direction or at least drawn on right hand side towards the rear.
A funnel appears to be visible at base of RFB in a wall cloud like structure, as the bell scud disapates 1:27, 2,27-2.36, 3:21-3:24.

This funnel area is apparent as a lowering after the bell scud has disapated highlighted in the pic below, the remnants of the funnel goes highlight rotation. Moving from right to left at the rear indicating anti-clockwise rotation in that portion of the storm base.

Another point to note the Bell lowering/Scud has a base which does not rise where the Scud below it moves rapidly upward.
There appears to be several possible ground vortices and also one possible point where a funnel almost appears to have organised for app 10 seconds (real time)
Funnel "like" structure behind rising scud below the base of the "bell lowering"-

Again same possible funnel like structure near ground a few seconds later-

and app 30seconds (real time) later what appears to be 2 remnant rotating vortex like structures on ground. The one on the left is stationary the one on the right is moving to the right.

Now I pinned down the locations in the above image & I've checked the immediate ridge area in several traverses near the ridge top at the location of the suspected vortices's in the above pic and in between and also checked for damage along the ridge top up to 500m Nth and 1km Sth, and sadly no cigar- whatsoever,.. at least on/near the ridge top.
So either the funnel "IF" present was further back behind the rising scud and if damage occured it was further toward the west base of the ridge or in open ground ( I did check from a distance but, if the damage was not overly severe it was certainly not visible from a distance)
So my thoughts are the storm was a developing supercell which did go on to show better signs of being a supercell in the next couple of radar images before being engulfed by the approaching storms from the west. The event was more borderline supercellular/non supercellular and although to me it appears to have at least produced a clear funnel at the cloud base. Funnel structure behind the bell lowering is obscured, and below the bell scud it is at best conjectural, or was fairly weak, or short lived or all three.
So what are we left with an interesting feature which I would list as far as tornadoes are concerned between the "possible to unlikely" category  Unless of course clear evidence is located on the ground.
Anyone willing to take up the battle with the Lantena Gods?
Cheers
Paul D

6 thoughts on “Oct 15th 2011 “Bellthorpe-Stony creek” storm including funnel structure

  1. Cameron Creswell

    (Accidently put this on the Nimbin discussion, thought I was still on this one.. My mistake.)

    I was watching the radar, and the Caboolture cell in particular did end up with most of my attention…. It is hard to see but it does look like a hook echo (to my untrained eye anyway) at 5:00pm which would add even more evidence to the suspect pictures above… Im leaning towards it being a weak tornado though based on what I’ve seen. Some one with some experience (like Jimmy) may be able to see if there is anything in the radar or not.
    Here (if it attaches correctly) is a screenshot of the Radar at the time of the above pictures, showing development of the storm, and the doppler wind on the small captures on the left showing shear inside the cell; the doppler wind on the left are lined up next to their corresponding radar image, give or take a minute.

    – Cameron.

  2. hail

    Hi Cameron,

    Thanks for the sequence of images indicating the movement of the cell. Given the cell was moving east, this is most likely not a hook at all but probably part of the flanking line. The feature in other words is on the wrong side.

    I know there are always watchful eyes in this country for any evidence of a tornado. However, a tornadic hook will be pronounced and also longer lived. It takes typically about an hour for a supercell to produce sugnificant rotation that eventually leads to a tornado.

    Thanks once again.

    Regards,

    Jimmy Deguara

  3. Paul Devine Post author

    Hi All
    I probably should have left out the circles on the right mover Caboulture cell. As the Caboulture storm and subsequent splits were a separate storm which was not involved in the production of the suspect feature. The storm in question is the left hand circle positoned bettween Crohamhurst and Kilcoy (in the radar images in my post) with the location of the suspect feature just a fraction to the NE of the “y” in Kilcoy at exact time of the Bris Doppler image shown. Which at best seems to show a very small area of anticlockwise circulation.
    What probably interests me in the process of development is how much influence the area / development of downdraft at the rear of the RainFreeBase area had. Whether this is a true RearFlankDowndraft or interaction with outflow the developing cells to the west or simply be the clockwise wrapping of outflow from the same storm?.
    And how much influance the apparent “RFD” had on the developing rotation and production of the suspect feature.
    Whether the feature was a mild nonsupercellular funnel (which may or may not have reached the ground) or whether it was a form of spinnup in the right location to interact with a funnel in the rotating area of cloud base?
    Back in Feb (21st) this year I managed to film ( http://www.youtube.com/watch?v=gSi5e9kj4V0 ) a very simillar looking sequence where an apparent rear outflow/downdraft push seemed to initiate storm rotation or at least be coincidentaly timed with it. Only I lost the best section of footage. This time I was a bit far away. WIth luck maybe next time I’ll nail it.
    Cheers
    Paul

  4. Paul D Post author

    Hi Cameron & Jimmy

    The radar sequence Cameron has shown is 5:00pm AEDT – 6:00 GMT (5pm Daylight Savings Time) , The funnel feature occured at 5:01pm AEST (QLD time), or 7:01 GMT. (theweatherchaser radar shows Daylightsavings time in NSW, and EST in QLD) hence the confusion.

    Here is the radar shot at 5pm QLD time, with a pointer to the app location of the funnel feature and also a sequence, with the doppler including a pointer highlighting the same portion of storm base. The Doppler sequence is 1min advanced 5:00pm is 5:01pm which was spot on the time of the funnel.

    http://s979.photobucket.com/user/DavJR17/media/2011-10-15%20storms/Compositeradarshotdplsml2.jpg.html

    Areas of rotation within the storm base appear to be small scale max 1-2km diameter and not long lived.

    The earlier Caboolture storm showed little in the way of base features before it split.

    Here is the complete afternoon timelapse sequence and lightning captures including the earlier Caboulture storm.

    http://www.youtube.com/watch?v=podnNYZ5Wzo

    The storm Bellthorpe/Stony creek storm in question may have had some interaction with the outflow of storms to the west as it was beening engulfed which may have amplified localised areas of rotation in the storm base.

    Also prior to the funnel feature the storm was tracking in an easterly direction, but this appeared to change to a more ENE direction after the funnel feature was observed.

    Regards,

    Paul

  5. Jimmy Deguara

    Hi Paul,

    Nice timelapse sequence Thanks for posting it!! I am thinking the evening activity with lowered bases had more potential of a wall cloud than earlier activity. Earlier storm heights were multicells. Definitely not tornadic but you were in position for a nice days chasing!

    Regards,

    Jimmy Deguara

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