Climate drivers and the potential for monthly climate outlooks

Harvey Stern, Belinda Campbell, Michael Efron, and John Cornall-Reilly

Victorian Regional Office, Bureau of Meteorology, Box 1636, Melbourne, 3001, Australia.

h.stern@bom.gov.au, belinda.campbell@bom.gov.au, m.efron@bom.gov.au, jcr@bom.gov.au

In the longer term, it is envisaged that the generation of climate outlooks is best achieved via outputs from runs of an ocean-atmosphere coupled model. However, solid statistical relationships exist between historical monthly climate anomalies in Victoria and various measures of the ENSO, Indian Ocean Dipole, and Madden-Julian Oscillation phenomena.

A "real-time" trial of experimental automatically generated monthly climate outlooks for Melbourne, utilising these relationships, has now been ongoing for just over a year (Stern et al., 2010).

It is considered that verification of these statistically generated outlooks may indicate a 'baseline' level of skill, against which any dynamic modelling approach could be compared with.

The purpose of the paper is to present a summary of the statistical approach's performance during the thirteen month period June 2009 to June 2010 inclusive. The correlation coefficients between the forecast probabilities that the total monthly rainfall, minimum temperature and maximum temperature would be in tercile three, and the corresponding observed total monthly rainfall, minimum temperature and maximum temperature 1961-1990 deciles, were respectively +0.28, +0.25, and +0.32.

The probability that the three correlation coefficients would all be at least +0.25 by chance is 0.8%, suggesting that it is most unlikely that the skill displayed by the experimental monthly climate outlooks arose by chance.

Reference: Stern H, Cornall-Reilly J and McBride P (2010) Bridging the middle ground between medium range weather forecasting and seasonal climate outlooks: two-week day-to-day weather forecasts and monthly climate outlooks. 22nd Conference on Climate Variability and Change, 17-21 January 2010, Atlanta, GA.