The climate of New Zealand is varied due to the country's diverse landscape. Most regions of New Zealand belong to the temperate zone with a maritime climate (Köppen climate classification: Cfb) characterised by four distinct seasons. Winters are relatively mild and summers comparatively cool. The main contributing factors are the Pacific Ocean and latitude, although the mountain ranges can cause significant climate variations in locations barely tens of kilometres from each other. Conditions vary from extremely wet on the West Coast of the South Island to almost semi-arid in Central Otago and subtropical in Northland.
Weather
The Meteorological Service of New Zealand Limited (MetService), established as a state-owned enterprise in 1992, issues weather forecasts and official weather warnings.
Rainfall
Most cities receive between (as in Christchurch) and (Whangarei) of precipitation annually. Rainfall is normally distributed evenly throughout the year in most parts of the country, especially in the South Island. Northern and eastern parts of the country, including Auckland, Christchurch and Wellington see a slight winter maximum consistent with a Mediterranean climate. Summer and autumn maxima can be found in places closer to the southwest, such as Invercargill and Milford Sound.
How much rain a place receives is highly dependent on topography. The Southern Alps, the North Island Volcanic Plateau and surrounding ranges can produce large variation in rainfalls in places barely tens of kilometres apart. Milford Sound receives over 6,700 mm (264 Inches) of the rainfall a year on average while barely 100 km (62 Miles) away Alexandra in Central Otago receives only slightly greater than 300 mm annually, giving it a borderline oceanic/semi-arid climate. Air laden with water vapour from the ocean is pushed from the west in response to Earth’s rotation. This weather circulates the southern seas largely unimpeded by land until it reaches the Southern Alps. The humid westerly wind is forced up over the mountains, at cooler elevation water condenses and falls as snow or rain. This orographic rain explains the huge difference in conditions between the wet west and dry east of the South Island.
Snowfall
Snow falls in New Zealand's South Island and at higher altitudes in the North Island. It is extremely rare at sea level in the North Island. Snow is more common inland in both main islands, though snow to sea level does occur on average once or twice per year in the central and southern South Island.
Temperature
As with many islands in the world, the influence of the ocean curtails any extremes in coastal temperature. The greater temperature ranges are found in the interior of the Canterbury and Otago regions, and especially Central Otago. Central Otago and inland Canterbury's Mackenzie Basin have the closest New Zealand has to continental climates, being generally drier (due in part to föhn winds) and less directly modified by the ocean. These areas can experience summer temperatures in the low 30s °C (high 80s/low 90s °F) and snow and severe frosts in winter, the latter exacerbated by hoar frosts in the river valleys and basins.
Annual mean temperature
Mean annual temperatures range from in the south to in the north. The coldest month is usually July and the warmest month is usually January or February. Generally there are relatively small variations between summer and winter temperatures. An example of this is Auckland which has a variation of just 9 °C or 16 °F between the average mid-winter high temperature () and average mid-summer high temperature (). Temperature variation throughout the day is also relatively small. The exception to this is inland areas and to the east of the ranges with daily variations that can be over 25 °C and differences of up to 14 °C between the average summer and winter high temperatures. Temperatures also drop about 0.7 °C or 1.3 °F for every 100 m (300ft) of altitude.
Northern cities such as Auckland, Whangarei, and Tauranga experience mean yearly maxima of between and mean yearly minima of around . Eastern cities on the North Island such as Gisborne, Napier, and Hastings also have mean yearly maxima of between but have slightly lower yearly mean minima of around . The two largest cities on the South Island, Christchurch and Dunedin, have mean yearly maxima of and and yearly mean minima of and respectively.