Next week (2-5 September)

Outcome: A modest spring fall


Perisher Valley claimed 15 cm snowfall over two days; Thredbo 30 cm (bit of a theme there … hint: weather-wise they’re near enough to the same place; just 29 mm of marginal-temperature precipitation in the gauge at Perisher). The Victorian resorts received much less, and as usual were rather more honest about it than a certain NSW resort.

Again a warmish, shallow low tracked across the continent to deliver unexpected snow, and even Jane Bunn didn’t predict it this time. There’s something very odd about this season’s weather, likely related to an exceptionally warm Indian Ocean.

BOM surface chart archive

Update #1 (31 August):

The low track has shifted south a bit, but it sure does look warm. The US GFS model has thickness around 5500 m* and freezing level 2200 m for Wednesday night. The Bureau of Meteorology’s ACCESS-R model is a little better at 5450 m and 1900 m. We got snow from similar thicknesses from last week’s system.

GFS for late Wednesday night, 2 September (Levi Cowan)

BOM ACCESS-R for the same time

Regardless, it looks like there’ll be snow Thursday night and Friday off the tail of the system, though it moves away too quickly for anything substantial.

* The half-atmosphere thickness — the difference in elevation between the 1000 hPa and 500 hPa pressure levels — is a crude guide to average lower troposphere temperature and hence the likelihood of snow vs rain. A thickness less than about 5400 m (the “540 line”) generally indicates that it will be cold enough to snow on our alps.

Original post

Well that de-escalated quickly. Models show the approaching polar lobe peaking way too early, over Perth, then budding a cutoff low which tracks way too far north, across Adelaide and Sydney. If a useful snowfall is to ensue, the low track will need to shift to the south:

GFS for Wednesday, 2 September (Levi Cowan)

ECMWF for Wednesday (Levi Cowan)