Storm SEQ/NE NSW Rain & Storms 23rd-31st October 2020

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Ken Kato

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wow so the Lifted index was -13??
I wouldn't take that theoretical LI value of -13.2C on that sounding too literally @Gleno71 - that figure would only be valid if Brisbane's forecast max temp was reached (fell a degree or two shy yesterday) and even if it was, it'd only be valid for that time. Brisbane Airport from where the sounding was performed typically tends to be a fair bit cooler than the city.
Those particular soundings also rely on the assumption that parcels only rise from the surface. In reality on hot sunny days over land, parcels tend to rise from a well-mixed layer in the lower atmosphere, not just from the surface.

But you can see that even with the observed max temp of 30.5C in Brisbane and a mixed layer in the lower levels, the extremely steep lapse rates aloft mean that any parcels would be extremely unstable if they could make it up through that somewhat more stable layer in the lower levels. Of course it's better to also look at observed soundings a bit upstream of the location of interest, especially on a day like yesterday with such strong steering winds aloft advecting stuff into the area.... but you can see how generally unstable it was.
 

Gleno71

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Well I had a small storm again mid morning that popped up pretty quickly but died just as quick, managed 1.8mm from it.

The sky had a real unstable but messy look about this afternoon and nothing could really get going, everything was either to my south or north, but this little cell (picture below) tried hard and I persevered with it hoping something would form.
IMG_1087 by Eddy Groot, on Flickr
Then this to the left of the main cell formed and I was getting more hopeful and there was the odd rumble too.
IMG_1117 by Eddy Groot, on Flickr

Then it morphed into this, there was some rotation to be seen.
IMG_1138 by Eddy Groot, on Flickr

And yes I did think it, but that was about as far it would go.
IMG_1156 by Eddy Groot, on Flickr
All this was above Bulahdelah
In the end it threw out a few nice bolts.

Awesome pics mate, love the structure
 

chunky

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I was annoyed that I wasn't closer to some of these storm cores but seeing the incredible size of some of that hail I think I was extremely lucky. I moved out of the Gatton/Laidley area only to find out I just missed it. Was in Rosewood, missed that, Was in Purga and missed that and followed behind the storms that hit Ipswich and Springfield areas.
Few shots from last night! Was amazing just sitting on this back road at Como, watching cell after cell blow up in the same spot just to the north of Wolvi. The full moon came out too making it look like day time! Be interesting to see the full extent of damage in the area today. I can't remember a more widespread destruction storm event on this part of the coast (excluding debbie).
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Brilliant. Love the light one on the road with the lightning! Well they are very cool.
 

chunky

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Part 3

The signs were ominous heading back towards Purga. Unknown to me at the time is they were getting smashed with giant hail.

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I veered to Goolman to get a shot of hopefully the barn with lightning behind it. There was some but the dam trigger wouldn't fire.

I did however get some very nice rotation on the base of this cloud and I was hoping I would see my first tornado not thinking hey I am right below this.

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Rod H

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Aug 7, 2019
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Brought a new rain gauge , the old fashioned plastic type but good quality. I was sick of my weather stations tipping bucket system giving false reading so went manual.
Went out this morning to check the new gauge and was surprised to see just how much I received.
Had a very big amount of rain from yesterday's storm 325mm here in Maudsland.
In spite of this I noticed my rain water tanks were only just full so thought I might have blocked downpipes but no.
Found out the big reason--- bloody new rain gauge shows measurements that I did not quite read properly .
instead of 325mm it should have been 32.5 mm , missed seeing the decimal point.
That might just explain why my tanks are not quite full but almost.
Funny part is that the tipping bucket was dead accurate.
More care needed in making observations methinks!! :emoji_face_palm::emoji_face_palm::emoji_face_palm::emoji_face_palm::emoji_face_palm:
 

4107

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Here’s my report from yesterday, most of the pics I threw up on the run between driving yesterday, but there’s a couple of new pics aswell.....
Headed out towards Beaudesert a bit later then I wanted to do after needing to tend to a few more important things first. I turned off the Mt Lindsey Hwy at Glen Eagle and pulled up on Allen Creek Rd to check the radar, looking to my North West I could see straight down lightning bolts dropping a relatively short distance away, so headed that direction in hope of capturing one. I struggled to find an open location to stop at so hooked a left up a random side road and found a nice enough spot to try my luck, was a only a matter of minutes later though that the rain started up so I got out of there.

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Found a spot a few minutes up the road out of the heavy rain and watched that cell pass through to my South / Beaudesert area.

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I then headed back towards Beaudesert direction on Allen Creek Rd and pulled up before Glen Eagle area to wait and watch the radar. Sitting for about 20 minutes watching the radar, it was exploding to life with several black core cells heading towards me, the first one looked to be keeping just to my North through Jimboomba, the second one I thought would be a touch further South and hit right where I was, so I started thinking about escape routes as I snapped a few pics over an open field I’d stopped beside.

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PART 2 to follow
 

Orebound

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Jul 4, 2019
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I was annoyed that I wasn't closer to some of these storm cores but seeing the incredible size of some of that hail I think I was extremely lucky. I moved out of the Gatton/Laidley area only to find out I just missed it. Was in Rosewood, missed that, Was in Purga and missed that and followed behind the storms that hit Ipswich and Springfield areas.

Brilliant. Love the light one on the road with the lightning! Well they are very cool.

It's always tough when there is some faster storm motions, trick it to always keep positions downstream of anticipated storm tracks. I'll always keep an equatorward bias as well to allow for left deviations.

For instance I was in place (blue dot) for those storms near Willowbank as they were passing near Gatton, you'll never get in the right place trying play catch up. Believe it or not there are places around the world they are moving much quicker than that at times too by the way. There have been set-ups in the US for instance that I've started 20 miles behind a storm and tracked it across three states only to get no closer than.... 20 miles lol.

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Anyway, great posts on here. I'm on a flight home atm but I'll put up some stuff myself in the next couple days.
 
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4107

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I took a punt I’d have just enough time to slip North on the back road to Greenbank between the 2 black core cells hoping to avoid any hail, that didn’t exactly pan out as planned though.

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Somewhere along that road amidst the pouring rain the hail started up, it wasn’t massive but the vehicle took a a heap of decent thumps along the way, it appears for the most part the rear ally canopy took the majority of hits and vehicle looks mostly ok...(still haven’t had a thorough look at it though). I decided to keep punching through as other vehicles pulled up on the roadside due to a lack of visibility, eventually just before hitting Pub Lane area the sky started to clear some thankfully. Little did I know how lucky I got hail wise, have since seen pics and reports of the stuff that hit that surrounding area (family in Greenbank a few minutes from where I was have holes in their house roof from the hail). I started looking for somewhere to stop and photograph what I’d just driven through, it wasn’t until I got back to Calamvale on Beaudesert Rd that I could get a half decent view of some of it, so pulled up at Calamvale Community College and snapped a quick pic.

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The wind started picking right up as I snapped that pic so I knew it wasn’t far away, so I continued on towards home and detoured a short bit to Archerfield Aerodrome to see what it looked like there

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Not long after that I got home, 5 minutes later the first of 2 cells containing decent hail hit our place, but we were lucky and missed the really bad stuff. The rest of the arvo / evening was spent having a bbq and a few drinks reading about the carnage others had copped, the day ending with a beautiful sky to cap a pretty brutal day
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TweedStorm

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Here’s my report from yesterday, most of the pics I threw up on the run between driving yesterday, but there’s a couple of new pics aswell.....
Headed out towards Beaudesert a bit later then I wanted to do after needing to tend to a few more important things first. I turned off the Mt Lindsey Hwy at Glen Eagle and pulled up on Allen Creek Rd to check the radar, looking to my North West I could see straight down lightning bolts dropping a relatively short distance away, so headed that direction in hope of capturing one. I struggled to find an open location to stop at so hooked a left up a random side road and found a nice enough spot to try my luck, was a only a matter of minutes later though that the rain started up so I got out of there.

7E4BDE55-B181-4A60-9739-ED6BA1E8F914.jpeg


Found a spot a few minutes up the road out of the heavy rain and watched that cell pass through to my South / Beaudesert area.

35C57B8E-FF46-437B-ADD4-09C516866340.jpeg


BB08B235-474D-4316-9C99-FA9B04CF08BB.jpeg


I then headed back towards Beaudesert direction on Allen Creek Rd and pulled up before Glen Eagle area to wait and watch the radar. Sitting for about 20 minutes watching the radar, it was exploding to life with several black core cells heading towards me, the first one looked to be keeping just to my North through Jimboomba, the second one I thought would be a touch further South and hit right where I was, so I started thinking about escape routes as I snapped a few pics over an open field I’d stopped beside.

AC72C714-3A12-4FFC-A8D9-6C3D653B1E41.jpeg


PART 2 to follow
Fa tastic photos 4107... Just love it out there for storm chasing!
 

Ken Kato

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Great photos and reports everyone!

I just remembered that I'd saved the output from that 5-day severe weather script I sometimes run. Above was the output for yesterday. The dark blue contours = areas where large hail potential exists using a slightly modified version of the US Storm Prediction Centre's significant hail parameter. Green contours = potential heavy convective rainfall and colour shades = severe thunderstorm potential.
I didn't pay too much attention to this output at the time but it's probably not surprising that the large hail ingredients were present even though it was mainly concentrated in parts of SEQ.

I did quite enjoy my 4 rounds of hail last week where I was though.
 

Gleno71

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Great photos and reporting. Not sure the truth to this,but some of the chasers i kept in touch with yesterday, were saying because the storms were SE sliders , the structure was limited and was messy in places in comparison to when storms come in from the South West. Going by history, most of my cleaner looking storm shots were from those that started in the southern downs and end up towards Brisbane via the scenic rim , or if you are south of the border, storms that develop around Tenterfield and end up at Byron Bay via casino and Lismore.

Im suprised i havent seen a clear cut supercell structure photo similiar to what they get in the USA in yesterdays event. Could the other reason be because there were simply too many supercells close together ?
 

Ken Kato

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Great photos and reporting. Not sure the truth to this,but some of the chasers i kept in touch with yesterday, were saying because the storms were SE sliders , the structure was limited and was messy in places in comparison to when storms come in from the South West. Going by history, most of my cleaner looking storm shots were from those that started in the southern downs and end up towards Brisbane via the scenic rim , or if you are south of the border, storms that develop around Tenterfield and end up at Byron Bay via casino and Lismore.

Im suprised i havent seen a clear cut supercell structure photo similiar to what they get in the USA in yesterdays event. Could the other reason be because there were simply too many supercells close together ?
I suspect one of the reasons why the ones that had a more eastwards track were more photogenic was because they were left movers and therefore were stronger cells.
But also, the fact that those cells had a more eastwards track also meant that they moved a bit out of the main congo line of cells and therefore more of their structures were visible.

As for your last sentence, I'd probably agree with that. I know where I was, a lot of the structures of the individual cells were hard to see because they were obscured by the falling precip and cloud immediately before and after them. Had to be in the right place at the right time relative to each cell to see decent structure.
 

Orebound

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Great photos and reporting. Not sure the truth to this,but some of the chasers i kept in touch with yesterday, were saying because the storms were SE sliders , the structure was limited and was messy in places in comparison to when storms come in from the South West. Going by history, most of my cleaner looking storm shots were from those that started in the southern downs and end up towards Brisbane via the scenic rim , or if you are south of the border, storms that develop around Tenterfield and end up at Byron Bay via casino and Lismore.

Im suprised i havent seen a clear cut supercell structure photo similiar to what they get in the USA in yesterdays event. Could the other reason be because there were simply too many supercells close together ?

I know there was a fair balancing act going on between outflow dominance and periods of better inflow which tended to stifle better organised low level structures. I shot I very nicely organised mid-level mesocyclone yesterday but never really saw them take the next step structure wise as they rooted in the better moisture.
 

Mezo

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Dec 11, 2019
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As memorable as yesterday was, it was a long way from my ideal day from a chasing perspective. I much prefer those days with one or two isolated cells coming up from the south, with full structure visible from many locations. Yesterday there was just too much going on at once, all moving ridiculously fast, with insanely big hail that you need to stay out of the way of (unless you're happy to right your car off). Tough going if your main goal is to capture some cool storm structure.
 

whether

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we all love your input over the years mega ,, sure feel for you and your local weather. I have a mate very close to you at tiaro he has done quite well the last 2 weeks with over 100mm. I regularly send him screen shots of what’s coming , he has a tank and dam filler the other day filled his main tank in minutes ( from big shed).
All I can say life’s to short to hate where you live...... move mate , and enjoy life a little better maybe I now we would all love to see you post of storms , snow , rain , etc what ever you deliver.
Cheers

Tim
pics of my mates at tiaro.
Don't move to Townsville mega it has weather even more boring than Maryborough except for maybe one week a year when we get some rain.
 

chunky

Pool Room
Jul 24, 1998
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Great photos and reporting. Not sure the truth to this,but some of the chasers i kept in touch with yesterday, were saying because the storms were SE sliders , the structure was limited and was messy in places in comparison to when storms come in from the South West. Going by history, most of my cleaner looking storm shots were from those that started in the southern downs and end up towards Brisbane via the scenic rim , or if you are south of the border, storms that develop around Tenterfield and end up at Byron Bay via casino and Lismore.

Im suprised i havent seen a clear cut supercell structure photo similiar to what they get in the USA in yesterdays event. Could the other reason be because there were simply too many supercells close together ?
Were they the ones in the scenic rim near Kalbar? There was quite a few of them. I was a bit fustrated by the lack of structure but I think it was more my position and view because if were really close to the hail core there was visibility. With all that convergence almost upon each other I imagine they messed up the unique views each storm cell may have had, had they been isolated by themselves. The storm cell I captured on Wednesday afternoon tracked from the same area as Saturday's storms and it only got lost in the low cloud cover when it hit the central Scenic Rim area. I still managed to grab some nice ones though to my advantage later on I missed the hail. Had I been a few km's closer and pushed a bit more I would have been hit quite badly.
 

chunky

Pool Room
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I also noticed the GC storms seem to rip apart a lot more once they hit the coast than the ones north of Brisbane on the Sunshine Coast. While there was lightning activity at both locations I could see the lightning from the Maroochydore ones on the M1 coming back from the GC. The elevation of the storms must have gone to an incredible height. Had I the energy I might have pushed onto the Sunshine Coast but was pretty tired.
 

chunky

Pool Room
Jul 24, 1998
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It's always tough when there is some faster storm motions, trick it to always keep positions downstream of anticipated storm tracks. I'll always keep an equatorward bias as well to allow for left deviations.

For instance I was in place (blue dot) for those storms near Willowbank as they were passing near Gatton, you'll never get in the right place trying play catch up. Believe it or not there are places around the world they are moving much quicker than that at times too by the way. There have been set-ups in the US for instance that I've started 20 miles behind a storm and tracked it across three states only to get no closer than.... 20 miles lol.

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Anyway, great posts on here. I'm on a flight home atm but I'll put up some stuff myself in the next couple days.
Can't wait. I need a set up like that. I don't have to keep stopping and pulling over to check radar when I am solo.
 

Ken Kato

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Why was the instability not up as far north and concentrated down near SE Qld this time?
When you say "this time", it's actually more common to have greater instability and especially severe storm potential further south with systems that are essentially more of a midlatitude nature than tropical setups @Vinny

In yesterday's case, moisture was better the further south you went which is fairly typical of systems like these in winter to mid spring, shear was stronger further south although it was still decent a fair way north, forcing from the upper trough was better further south, much colder midlevels further south, it was more of a frontal nature the further south you went (refer to above MSLP chart), there was a low level jet of sorts further south which was also boosting low level shear, and there was stronger capping further north.

In short, the dynamics are generally better the further south you go with non-tropical systems.
 
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chunky

Pool Room
Jul 24, 1998
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Last ones for my chase. I was hoping to get further south but we were losing light too quickly so picked Currumbin to head to. It was here we got the last light of the day.

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Right enough of my pics. Prob sick of them. Anyway to recap my travels. It was just a smidge under 500km - 498 to be accurate. Out to Gatton, almost to Clifton, to Laidley, Rosewood, Purga, Kalbar, Goolman, back to Purga then to GC and back to Brissy. Saw many cells. Stayed at range but might try to be more adventurous next time though hail dropped from every single one. I can't remember a line up of storms like this in recent years at all for our part of the world like this in day.
 

MegaMatch

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we all love your input over the years mega ,, sure feel for you and your local weather. I have a mate very close to you at tiaro he has done quite well the last 2 weeks with over 100mm. I regularly send him screen shots of what’s coming , he has a tank and dam filler the other day filled his main tank in minutes ( from big shed).
All I can say life’s to short to hate where you live...... move mate , and enjoy life a little better maybe I now we would all love to see you post of storms , snow , rain , etc what ever you deliver.
Cheers

Tim
pics of my mates at tiaro.

Yeah Tiaro did well. I watched in envy as I observed multiple storms pass over them during the last few days. If you look at this chart along with the deciles you can see the main area that missed out. Maybe next time.
 

whynot

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What an interesting afternoon. Based on what I read in the numerical models, I try to build a mental picture before the event of what to expect. I wasn’t expecting as much hail as eventuated. I was expecting more wind and lightning. Yesterday was one of those days to be grateful for living in the donut hole. For us, nothing more than light hail, a useful ½” of rain, and a bit of wind. (By accident, I was caught out and about in my car in the January 1985 hailstorm. It was a terrifying experience and once is more than enough.)

Some interesting pictures from the safety of my home. First is a rear end view to the south east of a cell passing over Beenleigh, about 50km to the south. This was taken with a 10mm wide angle lens and has been cropped. The radar insert is indicative of the distance and angle. At the time this was taken, I estimated there was a 70 kph wind from the NNE. A question, would this surface wind be rear flank inflow? The storm was literally scuttling away.

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Eagle eyes may have noticed this cloud feature. Below is a zoomed in crop of the previous picture (keep in mind that this is a crop out of a 10mm wide angle lens). It definitely was rotating. But, by the time I raced inside, stuffed around with swapped the lens over to the 300mm and came back out, it was gone.

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The interesting feature of this image is the cloud right of frame. This was taken with the lens set at 20mm, which tends to flatten out the image. To fill in the picture, the wind had completely died down. This particular cloud (right of frame) had height. It reminded me of the spaceship out of the movie Arrival. It was tall. It seemed to be hovering with an unexplained power, and slowly but silently drifting along. It was a bit unnerving really.

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Orebound

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Orebound

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Phenomenonal capture, Thanks for sharing.

Thanks!

Here's one taken up under the updraft base of the first of the VDS cell out near Willowbank, at this stage we saw the first signs of a formative wall cloud with scud being pulled up hard into the updraft.

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Elevated mesocyclone from the second of the VDS storms to pass through the area, these would go on to merge and develop into the large HP storm that dropped the large hail south of Brisbane.

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Nature's Fury

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Nov 1, 2019
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After yesterday's incredible storms I had another detailed look at all the charts, forecasts and observations. I have actually saved almost every relevant chart I can find for my records. My prediction a few days earlier of how the event would unfold was quite off. I saw the linear shear, relative lack of turning winds and early initiation of storms and wrongly concluded that the main activity would be a multi-cell line with supercells less likely, especially once the main action kicked off. I clearly missed some of the nuances in the set-up, although I will admit that I think yesterday's activity did somewhat surprise and exceed everyone's expectations considering some of the potential problems in the set-up. I also wanted to understand why and how yesterday's event managed to be so significant.

Below is my thoughts on yesterday's events. I also have some questions or issues for clarification. I'm probably asking a bit much with this post, but I'm really keen to learn from this event. I hope that Ken and some others might be able to correct any of my misinterpretations and shed some light on these rather technical points.

Broader synoptic situation:

The overall synoptic situation was very favourable for significant storms in SEQ. Normally, cold fronts arc up from a low traveling east across southern Australia and we have an approaching trough initiating storms, rather than the front itself. Yesterday, the a strong upper low was situated over central, then eastern NSW with a cold front wrapping around. This meant that the cold front itself arced up all the way into central QLD in a slight NW tilt with a trough extending off the end northwards to the Gulf of Carpentaria. NW'ly winds in the upper levels and N'ly/NE'ly in the lower levels were flowing into the low pressure system as part of the atmosphere's usual system of seeking equilibrium in pressure and temperature with winds flowing from areas of high pressure into areas of low pressure.

QUESTION: Am I correct in assuming that a cold front would create greater forcing than a trough. Instead of just being an area of low pressure between two air masses that more draws in warmer, moister air and forces it to rise, the colder air mass approaching in a cold front undercuts the warm, moist air ahead of it forcing it violently upward, as well as providing freezing uppers and cool mids therefore dramatically increasing the lapse rate and the potential for very tall updrafts and large hail? I probably need a more nuanced understanding of the different effects of a cold front vs trough in severe storms.

QUESTION: Did the increasing speed of the approaching cold front further amplify the situation identified above by even more violently undercutting the air mass ahead and forcing storm formation? The BOM synoptic map indicates the front increasing velocity from 10kt at 5am to 20kt by 11am to 35kt by 11 pm.

QUESTION: Was the approaching cold front rather than a "standard" upper trough the reason we didn't see the usual cloud/drizzle/early kick-off we often see with upper troughs? Even with some of the cloud along the coast we still had plenty of sun and it heated up nicely to the low 30s.

Local set-up (all data using 1 pm 31/10 00z GFS charts and BOM real-time obs):

* CAPE/LI values: CAPE values were between 1600-2200 and LI values were -8 to -11 across SEQ. This suggets extreme instability. Parcels of warm, moist air would be rapidly rising from the surface and mixed air in the lower levels. This would enable very tall cloud tops and updrafts, one of the requirements for large hail, as well as propelling incoming, moist inflow rapidly upward to create opportunities for heavy precipitation in the downdraft.

QUESTION: Were the CAPE/LI values so high because of the advancing cold front violently undercutting the warmer air mass ahead forcing air up or because the lapse rates were so steep with the warm surface, cold mids and freezing uppers, or both?

* Lapse rates: Low 30s at 1.5 m, declining in the mids, -17 at 500 mb and -39 at 300 mb. While it was a little warm in the levels between 1.5m and 700 mb, the warmth at the surface and the very cold air in the mids/uppers allowed air parcels to ascend rapidly causing the moisture they carried with them to freeze. With the shear (discussed below), hail would have been tossed up and down, growing ever larger, their increasing weight withstanding the forces of gravity, until they grew so gigantic that they could no longer remain aloft and fell.

* Winds: This is the area that caught me out in my predictions, but was probably the big deciding feature of yesterday's set-up. The winds in the lower levels appeared to be converging into a surface trough aligned slightly NW/SE between Brisbane and Gatton. Crucially, there was a very powerful inflow coming in off the sea with 15-25 NE'ly kts at the 10m level and 20-35 N'ly kts at the 950 mb. I remember Mike commenting he was getting 70kph gusts at Bracken Ridge and Ken described it earlier today as a "low level jet". Brisbane Airport had NNE'lies at 40-50 kph gusting to the 70s and Archerfield saw NNE'lies in the 30s kph gusting to the 50s. This would have provided moisture to feed the storms, but also additional shear (speed and directional) to assist in the formation of supercells with powerful, tilted and rotating updrafts, allowing long-lasting storms that don't choke on their own downdrafts and allowing hailstones to remain aloft (rising, falling, rising) and become ever gigantic without dropping too early.

QUESTION: Why was this N/NE'ly so powerful yesterday? Was this because air was being violently drawn into the area of low pressure caused by the cold front undercutting the warmer air ahead of it? It couldn't just have been the usual temperature differential between a cooler ocean and a hotter land surface that causes the usual seabreeze in an afternoon, as surface temps were only in the low 30s.

Winds increased and backed a little with height. N/NW 25-30 kts at 850, N/NW 35-45 kts at 700, NW 50-55 kts at 500 and NW 60 kts at 300. There is clearly very strong speed shear that would enable the storm to move quickly and help keep the updraft and downdraft separated. However, directional shear needed to rotate the updraft did not appear on the charts to be that great. It looked to me that the directional shear was fairly unidirectional/linear, which would have encouraged a line of multi-cell storms rather than supercells, let alone conveyor belts of supercells. Steering was very fast at around 45 kts in the 600, but while storms were fast-moving they seemed to hold up a little after interacting in the seabreeze front (e.g. the Greenbank cell).

QUESTION: Even with the low-level inflow from the NE adding extra speed and directional shear, it still doesn't seem incredibly supportive of supercells. I suspect that the powerful low-level inflow is the culprit but there are probably further related reasons I'm not aware of.

QUESTION: Why did we see conveyor belts of supercells forming yesterday and continuing as the cold front progressed further eastward? I recognise it was because of the advancing cold front, but how was it that over a period of time in multiple locations up to 3 supercells seemed to initiate and track in the same line to the SE (e.g. Gatton had 3 supercells, Bris western suburbs had 3 cells). We never get this pattern in SEQ storm events, for example, in my 25 years of following storms we've never been hit with multiple hail storms in one day, let alone 1 hour. What caused clusters to constantly form in the same spots before tracking to the SE? Why did the 2nd/3rd cells moving along the tracks not become weaker from the stabilised atmosphere ahead or was the instability (and therefore energy) and inflow in the atmosphere that powerful that they had endless juice? How did they remain discrete while being positioned so close to each other and without blending into a thundery mess (or was this because the aforementioned conditions were so supportive of supercells that they could stay discrete, and if so what were the key conditions that enabled this)?

* Moisture: The charts seemed to indicate moisture would be a little lacking with 16-18 through SEQ at the 2m and mid-teens all the way through the lower levels. Further inland this was the case (e.g. Amberley sat around 16-17), but yesterday's obs indicate this was not the case around the coast. As the storms approached Greenbank, Archerfield and Brisbane were 19-20s. So this provided plenty of moisture in the lower levels to 950 mb while still allowing that slightly drier slot in the mids that encourages large hail?

SUMMARY:

The set-up for yesterday's severe storms was a rapidly advancing cold front, fairly sunny and precipitation-free start to the day, extreme instability (LI/CAPE), significant lapse rates, cold pool in the mids and uppers, strong speed shear, some directional shear, good moisture levels along the coast, and fast steering with storms slowing a little when encountering the seabreeze decent moisture. However, yesterday's low-level inflow was perhaps more powerful than expected, giving a significant boost of moisture and directional shear that provided that extra ingredient for supercells and particularly for large hail.

QUESTION: What other factors affected yesterday's storm formation that I'm not considering?

QUESTION: What were the major risk factors for yesterday's set-up that could have occurred and how were these overcome? Ken mentioned the risks as storms merging rather than remaining discrete, morning cloud cover and patchy rain areas with the approaching upper trough, not enough moisture from the NNE afternoon seabreeze and steering winds being too strong. I think I've addressed or asked clarifying questions about most of these issues, but were there any others?

QUESTION: What was the cause of the unusual hail spikes in the Greenbank storm yesterday (looked like a cannabis leaf)? Was that from violent winds within the storm and the downdraft throwing the hail around?

When this thread dies (so it doesn't annoy anyone trying to read or post), I will post all of the charts I've gathered for yesterday's storms on here so we have a historical record.
 

Ken Kato

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Jul 13, 2019
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Brisbane
upload_2020-11-1_20-33-7.png


After yesterday's incredible storms I had another detailed look at all the charts, forecasts and observations. I have actually saved almost every relevant chart I can find for my records. My prediction a few days earlier of how the event would unfold was quite off. I saw the linear shear, relative lack of turning winds and early initiation of storms and wrongly concluded that the main activity would be a multi-cell line with supercells less likely, especially once the main action kicked off. I clearly missed some of the nuances in the set-up, although I will admit that I think yesterday's activity did somewhat surprise and exceed everyone's expectations considering some of the potential problems in the set-up. I also wanted to understand why and how yesterday's event managed to be so significant.

Below is my thoughts on yesterday's events. I also have some questions or issues for clarification. I'm probably asking a bit much with this post, but I'm really keen to learn from this event. I hope that Ken and some others might be able to correct any of my misinterpretations and shed some light on these rather technical points.

Broader synoptic situation:

The overall synoptic situation was very favourable for significant storms in SEQ. Normally, cold fronts arc up from a low traveling east across southern Australia and we have an approaching trough initiating storms, rather than the front itself. Yesterday, the a strong upper low was situated over central, then eastern NSW with a cold front wrapping around. This meant that the cold front itself arced up all the way into central QLD in a slight NW tilt with a trough extending off the end northwards to the Gulf of Carpentaria. NW'ly winds in the upper levels and N'ly/NE'ly in the lower levels were flowing into the low pressure system as part of the atmosphere's usual system of seeking equilibrium in pressure and temperature with winds flowing from areas of high pressure into areas of low pressure.

QUESTION: Am I correct in assuming that a cold front would create greater forcing than a trough. Instead of just being an area of low pressure between two air masses that more draws in warmer, moister air and forces it to rise, the colder air mass approaching in a cold front undercuts the warm, moist air ahead of it forcing it violently upward, as well as providing freezing uppers and cool mids therefore dramatically increasing the lapse rate and the potential for very tall updrafts and large hail? I probably need a more nuanced understanding of the different effects of a cold front vs trough in severe storms.

QUESTION: Did the increasing speed of the approaching cold front further amplify the situation identified above by even more violently undercutting the air mass ahead and forcing storm formation? The BOM synoptic map indicates the front increasing velocity from 10kt at 5am to 20kt by 11am to 35kt by 11 pm.

QUESTION: Was the approaching cold front rather than a "standard" upper trough the reason we didn't see the usual cloud/drizzle/early kick-off we often see with upper troughs? Even with some of the cloud along the coast we still had plenty of sun and it heated up nicely to the low 30s.

Local set-up (all data using 1 pm 31/10 00z GFS charts and BOM real-time obs):

* CAPE/LI values: CAPE values were between 1600-2200 and LI values were -8 to -11 across SEQ. This suggets extreme instability. Parcels of warm, moist air would be rapidly rising from the surface and mixed air in the lower levels. This would enable very tall cloud tops and updrafts, one of the requirements for large hail, as well as propelling incoming, moist inflow rapidly upward to create opportunities for heavy precipitation in the downdraft.

QUESTION: Were the CAPE/LI values so high because of the advancing cold front violently undercutting the warmer air mass ahead forcing air up or because the lapse rates were so steep with the warm surface, cold mids and freezing uppers, or both?

* Lapse rates: Low 30s at 1.5 m, declining in the mids, -17 at 500 mb and -39 at 300 mb. While it was a little warm in the levels between 1.5m and 700 mb, the warmth at the surface and the very cold air in the mids/uppers allowed air parcels to ascend rapidly causing the moisture they carried with them to freeze. With the shear (discussed below), hail would have been tossed up and down, growing ever larger, their increasing weight withstanding the forces of gravity, until they grew so gigantic that they could no longer remain aloft and fell.

* Winds: This is the area that caught me out in my predictions, but was probably the big deciding feature of yesterday's set-up. The winds in the lower levels appeared to be converging into a surface trough aligned slightly NW/SE between Brisbane and Gatton. Crucially, there was a very powerful inflow coming in off the sea with 15-25 NE'ly kts at the 10m level and 20-35 N'ly kts at the 950 mb. I remember Mike commenting he was getting 70kph gusts at Bracken Ridge and Ken described it earlier today as a "low level jet". Brisbane Airport had NNE'lies at 40-50 kph gusting to the 70s and Archerfield saw NNE'lies in the 30s kph gusting to the 50s. This would have provided moisture to feed the storms, but also additional shear (speed and directional) to assist in the formation of supercells with powerful, tilted and rotating updrafts, allowing long-lasting storms that don't choke on their own downdrafts and allowing hailstones to remain aloft (rising, falling, rising) and become ever gigantic without dropping too early.

QUESTION: Why was this N/NE'ly so powerful yesterday? Was this because air was being violently drawn into the area of low pressure caused by the cold front undercutting the warmer air ahead of it? It couldn't just have been the usual temperature differential between a cooler ocean and a hotter land surface that causes the usual seabreeze in an afternoon, as surface temps were only in the low 30s.

Winds increased and backed a little with height. N/NW 25-30 kts at 850, N/NW 35-45 kts at 700, NW 50-55 kts at 500 and NW 60 kts at 300. There is clearly very strong speed shear that would enable the storm to move quickly and help keep the updraft and downdraft separated. However, directional shear needed to rotate the updraft did not appear on the charts to be that great. It looked to me that the directional shear was fairly unidirectional/linear, which would have encouraged a line of multi-cell storms rather than supercells, let alone conveyor belts of supercells. Steering was very fast at around 45 kts in the 600, but while storms were fast-moving they seemed to hold up a little after interacting in the seabreeze front (e.g. the Greenbank cell).

QUESTION: Even with the low-level inflow from the NE adding extra speed and directional shear, it still doesn't seem incredibly supportive of supercells. I suspect that the powerful low-level inflow is the culprit but there are probably further related reasons I'm not aware of.

QUESTION: Why did we see conveyor belts of supercells forming yesterday and continuing as the cold front progressed further eastward? I recognise it was because of the advancing cold front, but how was it that over a period of time in multiple locations up to 3 supercells seemed to initiate and track in the same line to the SE (e.g. Gatton had 3 supercells, Bris western suburbs had 3 cells). We never get this pattern in SEQ storm events, for example, in my 25 years of following storms we've never been hit with multiple hail storms in one day, let alone 1 hour. What caused clusters to constantly form in the same spots before tracking to the SE? Why did the 2nd/3rd cells moving along the tracks not become weaker from the stabilised atmosphere ahead or was the instability (and therefore energy) and inflow in the atmosphere that powerful that they had endless juice? How did they remain discrete while being positioned so close to each other and without blending into a thundery mess (or was this because the aforementioned conditions were so supportive of supercells that they could stay discrete, and if so what were the key conditions that enabled this)?

* Moisture: The charts seemed to indicate moisture would be a little lacking with 16-18 through SEQ at the 2m and mid-teens all the way through the lower levels. Further inland this was the case (e.g. Amberley sat around 16-17), but yesterday's obs indicate this was not the case around the coast. As the storms approached Greenbank, Archerfield and Brisbane were 19-20s. So this provided plenty of moisture in the lower levels to 950 mb while still allowing that slightly drier slot in the mids that encourages large hail?

SUMMARY:

The set-up for yesterday's severe storms was a rapidly advancing cold front, fairly sunny and precipitation-free start to the day, extreme instability (LI/CAPE), significant lapse rates, cold pool in the mids and uppers, strong speed shear, some directional shear, good moisture levels along the coast, and fast steering with storms slowing a little when encountering the seabreeze decent moisture. However, yesterday's low-level inflow was perhaps more powerful than expected, giving a significant boost of moisture and directional shear that provided that extra ingredient for supercells and particularly for large hail.

QUESTION: What other factors affected yesterday's storm formation that I'm not considering?

QUESTION: What were the major risk factors for yesterday's set-up that could have occurred and how were these overcome? Ken mentioned the risks as storms merging rather than remaining discrete, morning cloud cover and patchy rain areas with the approaching upper trough, not enough moisture from the NNE afternoon seabreeze and steering winds being too strong. I think I've addressed or asked clarifying questions about most of these issues, but were there any others?

QUESTION: What was the cause of the unusual hail spikes in the Greenbank storm yesterday (looked like a cannabis leaf)? Was that from violent winds within the storm and the downdraft throwing the hail around?

When this thread dies (so it doesn't annoy anyone trying to read or post), I will post all of the charts I've gathered for yesterday's storms on here so we have a historical record.
I haven't gone through the events with a fine tooth comb yet and I'm a bit short on time at the moment but a few things I will say which stood out for me about this one in addition to all the traditional favourable factors are:
1. Forecast (and observed) soundings looked a bit dryish. I believe this helped prevent much of the activity from merging into a big disorganised mass or line like it so often does in this area on favourable days until the very final stages as it was heading out to sea. This likely helped keep a lot of activity discrete. Discrete cells on such a volatile day like yesterday = alarm bells.
2. The positioning of the front and trough was just about perfect. Any further inland and the main focus for the activity probably would've been more inland (especially given the NW steering winds) and away from the enhancing effect of the seabreeze front, moister air, and greater turning. Further east and it would've just been a case of drier air invading all but the very coastal fringe. The position it was in meant that we'd get the best of both worlds - we were as close as possible to the front and trough for maximum uplift combined with the storms running into the seabreeze front, moister air and greater turning in the lowers.
3. Having such a hot day with such cool air aloft for this time of year guaranteed amazingly steep lapse rates.
4. The remarkably strong NNE winds blowing over the coastal plains may have also helped keep the vertical gradient of the outflow boundaries from each cell a lot steeper (think of the strong NNE flow pushing up against the northeastern flanks of the outflows trying to surge east and northeastwards), and prevented the outflows from surging out too far ahead of the storms and causing storms to become outflow-dominant.
This vertical gradient of outflows from storms is something that's been researched in this region in the role it plays for whether storms in this region become too "outflowed" and weaken, or maintain or even increase in intensity.

Above is a GFS sounding for the Springfield Lakes area at 03z. Even after taking into account any assumptions of slight model error, etc, you can see its suggestive of enough directional shear in the lower levels to support supercell activity after the seabreeze effect started to turn winds near the surface around to a more NNE direction.
 

Michael Hauber

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Jul 4, 2019
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I'll have a stab at that huge pile: (Have only had a quick look through Ken's response posted while writing this all up)

Does a cold front cause stronger forcing than a trough: In general I would think yes. One key issue is convergence - if winds are flowing towards each other then some air has to move up to get out of the way. In a trough there tends to be convergence as well, but not as dramatic. Trough might be NE vs E winds. Front can be W vs NE winds.

Does the speed of the approaching cold front matter? I would think the important factor is the strength of convergence. However a rapidly moving front may cause a more rapid change in wind direction than a more gradually moving front. Also a more rapidly approaching front could cause the same increase in instability as a slower, but there is less time for energy to be released in convection gradually over time.

Did the approaching cold front prevent early morning cloud/drizzle? Only to the extent that a fast moving front could cause an abrupt change of atmospheric conditions from stable to unstable, whereas a broader trough would cause a more spread out instability. In general I think the majority of instability was a combination of the upper trough and the warm moist air in the pre-frontal air mass so the front would have made little difference.

Was it cold air undercutting warm air, or lapse rates with warm surface and cold uppers that caused high CAPE/LI? My understanding is that the lift from convergence due to a front is not considered in cape. Temperature at different levels and available moisture content are the two factors considered. My question - Are there any other factors considered in CAPE?

Why was the N/NE'ly so powerful? The strength of this flow would have been primarily driven by the pressure gradient between the approaching trough and the ridge to the east. This will also be driven by the amount of instability forced by the upper divergence present in the upper trough with broadscale divergence requiring air from lower down to be lifted to replace this diverging air, creating lower pressure.

Even with the strong N/NE was this enough for supercells and were there other factors? Upper divergence in the upper trough would be the other factor promoting lift of air. The storms would largely be driven by lifting of air, sheer for separating up draft from downdraft, boundaries from sea breezes and previous storms, and the amount of energy for further lift driven by condensation of water vapor to clouds (which is part of CAPE)

Last few questions I don't have much to add.
 

Ken Kato

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Jul 13, 2019
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Brisbane
My question - Are there any other factors considered in CAPE?
CAPE is purely the vertical integral of the area on soundings where the theoretical air parcel is warmer than the surrounding environmental air. It doesn't take into account any mechanical forcing from synoptic systems. It's purely thermodynamic. But since the theoretical air parcel used is based on a number of assumptions (and some potential model error), even a slight error in these assumptions can make a sizeable different to the real CAPE.
 

Gleno71

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Jul 4, 2019
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Gold Coast, Queensland
What an interesting afternoon. Based on what I read in the numerical models, I try to build a mental picture before the event of what to expect. I wasn’t expecting as much hail as eventuated. I was expecting more wind and lightning. Yesterday was one of those days to be grateful for living in the donut hole. For us, nothing more than light hail, a useful ½” of rain, and a bit of wind. (By accident, I was caught out and about in my car in the January 1985 hailstorm. It was a terrifying experience and once is more than enough.)

Some interesting pictures from the safety of my home. First is a rear end view to the south east of a cell passing over Beenleigh, about 50km to the south. This was taken with a 10mm wide angle lens and has been cropped. The radar insert is indicative of the distance and angle. At the time this was taken, I estimated there was a 70 kph wind from the NNE. A question, would this surface wind be rear flank inflow? The storm was literally scuttling away.

DSC_9890-a.jpg


Eagle eyes may have noticed this cloud feature. Below is a zoomed in crop of the previous picture (keep in mind that this is a crop out of a 10mm wide angle lens). It definitely was rotating. But, by the time I raced inside, stuffed around with swapped the lens over to the 300mm and came back out, it was gone.

DSC_9890-c.JPG


The interesting feature of this image is the cloud right of frame. This was taken with the lens set at 20mm, which tends to flatten out the image. To fill in the picture, the wind had completely died down. This particular cloud (right of frame) had height. It reminded me of the spaceship out of the movie Arrival. It was tall. It seemed to be hovering with an unexplained power, and slowly but silently drifting along. It was a bit unnerving really.

DSC_0100s.JPG

Awesome photos well done
 

Gleno71

One of Us
Ski Pass
Jul 4, 2019
1,191
6,914
363
Gold Coast, Queensland
Last ones for my chase. I was hoping to get further south but we were losing light too quickly so picked Currumbin to head to. It was here we got the last light of the day.

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Right enough of my pics. Prob sick of them. Anyway to recap my travels. It was just a smidge under 500km - 498 to be accurate. Out to Gatton, almost to Clifton, to Laidley, Rosewood, Purga, Kalbar, Goolman, back to Purga then to GC and back to Brissy. Saw many cells. Stayed at range but might try to be more adventurous next time though hail dropped from every single one. I can't remember a line up of storms like this in recent years at all for our part of the world like this in day.

Fantastic photography mate, great work
 

TweedStorm

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Jul 6, 2019
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Banora Point
Yeah that first and third photo are bloody rippers! Well done Chunky.

Great reading there from Mike and Ken. I think that scenic rim is a great trigger for storms up here. Nor /nor easters blowing into that horse shoe shaped mountainous topography and the surrounding hinterland. Best nesting ground for storms when you have the moisture, heat and instability as well.
 
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