Flood East Coast Wet Spell 17 February - 27th February 2021

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Bello Weather

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Details on this one are still sketchy but we haven't seen many events recently, so going to take the opportunity while it is there...
For some days now the models have been turning the winds onshore across the east coast from mid week. Initially there was not much upper support showing...but over time it's looked more favourable up high for some bigger falls. Models have also started indicating that a tropical system could get swept up into the event - and if that happens then some much larger totals are possible. Here's the latest EC run with the onshore flow developing and uppers swinging a low down just offshore:

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EC trend over the last three runs shows how up in the air the low developing / location is:

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...and here's the latest GFS take...also shows a low moving down, then finally being swept onshore:

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Regardless of whether we see larger impacts from a low moving onshore, we've still got the onshore flow and the potential for some decent accumulating totals. Here's the three models out to 240 (prior to any low making it ashore with EC and GFS, ACCESS has it coming ashore more quickly) - with some big differences in the forecast totals as a result:

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...totals and timing should firm up over the next few days. The EC ensemble out to 240 shows some good potential for large sections of the coast:

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...and heading out even further to 360 on the ensemble it shows totals still growing...so indications are there that this wetter spell could last for some time:

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Still some to way to go...but right now it looks like a significant section of the coast is still in the running for some big totals from the onshore flow, and there is the potential for a Coral Sea disturbance to keep us on our toes...though an offshore event is of course possible, with little but swell onto the coast...
Images: Meteologix, Tropical Tidbits
 

Bello Weather

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That's why I asked about EC. With my very basic skills at reading models, it seems that low is now just far too offshore for SE QLD.
It is on this run...but a few things to remember...(1) this is out at the end of the model runs...and even EC at this timeframe can (likely will) change a heap over the coming days (2) GFS shows a similar situation at 240 but then swings the low onshore (3) ACCESS has it coming ashore earlier (4) even without this low...some areas will see some BIG totals just from the onshore flow...most likely where the topography helps out. Something to watch for now, with the outcome likely to change a heap over the coming week :)
 

MegaMatch

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I'm still going to buy some extra icecream because it's the best its looked for a while. I won't open it till 3days from now because a lot can change and see if this area is included this time. out of tank water.

Does it look like a desert up there yet? It does here. It's all dead. We went for a drive up around that Toogum - Burrum Heads area a couple of months ago and it didn't look so bad, but I don't think they've had much if any rain since then so I'd say it must be starting to look just as bad there now.

Too far out still to get into specifics, but I really hope that main focal point around northern NSW somehow shifts further north into northern SEQ/CQ. I am sick of seeing that area constantly suck whatever moisture there is away from us.
 

Itsjustme

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Does it look like a desert up there yet? It does here. It's all dead. We went for a drive up around that Toogum - Burrum Heads area a couple of months ago and it didn't look so bad, but I don't think they've had much if any rain since then so I'd say it must be starting to look just as bad there now.

Too far out still to get into specifics, but I really hope that main focal point around northern NSW somehow shifts further north into northern SEQ/CQ. I am sick of seeing that area constantly suck whatever moisture there is away from us.
Yep dry alright. if it wasn't for december (just short showers) it would have been a lot worse. This month not a drop yet. Wet season hey.
Jan Dec
2020 124.0 275.0 30.0 3.0 13.0 25.0 30.0 37.0 33.0 19.0 0.0 119.0 708.0
2021 20.0
 

Bello Weather

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Looking at this stage that the upper support is not going to be as strong inland...as such the low which is forecast to develop looks more likely to follow most others into the graveyard. Here's the EC take on it....GFS is even more extreme in taking the low away...ACCESS is closer to EC...

ecmwf_z500_mslp_aus_fh168-240 (2).gif


As noted in the first post...even without the direct impact of a Coral Sea low we're still looking at some decent coastal accumulations. Here's the 00z totals from EC, ACCESS and GFS:

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Ken Kato

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Some miscellaneous graphics above from weathermodels.com
1st and 2nd maps - Comparison between the 10-day totals from the current version of EC and the pre-operational version respectively that's due to become fully operational this winter.
3rd and 4th maps - 10-day forecast storm tracks (both extratropical and tropical) from the GFS and EC ensembles respectively. They both go out to 15 days but they look messy out that far so I've limited it to 10 days. The common theme appears to be that both of them have a fair number of members a bit off the coast with some a bit inland or crossing the coast.
 

Flowin

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Access G 12Z going for more in its latest - times like this I get frustrated that the ACCESS ensemble or least it’s spread is not available to the public

Others going for less in their latest - pic is the EC EPS average 10day precipitation

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Michael Hauber

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Access EC and GFS all agree on a significant low near the coast towards the weekend. A direct impact looks a low chance, but indirect effects look substantial with windy weather and moderate falls of rain a high chance for some areas. Models have been consistently predicting a substantial upper trough to form inland so even though a low may end up being further east than predicted and pull most of the rain out to sea in the later part of the event it is not likely to pull the rain in the earlier part of the event as the upper level trough starts to have an influence. Almost no chance of a non-event in my opinion, although it may be a lot weaker than hoped for and needed, and some areas may miss out.
 

Ken Kato

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Access EC and GFS all agree on a significant low near the coast towards the weekend. A direct impact looks a low chance, but indirect effects look substantial with windy weather and moderate falls of rain a high chance for some areas. Models have been consistently predicting a substantial upper trough to form inland so even though a low may end up being further east than predicted and pull most of the rain out to sea in the later part of the event it is not likely to pull the rain in the earlier part of the event as the upper level trough starts to have an influence. Almost no chance of a non-event in my opinion, although it may be a lot weaker than hoped for and needed, and some areas may miss out.

You'd think with a distinct change in the pattern (albeit likely short-lived) like this later in the week involving such a long fetch of easterlies that we'd get at least an increase in coastal showers regardless of whether a surface low or troughing forms off the coast and drags any rain areas away later on. EC 10m and 850hpa winds above for later in the week.

EC's also currently going for deep troughiness through inland eastern Oz after this with even a small low in there but a bit ridgey up the coast.

As I mentioned in the day to day thread earlier today, a general rule of thumb which some oldschool forecasters have used in the past and which I often find works fairly well is that whenever there's a big long fetch of easterlies, a low or deep troughing often inevitably ends up developing over water somewhere in this flow, especially if there's an upstream approaching upper trough to lend a hand. It's a bit of a chicken and the egg type of setup (which comes first - the low/trough or the easterly flow) but I often find any significant lows or deep troughing occur soon after the flow develops.
 
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Michael Hauber

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Latest EC quite disappointing with a weak low moving in from New Caledonia blunting a lot of impact, especially Widebay to Capricornia. Decent onshore winds are restricted to north Qld and SEQ.

EC Friday 1pm:
Ec Fri 1pm.PNG


GFS and BOM look to have a good upper trough but low forming too far out to sea to be much interest. In contrast EC has a low close enough to be a tease, but with limited use unless it moves back closer.

I have been a little surprised with the persistence of the weak low that formed yesterday. And the fact it has moved with a bit of a westerly component instead of away to the east (movement roughly NNW parallel to coast - was a similar distance off the gold coast yesterday am). Maybe its a good omen for this approaching event.

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Bello Weather

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Bellingen special imo.
Haha, will let you know how it goes. To be honest I was hoping this one would give good rain to a heap of other areas as well... @Michael Hauber - thanks for that update...will keep watching this one...if there is one thing worse for rain totals than no low, it's one that forms offshore, sucks up all the rain but stays far enough out to keep the bigger totals offshore. This low looks like forming way too far offshore to help out. Would need the upper system much further west. Wondering how climate change impacts upper patterns - are we just unlucky or do increasing temperatures at the surface impact on the local of upper systems? That one is way beyond my knowledge...
 

Ken Kato

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Wondering how climate change impacts upper patterns - are we just unlucky or do increasing temperatures at the surface impact on the local of upper systems? That one is way beyond my knowledge...
It's a tricky question with no definitive blanket answer at the moment because a) it's not just the surface that's warming but also various levels of the troposphere, b) the exact magnitude of the warming in surface temps has higher certainty than the exact magnitude of warming higher up in the troposphere...... and the exact ratio of warming of the surface vs different heights of the troposhere also has a lot of regional variations e.g. there's evidence to suggest that the very upper parts of the troposphere in the tropics near the tropopause are warming faster than the surface but less evidence of that in the midlatitudes..... many parts of the interiors of continents are also warming faster at the surface than the upper troposphere and c) it's hard to verify using only radiosondes on balloons what the exact increase has been aloft because there's been no single global standard for decades that regulate the quality of radiosonde temp sensors and bias correction, and those sensors have changed over time with different technology. Reliable reanalysis schemes can help here though.
You could also add a d) to that in terms of changes in large scale atmospheric circulations such as the ongoing expansion of the Hadley cell/subtropical high pressure belt and contraction/strengthening of the southern polar vortex because they're tied in with all of the above and the potential effects on the mid and upper level systems.

Midlevel heights at the 500hpa level have also risen overall but again, there's regional and seasonal variations with that.

Satellites can estimate temps aloft in the troposphere but they currently still have higher instrumental uncertainty/margin of error than conventional instruments.

So bottom line is, it's hard to say what effect this would have on an individual setup like the one covered by this thread unless you do a specific attribution experiment on it and even then, you'd have to take into account some uncertainty.
 

Bello Weather

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Always a sign of a desperate weather nerd...getting sucked in by random model runs that show something interesting happening. I've liked ICON at times in the past, and this run shows a different outcome with the low sitting off the SE Qld coast and sending some monster falls into NE NSW:

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UK out to 144 also keeps the low close to / over the coast with some bigger totals as a result:

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@Donzah there's your Bello special ;) Other models not following this outcome at this time...the chances of the low giving falls onto the coast is pretty slim, but seeing the odd run giving something interesting (if only for NE NSW) tells me to keep one eye on future runs...Currently sitting in the sweet spot where the 00z runs from these models are out but the EC run is not out yet :D
 

Bello Weather

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not really anything special about it when it happens multiple times a year.
I hear you, but it actually is fairly special down here, as numerous locals can get cut off by the bigger flood events and the forecasts give everyone a time to prepare and get supplies in. Appreciate that we get a heap more rain down here and, believe me, I would send it up to you guys in a flash if there was any way of doing so. Hope you get some bigger totals soon. If it's any consolation you'll likely see the big falls offshore again in upcoming runs.
 

Ken Kato

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Above: consensus map using the 12z runs of EC, ICON, and GFS re the areas they're favouring for greater than 25mm accumulations within the next 5 days.
It should go without saying that the white areas doesn't equal lack of rain. It doesn’t even mean a total lack of >25mm falls since convection can easily cause localised good falls. And in any case, those green areas will continue to shift around a bit since the tail end of the rainfall’s still a number of days away. But it does give a bigger picture as to where these particular models are currently favouring the better falls.
 
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