Event East Coast (Qld-NE NSW) surface trough possible heavy rainfall 2-9 April 2021

Nature's Fury

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Yeah it is very interesting - but also very sobering for just how catastrophic the impacts would be.
And remember that one outlier EC forecast for TC Oma in 2019 - I think it was something like over 1000 mm in five days over a large part of SEQ - potential outcome of that is shown diagrammatically below.

extreme flood scenario.png

It's always small margins. If the falls from the hybrid low had been 100 km west of the most aggressive modelling we would have had another flood event. If Oma had struck in 2019 we wouldn't have had an SEQ drought and fire event later that year unlike the rest of eastern Aus. As it is, it may well be years before we get another flood opportunity with a major potential rain event on a saturated catchment.

Oma modelling below - still the best model forecast I've ever seen for SEQ. Shame it never happened but one day surely...

ec3.jpg
 

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Ken Kato

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Above: Running 48hr totals so far for some of the gauges.

And yep I agree. A bullet was dodged by only a small margin re this event. Not withstanding the fact that for some areas, it's come down to a beggars can't be choosers scenario and it probably would've been needed despite the flooding potential.
Orchid Beach has had 220mm during the Sun-Mon period (thanks for posting the link to those unofficial gauges the other day Nic Bri) so it goes to show just how much the rainfall increased as you went even a short distance further east.
 

Nic Bri

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Yeah it is very interesting - but also very sobering for just how catastrophic the impacts would be.
And remember that one outlier EC forecast for TC Oma in 2019 - I think it was something like over 1000 mm in five days over a large part of SEQ - potential outcome of that is shown diagrammatically below.

extreme flood scenario.png
That Story Bridge pic was my exact notion when going to Howard Smith Wharves the other day. All my mates were talking about how great it is and all I could wonder was how the hell is this place going to go with the next big flood. Seems crazy to me they developed that precinct.
 
Sep 27, 2019
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It's always small margins. If the falls from the hybrid low had been 100 km west of the most aggressive modelling we would have had another flood event. If Oma had struck in 2019 we wouldn't have had an SEQ drought and fire event later that year unlike the rest of eastern Aus. As it is, it may well be years before we get another flood opportunity with a major potential rain event on a saturated catchment.

Oma modelling below - still the best model forecast I've ever seen for SEQ. Shame it never happened but one day surely...

ec3.jpg
Hey, NF, if I didn't know better, you sound like one of those schadenfreude types, but I know you're not. However, surely you would not wish a cataclysmic flood event such as the one Oma posed a few years ago? "Flood opportunity . . . on a saturated catchment"? I'm all for good rain, but when it has the potential to be destructive and deadly - please count me out.
 

Weathertraveller

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That Story Bridge pic was my exact notion when going to Howard Smith Wharves the other day. All my mates were talking about how great it is and all I could wonder was how the hell is this place going to go with the next big flood. Seems crazy to me they developed that precinct.
It would indeed be catastrophic if that happened. Nic do you have the link to the unofficial gauges? I searched through and couldn't see it and would like to keep it to refer to in future. thankyou
 

Multiversity

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that would be a big flood. I wonder what the reverse would be - a big tsunamigenic earthquake on Aust/Pacific plates NE/E of SEQ sending a tsunami into Moreton Bay and pushed up Brisbane River. The 2011 Tohoku quake/tsunami in NE Japan showed how a 10m wave could produce 40m high runups when squeezed into bays and valleys. Don't know if our disaster preparedness dept has modelled this. They do for cyclone storm surges.

Yeah it is very interesting - but also very sobering for just how catastrophic the impacts would be.
And remember that one outlier EC forecast for TC Oma in 2019 - I think it was something like over 1000 mm in five days over a large part of SEQ - potential outcome of that is shown diagrammatically below.

extreme flood scenario.png
 

glenesk

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Is that band of rain going to drift Eastwood at any stage.
We seem to have got the dreggs of what came from the east and now all the heavy stuff us to our west.
Not complaining the 20 odd mm we have received so far is most welcome. But it is hardly dam filling for winter.
 

Flowin

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Interesting the Radar images the last day or so with different rain areas travelling in almost opposite directions.
I explored this a little bit with the WeatherWatch site 3D radar for the current rain patterns.
It appears that the rain areas south west of the radar over Lockyer valley and Scenic Rim which appear to be travelling in south east direction is at rain originating at about and above 4km height.
It appears that rain areas over the radar site and north east of the radar that appear to be travelling in a north west direction is rain originating about 1 to 2km height.
 
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Nic Bri

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It would indeed be catastrophic if that happened. Nic do you have the link to the unofficial gauges? I searched through and couldn't see it and would like to keep it to refer to in future. thankyou
No probs details 5 different locations on the island...very handy if heading up the beach.

https://fido.org.au/weather
 

Nature's Fury

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Hey, NF, if I didn't know better, you sound like one of those schadenfreude types, but I know you're not. However, surely you would not wish a cataclysmic flood event such as the one Oma posed a few years ago? "Flood opportunity . . . on a saturated catchment"? I'm all for good rain, but when it has the potential to be destructive and deadly - please count me out.

Just talking about how these scenarios don't happen very often and often it comes down to small margins. I'm always fascinated by how big and small variations could mean the difference between floods in SEQ, life arising on Earth and lots of other scenarios.
 

Nature's Fury

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that would be a big flood. I wonder what the reverse would be - a big tsunamigenic earthquake on Aust/Pacific plates NE/E of SEQ sending a tsunami into Moreton Bay and pushed up Brisbane River. The 2011 Tohoku quake/tsunami in NE Japan showed how a 10m wave could produce 40m high runups when squeezed into bays and valleys. Don't know if our disaster preparedness dept has modelled this. They do for cyclone storm surges.

I'm not sure we could get a major tsunami impact on Brisbane due to the Moreton Bay islands. GC and NE NSW would be exposed though. I believe studies show that an eastern Aus tsunami would have to be triggered by a major earthquake over 7 on the right region of the Kermadec.
 

WarwickEye2Sky

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The donut hole over Warwick seems to have filled in a bit over the past couple of years. Just my observation anyway. Although areas south of here like Murray’s Bridge/Killarney area seem to fare better. Also Clifton/Allora area is always a hot spot, but we get our fair share. Speaking of wet stuff, I heard that NOAA has predicted a 50/50 chance of a double dip La Niña?
 

Mezo

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Dec 11, 2019
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I just wish people gave the same amount of scrutiny to the models as they do praise them. The first half was diabolically modelled....in real time. That's all.

It's technology trying to predict how the natural world will behave. It's never going to be perfect. It's astounding that it's even at the level it's at now. Well, to me, anyway.
 

Weathertraveller

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Interesting the Radar images the last day or so with different rain areas travelling in almost opposite directions.
I explored this a little bit with the WeatherWatch site 3D radar for the current rain patterns.
It appears that the rain areas south west of the radar over Lockyer valley and Scenic Rim which appear to be travelling in south east direction is at rain originating at about and above 4km height.
It appears that rain areas over the radar site and north east of the radar that appear to be travelling in a north west direction is rain originating about 1 to 2km height.
I noticed that the rain originating from around 4km height over to my west around Lockyer Valley way has been there for hours moving very slowing to the south east or east. I'm wondering if that rain will possibly make it toward the east to the coast around greater Brisbane tonight. I think someone asked a similiar question about that earlier today, but I don't think it was answered.
 

Delta-T

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Oct 8, 2019
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Peachester, Queensland
Rainfall for my place (Peachester):
January
28th......26.9mm
29th......11.2
30th......45.2
31st......60.2

February
1st......273.8
2nd......505.9
3rd......907.0
4th......273.3

11th......223.0

17th......404.1

Plus an additional 8 days of over 25mm in the month. Total for February 2999. Had a tidy 338mm on June 10th for good measure. Ok, so it was 1893 and it was 5km up the road at Crohamhurst...but what a run!
 

glenesk

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I noticed that the rain originating from around 4km height over to my west around Lockyer Valley way has been there for hours moving very slowing to the south east or east. I'm wondering if that rain will possibly make it toward the east to the coast around greater Brisbane tonight. I think someone asked a similiar question about that earlier today, but I don't think it was answered.
Looks like it will, just took awhile to get organised to move south of the wivenhoe wall and split at the northern end to create the hole. i mentioned in a earlier post.
 

Weathertraveller

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Looks like it will, just took awhile to get organised to move south of the wivenhoe wall and split at the northern end to create the hole. i mentioned in a earlier post.
yes I saw your post earlier about the "hole" To tell you the truth I hope it doesn't fall around my place during the night, my ground is very saturated, I'd much rather you have it out your way.
 

Flowin

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Rainfall for my place (Peachester):
January
28th......26.9mm
29th......11.2
30th......45.2
31st......60.2

February
1st......273.8
2nd......505.9
3rd......907.0
4th......273.3

11th......223.0

17th......404.1

Plus an additional 8 days of over 25mm in the month. Total for February 2999. Had a tidy 338mm on June 10th for good measure. Ok, so it was 1893 and it was 5km up the road at Crohamhurst...but what a run!
Ha ha ha... I was reading that and thought man you need to recalibrate your rain gauge, or otherwise change from old “points” scale to millimetres. When I was a child all the talk of rain was how many points did you get, never here that anymore.
 

Weathertraveller

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Jan 23, 2020
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Rainfall for my place (Peachester):
January
28th......26.9mm
29th......11.2
30th......45.2
31st......60.2

February
1st......273.8
2nd......505.9
3rd......907.0
4th......273.3

11th......223.0

17th......404.1

Plus an additional 8 days of over 25mm in the month. Total for February 2999. Had a tidy 338mm on June 10th for good measure. Ok, so it was 1893 and it was 5km up the road at Crohamhurst...but what a run!
Do you have the figures for March and April ?
 

Ken Kato

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Is this event lingering a bit longer than expected?
Nah not really. The axis of the midlevel trough/low has never really been forecast to come through before the current time. Even then, it's not a sharp well-defined axis by the time it reaches us. So until it's cleared out of the region, the window of opportunity remains for further precip enhanced by the upper support.
 

Delta-T

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Ken Kato

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Interesting the Radar images the last day or so with different rain areas travelling in almost opposite directions.
I explored this a little bit with the WeatherWatch site 3D radar for the current rain patterns.
It appears that the rain areas south west of the radar over Lockyer valley and Scenic Rim which appear to be travelling in south east direction is at rain originating at about and above 4km height.
It appears that rain areas over the radar site and north east of the radar that appear to be travelling in a north west direction is rain originating about 1 to 2km height.
Yeah that's a very common sight during rain events here. Unless you were referring to the steadier rain areas moving in different directions rather than showers vs rain. Showers riding in on the low level southeasterlies while stratiform rain areas falling from midlevel cloud decks stream down on the midlevel northwesterlies. It's also a good visual signature of backing winds with height which are part of large scale ascent of air that enhances rainfall.
 

Ken Kato

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51098575907_89f180d815_b.jpg


The posters saying that this was too hard to call look like they'll be right. Wasn't the heavy rain that went out to sea not directly related to the low & as well as this rain now stretching from Sunny to GC? I've just had a look at the pressures along the coast & they all look pretty constant at around 1014-15hPa so the low has slipped out to sea I'm assuming? Convergence doesn't seem to going anywhere so be interesting to see totals o/n.
The heavy rain was part of the low and was occurring on the SE flank of the low as a big blob of convection helped by strong warm air advection aloft and upslide in its southeastern flank @Multiversity
Meanwhile the rain that stretched from the SC to the GC was the result of wind convergence and strengthening moist onshore flow in the lower levels on the southern side of the trough/low, helped by a 700hpa trough as well as the upmotion ahead of the broader midlevel trough and low over the inland.

Speaking of rain, the rain here tonight hasn't been that heavy but it sure has been steady and soaking again. It comes on the back of constant periods of drizzle and some intermittent rain with showers throughout the day. Everything's sodden. Current radar image above showing somewhat heavier lumps mixed in with the lighter falls again.
 

Stumer1

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I'm not sure we could get a major tsunami impact on Brisbane due to the Moreton Bay islands. GC and NE NSW would be exposed though. I believe studies show that an eastern Aus tsunami would have to be triggered by a major earthquake over 7 on the right region of the Kermadec.
What about an asteroid impact in the Pacific somewhere? The tsunami waves would just wash over the islands.
 

Ismellrain

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Sep 20, 2019
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Can we please get another 30mm or so in the somerset and wivenhoe catchments please weather system.

What is the likelihood I wonder, of getting a similar burst of convergence rain like we did last night with some reasonably widespread heavy falls.

Contrary to the useless media, water doesn't immediately hit the dams. Yes, on the news tonight, they said it hasn't made any difference with Wivenhoe sitting at 38% or something like that. However, we knowledged weather followers know different, and the action upstream of the Dams are a different kettle of fish. Somerset is experiencing great inflow, and the Stanley River at Woodford is almost hitting the bridge. These inflows take time which I am sure the media, lacking the knowledge in the physics of water flows, do not understand :)

Oh, and Mt Glorious is being hammered by rain at the moment and will just add to the flows into the dam.
 

mcspero

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Feb 10, 2020
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There is probably a good 20000 ML worth of inflows to make their way down yet and most will get tipped into Wivenhoe since Somerset is at 80%.

The problem with heavy falls at Mt Glorious is it depends on which side of the mountain the rain falls. Many times I have seen heavy falls at Mt Glorious make little difference to the Wivenhoe dam level.

Unfortunately there are no gauging stations on Branch Creek or Northbrook Creek to get an idea of the inflows to Wivenhoe on the eastern side. When I study these rain events, I tend to use the gauging at Reedy Creek (Mount Byron) as my go to gauge to indicate if things are happening on the eastern side. Reedy Creek flows into the joining river between somerset dam and wivenhoe dam and is flowing at about 2000 ML/day with the recent rain having peaked earlier today at about 1.9m.
 

Multiversity

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Brilliant analysis KK. This has been an event that just keeps on giving - been plenty of surprises. The heavier rain tonight to the west of the city sure caught me out.


51098575907_89f180d815_b.jpg



The heavy rain was part of the low and was occurring on the SE flank of the low as a big blob of convection helped by strong warm air advection aloft and upslide in its southeastern flank @Multiversity
Meanwhile the rain that stretched from the SC to the GC was the result of wind convergence and strengthening moist onshore flow in the lower levels on the southern side of the trough/low, helped by a 700hpa trough as well as the upmotion ahead of the broader midlevel trough and low over the inland.

Speaking of rain, the rain here tonight hasn't been that heavy but it sure has been steady and soaking again. It comes on the back of constant periods of drizzle and some intermittent rain with showers throughout the day. Everything's sodden. Current radar image above showing somewhat heavier lumps mixed in with the lighter falls again.
 

Gleno71

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Jul 4, 2019
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When you think about it, i feel the models did fairly well, even though we didnt get the heavy rain that was mainly offshore, we still got good soaking rain for the days that the models predicted. Like i have said before, with technology these days ,i feel some people out there expect perfection when it comes to rainfall amounts. I dont recall the BOM, or other weather agenices ever putting a rainfall figure in there forecasts back in the old days, do you think they should ditch that and just say " showers" or "rain at times" without placing in a forecast amount of rain in mm ?
 

Weathertraveller

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Jan 23, 2020
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All up that "rain bomb" (media term - not a technical term) that ended up several hundred kilometres to the east produced just over 1000 mm in 72 hours based on Satellite Obs.

upload_2021-4-7_7-32-10.png
We would have had a real problem if that had fallen on land. It would have been a catastrophic flood. All up here 115mm for this event. My yard is very soggy again now. However when I heard the heavier rain last night again I thought there'd be more in the gauge this morning. But that's enough rain here, just wish some had fallen further inland. Thankyou for all the updates during this event Flowin, much appreciated. A couple of patches of blue sky here now, but plenty of clouds around and moving fast.
 

Flowin

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When you think about it, i feel the models did fairly well, even though we didnt get the heavy rain that was mainly offshore, we still got good soaking rain for the days that the models predicted. Like i have said before, with technology these days ,i feel some people out there expect perfection when it comes to rainfall amounts. I dont recall the BOM, or other weather agenices ever putting a rainfall figure in there forecasts back in the old days, do you think they should ditch that and just say " showers" or "rain at times" without placing in a forecast amount of rain in mm ?
Gleno, There are situations where some idea of the rain amount is needed such as flood risk, water management operations, agriculture, and people who run business involving outdoor activities or construction such as concreting or earthworks etc. So I think there is a need to forecast rain amount, but people who read the forecasts just need to appreciate that rain amount for a specific location is quite difficult to forecast compared to many other weather parameters.
 

PlumbBob

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Jul 5, 2019
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Molendinar
April: rains to 9am each day for Molendinar, GC.

1st 1mm
2nd 5mm
3rd 2mm
4th 5mm
5th 12mm
6th 90mm
7th 43mm
Total 158mm


Currently: Temp 24*C,,,, DP 19*C,,,, Humidity 74%,,,, Wind SSE Mild varying from 5-15k with gusts to 20k,,,, Partially broken skies with 85-90% clouds

Forecasts for Gold Coast:

07.JPG
 
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