Melbourne has a temperate oceanic climate with warm to hot summers and mild winters. Melbourne is well known for its changeable weather conditions, mainly due to it being located on the boundary of hot inland areas and the cool southern ocean. This temperature differential is most pronounced in the spring and summer months and can cause strong cold fronts to form. These cold fronts can be responsible for varied forms of severe weather from gales to thunderstorms and hail, large temperature drops and heavy rain. Winters, however, are usually very stable, but rather damp and often cloudy.
Port Phillip is often warmer than the surrounding oceans and/or the land mass, particularly in spring and autumn; this can set up a “bay effect”, similar to the “lake effect” seen in colder climates, where showers are intensified leeward of the bay. Relatively narrow streams of heavy showers can often affect the same places (usually the eastern suburbs) for an extended period, while the rest of Melbourne and surrounds stays dry. Overall, Melbourne is, owing to the rain shadow of the Otway Ranges, nonetheless drier than average for southern Victoria. Within the city and surrounds, rainfall varies widely, from around 425 millimetres (17 in) at Little River to 1,250 millimetres (49 in) on the eastern fringe at Gembrook. Melbourne receives 48.6 clear days annually. Dewpoint temperatures in the summer range from 9.5 to 11.7 °C (49.1 to 53.1 °F).
Melbourne is also prone to isolated convective showers forming when a cold pool crosses the state, especially if there is considerable daytime heating. These showers are often heavy and can include hail, squalls, and significant drops in temperature, but they often pass through very quickly with a rapid clearing trend to sunny and relatively calm weather and the temperature rising back to what it was before the shower. This can occur in the space of minutes and can be repeated many times a day, giving Melbourne a reputation for having “four seasons in one day”, a phrase that is part of local popular culture. The lowest temperature on record is −2.8 °C (27.0 °F), on 21 July 1869. The highest temperature recorded in Melbourne city was 46.4 °C (115.5 °F), on 7 February 2009. While snow is occasionally seen at higher elevations in the outskirts of the city, it has not been recorded in the Central Business District since 1986.
The average temperature of the sea ranges from 14.6 °C (58.3 °F) in September to 18.8 °C (65.8 °F) in February; at Port Melbourne, the average sea temperature range is the same.