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

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MegaMatch

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I'll kick this one off. A strong upper level trough currently moving into western QLD and NSW will begin to slow in the next 24-36 hours before virtually stalling across the west of both states. This trough will assist a surface trough in producing widespread rain, shower and storm activity across the west of the state tomorrow, possibly leaking into SEQ tomorrow night.

During Sunday and Monday, this surface trough will push east, contracting the main area of rain and storms further eastwards. There is now good agreement that the southern section of this active trough will move off the SE coast sometime during Monday while a strongish SE change pushes up the SE coast (sadface). However, there is still considerable disagreement as to this change's timing, how far north it gets and its longevity. Storm chances near the coast should temporarily lessen following this change, but I'd probably still expect storms inland especially during the day.

It gets tricky during the middle of the week. At this stage it's looking as though the upper trough could finally make a move eastwards while the surface change either washes out or angles back down the coast, which will once again create that warm, humid, stormy environment again over SEQ, possibly leading to more storms in the later part of the working week. We are getting into highly uncertain territory here though.

Rainfall totals will be very hard to predict...imagine that anywhere in the green on the following chart has the potential to see heavier falls than as shown, it's just that where those heavier falls end up will be highly dependant on factors like small mesoscale features, exactly where the best storms end up forming etc. Some unlucky people will probably be left disappointed while I think most will be somewhat satisfied with the results (here's hoping).

I'm sure Ken and others have many more informative charts to show, so I'll just leave you with WATL:

y7bCWDN.png
 

Ken Kato

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So using that EC rainfall calibration database that I was building, here's the comparisons between the historical 24hr rainfall amounts that the EC's 12z runs has forecast for Archerfield in the past (after its last upgrade) and what actually fell:

Forecast lead time of +60hrs (applicable to 10am tomorrow to 10am Sunday): 0.1-9mm (forecast) => 38% resulted in below 0.2mm observed, 54% resulted in 0.2-9mm, and 8% resulted in 10-24mm.

Forecast lead time of +84hrs (applicable to 10am Sunday to 10am Monday): No past cases of the forecast 25-49mm because it's been so dry!

Forecast lead time of +108hrs (applicable to 10am Monday to 10am Tuesday): 0.1-9mm (forecast) => 29% resulted in below 0.2mm observed, 64% resulted in 0.2-9mm, and 7% resulted in 10-24mm.

Forecast lead time of +132hrs (applicable to 10am Tuesday to 10am Wednesday): 10-24mm (forecast) => 20% resulted in below 0.2mm observed, 40% resulted in 0.2-9mm, 20% resulted in 10-24mm, and 20% resulted in 25-49mm.

One thing to be aware of with the 0.2-9mm forecast figures is that I've found the seemingly small difference between the lower threshold of 0.1mm for forecasts and the 0.2mm for obs makes a sizeable difference.... enough to treat the forecast vs obs correlations for no rainfall with a lot of caution. So I've started adding another column specifically for the 1-10mm figures.

Most importantly though, the sample size of those rainfall amounts is still fairly small because it's been so dry so I wouldn't be drawing firm conclusions from them just yet.
 

Ken Kato

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I should've added that it still looks like Saturday will feature fairly cloudy skies with some showers and patchy rain areas slowly starting to creep into our region from inland ahead of the approaching upper trough (although these may still favour inland and southern parts of our region due to the NNW then NW steering winds aloft).
Storms... maybe, but the amount of cloud cover and inland rain areas may limit extent and severity.
 
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Lani

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Totals for this weekend dropped significantly in last nights runs which is frustratingly disappointing as we had a race event cancelled today due to the forecast rain that may not now be significant enough to have impacted it. I hope the downgrade is wrong and we get something worthwhile.
 

Ken Kato

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Totals for this weekend dropped significantly in last nights runs which is frustratingly disappointing as we had a race event cancelled today due to the forecast rain that may not now be significant enough to have impacted it. I hope the downgrade is wrong and we get something worthwhile.
Hope you get something worthwhile there @Lani but I also hope you remember the golden rule whenever it comes to rainfall from showers or storms to avoid any possible disappointmnt (avoid taking forecast amounts too literally because some places will get much less or more than others).
Having said that, it does look like most people will eventually get some heavy rainfall given the expected widespread nature of the activity, even though there'll be the odd day when it's a lot quieter.
 

chunky

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Models have northern downs as the hotspot (Tara - Dalby ) however lightning forecastr and forecast radar has stuff happening over brisbane. The problem with these set ups is you cant go by Access C when it's tain embeded storms as it's difficult to determine which is what
I'm hoping to get the shot with the supercells or some cell forming. Issues I have found with anything east of the ranges is getting to a spot with a vantage point far enough off into the distance to get something. Whereas west of Toowoomba or tracking up from Allora you get the wide open plains.
 

Gleno71

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I'm hoping to get the shot with the supercells or some cell forming. Issues I have found with anything east of the ranges is getting to a spot with a vantage point far enough off into the distance to get something. Whereas west of Toowoomba or tracking up from Allora you get the wide open plains.


exactly which is why im tempted to go out that way. CAPE seems very low which is a concern.
 

chunky

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Any thoughts from anyone to try and intercept something. I was thinking of heading towards Allora and moving north from there though Gleno71 mentioned Tara/Dalby as a good spot. Once you get into the trees nearer to Tara it is harder to see long distances across the plains unless someone knows a good spot out there.
 

Ken Kato

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The forecast NNW steering flow which then turns more NW'ly later will probably cause convection to have a bias towards inland and southern parts of our region today.
But unless you go to an area with a bit less extensive cloud cover, I'm not sure if there'll be many photogenic opportunities in terms of capturing the vertical structure of any individual cells since a fair bit of the convection will probably be embedded. May be able to capture lower level structures like shelf clouds, etc though.
Should also be noted that the extensive cloud cover itself may somewhat limit storm extent and severity in the SE Coast district.
 

chunky

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The forecast NNW steering flow which then turns more NW'ly later will probably cause convection to have a bias towards inland and southern parts of our region today.
But unless you go to an area with a bit less extensive cloud cover, I'm not sure if there'll be many photogenic opportunities in terms of capturing the vertical structure of any individual cells since a fair bit of the convection will probably be embedded.
Yeah I am worried about that too. Driving all that way to get some nice gray oh and look more gray shots with no formations visible.
 

Ken Kato

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I finally managed to run that minimum rainfall scenario script after recent datafeed outages of the server I pull the data from...... but unfortunately, the latest runs still haven't been able to be populated on the server so I've been forced to use two older runs (the 00z run from two days ago and the previous 18z run).

Nevertheless, it's encouraging to see that even the most pessimistic scenario out of the 62 members was still going for reasonable amounts (forecast period covers from 10am today to 10pm next Thursday therefore it doesn't include any rain that's already fallen over the inland in the last few days). I'd still use caution though just due to a fair bit of the rainfall probably being convective and some places getting less than others.... and also the fact that these aren't the latest runs which may have changed since the older runs.
Also below is the lightning detected by the Blitzortung.org community network of sensors from 4am Wed up to 4am this morning:

50521958586_6c8f1bb679_b.jpg


50521944981_69a89a90a2_o.png
 

Gleno71

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Yeah I am worried about that too. Driving all that way to get some nice gray oh and look more gray shots with no formations visible.

thats why western downs a better option, you get towards the edge of the cloud band , possible structure beyond that, always a risky thing when you chase. Yet you can get someone in a apartment block that never chases and can get one of the photos of the year lol
 

MegaMatch

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Monday now looks total rubbish, riddled with dry air even ahead of the SE change. I did not expect this. GFS has still been going for big storms on this day especially ahead of the change but I'm not buying it at all. All other days until about Wednesday still look ok though.
 

TweedStorm

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Monday now looks total rubbish, riddled with dry air even ahead of the SE change. I did not expect this. GFS has still been going for big storms on this day especially ahead of the change but I'm not buying it at all. All other days until about Wednesday still look ok though.
That leaves tomorrow and maybe Tuesday. Excitement has waned a lot everyday there's some inhibiting factor. It's an overcast mess here today. Hope something evolves on Sunday and Tuesday folks.
 

MegaMatch

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Even that 512 range looks dodgy.
Screenshot_20201024-112225.png
Yep, it's awful. I don't know what they were thinking if this was indeed intentional. There's a huge hole now over the NW Burnett and southern Central Highlands, ie. places like Taroom and Mundubbera.

Edit: I noticed this at the top of the Warrego radar page, but I'm not sure if it's related?

"Due to a minor software issue, rainfall might not be shown in some sections of some 256km and 512km radar images. Please access the 128km radar image, which is not impacted by this issue, and monitor the Bureau's observations, forecasts and warnings."

edit again: So I've noticed the above notification is also displayed at the top of the Newcastle's radar page which is experiencing the same issue...so it sounds like it's just a software issue that'll hopefully be fixed soon.
 
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