Yes some similarity there, but I did notice something. That cold change in 2004 as well as other good ones that I remember now seemed to push a cold pool further NE after crossing the CT's. In 2004 a cold pool ended up also well to the NE in the Tasman. Its like they had some momentum that kept them going further. So far this year all our cold changes seem to be running into brick walls as they travel north and rather than continue NE a little more they seem to be steered back SE just as they reach north enough. Same with this weekend, the cold pools get sucked back south into the southern Tasman rather than continue a little further NE, both EC and GFS show that same problem.

Similarly by rights cold changes like the ones that affected Adelaide so far this year also should not go tracking back south so fast, but rather keep tracking east as a minimum to affect Orange and the rest of the CT's. Its a pattern that seems to be sticking around for now which could ruin our winter.

Anyway still hopeful this will change soon, never know, could be better this weekend, but will need model improvement.

Looking at 06z GFS I still feel pretty sure that this change will also die in the ass. Not 100% certain, but much more than 50% at least that it will be another fail.

Snowbaby, the forecast soundings on the BSCH site based on GFS indicate a significant tropopause inversion at 400hPa (7088m) for 7am Sunday morning [here] although it is not strictly the tropopause. This is defined as the point at which the temperature as you rise through the atmosphere becomes isothermal (maintains an equal temperature), or begins to rise. This forecast sounding shows temperatures continuing to drop, though ever so slowly, right up to and beyond 100hPa, so all we can say is that there is a very broad tropopause zone beginning at around 400hPa (7088m). I had a quick look through Haby's brilliant and extensive site [here] but couldn't find a reference to this.

I think that the 500-1000hPa thickness or the height of the 500hPa surface are better indicators of the overall temperature of the airmass that will affect us at ground level. Haby has a good introduction to tropopause, calculation of its height and operational significance [here].

Looking back at the 7-8 July 2004 event in Blizz's photos, it was an interesting case of dynamic development and I can't remember how well it was forecast. I'm using only my quick-and-dirty archive which omits some data, like 500hPa temps.

During 6 and 7 July, a southerly jet of up to 70 knots at 200hPa blew from south of 60S up to the west of TAS to join a moderate (~120knot) and broad sub-tropical jet oriented roughly Adelaide to Brisbane. (The speeds in this southerly jet limb were probably greater at 300hPa.) At 500hPa at 10pm 5 July, the first of two troughs in a significant broadscale upper trough was passing through eastern NSW, with a geopotential height over the OP of about 557gpdm. The second trough was lying well SW of TAS and south of about Esperance and was showing considerable vorticity. By 10am 7 July, this second trough had responded to the southerly jet and had tightened to the point where a cut-off moving NNE was imminent, and was located off the TAS East Coast with a height over eastern TAS of 534gpdm and rapidly falling thicknesses over SE AUS. By 10pm, a broad area below 546gpdm at 500hPa covered eastern VIC, SE NSW and most of the SW Tasman Sea, and this moved NNE then NE during the 8th.

At the surface, developments mimicked those at the 500 level. A 998hPa low developed SE of TAS at 10am 7 July moving to 1008hPa off Gabo Island by 10pm and 1012 near Lord Howe Island by 10am 8 July. This turned the winds on 8 July to the SSE when Blizz's sunny photos were taken. Of significance was a closed area of very low thickness (<534gpdm) at 10pm 7 July covering most of SE NSW including the CT. The conditions that caused this low thickness probably also caused the snow on the OP and surrounding areas.

The situation at 850hPa was fairly unremarkable though instructive in indicating why there was just light snow with icy conditions. The 850 temp first dropped below zero for the OP on the 10pm analysis for 5 July and stayed between zero and -1 until it rose above zero around 10am 8 July. Wind was westerly turning gradually SW by 10pm 7 July, then SSE at 10am 8 July. I only have 850 moisture information easily to hand, but these varied between 75 and 90% over the OP area during the 6th and 7th, and overall precipitable water calculations for the area were around 6 to 8mm, so I suspect 700 moisture would have been very thin.

I think this analysis shows (a) why there were icy conditions and snow was light but quite widespread (you can see this in the distance in Blizz's top right photo), and (b) that in a dynamic atmosphere, the sudden development and northward movement of the upper low in the second upper trough may well have been a difficult item for models to forecast, especially a few days before the event. It's also demonstrates that you don't need all the precursors to line up ahead of a snow event, and that what happens may turn on just one or two unpredicted parameters.

Got the chart from the same link Blizzard posted earlier in this thread. Perhaps I have fallen foul of a little bit of knowledge being a dangerous thing. I thought it might have some predictive use at longer range. Anyway didn't want to hijack the thread.

Very well described Laurier, especially liked the last paragraph.

History does tell us that those one or two unpredicted parameters has produced fascinating events in the past. This could be one of them, who knows. We are still not inside the +72 hour window for this system, so a lot of things can change yet.

There are enough ingredients and potential outcomes to keep one eyebrow raised for sure. I'm very keen to see 00z tonight and also tomorrows scenarios will be an interesting read. We live and learn.

Latest runs of EC, GFS and ACCESS-G are fairly well in alignment, with some pretty respectable figures for Sunday morning. They all have the upper trough moving across the CT soon after dawn, and have 500 temps around -28, 850 temps between -2 and -4, and thicknesses between 536 and 532 - all for much of the day. There's good low level and reasonable mid-level moisture and some decent instability as well as broad-scale uplift due to vorticity convergence. ACCESS has eased back on its precipitation forecast for the CT, but still has 5-8mm (although it doesn't show on the WZ maps), and EC also has a similar figure, though GFS is drier. The high-level jet is still very nice, with GFS and ACCESS now giving it due southerly at around 90kts from well below 55S into the back end of the upper low which looks like moving either over or under TAS on its way northeast.

I'm away from computers for the next 36 hours or so, so will be interested to see what's happened on the models when I return without waiting for each new model run to be either disappointed or overjoyed with.

Predictions for the Alps based on those forecasts?

For the Alps, I would expect in the region of 20-30cm across the weekend.

This system will not be a great in terms of quantity but it should be nice, dry and powdery.

Driving on nearby sub-alpine approach roads could get a bit more interesting with snow likely in Jindabyne at 1100m and even down to Berridale and Cooma at 800m. Depending on how extreme the event pans out some snow flakes may also be possible further north along the Monaro highway in the 800-600m zone.

Hey guys, I know this is a NSW snow thread but just wondering what you think the snow level will be in Victoria at this stage for this event? 600-700 metres or lower? Would love to hear what the experts think.. Peter, Laurier, Blizz or anyone else. Cheers

Johnno, speaking of snowline, that is something that I wish was more accurately talked about and forecast. So often the figures thrown around are not really a snowline or snow level anyway. Some people seem to consider seeing one snowflake as a snowline but I disagree with that. Snowline according to me is when snow has settled at 0deg or less. In saying that the snowline has not even been reached so far this winter at my location. Last winter it was reached 4 times. Possibly just touched on just once at 1300m on the OP. There is a zone up to 500m below the snowline where wet snow can fall, but that should just be called pretend snow.

In saying that given the figures on the models, I would expect the snowline to get to 900m in Victoria, 1000m in the Snowies and 1100m hopefully on the CT's. Will be interesting to see what the readings will be at Mount William on Saturday morning as that will give a good indication of what is to come for the rest of the SE. Hopefully Mount William could see between -1 and -2 on Saturday morning which should put the snowline a little below 1000m. However most places in Vic and NSW will not see a lot of snow from this system probably because it lacks a strong SW flow.

(Mind you some interesting readings on Mount William last night with -2.4, looks like there might have been some rime that froze the wind gauge for some time)

The thing that this cold change has going for it atm for the CT's is that models show the cold pool at least moving off Sydney and keeping a northern position after crossing the CT's which is an improvement on yesterday. This means the cold air might not get sucked back south too fast. Better still would have been if it continued to track NE a little longer, that would suggest that the southerly jet stream had enough punch to get the cold air here. It still looks very marginal to me to be any good, most likely just another tiny insignificant snow with fragmented cold. But I agree there is still a chance it could hold together enough to be passable for ok.

Defining "snowline" opens a can of worms - I might come back to talk about it when I have more time. The Bureau avoids its use by saying "snow falling to" or "showers falling as snow to", which I think is a wise move. For the snow to settle involves many more parameters, and even working out the level at which snow turns to sleet/rain is hard enough.

Currently, NSW state forecast has showers "falling as snow above 1200m" in the Alps for Saturday while VIC has "snowfalls lowering to 1200m later in the day" in central and western districts for Friday and "above 900m" in southern and mountain districts, extending to the NE on Saturday. TAS only has snow on the higher peaks on Saturday, reflecting the fact that the cold air is passing north of TAS. It will be interesting to see what they say when the Sunday forecasts are issued later today. Their forecasts for Saturday look pretty good to me, though I think showers (falling as snow to maybe 1000m) will linger into Saturday in central and, possibly, western districts of VIC.

Yeah sorry guys I should of said where you think snow will settle at

ACCESS-R 00z is getting interesting, don't have time to go into any detail at present but improved lower mslp pressure across eastern NSW and a complex low setup stretching from NW of Tassie and from there into the Tasman. Broader cold temps at 500hPa too and still nice 300hPa winds as well. 700hPa is improved under that instability also.

There are early signs of better instability as of 00z and the tot tots reflect this too.

I'll be heading down the Perisher Valley region again this Sat to try and get that elusive good snow footage that i need for the ASWA intro film. Even better if it's blizzard conditions. I should make it to Sponars Chalet by 7am.... so if anymore sees a black 4wd, you'll know it's me:)

The very last run for ACCESS looks the goods... nice broader cold temps, even at 850 i think will have the temps easily where they should be. I like the moisture at 700 too. Something should fall as snow.... just as long as it's not the sleety marginal stuff.

Wow, its been a while since I posted on a winter thread, or even a typical NSW weather thread. I am slowly coming out of my college bubble for this semester and actually really anticipating this event particularly after checking out 00Z GFS, the temperature of -31c @ 500 and -2 to -3c @ 850 with reasonable amounts of moisture really grab my attention. Have been following the posts on here. Some people doubt, other people stay optimistic. I am definitely the optimist as well. I like to hope even when its looking ordinary. However I am certainly glad I didn't head up for last event.

P.S. Greg, I certainly think you'll get your oportunity for some nice snow footage, although it might be a bit windy on the snowy mountains. Its so much nicer to record heavy snow in non blizzard condition from experience. Comes up so much nicer too. Up to you though, all the best mate!

Not to mention a VERY healthy -11c @ 700. I do realise its subject to potential change but by CT standards this is a substantial front in terms of temperature figures! Hopefullly the ingredients can line up well this time. With these temperature figures, the snow could potentially settle as low at 800-900m comfortably with potential to go a bit lower under heavier bursts.

Yeah, this is just how we want fronts to develop, gradually and generally trending to stronger, from a mid range starting point. There is still disagreement on mslp and what exactly will be happening there but that is pretty common so far from an event.

I don't mind too much if the BM gets little or nothing as I am so used to that now but it would be great for areas like Orange to see snow and higher up of course. Snow for Orange is a real prospect at the moment.

Of course, we will have to wait for another couple of days to confirm genuine potential but it is looking encouraging at present.

I do not like Access as a model generally, tends to come up with mostly standard outputs that mostly do not happen anyway. I think they take the easy way out, but that gives you little information on the character of a system in return.

By 00z GFS there are some good things about it but also some bad. The cold change by GFS now tends to break away more distinctly into a drift away cold pool. That is bad for the Snowies but better for the CT's. I think this could always have been expected given the way the EC ensemble has looked with a fairly small but distinct LWT in our region. Its the lack of a proper cold surge and lack of proper westerly flow that should allow what cold air is there to break away north.

Normally this would be quite good for the CT's but in this case there seems to be little moisture to bring much snow because there are no proper moisture infeeds, not from the SW because of lack of westerly flow not from the SE because its not quite an ECL or from the North qaudrant because there are no NW cloud bands.

If the cold pool drifts far enough north it could still introduce some moisture from the SE to get the snow going on the CT's, I think that could be the main hope but not likely atm. A little moisture tries to build up from the SW on Sunday but fails to reach the CT's and also by then the cold pool could be fragmenting.

So in summary early Sunday could be the best chance with near -30 at 500mb on southern CT's, but moisture is severely lacking. At this stage from me its the same old same old, few flakes here and there but still essentially a fail.

Wundermaps snow forecast for OP seems encouraging

Hey Shane, long time no hear champ! I hope your studies are going well.
After getting blizzard conditions on cam i was going to pull back to 1200-1400 to get the heavier flurries in protected areas. I'd like to pop over to Old Adaminaby if i get the chance.