Table 1.

Transition probabilities for highs and lows for field observations and the ECMWF model predictions

City name	Conditional probabilities
	Field observations			ECMWF model predictions
	P(Ht|Ht−1)	P(Lt|Lt−1)	Skewness	P(Ht|Ht−1)	P(Lt|Lt−1)	Skewness
Darwin	0.838	0.843	−0.37  ±  0.02	0.855	0.870	−0.36  ±  0.09
Townsville	0.827	0.836	−0.52  ±  0.02	0.861	0.835	−0.63  ±  0.09
Perth	0.638	0.547	−0.01  ±  0.02	0.680	0.624	−0.23  ±  0.09
Sydney	0.703	0.575	−0.12  ±  0.02	0.661	0.542	−0.31  ±  0.09

Here, we condition on high and low values that are more than 0.75 standard deviations from the mean. As a correction for the skewness of the distribution of the barometric pressure, the standard deviation is calculated separately for points on either side of the mean. The table shows that there is a strong asymmetry in the transition probabilities in the field observations for the temperate sites (Perth, CHI² = 68.32, P < 0.0001; Sydney, CHI² = 103.4, P < 0.0001) which is absent in the tropics (Darwin, CHI² = 0.3895; Townsville, CHI² = 0.8791, both not significant). Moreover, the asymmetry at the temperate sites is less marked in the ECMWF forecasts (Perth, CHI² = 0.906, not significant; Sydney, CHI² = 4.222, P < 0.05).