There's no doubt that the first cell that Hit Canungra and the Gold Coast Hinterland is a Supercell. It's obvious in both the reflectivity and in the doppler scans. In fact this cell exhibits I believe by far the best structure of any cell on the day.
The cells that took out Brisbane is in fact a severe squall line that followed the supercell.
In my opinion after carefully examining all three Brisbane radars the severe damage was most likely caused by a Rear Inflow Jet interacting with the surface along a section of the squall line. In all three radar scans you can see a small notch in the vicinity of the worst affected areas at the time they were being hammered. What happens then is that a portion of the squall line accelerates faster than the rest which is likely a Line Echo Wave Pattern. More evidence for this theory is seen in the Brisbane Airport radar which shows a probable anti cyclonic book end vorticy at full maturity at 0740 utc to the north and cyclonic book end vorticy in the airports vicinity. Eventually the rest of the squall line catches up and the whole thing evolves further along the Sunshine Coast.
Rear Inflow Jets can be very powerful depending on the strength of the mid level jet but in the case of this storm 80-100 kts is very likely. Tornadoes can occur in conjunction with these features but would likely be very hard to prove without video or photos of funnel.
Of interest also is the way the squall line interacted with the outflow boundary of the earlier supercell. You can see this interaction best in the doppler scans and it could well have contributed to the strength and severity of the squall line in that area.
Btw, please feel free to shoot my theory down in flames ;-)
Regards Jeff.
Brisbane Airport Radar. Check out the bookend vorticies at 0720 utc.
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Brisbane Airport radar loop
