Climate of Kalgoorlie-Boulder

Kalgoorlie-Boulder has a dry climate with hot summers and cool winters. The average annual rainfall is 260mm on an average of 65 days and, while the average rainfall is fairly evenly distributed throughout the year, there is considerable variation from year to year.

The climate is strongly influenced by a band of high pressure known as the sub-tropical ridge. For much of the year this ridge is located to the south, allowing east to southeast winds to prevail. The ridge moves north during winter allowing the occasional cold front to pass over the Goldfields.

January is the hottest month with an average maximum temperature of 33.6°C, but temperature above 40.0°C occur nearly once a week when hot, dry, north to northeasterly winds arrive. Such high temperatures are usually followed by a cool change from the south and occasionally with a thunderstorm.

By contrast winters are cool with July average maximum and minimum temperatures being 16.5°C and 4.8°C respectively. Cold wet days with maxima below 12.0°C occur about once every winter. The lowest maximum temperature recorded is 7.2°C on 19 July 1961. Overnight temperatures fall below freezing about 4 times in a typical winter. Such events occur on clear nights following a day of cold southerly winds.

The most reliable rains occur in winter from cold fronts arriving from the west, and cloud bands from the northwest. June is the wettest month with an average 32.2mm on 9 days. Thunderstorms provide most of the summer rainfall, often producing heavy localised falls in short periods. Although rare, decaying tropical cyclones, originating off the northwest coast can move through the Goldfields, producing heavy rains and sometimes flooding. The highest annual rainfall total was 530.8mm in 1992, resulting from a high number of thunderstorms and cloud bands during autumn and winter.

It is not uncommon for very little rain to occur for months, particularly during spring. One of the driest periods occurred from December 1939 to July 1941, when just 181mm fell. Other dry periods occurred in 1923-24, 1944-47, 1969-72 and 1976-77.

The majority of the annual average evaporation of 2664mm occurs from November to February. The average rate in January is 12.7mm per day, while on a hot, windy day the evaporation can be over 20.0mm. During the winter the average daily evaporation decreases to 2.6mm. The relative humidity averages less than 30% at 3pm during summer while the 9am winter figures are typically around 70%.