14-16 July

Outcome: About 25 cm at Perisher Valley


This interval managed an aggregate of about 25 cm of snowfall at NSW resorts, with a little less in Victoria. That’s despite the main snow system tracking across central and northern NSW instead of the alps. A couple of little subsidiary disturbances drifted close enough to deliver the goods, the best being this one on Thursday:

JMA precipitation inferred from satellite imagery

BOM surface chart archive

Update #4 (13 July):

This one is probably dead I’m afraid — the little low tracks north and dissipates, before reforming as a weak and ineffectual east coast low late in the week. (I hope that moves rapidly away as prognosed, or there could be more rain damage on the weekend.) A little snow is showing tonight (Monday) and probably tomorrow night, perhaps also Thursday night, so it’s not a total loss. Look to next week, which appears fragile (may be peaking too early).

Update #3 (12 July):

The models agree on the midweek low location to within 100 km, but the outcomes are far from the same on my reading. The Bureau of Meteorology’s high resolution ACCESS-R model and the European ECMWF have the low tracking too far north to deliver much snow initially. It deepens after reaching the Tasman on ECMWF, but then moves rapidly away. The US GFS model has the low tracking a little further south, bringing snow, including well after it reaches the Tasman and deepens late on Thursday. Which? Unusually, I favour GFS’s scenario. As it happens, BOM’s low resolution and rather lowly-rated ACCESS-G is similar. Maybe it’ll all be clearer tomorrow…

GFS for Wednesday morning, 15 July (Levi Cowan)

ECMWF for Wednesday morning (Levi Cowan)

BOM’s ACCESS-R model for Wednesday morning

For those who like to follow the Bureau of Meteorology’s 4-day forecast charts, note that they’re still drawn almost exclusively off the European ECMWF model. Why? Ask BOM; one can only presume inertia from the days when BOM’s own models weren’t really up to the task (that’s certainly no longer the case). Here’s how the forecast charts look at the moment, showing ECMWF’s progression of the midweek low (linked image will update):

Update #2 (11 July):

The major models now agree that there will be a second low, a little later than I’ve had so far (I’ve moved the dates forward by one day):

GFS for Wednesday night, 15 July (Levi Cowan)

ECMWF for Wednesday night (Levi Cowan)

BOM’s ACCESS-G model for Wednesday night

But does it track east, bringing more (and perhaps rather wet) snow … or is it north / retrograde into Western Australia (before dissipating)? That’s what the European ECMWF has, usually our best long-range model. I now think an easterly track looks more likely, but perhaps well to the north. Hold hats…

Update #1 (9 July):

The models are still divergent for this interval. Maybe the low in the Tasman from the previous post just moves quietly away, with little weather beyond Tuesday morning (BOM’s ACCESS-G), or perhaps it deepens into a fierce east coast low on Monday, with a little wandering bubble low showing up Thursday-Friday (US GFS model), or does it move off to be followed by another proper polar outburst Wednesday night (European ECMWF model). Sorry, but these extraordinary computer codes have no idea, and neither do I.

GFS for Monday morning, 13 July (Levi Cowan)

ECMWF for Wednesday night, 15 July (Levi Cowan)

Original post (6 July)

This is the second leg of the approaching major complex of snow systems (the first leg is discussed here). It’s still too early to study this part in detail, but given the model ensemble support (see the spaghetti plot below), it would be surprising if a substantial further fall did not eventuate.

Interestingly, both legs of the complex should fall within a single Snowy Hydro snow depth measurement interval (usually Thursday – Thursday), so it’s possible that the aggregate accumulation will fit my definition of a “dump” (greater than 50 cm week-on-week gain at Spencers Creek, midway between Perisher Valley and Thredbo).

That would be a pleasant turn-around to a near record-breaking miserable start to season 2015.

Here’s the current US model ensemble view; note the suggestion of a deep east coast low (“ECL”, click chart for source):

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