Severe Storms Through SE QLD!

January 5, 2000

The day was looking quite promising a few days before, with winds backing with height combined with strong shearing, cool air aloft, and DP's in the low 20's with temps in the low 30's.  However, the day before, it was obvious that our potentially great storm day would be thrown into jeopardy.  The central NSW coast didn't achieve its potential, with a NW'ly wind ahead of a SW'ly being the main culprit. The low cap didn't help either.

A low had formed to the east of Victoria, and instead of rapidly moving SE like most lows do during summer, it moved ENE very slowly.  This changed the tilt of the trough causing WNW/NW winds ahead of the trough,and allowed a weak SW'ly to drift ahead of the main S'ly surge.  As a general rule, a SW'ly change will never cause thunderstorms, or if they do, they'll be short lived (20-30minutes). I'm yet to find or devise a satisfactory explanation as to why this is the case.

The night before, a line of showers and thunderstorms moved over SE QLD - this increased DP's to the low 20's.  However, in the morning, the winds quickly turned to the NW, and W'ly just inland.  The temperatures rapidly rose, with the Brisbane AP recording 30C at 11am (EST).  Jonty arrived at my house just after 11am, we had decided to go to the Boonah lookout for a good observation point.  It was looking very bleak, with winds turning to the WNW, and the surface and lower layers were drying out rapidly.  At about 12:15pm the first towers popped up, and a Cb in NE NSW also formed.  Unfortunately, this development collapsed soon after, but it was followed up by continual development.  Ross and Ben met up with us at the Boonah lookout at around 12:30pm.  The development continued for over two hours, with most of the updrafts being very strong, but not being able to sustain themselves.  The updrafts were also being blown over by the shearing winds too, something was lacking - most likely, moisture!  At this stage, we needed the seabreeze front to come through, which was quite possible given the relatively light winds we experienced.  Some more promising development occurred to our north, with very strong, sustained updrafts, and eventually some of these were developing into Cb's.  There was one interesting cell to the south that kept my attention though, a very interesting base, and it gave some very impressive virga, and eventually precipitation shafts.  I believe all it needed was a north-easterly component in the winds, and this would have begun to rotate.

We headed just south of Boonah to get a better view of it, to observe the cell and decide what to do.  A small meeting was held just to the south, and Jonty, Ben and Ross wanted to head north to the developing cells near Crows Nest to Caboolture.  Majority rules!  So we quickly went north, while also keeping an eye on this cell that formed just NW of Boonah.  While the actual first cell died, it spawned new cells just to its north while collapsing.  These were quickly developing and intensifying rapidly.  A rumble of thunder, and then just a little later a spectacular pulsing CG was observed from it.  We still continued NE, wanting to get onto the Bruce Hwy to head north.  The new cells were continually developing, and eventually formed a small line and a rather nice shelf cloud.  We stopped in the emergency section of the Logan Motorway (yes, this was an emergency <g>).  At last, we finally received an update of what was happening!  James Harris gave us a radar and satellite photo update, which made me insist that we stay with this cell, rather than head north.  We decided to go to the Mt Gravatt lookout to get a better view, but soon decided against it, and headed for Sunnybank Shopping Plaza (an excellent advantage spot that looks south!)  And what a sight it was!  A spectacular shelf cloud had formed, it was very photogenic.

A rain foot was evident on the cell, as well as very heavy rain shafts, with hail shafts!!!  The shelf cloud was very smooth in one section, and the storm had gained a lot more height, with nice glaciation on the edges, and a defined, fairly crisp anvil.  We witnessed a great CG, with a crack of thunder about two seconds later (I missed this on video!)  Although I did manage to get several other CG's during the course of when we were up there.  We had a security guard come up to see what we were doing, he had mentioned that they get quite a few people come up to the top of the car park to witness thunderstorms!!!  He left soon after when he found out we were harmless.  The storm was just about upon us, and we had to travel with it - we decided to travel to Mt Cootha to get a view of it as it went over the eastern suburbs.  It did take a little longer in peak hour traffic at 5pm (had to go over the Riverside Expressway which services the CBD), but we still made good time.  Possibly a better option would have been to travel to the eastern suburbs and go to Murrarie reserve (another good advantage spot), but we still had an awesome sight from the top of Mt Cootha!  We were able to see the storm go over the eastern suburbs, it had a massive rain foot (digital camera pictures not available of this rainfoot - SLR pics to come)- at least over one kilometer ahead of the main precipitation shaft!!  We all agreed that there were severe winds in that cell.  Later we discovered that 11 houses were damaged (mainly due to falling trees), and hail up to the size of 10c coins was also reported - the next day I surveyed the damage, and estimated winds of around 90km/h - a few trees down, mostly large branches though.

We also were looking at a cell near Caboolture, it was also very photogenic, with very strong updrafts, with a defined and crisp anvil!

 At around 5:40-5:45pm, we spotted what appeared to be a wall cloud on the NW flank of the storm.  It was very convincing, with an inflow band into it, but we were a bit too high up (200m in elevation), to see if it was rotating.  It looks very suspect, and it was certainly in the right place, and with the NE wind finally in, there was 180 degree backing with height shear in the lowest 3km.  It did appear to take a 'gusted out' appearance about 15-20 mins later though, which makes me have my doubts.  But it was still very interesting!  A funnel cloud was reported near Boonah, and another wall cloud was sighted out to sea by another ASWA member, so it was quite possible!

We decided to head out to Redcliffe to get a view of the thunderstorms as they moved out to sea, and hopefully get a good lightning show.  While there was some lightning (and the occasional CG, or strike that shot up into the sky!) it wasn't overly spectacular, even at night.  But this was made up for it by the absolutely spectacular/awesome/beautiful/fantasmagorical sunset Cb!!!!

Overall, it really was a great day!  I didn't want to head north to the Cb's over the Brisbane Valley, as it's an unfavorable area for chasing.  We did see some great Cb's, and some great structure - so I'm not disappointed at all!