G’day everyone, it’s that time of year. And we have been thrust into the game with a major 50cm+ system over the last few days. We are here today to see if that will continue deeper into the snow season.
So we are going to look in this article about the potential for the season as a whole, using model analysis and climate drivers later on. If you aren’t keen for the technical details, the conclusions are near the bottom.
My prediction for 2019 at Spencers Creek was 176cm, we actually ended up with 228.8cm as our season highest snow depth. My third year of being outdone by Mother Nature. One may see this is good, but for me, it’s always a sign that more work needs to be done for this forecast to remain as close to the final depth as possible.
One thing I have found is that the arbitrary number is inflexible with the way I weighted climate drivers in the past few years. So you will notice that I will become more liberal than usual with that weighting process. But it is best to consider the final number for what it’s worth, and focus on the climate drivers themselves and the overall vibe of the season as depicted by the outlook. But that said, I will provide a number at the end.
EUROSIPS (including premier European models such as ECMWF and UKMET) paints a troughing picture for Southern Australia, particularly for the latter stages of the season. The troughing tends to favour the WA/SA part of the continent more, but it would lead to improved snowfall outcomes for SE Australia, just perhaps not as much as if that trough centered on the East Coast.
CANSIPS (Canadian model) points to a wet and cold outlook for SE Australia and the Australian Alps. This certainly would be a good sign for us.
CFS (American model) points to troughing peaking in the Bight. That’s not awful for us, there should be some systems that break through to the Alps, but that sort of setup emphasises sliding systems and as CFS forecasts, a wet outlook with prefrontal rains.
JMA (Japanese model) only covers May-June-July, but I am just showing it due to some interest in it’s abilities in the weather community, with it giving us a good outlook for snowfall at least in the early-mid season.
Okay, now with the models checked, we can do the traditional climate driver analysis. We will start at 194cm this year, our 10 year average, 8cm higher than last year’s 10 year average of 186cm. This is due to the last three years being consecutively very good seasons, in amongst an otherwise average decade. The use of this number reflects me trying to stay in with the current climate, but of course outliers pose a threat to a small base of years.
Pacific Decadal Oscillation
The PDO is currently negative and while the -SSTAs are weakening off the California coast, the North Pacific warm pool is forecast to stay in place. A negative PDO is forecast for this winter, which increases rainfall prospects for Australia a bit. Hence it increases snowfall chances a bit for us. 194 + 2cm = 196cm
Southern Annular Mode (SAM)
There is a fairly strong correlation between negative SAM and more snowfall for the Alps. I talked about the seasonal prediction of SAM here.
- El Niño Modoki (the only seasonal prediction factor of SAM, other than a weaker correlation to Eastern Pacific Nino) is at a neutral phase, and is likely to get cooler towards winter.
- July and August ECMWF and EUROSIPS modelling show some ridging around the South Pole, which increases the likelihood of a negative SAM, which is good for us, but only just in our favour.
- Climate Change as a general trend is causing a more positive AAO.
- The general trend if it continues to hold over this winter is towards a positive SAM.
Overall I think I will go with 196 – 8cm = 188cm, because I am falling towards that general trend. You would hope that there are some negative periods in that trend during the season, otherwise that moisture from the north that I forecast below is likely to fall as rain. The biggest caveat of all, is that there is a fine-line between “cold and moist”, so heavy snow, and “warm and wet”, so heavy rain. This is why the timing of negative SAM events is critical for a good season.
Indian Ocean Dipole/Northern Australia SSTs
This was causing some issues over the summer, contributing to the terrible recent bushfire season, in coordination with climate change. But now we are in better shape for the winter ahead with the IOD.
There is a correlation between the Australian snowfall and the IOD. I am growing more fond of more specific regional SST trends, rather than relying on big global ideas such as the IOD, so of particular note to us is the warm waters north of Australia. These will deliver good moisture to south-east Australia, to help fuel our snow systems. The major models all point to a negative IOD during winter, which is good news for snowfall in the Australian Alps. But keep an eye on the warm waters in the north here, as this is what will decide our fate in terms of moisture.
For here, 188 + 9 = 197cm.
El Nino-Southern Oscillation (ENSO)
There is a correlation between ENSO and Australian snowfall. The current model predictions show a fairly cool neutral state going into winter, perhaps borderline La Nina towards the end of the season. This would make our snowfall season a bit stronger especially towards late season, but the impact is likely to not be strong. What is important here is warm water is pushing towards Australia as part of local trends, so it does look somewhat decent (I do take this into account with the IOD section above).
Atmospheric Angular Momentum (AAM/GWO) (more here) indicator is become more neutral (albeit slowly) after a long period of strong positive cycles. I predict a warm neutral Atmospheric ENSO, and perhaps a weak Nina effect. I will put this in the win column, but only just.
197 + 3 = 200cm
Australian snowfall and MJO have a very strong correlation. The CFS model shows a signal for Phase 1-2-3, the seasonal signal moving closer to Australia slowly as the season goes on . This is okay if we can get moisture from the Indian Ocean to come across, and at least it means that there is likely to be an active tropical signal throughout the winter.
The weakening in GLAAM/GWO positive cycles (see link in ENSO section for more info) means that the MJO is probably going to lose some of its strength, but I’d be surprised if we went into full-on -AAM cycles until later in the season. MJO tends to be stronger in oceanic La Ninas, particularly building towards a Nino (basically the opposite phase of which we are in).
I think there will be some sort of decent tropical signal, particularly with warm SSTAs in our region, 200 + 3 = 203cm
203 – 2 = 201cm
If a large stratospheric volcano explosion occurs, Australian snowfall substantially increases for that winter. None have occurred in the last year, so our forecast won’t be affected.
201cm, no change
Southern Australia SSTs
The bight is colder than average (link updates), which is good for Australian snowfall. The Tasman is a little warmer than average. The Bight is forecast by EC to stay cold at least until late-season, where it might start to warm up. CFS and CANSIPS like cold seas surface temperatures throughout the season, which is a good sign. Meanwhile, the Tasman is expected to heat up a bit more, but it’s not going to be crazy warm. Conditions particularly in the GAB are pretty good for the ski season, albeit deteriorating potentially into Spring.
201 + 6 = 207cm
So my final maximum Spencer’s Creek Snow Depth for this year is 207±30cm. This number has came around from hours of analysis, tinkering and changing. The model outlook in the first section of the blog, is roughly in favour of a snowier than average season, though it may come with significant rainfall. The 207cm figure is higher than the 10 year average of 194cm mentioned above. Taking this into account, I am forecasting a moderately better than average snow season for the Australian Alps.
In terms of when the season will be best, the factors seem to be weighing against each other, with the MJO being best earlier in the season IMO, and ENSO and the IOD being “better” later on in the season. I think it will be a pretty typical season, in terms of timing of snowfall, all in all. But as I said above, the AAO/SAM will be critical in determining this season’s fate.
I hope you enjoyed this analysis, and I will see you for a long range outlook before opening weekend. Please share this with skiing or boarding family and friends, I really appreciate all the support.
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