August 17-18 event ... dip

How did I miss this?  Like many others I expected a rain event, but as with the 15-16 June system earlier this year, this one delivered marginal wet snow to Perisher Valley and Thredbo (but little to Victoria).  These upper atmosphere driven systems can be tough to pick.  It’s interesting that the NSW office of the Bureau of Meteorology had it pretty close from 48 hours out; I think more from old fashioned manual forecasting skill that from the numerical models.

Outcome:  Aggregate ~75 mm of precipitation at Perisher Valley, most at temperatures in the 0-2°C range (at 1730 m).  The resort is claiming a total of 23 cm snowfall, which is probably fair.  There would have been much more at higher elevations; potentially over half a metre on parts of the main range.  The Spencers Creek reading this week will be very interesting.  A new peak is now likely, blowing my season forecast.

This surface chart looks far too warm:

…but the action was coming from way up high:

The 850 hPa temperatures are instructive, because that’s typically close to the altitude at which our snow hits the ground. The chart below is very hard to read — in our area of interest it says 3°C at 1380 m, which is low enough for there to be snow at higher levels from a cold upper atmosphere system. [BOM’s ACCESS-R model forecast (the chart is from the later ACCESS-R analysis) had this temperature about a degree higher at a similar or slightly higher elevation, which could have seen a different outcome. That illustrates, yet again, how marginal the snow prediction game can be.]

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