Models have been suggesting for about 3 days now that there will be a significant disturbance in the current fine weather pattern during the second half of next week. There is a clear window of opportunity there when colder air moves through the Bight and the current flat high ridge over southern Australia gradually weakens and moves east. I agree that exact events are still very sketchy and I cannot make a proper forecast yet. But there will be an event of some sort and it will be interesting to discuss the upcoming week with others, most of NSW should get some interesting and useful weather out of this.

It seem pretty likely now that there will be rain ahead pool and cold fronts utilizing some moisture from Queensland that will affect Eastern and NE NSW. Then there will also be at least a cold pool and/or cold fronts that will bring snow to the Snowies. Currently it looks like there could be potential for snow and cold to be significant enough to include the first snowfall for the CT's, but its still too early to be sure of that. What seems quite likely now is that a cold pool will begin emerging into the Southern Bight by Tuesday after which the moisture from Queensland will begin to get organised. What happens next is still quite uncertain, but there seems to be a fair chance for the cold air to track into NSW by latter in the week.

Finally might get a bit wet in Sydney! Still a bit far off but might get 10mm or so out of the event here.

Nice opener there PD - sets it out well - your thoughts far more organised than mine

Will be interesting watching the sat pic and models in the days to come.

Not sure what to make of EC.. Looks wild but seems to have held up that 1st low and pool of cold air allowing a rain event to unfold similar to GFS through Eastern Oz and SE Oz but the low still moves close to Victoria unlike GFS where it sinks it south and EC still shows that 2nd burst of cold air late Friday into Saturday South of SA and SW of Victoria which EC has been consistent on

ACCESS gone more traditional Tonight with just a straight out cold blast but penetrating well inland and a serious rainband over the East coast proceeding this major cold pool

Thanks DaveM, but still not as organized as I would have liked, still managed a typo in the start of the second paragraph..
"rain ahead pool and cold fronts" meant to be "rain ahead of cold pool and cold fronts" or something like that anyway.

Yes Johnno, EC is wild with some strong winds even from the north as the moisture is dragged down from Queensland. Funny how Access dropped that silly cut off, but EC and GFS are at least believing the low not far from Esperance and both have one there now. Why Access changed so much in one run when it at least partly has the right idea is beyond me, just a bit unreliable in my books just like the old GASP, not that much has changed.

But speaking of that low just east of Esperance which both EC and GFS now have in some way although not the same. That reminded me of the cold change at Anzac day which also had a low in that area and did lead to a reasonably cold change with some snow in the Snowies. Since weather patterns do often follow consecutive repeats you would have to expect something like what we had at Anzac day only on a stronger scale this time.

My post from before....on 04/18/12

Still no more detailed clues really from the models on next week. EC stalls the cold pool much sooner which would make it more a rain bearer than snow. GFS is still in between with the rain ahead of a colder change and then some snow also showing a possible couple of cold changes after the rain from Queensland. Access seems to be ok up to about 5 days, but really has no idea after that.
Laurier, Blizz and others how does the Access 200mb and 500mb pattern look to you for Tuesday 12z? Agrees ok with GFS 500mb and 300mb and even with EC 500mb pattern.
I guess that is the conundrum not really having any consistency after Tuesday next week.
From my experience I have tended to find the EC is the winner for guidance at almost any time scale and certainly beyond 5 days. But still only guidance, given considerable discrepancy with GFS atm both will have to change. Access seems to go out on its own after 5 days and just chops and changes too much. At least there is still a common theme with EC and GFS that will be resolved over coming days.

Got a busy day PD, will try and have a look later today but it may be tomorrow or the weekend before I get a chance to peruse the details.

Whilst those models today are still different, they have come a bit more aligned in some ways, they have at least all come to the position that at some stage that cold air should push into NSW. Access has it much sooner, EC tends to like the second front type of thing and GFS has gone a bit spotty.

I think this change will be quite good for the Snowies and maybe we will get some good weather too. Just the timing and extent is still wobbly, though it will firm up.

Personally I hope we get a bit of rain - it's getting quite dry around here - been a while since the last good drink.

EC ensemble and EC are chalk and Cheese which is abit of a worry.. EC Ensemble doesn't have anything remotely close to a low late next week

EC ensemble spread chart for 12z Thursday for 500hPa [here] shows a pronounced trough through Kangaroo Island as the mean of all the runs, with an 11gpdm spread among the ensemble members on Kangaroo Island. Put another way, at Kangaroo Island the mean height of the 500hPa surface is 5520 geopotential metres above sea level, but the various ensemble members could be +/-110gpm which is quite a lot, but not unusual this far out (192 hours). The greatest area of uncertainty lies behind the mean trough, under Eyre Peninsula. The main EC run [here] may be one of the ensemble members that goes for lower height here in the form of a cut-off. I don't know if the main EC run is used as one of the ensemble members or is a separate run, however there will always be variations between the main run and the ensemble mean because they are two different things.

The GFS ensemble spread [here] and main run forecast [here] are also quite different, but the main run puts the 500 trough ahead of the mean of the ensemble. The GFS ensemble mean is very similar to the EC mean and places the trough axis through Kangaroo Island at 552gpdm. However it shows far greater uncertainty than EC, with three lobes of uncertainty through central VIC, central SA and SW WA.

We've talked about ensembles for a while, and it's occurred to me that some people on the list may be a bit mystified by them. However they are the way of the future in numerical modelling and certainly help debunk any notion you may get looking at a standard +192 hour chart and trying to think of it like today's weather map. The ensemble mean and spread charts are a bit easier to understand if you look at the spaghetti chart, which shows (for selected isopleths or lines only) the output for each of the ensemble members. The GFS spaghetti chart equivalent to the spread chart above is [here]. The spread chart calculates the spread of these variations for each point on the grid, then calculates a mean of these variations, and once you understand what you're looking at is easier to grasp. The WeatherOnline explanation of ensemble forecasting and what "ensemble members" is all about [here] is a great introduction.

Great summary Laurier. Im pretty confident for higher parts of the Main range and by extenstion the higher parts of the main resorts. Hopefully the prefontal band gives us a bit of a drink this side of the GDR. Not enough time to look at charts more closely but my original sentiments from the 2012 Snow Season Thread remain. Touch and go for the CT's at this stage but AXS looks promising as does EC. GFS is still fumbling around in the outfield however but it tends to do that lol.

Laurier, thanks for that excellent explanation and all those links. I like that spaghetti chart too showing all the possible options.
I guess I try to estimate all those options and means by carefully looking at every model run and judging the variance by memory and intuition, does not always work though.
Also a good chart showing those differences from EC is this one..
Ecmwf mean and output
As you step forward through the valid time you see the 2 charts gradually diverge, one being the mean and the other the main output. The first 3-4 days the differences are barely noticeable, but then they diverge more and more, but still keeping a common theme of the position of the LWT.

Hmmm, latest OCF has a top of 7.5c and 17mm of rain for Orange next Friday, so something much be brewing in the 00z models!

Thanks for the link, PD. I also like the new MOD facility [here] on WeatherOnline that allows you to compare many models (including mean ensemble versions) side-by-side. I've set this up to show deterministic (i.e. "normal") forecasts for GFS, CMC, UKMO, EC, NOGAPS, RHMC (Russian) and JMA (Japanese) along with ensemble means for GFS, CMC and EC (the second ECWMF is the ensemble one, and should be labelled ECMWF ENS).

Gee GFS has thrown up an ECL scenario.

What a shock.

An ECL would go down nicely at this point as it's the only way we're going to get a drink until October. Not too good for snow though of course, unless you're high up on the Barringtons.

Simmer down, guys. The "ECL" scenario is 11 days out. Much as I'd love it in my dreams, it won't happen.

The ACCESSG scenario looks much more plausible to me, with the deep upper thermal trough producing a deep low in the southern Tasman, which in turn swings a hefty tongue of cold air northwards over VIC and NSW. There's even some remnant moisture available at 700 to go with 850 temps of -2. That would be nice.

EC and GFS have been suggesting a cold pool to break off from the main cold air in the Bight for days now so that is no surprise. However where this may form any ECL is far from clear and not yet predictable as Laurier has mentioned. I have high doubts about Access though especially for anything beyond 5 days. I think Access will generally output a standard system just based on the mean values about where the LWT will be, although yesterdays weird output was a surprise. I guess it was picking up that big surge of cold air that will happen just east of Esperance where it had that big cut off low.

EC and GFS are quite consistent up to about Tuesday when the cold surge pushes into the Bight. Even not that much variation on Wednesday and Thursday morning when they both have 850 temps of zero just reaching Uluru in SW NT, however precipitation will stop short of the border. There is a slight chance of snow at Mount Woodroffe in SA, but even there precipitation will most likely be lacking.

Then from Thursday onwards we are still in unknown territory, EC brings the cold air into NSW latter not until next weekend, but GFS brings it in by Friday and on the weekend. Then there is still lots of discrepancy where cold pools will go, possible ECL and possibly an extra cold front Sunday. Either way its pretty clear there will be rain and snow and some strong winds at times when cold air approaches.

Going by the models atm there would be snow on the CT's next weekend, but where most snow/rain falls is still highly variable depending on how the cold air arrives. Could still end up just a Snowies snowfall, but given the number of options over a few days the chance for the CT's passable.

I may (I hope) have to eat my words. The full duration 00z EC run is complete and has produced a true ECL [here]. On Saturday week 00z it is off the NSW South Coast at 994hPa, and 24 hours later it has drifted to ~300km SE of Gabo Island and bombed to 970hPa (the full size chart is [here] but you can click on any chart in the panel in the first link to get full size).

As PD has been saying, the EC has remained fairly consistent - its run yesterday at 00z is [here]. That run had a bomb to 974 farther south and earlier - about 300km east of TAS and on the Saturday. Both today's and yesterday's 850 temps (dashed lines) show a massive injection of cold air into the continent, the difference being that today's run brings sub-zero conditions much farther north and over a wider area.

The 500 charts for yesterday's 00z run [here] and today's [here] suggest why EC has moved the cyclogenesis north. The critical days are Thursday and Friday. Today's run moves an elongated trough and cutoff farther north than yesterday's. The result is that for Friday 00z what was a surface trough in the westerlies off a developing low west of Bass Strait yesterday [here] has become an extensive trough in the easterlies [here] extending SSE from the Gulf of Carpentaria. This trough drifts SE and the low forms off the South Coast.

Still a long way to go in this saga.