Wednesday 14th of December 2005
Chase Duration: 5.5 hours
Chase Distance: 250km
Report By: David Findlay
Photo Gallery
Rotating Updraft Timelapse - High Definition (1.7mb)
Chase Report Video with Commentary (15.5mb)
Radar Loop
Other Chaser's Reports:
Weatherzone Breaking Weather Thread
Weatherzone Briefing Room Thread
Zeus's Photo Gallery
Chase Report
The BOM had predicted only a chance of showers for Wednesday. A south-easterly change was moving up the coast from NSW and passed through the Gold Coast during the afternoon. Around lunchtime some cells developed on the border ranges east of Rathdowney and moved mostly east. They were mostly scattered and not very well organised but various cells produced severe weather. At least one became a classic supercell with a corkscrew rotating updraft visible. Other cells formed on the Sunshine Coast including one supercell spotted by Ben Quinn.
I left Redcliffe at 12:30pm and headed down the Gateway Motorway after some nice activity that seemed to be building behind the Gold Coast. Zeus joined me at Toombul Road and we travelled in convoy for the rest of the afternoon till I left at 4:30. As we were travelling down the Gateway Motorway and M1 large cells with strong updrafts were evident to the southwest. At Beenleigh we dropped off the motorway and headed for Mt Tamborine via the Beenleigh-Beaudesert Road. Along this route we were experiencing strong winds, around 40-50km/ph blowing towards the southwest. There was quite a bit of debris coming off the trees. On the way the updrafts to the south and southwest seemed to be exploding upwards, and in gaps between trees I could occasionally see lowerings and scud underneath.
First major stop was at Mt Tamborine, at around 2:40. From a lookout at North Tamborine we could clearly see some strong updrafts on the cell to the south of us. It appeared to be moving mostly east, although expanding somewhat towards us. There was also a suspect lowering that formed, but dissapated shortly thereafter. I got a radar update from John Hayes and he said that the cells were moving east and weakening. It seemed to be heading for Southport or Coolangatta. We left Mt Tamborine and headed down via the direct road the Nerang. This is a quite steep twisting road, but it offered some great views to both the north and the south. The Gold Coast seemed to be covered with some low stratusy cloud like a fog, about 300 metres above the ground. The cells were visible beyond this.
Turning on the the M1 southbound again, we headed south to Neilsens Road, where we turned off to the left because of a traffic jam ahead. On the way down the M1 the low cloud had passed over us. It was like a tongue of cloud, almost maybe a roll cloud of some sort, with no visible features. My picture didn't come out well because I was driving though. From here we headed via Robina Parkway to Robina Town Centre, stopping near a construction site with a clear view to the south and west. At this point I took a pan, then a timelapse video which showed the corkscrew updraft. Initially I did think it looked a bit like a supercell, but I wasn't willing to call it at that point. There was a definate inflow band, and a lot of rainfree base visible. The rotation wasn't visible to us at the time because of the low contrast due to haze and low light. It's clearly visible in the time-lapse video which was taken over the period of about 6 minutes. I took a new frame initially every 5 seconds then later every 10 seconds as I was running out of card space. Next time I must remember to take my laptop. I had the cable, but not the laptop. In retrospect, I've I'd been paying attention to the storm rather than taking the timelapse I probably would have noticed the rotation as there's quite a difference from frame to frame.
It looked to me like the cell was moving somewhat north, so after about 20 minutes we decided to head northwest. We travelled up the M1 northbound to Mudgeeraba Road then turned left to the south and eventually stopped in Monaro Rd, Mudgeeraba at about 4pm. From here we had an excellent view of the cell directly to our south. It had a very brightly visible sun-illuminated hail shaft and we finally had a clear view of the sunlit updraft. It was now visibly rotating. Over the period of 20 minutes 4 or 5 prongs developed, all of which were rotating at about 30 to 40 km/ph by the look of it. Several began to take on the appearance of wall clouds, but I'm not certain of this. I'll let others be the judge of that based on the photos and video. The updraft itself seemed to be pulsing. It would go through a period of massive expansion and rotation, then stop, then the base would show lots of rotation and develop prongs. This repeated 4 or 5 times. The cell stopped producing a visible hailshaft 10 minutes after we arrived and seemed to suddenly begin moving faster toward the east. At one stage it took on a clear corkscrew appearance, but looked to be slowing weakening. I left at 4:25pm, and by this point it was clearly weakening and moving east. In my rear vision mirror on the way home it seemed to completely disappear not long after I left. Zeus continued on, and hopefully he should have some more excellent photos.
I believe this was a definate supercell, as it had a persistant rotating updraft for more than an hour. I'd really like to hear from anyone who was chasing or observing in the area before we got there. How long was it rotating before we got there? Were any of the other cells rotating? If you've got a report or images send me a link and I'll link it in "Other Chaser's Reports" above. Otherwise comment below.
