Thunderstorms 24 September 2014

Today was an interesting setup, and something that I can’t recall seeing very often at all. Overnight a rainband had significantly moistened the lowers leading to widespread dewpoints of 12 degrees, up to 14 degrees in places with 20 degree or so temps. There was very slack shear, predominantly from the SW up to around 25 knots at the steering level, decreasing further east with the upper trough. Even the 300’s into what would become an upper low were very slow. However this upper feature had a cold pool and caused lapse rates to be steep enough to quite a depth, and with the dewpoint and temperatures so close we had relatively low bases (for SA). This led to rather deep convection and whilst CAPE was quite skinny, it was enough. There were broad area of high and mid level cloud earlier on, and storms formed in areas that managed to attract sunlight.

Convergence over the Murraylands led to a line of storms during the arvo, which kept back building along flanking lines, and this was the main point of interest storm wise this day. However a small cell developed over the gulf just south of Port Wakefield, probably in response to the SBF and moved NE towards Clare. I noticed it, and looking at the skies knew it would either be a long drive SE to see anything, or this small chance. It weakened, however a line of convection formed ahead of it and I sat just east of Clare watching to see what it would do. After one cell grew particularly tall, it rapidly died and I noticed the top of a tall cell to the SW, and once checking radar, realised another cell had formed on the flank of the previous.

It was glaciating as I left the ranges, and by the time I arrived at Blyth was thundering away nicely. It was incredibly discrete compared to all of the other cells seen this day, even at initiation there was hardly any competing convection, with just a flanking line of cells, and a couple mediocris to congestus to the south.

As the first significant downburst of the multicell occurred, first time glaciating as well.

Closer view

Just west of Blyth, you can already seen that initial downburst has started to subside, and another RFB was developing behind it. Thundering away nicely at this stage.

Shows the extend of the clear air behind this.

I corepunched straight into it, the first core was in the stages of decay but was still heavy, out the back another cell was just bursting, and there was a magnificent updraught and base right next to it. The cutoff from the wet to dry was merely meters, and was seriously heavy. Enough rainfall was produced to creates quite  a bit of runoff on the sides of the road.

Strong updraught and nice RFB, just west of Blyth, was looking very mean!

Downburst in the paddock next to me, not a drop of rain where I was.

I followed the cell north, watching the flanking cells strengthen then dump in spectacular fashion, the lack of shear meant it was straight up then straight down, nearly every new cell produced a rock solid rainshaft and rainfoot. The thing was producing near constant thunder by the time it was north of Blyth and frequent flashes. Some real nice cracks in there as well.

New cell going up, anvil can be seen here as well. Ultrawide view, the top stuff was almost above me.

And down it comes!

A short time later, a new downburst, and more development alone flanking line.

It weakened off soon after and I was hesitant to stick with it, given I could see a whales mouth out just ahead as the multicell became outflow dominant. I decided to stick with it given the lack of anything else within 1 hours drive, and had to work around horrible road networks to get back up behind it. At this stage a long line of flanking cells nuked in spectacular fashion just out ahead of me. I wanted to get back in front so was forced to core punch. It wasn’t too bad at first but the inevitable downburst occurred just to my west and moved overhead just south of Spalding. The rainfall rates, while relatively narrow were rather impressive, a complete whiteout, I could only just make out the road and there were sheets of water on the road in a couple of very narrow strips. Towards the front there was also plenty of hail, up to maybe half a cm in size.

Large cell ready to dump as I drove into it from the south. Frequent cc’s and a couple of massive cg’s (maybe positives) dropped out of this.

I got north of Spalding and the cell that had dumped was rapidly collapsing and proceeding to decay but still presented a spectacular sight. The flanking line was still in decent shape, so I followed it up to near Jamestown, before it eventually gave up.

Once I eventually got out of the rain north of Spalding the cell had already weakened dramatically, as was the theme of the day. Still looked rather cool however.

And yet another cell on the flanking line dumping. This was taken at the same time as the above image.

Sun finally out given the line a mean look.

Still not giving up! Nothing strong but really cool skyscapes with beautiful light at this time, a real treat.

The convergent storm line to the SE looked very spectacular at this stage, boiling away in the distance, and so I drove to Burra given it wasn’t far out of the way to get a closer look. I ended up driving a little way down onto the plains and watching the cells during sunset. Whilst not huge, the convection was nice and the colours tremendous.

Line of weak cells at sunset.

Distant cell and subtle hues make for a peaceful scene.

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2 Responses to Thunderstorms 24 September 2014

  1. Great chase Mark and very well documented by text and graphic photos!
    There’s a lot to be said for little shear and relatively light steering winds. Chasing in SA rather than in the USA has the benefit that we can corepunch or get under developing cells without much fear that our vehicles will be pummelled by damaging hailstones 🙂

    • MarkDawsonPhoto says:

      Haha yeah, can be good or bad depending on how you look at it, always more hesitant on more solid days to punch through cells. Thanks for the comment!

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