Welcome back to another blog update, featuring Australian snowball prospects on the long term. Here we take the model outlooks, give the dates for potential events, and look at the drivers in terms of long term climatic trends.
This period has been signalled by EC, ACCESS and other models in the past few days.
There is a clear moderate longwave passing over SE Australia around this time. But the increasingly +AAO state mitigates potential in this system. More on that later…
Looks like a decent top-up for now, 5-15cm would be my guess.
Into August, we see our next potential system period. The LWT node we refer to is the one to the left hand side, which is currently moving faster than we would normally expect, so it will peak early around the 3rd of August.
EPS Control has been dancing around snow-bearing scenarios for a little while, but it’s only one member of the ensemble. What we are interested in is the mean, which is showing some sort of event around the 3rd, probably heading into the 4th.
It’s worth noting that the broader EC monthly ensemble isn’t a big fan of this period. So we take that under advisement, but it looks like we will have some sort of top-up here.
If you look back at our second LWT chart above, the second node after the 1-5 Aug node is down the bottom towards Africa. This is estimated to peak in SE Aus around the 11-12th of August. EC Monthly is slightly interested in this time, but expect that to progress over the next two weeks fluidly.
EC Monthly control above shows something around the 9th and 10th, CFS shows something around the 12th and 13th. The idea is not the specific dates, but more the general support for something around this period.
This is talking very very broadly, but EC Monthly and CFS both have some support for this timeframe, and is the logical progression from the last system. Just worth of a little note.
The AAO is currently heading towards positive values, which is bad for Australian snowfall.
This is caused by among other things a stronger than normal upper stratospheric vortex, that propagates into +AAO values at the troposphere.
Plantary waves propagate from mountain torque largely from the Andes create a weakness in the stratosphere. That is currently occurring, and is contributing to more disturbances this season than expected, along with the larger than normal Brewer-Dobson Circulation, bringing more momentum from the NH.
This unlike the previous event earlier in the month, looks to be at higher parts of the stratosphere, therefore more likely to make a difference. So I expect this stratospheric disturbance to propagate -AAO anomalies into the upper troposphere around the last days of the month. I expect the strength of the previous +AAO anomalies to prevail into August, but in the second third (10-20th Aug, perhaps a bit earlier) I expect to see these -AAO anomalies to propagate down to the troposphere, and improve our chances of snow in Mid-Late August.
The MJO is likely to stay neutral, even as it passes our region around the end of the month. I wouldn’t hold my breath for much activity soon.
We expect the +AAM over the next 10-15 days will weaken snowfall chances for the short-term, but the specific positive Andes Mountain Torque (my forecast as the green line in the graphic above) to weaken the stratosphere, and in cyclical nature come back as a -AAO phase in Mid August. So it’s not great for now, but it will get better next month.
So we have had a good first half of the month, with the real first dump of the season. But now we will see it weaken snowfall chances on account of the +AAO and the +AAM and Strat influences that control it. But we should see some top-ups over the next few weeks, and we should see it get better in Mid-Late August.