What do forecasters mean by “wetter or drier than average”, or “warmer or cooler than average”?
These comments mean that it has been above or below the median rainfall, average maximum temperature, or average minimum temperature for the three-month period. The median is a useful measure of “normal” rainfall. In the long term, rainfall is above median in one half of years, and below median in the other half. For example, from July to September at Mackay in Queensland, one-half of 3-month rainfall totals have been below 80mm, and one-half have been above. If rainfall was above 80mm in that period it would be “wetter than average” or above median. Over the long haul there is a 50% chance of this occurring. In terms of odds this is even money. Note that the average maximum temperature is the average of all the daily highest temperatures for the period.
