My pre-season prediction for the 2012 Spencers Creek peak snow depth is 105 - 210 cm, with best estimate 160 cm
My method uses a statistical model based on multiple linear regression with the winter (JJA) averages of AAO, SOI and IOD, and with calendar year. I exclude periodicity (because there is none
) and PDO (because the correlation is poor - below). The basic correlations look like this (2011 highlighted):
That leads to the regression model: Peak depth (cm) = 1330 - 28 x AAO + 1.65 x SOI - 10 x IOD - 0.57 x Calendar Year
...which performs as follows:
The correlation coeficient is 0.3 and the standard error is 53 cm, so about 70% of historical years fall within +/-53 cm of the model.2012 ParametersAntarctic Oscillation
(AAO; also called "Southern Annular Mode")
AAO is a measure of how tightly the circumpolar winds ("polar vortex" in one usage) blow around the pole. A loose pattern (negative AAO) leads to more polar storms reaching southern Australia, and more snow.
This is the most important parameter and the hardest to predict. The data look like this:
My prediction for the 2012 winter is +0.5 (slightly negative for snow).Southern Oscillation Index
(SOI, an indicator of ENSO)
SOI is the difference between Tahiti and Darwin surface atmospheric pressures expressed as monthly standard deviations x10. It is an indicator of the El Niņo Southern Oscillation, an east-west quasicycle in Pacific Ocean surface temperature and wind patterns which correlates with precipitation across much of Australia, including with alpine snow. A positive SOI is associated with more (and some say wetter) Australian snow.
The various numerical ENSO forecasts look like this (for the Niņo3.4 sea surface temperature index, which is negatively correlated with the SOI):
My prediction is that Niņo3.4 will be slightly positive and therefore SOI slightly negative at -5, which is slightly negative for our snow.Indian Ocean Dipole
The Indian Ocean Dipole is an ENSO-like variation in the smaller Indian Ocean, which correlates with precipitation across southern Australia, including with alpine snow.
The BOM numerical prediction is neutral:
My prediction for IOD this winter is 0, which is neutral for our snow.Prediction
Based on those parameter predictions, I predict that there is about a 70% chance that the 2012 peak snow depth at Spencers Creek will be between 105 cm and 210 cm, with the most likely peak depth 160 cm. The probability of a peak depth above 2 m is a little over 20%.