Flood E NSW SE QLD East Coast Rain Event 11 Dec - 20 Dec 2020

Bello Weather

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We've been in a La Nina pattern for some time now, but the easterlies have been missing. It looks like they could come back with a bang over the coming week, with a deep and long easterly flow over above average SSTs come pushing into the east coast. Very supportive uppers are also likely...Here is how EC sees it - long lasting event with troughing close to the coast from time to time and an ocean trough (possible low) looking to move onshore:

ecmwf_z500_mslp_aus_fh24-240.gif


GFS has the event moving offshore more quickly but also develops a nasty looking low that it then moves quickly onto the NSW coast:

gfs_z500_mslp_aus_fh24-240.gif


GFS has been chopping and changing from run to run, with EC and the local ACCESS model a lot more consistent. They all give some big falls onto / close to the coast...though the synoptic pattern that GFS is showing would, IMHO, give bigger falls further inland close to where the low makes it ashore...but either way it's looking like it could get wet along the NSW and SE QLD coast. Focus right now looks to be NE NSW, buty could change - EC has been keeping big falls into SE QLD too. Here is the forecast rain out to 180 hours from EC (which has been consistently forecasting some big totals), GFS (up and down from run to run), ACCESS (as with EC consistently forecasting some big totals) and, as a bonus prize, ICON (getting to like watching this model):

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Flowin

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Thanks for starting this event thread @Bello Weather
Just repeating what I put in the day-to-day chat - as it is relevant to this thread.
The EC 12z ensemble "spaghetti variations" of potential positioning for the upper low (1000 AEST Friday to Tuesday)
We in SEQ will be hoping for a more northerly positioning of the upper low - but hey you don't always get what you hope for!
modez_20201211_0000_animation.gif
 

Slovenski

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Latest GFS run brings the rain right the way down the NSW coast now - could be a very wet event for many. Here's the 12z run and then the latest 18z run out to 240:

ezgif.com-gif-maker (10).gif
Thanks for starting the thread Bello, looking at that latest GFS map, we be getting dregs up here again. I'm more inclined to believe EC or Access G3 tbh but both of those are also following GFS atm. A non event for up here I suspect. Hope something changes.
 

Ken Kato

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Yep, that southwards trend started becoming more obvious yesterday. Goes back to my earlier musings about how these types of setups so often end up favouring NSW for the heavier falls. Having said that, I haven't had a close look at the latest yet except for precip maps to see if much has changed so will reserve any further opinion on it until I do.
 

Flowin

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Latest GFS run brings the rain right the way down the NSW coast now - could be a very wet event for many. Here's the 12z run and then the latest 18z run out to 240:

ezgif.com-gif-maker (10).gif
I was looking at the 18Z GFS run, and thinking like others - damn still too far south for us in SEQ.
Then I was about to look away at something else and thought whats the bigger picture, when I noticed what GFS does in the week after that.
Don't take this seriously it is too far lead time, and GFS does have a habit of throwing up some random scenarios which are at best just useful for entertainment purposes.
Below animation Tau +108 to +360 hours.
gfs_mslp_pcpn_swpac_fh108-360.gif
 
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Long Road Home

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Either way this is only the first event of many to come as the patterns have finally flipped in this late blooming La Nina with the high belt sitting well to the south for as far as the models can see. This will open up the easterly 'alleyway' to feed those east coast troughs. For C and N QLD the break will likely come from a GOC tropical depression.
 

Ken Kato

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upload_2020-12-9_13-10-5.png


upload_2020-12-9_13-10-14.png


The 2nd ACCESS-S map above is beyond the end of the period covered by this thread so it's just for info purposes but the 1st map isn't and could be relevant to us if any tropical/non-tropical system that swings through the southwestern Coral Sea and into the Tasman Sea turns winds more SE or SSE'lies for us in its immediate wake.
 
upload_2020-12-9_13-10-5.png


upload_2020-12-9_13-10-14.png


The 2nd ACCESS-S map above is beyond the end of the period covered by this thread so it's just for info purposes but the 1st map isn't and could be relevant to us if any tropical/non-tropical system that swings through the southwestern Coral Sea and into the Tasman Sea turns winds more SE or SSE'lies for us in its immediate wake.

More SE'lies, we cannot seem to catch a break.
 

Michael Hauber

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Looks like game over for north of the border.

I'll say its like we just lost 3 quick wickets to be 6/150 chasing 250. And our team has been batting poorly for the last few games. But we do have la nina batting at the crease. Hasn't been in great form the last few games, but a top hitter when in form.

On current runs there is certainly potential for good shower activity on Saturday ahead of the trough/low digging in and focusing rain further south. However the upper trough comes from the SE, on Saturday it is sitting almost over SEQ so a bit too far east for my liking, and then shifting into a better position over inland Qld by Monday, but by then trough/low is digging in and dragging rain south.

Some good showers on SS Coast could easily deliver 20-50mm, which on top of great rainfall from storms Monday would be a great result turning around a short sharp drying trend through November. Further inland or further north, not as much rain and where ever the soil is still quite dry lower amounts of rain won't be all that helpful unless we get quick follow up.

For NSW this event has one very important serious flood ingredient - a slow moving rain generator, specifically that upper low. Heaviest rain looks like it might spin around the low though alleviating the risk of heavy rain in one location for an extended period.
 

Stumer1

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I was looking at the 18Z GFS run, and thinking like others - damn still too far south for us in SEQ.
Then I was about to look away at something else and thought whats the bigger picture, when I noticed what GFS does in the week after that.
Don't take this seriously it is too far lead time, and GFS does have a habit of throwing up some random scenarios which are at best just useful for entertainment purposes.
Below animation Tau +108 to +360 hours.
gfs_mslp_pcpn_swpac_fh108-360.gif
Cyclone hitting just south of Fraser Island would make things interesting, where did Wanda cross the coast in 1974?
 

MegaMatch

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fwiw, 00z UKMET and CMC have shifted the focus further north into SEQ. UKMET has a huge blob over SEQ with a bullseye of 375mm over the Sunshine Coast, and that is until Tuesday next week. In fact, it looks eerily similar to the February event, except it isn't expected to last anywhere near as long as that one did. GFS/ICON still like the heaviest falls offshore and into NE NSW. Feels as though this one could go either way yet...(speaking for you guys down in the real SEQ region, not us up here where either way the only real difference will be more wind and maybe a few more showers).
 

MegaMatch

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EC still with the upper low further NW than GFS @ 96 hrs. Low pressure system forming along the CS trough well east of Fraser Island. This could be real juicy for SEQ.

Edit: Low pressure trough hits the southern coast @ 120hrs. Upper low and possible surface low further north over the WBB. As usual with these hybrid-type lows, heavier falls wrapping in to their south (in this case, SEQ, extending into northern NSW).

@144 hrs, the low pressure trough has crossed the coast and weakened while the upper trough (once upper low) slips inland while also weakening.

So while this could (will) still change between now and then, if it were to happen it's definitely deluge material...but unlike the Feb event, the whole thing is moving a lot quicker rather than sitting there generating pulse after pulse of heavy bands of rain and storms for several days.
 

Bello Weather

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EC still with the upper low further NW than GFS @ 96 hrs. Low pressure system forming along the CS trough well east of Fraser Island. This could be real juicy for SEQ.

Edit: Low pressure trough hits the southern coast @ 120hrs. Upper low and possible surface low further north over the WBB. As usual with these hybrid-type lows, heavier falls wrapping in to their south (in this case, SEQ, extending into northern NSW).

@144 hrs, the low pressure trough has crossed the coast and weakened while the upper trough (once upper low) slips inland while also weakening.
Sure enough EC still has some good falls coming into SE QLD. It's been persistent on this one, though now has the earlier falls further south:

xx_model-en-304-4_modez_2020120900_123_12880_157.png
 

MegaMatch

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Sure enough EC still has some good falls coming into SE QLD. It's been persistent on this one, though now has the earlier falls further south:

xx_model-en-304-4_modez_2020120900_123_12880_157.png
Yeah GC southwards probably still the safest bet atm but usually SEQ as a whole still does reasonably well when there's an upper low as far north as up here. Still think it looks better than some of the earlier fizzer predictions at least.
 

Gleno71

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Either way this is only the first event of many to come as the patterns have finally flipped in this late blooming La Nina with the high belt sitting well to the south for as far as the models can see. This will open up the easterly 'alleyway' to feed those east coast troughs. For C and N QLD the break will likely come from a GOC tropical depression.
i think it's more of the shape of the the high not so much it's position, but i could be wrong. Im fairly sure there have been highs the last few months near tassie but they ridge up the coast giving us fine conditions, for some reason this high is different
 

MegaMatch

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i think it's more of the shape of the the high not so much it's position, but i could be wrong. Im fairly sure there have been highs the last few months near tassie but they ridge up the coast giving us fine conditions, for some reason this high is different

Because upper lows/troughs that are strong enough can actually modify the shape of the ridge.
 

PeteJ

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.and EC still has big / huge totals right through NE NSW...I've got a streaming floodcam in Bellingen as well as a weather station - as well as a backup generator for the inevitable power failure...could get pretty busy over the next week or so if anything like EC comes off - too much rain can be as much of a curse as too little:
Lismore could be an interesting place to be. Hope it's only minor if any flooding occurs. If I remember Wanda was just a cyclone. Probably would not be by today's definitions.
 

Steve777

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The focus of this event is in NE NSW. Significant falls there start on Friday 11th. Should we change the date in the thread?

Here are the totals forecast by the BOM this afternoon for Dec 10-16 (mm) for sites on the NSW North Coast:

Lismore: 65 - 210
Coffs Harbour: 100 - 290
Port Macquarie: 65 - 170

So quite significant, especially at the upper end. Even at two days out, there’s still a lot of uncertainty.

Southwards totals are much lighter - in the range 10 - 50 mm for Newcastle and Sydney - a lot of uncertainty there too. Down here it might just turn out to be one of those spells of cool, overcast weather with little rain that can be the curse of Sydney Summers (we don’t mention them in tourist brochures).
 
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Flowin

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Latest from the members of the 00z GFS ensemble for Brisbane out to 16 days. The white line is the ensemble mean:

upload_2020-12-9_17-22-5.png
Thanks for posting ensemble rain for GFS. The deterministic models runs for various models posted a few hours ago are only part of the picture IMHO. Ensembles to me give a better context of each models ‘range’ of possibilities. Below is the EC EPS upper levels ensemble spaghetti for potential positions of the upper low.
Relevant for model runs initialised 00z today.
It’d be nice to get similar from models other than EC EPS but I am not aware of any.
734ECBD9-162F-474B-9A27-857B3C0F3B0F.png
 

Ken Kato

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The minimum being nearly 50mm is a good sign. Compared to last month even that would be fairly decent rain.
The minimum scenario's more like around 35mm and that's accumulations out to Christmas Day... and could still change... but yes I know what you mean, at the very least you'd think we'd get something if not a huge flooding deluge. Like you said, it wouldn't take much to beat last month's pathetic effort here!
 

PlumbBob

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Sheeze, amaizing post's going on 'ere, so many variables, where, how much etc; only time will tell, tho exciting to follow..

I assume/wonder if some 'weather modelling agencies' are noting what is actually happening in rgrds of Nino activity before & during this big event, location and strengths etc of the IOD, MJO, Trade winds, Walker Circulation Etc ?
Guess it be all stored in Data Banks after the event - and comparisons made for more accurate predictions down the track. .

Looking on with intererest for this event, hope some of the major Dams get a good top-up, Wivenhoe & others could sure use some ?
That said, I hope some good falls find its way over western seqld parts as well,, while most at this stage tending to be predicted below the border 'bugga', can only hope 'Some' still could hit the dryer parts in our region, bit of respite would certainly go down as handy ?
 

Long Road Home

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I assume/wonder if some 'weather modelling agencies' are noting what is actually happening in rgrds of Nino activity before & during this big event, location and strengths etc of the IOD, MJO, Trade winds, Walker Circulation Etc ?
Guess it be all stored in Data Banks after the event - and comparisons made for more accurate predictions down the track. .

Indeed, every single piece of data goes into the database. This is how they create seasonal outlooks - it's a model based primarily on this historical data which is then derived into the probabilities we're given.
 

Rainbow Serpant

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The poor mans ensemble below “WATL”.
A good guide for any body who wants a good starting first guess.
For all folk that live around or near central QLD, I’d think you would be entirely justified right to be peeved by this.
3AB451BD-ED1F-4478-8BB3-EA39F8FBB47D.png

We see this time and time again, it’s become standard to simply miss out on rain events. I don’t even bother looking at models or reviewing forecasts anymore as I just know this area will miss out on everything
 

Bello Weather

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Looks game on this morning. EC moves a low in across Fraser Island - that would sort the fire out:

modez_20201213_1800_animation.gif


... With some decent totals across SE QLD as a result:

xx_model-en-304-0_modez_2020120912_240_12749_157.png

Big totals also forecast to run right down much of the central and northern NSW coast:

xx_model-en-304-0_modez_2020120912_240_13007_157.png


Most models on board with similar totals now - the biggest difference between then being the northern / southern extent of the event. Flood watch today from the BoM? Also thinking we could see some strong wind impacts south of where that low comes ashore. GFS has it further south but if it comes ashore as per EC Fraser could be hit twice - first fire and then storm.
 

Nic Bri

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Looks game on this morning. EC moves a low in across Fraser Island - that would sort the fire out:

modez_20201213_1800_animation.gif


... With some decent totals across SE QLD as a result:

xx_model-en-304-0_modez_2020120912_240_12749_157.png

Big totals also forecast to run right down much of the central and northern NSW coast:

xx_model-en-304-0_modez_2020120912_240_13007_157.png


Most models on board with similar totals now - the biggest difference between then being the northern / southern extent of the event. Flood watch today from the BoM? Also thinking we could see some strong wind impacts south of where that low comes ashore. GFS has it further south but if it comes ashore as per EC Fraser could be hit twice - first fire and then storm.
Wow wouldn't that be wonderful if it happens really hoping it does! Nature taking care of the disaster the jetski bogans started.
 

Flowin

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@Bello Weather
Not sure about the surface low over Fraser Island on the EC high Res deterministic, though Access G3 has it as well but a bit later.
I scanned through each of the 12Z EC EPS ensemble members and there is a fair bit of variance on the positions and strengths of surface low and the upper low as well.
But there are still a reasonable number of ensemble members that have a more northerly positioning of the upper low, which I'd think would help with a more northerly position of the surface low.
Contrasting that some have a surface low staying off shore and further south.
accuracy-vs-precision.jpg

Don't know how to show all the variation without posting heaps of pics of each ensemble members which would just clutter the thread.
Anyway probably the easiest overall pic is the ensemble mean for the 500hpa for the upper low, which could be said is guide to a quasi accurate - not precise estimate :rolleyes:

upload_2020-12-10_6-57-27.png
 
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