The Boonah-Redland Bay Supercell
December 10, 1999
storm report
The Spring-Summer period over SE Qld has been unusually cool and often cloudy with SE winds. December 10 was very different, with temps reaching the low 30's (C) and humidity around 60% making it a very oppressive day. During the morning the sky was very hazy, suggesting a heat inversion and the only clouds were mid level: altocumulus with patches of castellanus holding the promise of storms later. However many of us had become pessimistic during the previous few months when system after system seemed to pass us by, or weaken without delivering any storms. We knew there was a good chance of storms on this day, but we were not positive at all! The charts had a front moving up the NSW coast and there was the hint of an upper trough as well. In hindsight however, the severity of the storms could never have been forecast by the way the weather models had been looking.Radar and Satellite loops, provided by the Bureau of Meteorology:
a/ High Resolution Radar; b/ Low Resolution Radar; c/ 3D Radar (links to come soon)
At around 1pm storms started to develop over the Qld/NSW Border Ranges and also the NSW Northern Tablelands. Radar for the afternoon shows that up to 3 supercells occurred over the area:
The first possible supercell showed up on the Brisbane Local Radar south of Kyogle at about 1.10pm and by 2pm it started to affect the Mullumbimby-Byron Bay-Brunswick Heads area of the Northern NSW Coast dumping pea-marble size hail at depths up to one metre!
The next possible supercell later affected the Gold Coast (South of Brisbane) sometime after 4.40pm - it was first seen developing on radar at about 1.30pm more than 50km WSW of Stanthorpe. On its way over the Border Ranges towards the Gold Coast it assumed huge proportions, regularly showing off all sorts of shapes on radar. Steve Baynhem, an ASWA member on the Gold Coast captured some awesome video footage of winds over 100km/h blowing torrential rain and hail up to 3cm in diameter horizontally.
Now we come to the big one.
<Chase Report by David Petrie below> At 2.20pm, about 100km WNW of Stanthorpe, a thunderstorm developed and began to track swiftly east. By this time, there were many thunderstorms on both sides of the Qld/NSW Border - mostly of pulse variety. The main storm first showed an indication of hail on the 4pm radar image when it was positioned just east of Warwick. It was a solid mulitcell storm at this stage, moving a little north of east. As the storm intensified, it noticeably started changing direction (NNE) - the first obvious signs were on the 4.20pm image. Soon after, the supercell smashed through Boonah, unroofing 11 homes and dropping golf ball hail. Winds in the area would have reached 150km/h, and when you combine that with large hail, its frightening! At a local high school, most of the roof of the main building was ripped off and dumped over 100m away on houses.
From Boonah, the supercell moved NNE or NE across Beenleigh, Kingston, Redland Bay and out to sea NE of North Stradbroke Island. The damage track was continuous after Boonah, but less severe. It appears that golfball size hail fell throughout the track along with winds not much over 100km/h. A lot of tree damage occurred with this (in areas like Kingston, Beenleigh) but little structural damage fortunately.
As the supercell marched across the Bay, a strong line of storms came in from the WNW of Brisbane, moving across the city after 6.30pm. Some damage is believed to have occurred north of Ipswich but this is unconfirmed. The storms, like the many others during the day, dropped hail - only pea size however. The supercell and this line of storms shot out tremendous bolts of CG lightning as well. All up, 35 000 premises were left without power during the storms.
Below: A series of further photographs I took from the Sunnybank Plaza Carpark. These were all taken during a 7min period - the storm was really moving! The solid updrafts pictured do have a "rotational" look to them, indicative of supercells.
* A special thanks to Ben Quinn and Anthony Cornelius of ASWA for gathering some of this information and again to the Bureau of Meteorology for allowing me to use their radar images. Big thanks also to David Petrie for the chase report and Judi Childs for the tornado report.
Tornado Report by Judi Childs
As for the tornado. I both saw and heard it. No photos unfortunately as I was just getting the dogs inside when it came into the front paddock. I heard it first, that noise is not something you can mistake....sounds like a diesel train going full speed or a jet engine on takeoff. The tornado itself was basically fairly white when it hit my place, due I guess to the fact that there was little debris for it to pick up in the last couple of hundred metres before it hit me. It was hurling out roofing iron and tree branches predominantly. There was a complete whiteout as it came over the corner of my house and across the back yard. Amazingly, I had a plastic outdoor setting just outside the back door, and that remained untouched or indeed unmoved, yet only 20 or so metres away, everything was destroyed. I went for a drive back along its path the other day.
As you would expect, most of the debris is gone and there is a lot of re-growth. The track basically followed the Waterford-Mt Tamborine Road north between Steggman Rd and just past Dairy Creek Road, then curved more easterly across my place and the last sighting that I am aware of was at the Palm Lake Retirement village on Logan River Road at Bethania. I have spoken with some guys who saw it near the intersection of Weaber Road and Waterford-Tamborine Rd, Buccan. These guys were helping the SES clear some fallen trees as a fire truck was trying to get through to a house fire at the height of the storm. They noticed it when they saw trees being spun up out of the ground! Guess those chainsaws are pretty noisy!
As for pics of the damage, I have attached a photo taken at my place the day after. To the left of the barbeque area were three kennels. In this pic was basically all that we found. The large beam lying across the pile in the foreground was one of the big roofing beams in the barbeque area, and this is what we found about 400 metres away. The iron roofing sheets that we found had big tears in them and some were badly twisted as well.
After working for the past few big storm days I was exited on Friday the 11th, that I had the day off, and that there was the chance storms might develop during the afternoon. With the sky clear early I headed into uni to check that storms were still forecast and also read my e-mail etc...
I headed home (New Farm) around 1pm with the tops of storms now visible through the haze. With widespread cumulus to the west I headed out on the western freeway, hoping that something was developing behind the haze out near Warwick. I continued past Ipswich and then began to feel disappointed that storms were developing north-west of Brisbane (the opposite direction to where I was headed) and also to the South-east behind the Gold Coast. But with Triple J blearing and temperatures still very high, I continued with the hope that my luck would change.
As I continued, my optimism grew as a cumulonmbus cloud developed less than 20km in front of me. At the same time I heard the first thunderstorm warnings over the radio as well as reports of heavy falls of hail in northern NSW.
I pulled off the road and watched the cloud continue to intensify and develop with explosive speed. It was at this stage that I realised I had quite a storm ahead of me and that it was moving east very fast. (away from where the road was headed) With this in mind I thought that I could head towards Boonah and get in front of the storm to see it at its best.
Once again I stopped the car (this time for fuel) in Kalbar, where I noted many strong CG lightning strikes and an awesome updraft on the northern side of the rain shaft (which was also turning white, making me believe that this storm was definitely carrying hail and meant business) I also saw several horses going crazy in a near-by field. (my excitement was building)
After refueling I continued towards Boonah, but the storm was moving too fast, I was now almost beneath the rain shaft with wind and light rain blasting me from the south. At this point I stopped due to the number of tree branches and other debris being blown around, as well as the fact that power lines were now swaying violently on the side of the road that the wind was coming from (ie. that if they had of fallen they would have landed on me) So, I turned around and thought that I'd try and cut it off again before it went out to sea. On my returning trip to Brisbane I stopped several times to witness the awesome power of this storm. For this entire time the storm generally retained a similar appearance. The north-eastern quarter was feeding into the storms heart, the rear was streaky and white, while the core was a ragged brown black colour, with numerous CG lightning strikes. (I couldn't believe that the storm was real and that I was chasing it. It was great!!!)
By the time I'd made it back to Brisbane the storm was now clearing the coast while a long cigar shaped roll cloud followed further to the north-west. The roll cloud appeared to move across Brisbane's inner-southern suburbs and merge with another storm that was developing to the north-west of the city. On returning to New farm, I had a beer and watched the light show as this second much weaker storm moved south-east and out to sea.
