Models had been progging a large easterly infeed with a surface trough dragging in moisture from Eastern Australia into South Australia. At the same time we had a large upper low, retrograding westwards from New South Wales, passing through the north Mid north area, delivering easterly winds. This essentially created a situation where winds came from a generally easterly direction from the surface all the way up to 200mb, with winds on the Wednesday topping out at 35 knots at 600mb, a rather rare thing to see! The upper low also cooled the mids and uppers, which was vitally necessary as surface temps and moisture were far from special, low to mid 20ies and low to mid teens for the dewpoints. However the upper low also fed a jet exit over us on the Wednesday evening of reasonable strength, and sure enough we had some cells form.
They formed initially in no Mans Land, with local cells struggling with dry air in the mids inibiting convection. However a multicell storm formed on the outflow of of the No Man’s complex and trained towards northern Adelaide, moving at about 45km/h from the ENE, extremely quick for an easterly storm. It seems new storms would form from the flanking line of this storm, and it died rapidly before reaching Adelaide, before reigniting from newer cells on the southern edge, perhaps in response to the sea breeze front interacting with outflow, about 25 minutes before reaching me.
The nukage was quite spectacular on approach with solid convection, however the storm still retained more of a hybrid coldie/warm thunderstorm look from the front end. By radar, it dumped very heavily just to my east, maybe 5-8km, likely with hail and I was soon engulfed by strong outflow and very heavy rain/small hail. Winds exceeded 80km very briefly, over a period of 5 seconds and a few dozen pea sized hail pellets were seen to hit the window, it really was quite intense for a moment there. The storm dropped a quickfire 8mm at Virginia, in a period less than ten minutes. It was also a reasonably noisy cell, with plenty of flash and rumble, and a couple of closeish Cg’s seen/heard in the core.
It weakened rapidly, and the southernmost cell produced a gust of 104km at Outer Harbor so some damaging winds were to be had in these cores. These images from behind show the rear structure much more typical of warm cells.
At the same time a couple of other cells had formed, a reasonably strong one north-east of Mannum, and this very rapidly pushed towards Adelaide. It seems at some point it pushed out a strong OFB from a downburst and this caused it to propogate small cells in a WNW direction on the northern flank, aiming it directly at the northern side of Adelaide metro again. This OFB changed the game in Adelaide, and suddenly we had very solid and tall convection rapidly developing and cells became scattered, with local thunder.
The cells that developed over the northern burbs and then moved out off the coast were the most interesting however and one in particular was the strongest cell of the day IMO. I watched it grow from birth, presenting a very solid Calvus head and showing various signs of being severe. The backend updraught was one of the very few I seen that remained verticle, evening bulging out into the strong easterly winds. A large, slightly lowered RFB formed, frequent Cc lightning in the upper parts of the cloud stucture (picked up very poorly by tracker), and from pictures I have seen from the south, a gradually increasing rain intensity, with a sharp cut-off and very heavy rain curtain on the back end of the storm.
The radar returns showed an organised storm, with an almost supercell like signature (this was short lived and I don’t necessarily think this was a supercell), diverging V-shaped anvil to the storm and focused updraught and heavy rain cut-off on the northern side of the storm.
I was watching it from St Kilda and for a while had a great view of the entire structure, indeed some of the best updraught structure I have seen in my time. There was another storm to my north west which was rather weak visually with see-through rain curtains but it was pumping out Cc lightning quite well, with a flash every 10-15 seconds resulting in almost constant low rumbling. The stronger cell to the SW had wrapping inflow due to differing winds between the surface and mids but no mid level rotation could be noted. However at the surface there was a rotating, and reasonably active inflow region with decent upper motion feeding into the storm, stretching into a horizontal funnel, this can be seen in the timelapse. Certainly was interesting to watch and was quite low to the ground at times.
At this point, I was left with a weaker cell to the north obscurring my view of the main cell, but putting out plenty of lightning, so I let there camera run and caught half a dozen bolts, here’s a couple. Lightning tracker barely picked up a single bolt but there were dozens.
Radar showing the sequence of events proceeding the development of the gulf storm. A line of storms can be seen marking the leading edge to the east, rapidly surging west.
Overall a rather rare and very interesting event to watch. I’m glad I targeted the Adelaide Plains rather than going further afield, I would have missed out on watching an awesome cell had I done that.