Winter snow precipitation fraction

Inferred percent snow precipitation

This shows the inferred percent of total precipitation falling as snow at Spencers Creek near Charlotte Pass, Australia, based on snow depth information from Snowy Hydro Limited and precipitation data from the Australian Bureau of Meteorology for Rocky Valley Dam near Falls Creek.

Information on precipitation type in the Australian snowfields is surprisingly scarce. The Hennessy study provided some estimates for Mt Hotham from their snowpack model, generally in the range 80 – 85% snow (15 – 20% rain). It would be possible to use modern automatic weather station records (which measure co-incident temperature and precipitation) and apply some arbitrary temperature cutoff to obtain a snow percentage, but those records are short and tend to be unreliable.

This chart uses a simpler approach. It plots the winter snow depth increase at Spencers Creek (from 1 June to 1 September) divided by the total recorded winter precipitation (at a comparable but distant site), both expressed as water-equivalent. Assuming zero winter melt, that directly gives the winter average snow precipitation fraction.

Of course, there is winter melt, so there is some error (melt will appear as if it was rain). Also, Snowy Hydro Limited don’t routinely publish the snowpack densities required to calculate water-equivalent snowpack depth (they do measure them), so this uses published average figures (Bormann et al, 2013). For the precipitation I use the record from Rocky Valley Dam near Falls Creek, because closer precipitation records give unrealistically high calculated snow percentages (>>100%).

The two data sites are ~100 km apart, so this result can be no more than a crude indicator. Nevertheless, the average is generally consistent with the Hennessy et al estimate. Little emphasis should be placed on the trend shown, which appears excessively influenced by unreliable outliers early in the record.

I posted about this graph here.

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