Climate of Geelong

The climate of the Geelong region, ie, the region stretching from Werribee and the Bellarine Peninsula in the east to the Otway Ranges in the southwest and Meredith in the north, covers a very wide range of temperature and rainfall patterns. From the highest rainfall in the state at Wyelangta (near Lavers Hill) to almost the lowest at Lara-Little River, this region is worthy of meteorological interest.

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Even in a relatively small distance of 30 km from Ocean Grove north to Lara, urbanised virtually all the way, the annual rainfall decreases from around 700 mm to less than 500 mm. Central Geelong itself receives an average around 540 mm.

The seasonal variation in the number of rain-days per month gives an impression of a wet winter, but the rainfall graph shows May and October to be the wettest months. Rainfall is more variable in the summer, mainly due to there being more thunderstorms and flash floods during that period. In winter the generally lighter rains may be more frequent and puddles may lie for days due to the lower evaporation rate.

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The Otway Ranges have a noticeable effect on Geelong’s climate. As the moist southwesterlies blow in off the Southern Ocean, they are deflected by the rapidly-rising Otway Ranges. Such rapid orographic cooling of moisture-laden air results in very heavy rains, over 1500 mm, in the mountains. As those winds cross the Otways they decrease in altitude, and there is a corresponding increase in temperature. This means they are no longer subject to a lifting and cooling process the further they go to the northeast. Therefore, from the Otways right through to Werribee, the annual rainfall decreases by a rate of about 100 mm for every 20 km, although not evenly (see map below).

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Straight westerly winds blowing towards Geelong are¬†usually relatively dry because they have been blowing over low land for several hundred kilometres. ¬† The Geelong “rain shadow” is also noticeable when northwesterlies blow. These winds deposit moisture on the Great Dividing Range and have no lifting mechanism by the time they reach Geelong, unless additional frontal or convectional uplift occurs.

Sometimes low pressure systems over eastern NSW may bring rain to Geelong when southerlies or southeasterlies bring moisture from Bass Strait. The lack of orographic influences from this direction actually increases rainfall over Geelong because the moisture-bearing winds blow straight over Geelong from the Surf Coast.

But most winds from the northeast quickly lose their moisture as they approach Melbourne and rain in the Dandenongs, although many northeasterlies can cause large waves to pummel the Geelong waterfront.

The Surf Coast and most of Geelong are often influenced by a seabreeeze in summer, which moderates temperatures in the mid-afternoon. Corio Bay is not a major influence on Geelong’s climate owing to its small size and Geelong’s relatively sheltered location, however strong winds may often produce two metre waves.

Wind speeds at Geelong are sometimes high (over 60 kph) in the open rural spaces, and the urban area is sometimes susceptible to destructive storms, particularly spring and summer thunderstorms. Normally wind speed is generally lowest just before dawn, increasing to its maximum around midday, decreasing towards evening. But when high winds strike, they may occur at any time of day or night.

Geelong is particularly fortunate in that its major industries are situated in its northern suburbs near Corio Bay. Prevailing winds from the northwest and southwest generally dispell any air pollution quite quickly, although unexpected northeasterlies have sometimes caused health problems in Norlane and Corio.

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