The coastal Mid West areas experience a mild Mediterranean climate with hot/dry summers and mild/wet winters. Inland areas are subject to an arid climate with very hot/dry summers and cold/dry winters. A semi arid climate is transitional between the two. Rainfall decreases in a northerly and easterly direction.
Rainfall:
Most coastal areas receive an average 400 - 500 mm of rainfall per year while inland areas can expect less than 250 mm. Rainfall in inland areas tends to be more erratic and unreliable.
The City of Geraldton-Greenough records rainfall on an average of 80 days per year annually. June is the wettest month, with a long-term average over 100 mm at the Geraldton airport. Approximately three quarters of the annual total falls between May and October, on average, mostly as a result of the passage of cold fronts. Sometimes these fronts are associated with cloud bands from the northwest, which enhance the totals.
In contrast rainfall in the inland parts of the region is more erratic and usually the result of summer thunderstorms or rain bearing depressions that result from cyclonic activity on the northwest coast of WA. As over most of southwest WA, annual rainfall has decreased in the Mid West during the latter half of the twentieth century. Evidence suggests that both natural variability and the enhanced greenhouse effect have most likely contributed to this decrease. The 2006 and 2007 winter/growing seasons have been particularly dry with rainfall down more than 60% over both seasons compared to the average.
Temperature:
February is the warmest month across the Mid West region. In coastal areas the average temperature is roughly 30ºC. Prevailing winds dictate the temperature at this time of year with sea breezes as well as hot dry north easterly winds regular features on the coast. The Geraldton Meteorological Office records temperatures of 40ºC at the Geraldton airport nine times in an average summer.
In contrast, winters are mild with the July average maximum temperature being the lowest of any month at just under 20°C. August is the coldest month with the average minimum temperature just over 10°C near the coast. Overnight temperatures fall to 5°C at the Geraldton airport approximately seven times during an average year, though this frequency decreases closer to the coast. Temperatures below 2°C are rare.
Further inland temperatures are more extreme. January is the hottest month in Meekatharra with the average temperature 38ºC, however temperatures above 41 ºC typically occur once a week with hot dry northeast to northwesterly winds. High temperatures are usually followed by a cool change from the south and occasionally a thunderstorm.
By contrast inland winters are mild with the Meekatharra July average maximum and minimum temperatures being 18.8ºC and 7.4ºC respectively. Overnight temperatures fall below 5ºC about once a week in a typical winter. Such temperatures occur on clear nights following a day of cool southerly winds.
Wind:
The climate in the Mid West, particularly the major population area around Geraldton, is strongly influenced by wind patterns. Geraldton is known for its strong off and onshore wind making it a popular location for windsurfing.
Winter tends to be the season with the lightest but most varied winds. However cold fronts at this time of year occasionally bring strong wind and gales. Summer sea breezes frequently reach 46kmph or more near the coast.
Sunshine:
Geraldton is one of the sunniest locations in Australia with over 11 hours of sunshine per day on average in January. This value reduces to a minimum in June and July of between 5 and 6 hours per day. The annual mean is between 8 and 9 hours per day.
Source:
www.bom.gov.au