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

Discussion in 'Daily & Chat' started by Flowin, Mar 31, 2021.

  1. Flowin

    Flowin One of Us Ski Pass: Gold

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    Thought I would start an event thread as it has been discussed a bit in recent days about potential for significant rain along the Queensland Coast and possibly down into NSW starting near end of Easter and into next week:
    Short summary:
    • upper low well positioned over Queensland looks likely
    • the subtropical high pressure ridge along the Queensland coast retracting south
    • trough forming with the retraction of the ridge - still uncertainty on whether the trough will remain off-shore or get closer to or over the coastline - and the possibility of enclosed lows with that.
    Some overall graphics to start with:
    1. animation of EC 12Z initialised 30 March for 1-6 April period
      500 hpa geopotential and MSLP
    2. WATL PME 8 day rain total forecast issued this morning
      best guide without being biased by one model or another for now
     
  2. Ken Kato

    Ken Kato One of Us

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    [​IMG]

    Thanks for starting up this thread Flowin. Will duplicate my previous post here since it's relevant:

    MOSMIX (the system that statistically corrects a combination of EC and ICON by comparing their past forecasts and various predictors to what actually happened, as well as adjusting short-range forecasts based on current obs) which is the light blue line is still going for a decent increase for Brisbane.

    In saying that though, rainfall amounts for point locations are really hard to predict accurately so I don't usually pay too much attention to the actual amount.... just general trends.
     
    #2 Ken Kato, Mar 31, 2021
    Last edited: Mar 31, 2021
  3. Inclement Weather

    Inclement Weather Addicted

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    Good call Flowin in starting this thread for this increasingly likely, if not certain, event. Most of the major models in the latest run are starting to get in lockstep with each other. I think if the 00Z run is consistent, the BoM will no doubt ramp up its rainfall forecasts for Easter. I must say, I'm getting worried about the impact of this event with its potential for significant rain on top of the previous event. Runoff will be optimal leading to flash flooding, not to mention the risk for damaging winds if a low happens to intensify just off the coast. Anyway, the coming days will tell as to the intensity and the focus of this system. Let's hope if any low forms, it spins up way off the coast taking the rain and the wind with it. However, it's not looking good. I wouldn't have minded so much if it weren't for the recency of the last event. There's still a lot of people hurting from it.
     
  4. Vinny

    Vinny One of Us

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    Be nice if Rocky Yeppoon Gladstone and Bundy got the most of it. If the BOM is correct we will get the average for April of 71.5mm in 2 days !?
     
  5. Flowin

    Flowin One of Us Ski Pass: Gold

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    While there is no certainty - there is a good chance for those areas closer to the coast
    Below animation is the EC ensemble average 24 hour precip from this morning's 18Z (4am) model run.
    That is just one model though - but I do prefer the ensemble average rather than the main model when it is possible to get the ensemble products.
     
  6. Flowin

    Flowin One of Us Ski Pass: Gold

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    While the areas that received good rain recently still have overall root zone soil moisture (top 1m of the soil profile) the upper soil layer (top 0.1m) does dry out quickly.
    Two images below show simulated change in the upper soil layer from Wednesday last week to yesterday.
    I reckon catchments could soak up around 30 to 40mm, but still your point is relevant the potential for flash flooding is there if heavy rain occurs.
     
  7. DDstorm

    DDstorm One of Us

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    Great start/info flowin and to all the rest of the crew here for there detailed synopsis. Be watchin with bated breath and reading feverishly, just to keep up. Haha
     
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  8. Bello Weather

    Bello Weather One of Us

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    ICON has been consistent in bringing a low across the coast. Latest 00z run is still rolling out but looks like this:



    Forecast rain totals for this run:



    ...have to admit the total rain forecast positioning doesn't sit quite right with me when you look at the animation above - would expect the falls to make it further inland. @Ken Kato would love your thoughts on ICON - it's German so I'd expect it to be a decent model. Would be a worry if it came off as currently forecast. Here's how our main road from Bellingen to Dorrigo looks right now (image via Roads NSW) - unlikely to be open for weeks, even if the weather remains dry:

     
  9. Slovenski

    Slovenski One of Us

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    Cheers for the heads up Flowin.
    Definite upgrade to the cases of beer here to counter any possible event.
    Bring it on!
     
  10. Vinny

    Vinny One of Us

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    Our cliff came down in 2015 from repeated heavy rains,

    After , they uses shot crete and other stuff.



    Before

     
  11. Ken Kato

    Ken Kato One of Us

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    If I remember correctly, its overall skill with 500hpa heights was somewhere in between EC/UK and GFS. But I haven't checked for about a year or so now so I'm not sure whether that's changed.
    Subjectively, I've found it to throw up some unrealistic scenarios sometimes and it also has ACCESS-G's habit of cutting back rainfall amounts over land too much (which creates that really sharp rainfall gradient between land and sea that you always see with ACCESS-G).
    But overall, probably not too bad.
     
  12. PeteJ

    PeteJ One of Us

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    When I first looked at Bello Weather's post I thought that's insane, and also the same thought with the rainfall totals as being surprisingly low in some places. Think I will wait for this arvos' or even tomorrow's EC to get a hopefully more accurate view. Something else I am thinking of is the MJO and the probably last burst of the monsoon going to produce anything like a late cyclone out near the Solomon Is area. Keep up the excellent updates, please.
     
  13. Nature's Fury

    Nature's Fury One of Us

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    I can confirm this with my own observations in nearby bushland. Even after a few days, the top of the soil looked dried out and even more so this week. The week of sun and heat did wonders.
     
  14. dogski

    dogski One of Us

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    Seabreezes, Gleno71, Bisco and 9 others like this.
  15. MegaMatch

    MegaMatch One of Us Ski Pass: Silver

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    IMO if this hasn't crossed by Sunday night or very early Monday morning then it's never going to. Knife-edge stuff atm. ACCESS-G now crosses southern Brisbane/Gold Coast but I really doubt that happens.
     
  16. Nature's Fury

    Nature's Fury One of Us

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    EC/GFS go very close to a coastal crossing as well. So close to a major event here but it really is tight.

    ACCESS is the only model that has the low swinging inwards. The others all have it swinging out into the ocean.
     
  17. Flowin

    Flowin One of Us Ski Pass: Gold

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    The moisture feed (IVT) is good
    Just a matter of the features that can focus it and convert to precipitation and how close to the coast that is.
    First image GFS forecast IVT
    Second image EC Forecast IVT index for how much above normal

     
  18. Ken Kato

    Ken Kato One of Us

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    After so much frustration with googling for info, I FINALLY found a way to display the raw data from MOSMIX that the graphs on weather.us display. Above is an example for Brisbane. I need to go back and double check that those dates for the forecast probabilities in that graph are correct though.
    Just a shame rainfall amounts for locations aren’t a good example to use here because they’re one of the hardest aspects of weather to predict and accuracy is much lower than for things like temps.

    As I've mentioned previously, MOSMIX post-processes forecast data from EC and ICON by using correlations between their past forecasts and observations, hence why these forecasts are only available for select locations where there’s enough obs data.
    The first 24hrs of each forecast are also statistically adjusted by the latest obs data by comparing how the forecast is going so far to obs (the example above for 24hr amounts isn't adjusted by latest obs though).

    Correlations between certain predictors and obs are also used e.g. if a model systemically overforecasts max temps on days when lots of cloud cover is observed, it’ll apply the relevant correction to future forecasts. These post-processed model output statistics from both models are then combined in a way which has given the optimal past accuracy. 14 years of training data from EC is used as well as a number of years from ICON and statistical techniques are used to address model upgrades.

    Similar basic principle to OCF re the use of training data but with some notable differences.

    Apart from the usual stuff like temps, winds, etc, there’s also a number of other variables available for locations such as thunderstorm probability, visibility, etc but those don’t seem to be available for Brisbane for whatever reason. Probably not enough storms haha
     
  19. Bello Weather

    Bello Weather One of Us

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    Great work Ken! Wish it was available for more locations, but understand the limitations.
    Models look to me like they are coming together. Low forming, moving very close to the SE Qld coast before quickly moving away. Looks like the heaviest falls will be just offshore, but still some very decent falls across SE Qld and perhaps a little further north as well. Will be interesting to watch.
     
  20. Flowin

    Flowin One of Us Ski Pass: Gold

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    Well this morning's forecast updates brings another interesting mix of possibilities. Still uncertainty.
    Access
    EC
    GFS
    UKmet
    Icon
    CMC
     
  21. Ken Kato

    Ken Kato One of Us

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    I'll probably have a closer look at the details of the setup tomorrow when my shifts resume but from the quick glances I've been taking of EC and GFS, my general impression's been of a growing consensus that at the very least, the coastal fringe in SEQ and into far NE NSW will get good falls. The upper trough/low seems to be inland enough to prevent all the good falls from falling over the ocean.

    The higher uncertainty seems to be how far inland those good falls will reach.

    Even so, it's still a number of days out and given such a sharp east-west rainfall gradient, nothing's a done deal yet.
     
  22. Ken Kato

    Ken Kato One of Us

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  23. Vinny

    Vinny One of Us

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    BOM has 70 percent chance of rain 6-10mm on Friday, Saturday 90 percent 15-35mm, Sunday 90 percent 20-60mm and Monday is the strangest it says 40 percent chance 0-30mm.
     
  24. Flowin

    Flowin One of Us Ski Pass: Gold

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    EC EPS ensemble member #41 goes down a pathway to form twins.
    Very low chance of that occurring but still interesting from the perspective of what model physics can attempt to create.
     
  25. TweedStorm

    TweedStorm One of Us

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    I'm hoping for this scenario but given its the usual outlier with such events I'm not holding my hopes too high.
    Such a scenario would save us from another deluge around here which we don't need, but also give us a period of unsettled stormy weather which would be great.
     
  26. Bello Weather

    Bello Weather One of Us

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    Thanks for putting the animations together. From that what I can see is that the difference in the outcomes comes from the starting point of the lows -> EC and GFS start the dominant feature in the Coral Sea, and end up with an outcome which is further east, but the other models have the dominant feature moving down from Cape York, and thus have a more inland outcome.
    The take on that for me -> watch to see where the dominant centre develops, and you'll know the likely outcome...You can see the areas of interest in the latest WV image (via the BSCH site):



    I'll be watching this one over the next couple of days with interest :)
     
    #26 Bello Weather, Apr 1, 2021
    Last edited: Apr 1, 2021
  27. Flowin

    Flowin One of Us Ski Pass: Gold

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    I also think that slower boats in the Brisbane to Gladstone Yacht race will also be watching the forecasts closely.
    Good tailwind for the first two days, but could get ugly on Sunday. Many boats would get to Gladstone by then. I have not heard any news about it not proceeding.
     
  28. Ken Kato

    Ken Kato One of Us

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    [​IMG]

    Above is the consensus map for greater than 100mm totals within the next 5 days using the 12z runs of EC, GFS, and ICON.
    This only extends out to 10pm Tue so it won't show any further >100mm falls beyond that.

    No more lockdown after today to prevent people from going camping this Easter and getting wet if they're in the stronger green areas. Albeit with flooding risk.
     
  29. Flowin

    Flowin One of Us Ski Pass: Gold

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    This little friend emerged this morning
    Not if he or she came out cos Lockdown is going to end or because some weather may be on its way here

     
  30. Flowin

    Flowin One of Us Ski Pass: Gold

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    Trend across the last five runs of GEFS ensemble looks to be pushing more toward the coast in the last run (18Z)
    First image indicates:
    • ensemble average isobars of the high in the bight and high in tasman shifting further west in last run
    • ensemble member low pressure centres (red numbers) shifting further west in the last run
    • ensemble MSLP spread (colour shading) shifting further west in the last run.
    Second image indicates:
    • upper low (500hpa geopotential) shifting further west in the last run
    Edit add: I do wonder if the new GFS pushes weather systems along too quickly. I noticed in its testing phase over the last few months that particularly week 2 of the forecast was significantly different to the previous GFS and other models. Seem like it wants to develop movements to quickly. Just a limited observation I have no objective analysis to back it up.

     
  31. Nature's Fury

    Nature's Fury One of Us

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    There's a developing model trend on ICON and Access for a westward landfall around central QLD, which gives us a deep NE feed and dump over SE QLD. EC and GFS deterministic aren't really as interested yet, but you can see it starting to appear on the ensembles posted above.

    As was the case in the earlier modelling, if the low forms from the eastward region of low pressure in the CS it's more likely to be offshore. If it forms in the westward region (closer to Cape York as Bello mentioned) then much better chance.

    Still not definite we'll have a major event rather than just some decent rain, but it's looking far better than it did a few days ago.
     
  32. BrettSS

    BrettSS One of Us

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    Thanks for pointing that out. I hadn't noticed that. If what you're saying is true, then the models should come together once the dominant centre develops.
     
  33. Tsunami

    Tsunami One of Us

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    Wow good reading, thanks everyone
     
  34. Nature's Fury

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    Dominant centre should be clear by about Saturday, so about 48 hours prior to any potential action in SEQ/NE NSW.
     
  35. BrettSS

    BrettSS One of Us

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    Thank you. Hopefully, there'll be some good falls in the areas which are still in drought.
     
  36. Ken Kato

    Ken Kato One of Us

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    18z GEFS above. They're the percentages of the ensemble's members which are currently going for enough vorticity at the 850hpa level within the next 7 days to spin up a low/s through that height.
    The title says Closed Low but sometimes it can also be a deep trough with enough cyclonic vorticity to the flow going through it to show up on here as well.
     
  37. Flowin

    Flowin One of Us Ski Pass: Gold

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    Thanks Ken - very interesting. I've taken liberty to scribble on your chart two lines which resemble what some models, or alternatively some ensemble members of the ensemble models have been hinting at. The western inland one a bit weaker than the down the coast one.

     
  38. Bello Weather

    Bello Weather One of Us

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    ICON now following EC and GFS with a more coastal solution - compare the 12z and latest 00z runs:



    Latest GFS going for a very close-to-the-coast run:



    ...so ICON has moved east, closer to EC, and GFS has moved west, closer to EC. Looks like we are finally getting some consistency between the models :)
     
  39. Flowin

    Flowin One of Us Ski Pass: Gold

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    Flood watch just issued by BOM.

    Australian Government Bureau of Meteorology, Queensland

    This Flood Watch provides early advice of possible flooding within the specified catchments.

    Initial Flood Watch for coastal catchments between St Lawrence and the Queensland - New South Wales border extending inland to the Darling Downs
    Issued at 2:47 pm EST on Thursday 1 April 2021

    Flood Watch Number: 1

    MINOR TO MODERATE FLOODING IS POSSIBLE FROM SUNDAY EVENING

    A deepening trough along the Queensland coast is likely to bring heavy rainfall to the flood watch area from Sunday and continuing into Monday. Heaviest falls are likely to occur north of Fraser Island initially, extending southwards to the Queensland - New South Wales border by later in the day Sunday.

    Catchments to the north of the Sunshine Coast are generally dry and will be slower in responding to heavy rainfall. Catchments in the southeast corner however, are wet from recent rainfall and likely to respond quickly.

    Minor to moderate flooding is possible in the Flood Watch area from late Sunday into Monday. Isolated major flooding is possible.

    Localised flooding and disruption to some transport routes are likely.

    Catchments likely to be affected include:

    Dawson and Don Rivers


    Calliope River

    Boyne River

    Baffle Creek

    Kolan River

    Burnett River

    Burrum and Cherwell Rivers

    Mary River

    Noosa River

    Sunshine Coast Rivers and Creeks

    Pine and Caboolture Rivers

    Upper Brisbane River

    Lower Brisbane River
    (Specifically the Bremer River and Lockyer, Laidley, Warrill and Brisbane Creeks)

    Logan and Albert Rivers

    Gold Coast Rivers and Creeks

    Condamine Rivers
    (specifically southern and far eastern parts)

    See www.bom.gov.au/qld/warnings to view the current flood and cyclone products for Queensland.
     
  40. Nature's Fury

    Nature's Fury One of Us

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    I'd just like to see it move that little bit further west for a major event. It's so close it'd be a real shame if it didn't.
     
  41. Weathertraveller

    Weathertraveller One of Us

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    Thanks Flowin, looks like the rivers are going to be flowing high again. I received the text alert about half an hour ago. After the river at the back of me flooding just over a week ago, and today being the 4 year anniversary of having the Logan River floods and having the river near my backyard, it concerns me. The ground is still quite saturated from the last rain event. The river didn't go down until last Saturday, and flooded roads around here were re-opened by Monday. I'm not looking forward to this event at all. Heavy rain and wind with already saturated ground isn't a good combination.
     
  42. Nature's Fury

    Nature's Fury One of Us

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    The current track path gives SC, GC and NE NSW the higher falls because of the NW/SE track path and the NW/SE alignment of our coastline. If this continues I would suggest flash and creek flooding are higher threats for your region compared to riverine flooding as the upper reaches of the Logan river inland won't see as much rain with the very sharp reduction in rainfall from east to west. Still, westward by 50 km and you're right in the firing line.
     
  43. Ken Kato

    Ken Kato One of Us

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    Funny you mention that. I noticed a similar tendency a few days ago with the new GFS being a lot more progressive (like the previous version was) than EC with the speed of the system.
    The current version is supposed to have addressed that issue of GFS being way too progressive with systems (it used to be so extreme that you could consistently add an extra couple of days to GFS's ETA of a system five to seven days out and get it right most of the time).
    I'm not sure how fully it's been fixed in this current version though.

    I only looked at one run though so impossible to tell whether it was just a one-off or not.
     
  44. MegaMatch

    MegaMatch One of Us Ski Pass: Silver

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    There is still a pretty big difference in the modelling out to 72 hrs. Some (CMC, ICON) take a weaker system into the coast north of Bundaberg with heavy rain developing anywhere to its south, while others like UK and GFS have a stronger system just skirting the Hervey Bay coast, eventually ending up off the SC. The first scenario would probably bring more rain to everyone overall provided the associated trough continues to dip southward, the second scenario would mean the extremely heavy rainfall associated with the low itself would be a lot more coastal.

    edit: This afternoon's EC operational still agrees with the GFS/UK scenario.
     
  45. Nature's Fury

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    There were about 2 days of runs (2x4 runs) where GFS appeared to be about 24-36 hrs ahead of EC with the progression of the system.
     
  46. Slovenski

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    So much for my attempt at mowing. Long heavy squally shower. The beginning of wet weekend?
     
  47. Nature's Fury

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    00z EC swings the low into WBB and out. It ends up further east than GFS but actually delivers more rain than the previous run when it was further to the west. Big falls on WBB/SC but areas south of Brisbane miss out on the heavy stuff (if you can call 100-150 mm "not heavy"). I have noticed that EC has been going for the heaviest falls out of all the models. I'm guessing that's because it has a higher resolution and is picking up some orographic lift and other nuances in the circulation and rainfall formation than GFS?

    EDIT: GFS (Monday) has the system off SEQ about 24 hours earlier than EC (Tuesday)
     
  48. Ken Kato

    Ken Kato One of Us

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    EC does have slightly higher horizontal resolution (~9km vs GFS's ~13km) but a lot of the differences are due to the simple fact that all models treat the physics of the atmosphere in slightly different ways. Any differences in the way synoptic systems, cloud microphysics/precip, gravity waves, etc are treated will manifest themselves as noticeable differences in the forecasts between each model especially the further you look into the future.

    The data using GFS's native resolution of ~13km isn't available to most third party websites to use though. Publicly available data ranges from 0.25 degrees to 1 degree resolution and different websites will use different resolutions depending on how much they're willing to download with each run. The 0.25 degree datafiles are a lot bigger than the 0.5 and 1 degree files and when we're talking about 0.25 degree data files for every 1 and 3hrs for the entire globe with each run, it's a lot of data.
     
  49. Weathertraveller

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    Northern Gold Coast
    It will be interesting to see what happens, and exactly which areas receive the highest rainfall. Guess we'll know soon enough. Thankyou you're correct, when the river catchment areas, like Beaudesert receive anything over 100mm quickly the river comes up considerably right down here closer to the bay.
     
  50. Tsunami

    Tsunami One of Us

    Joined:
    Jul 6, 2019
    Messages:
    612
    Likes Received:
    3,561
    Location:
    Cleveland SE QLD
    Well it appears fearly locked in this event.
    Only uncertainty is who will need gumboots and rain coat and who will need a wet suit and life jacket lol

    Very interesting to say the least. Am watching weather maps and can see some might get a very substantial amount of rain