Weather and Snow Conditions
During winter, information about snowpack stability and avalanche risk is provided at www.avalanche.net.nz. Thanks to the New Zealand Mountain Safety Council.
Note: Anticyclones (high pressure areas) rotate in an anticlockwise direction, and lows rotate clockwise, the opposite to the northern hemisphere.
Main online sources of information about current and forecast New Zealand mountain weather:
- Department of Conservation. DoC provide MetService forecasts for mountain and national park regions.
- Metservice. The main national forecasting service. Site includes maps, rain and snow forecasts, mountain and marine weather.
- Metservice also has text (SMS), mobiile browsing, iPad and email warning services, accessible from this page.
- MetVUW. This site has excellent long range forecast charts, including expected precipitation levels.
- NIWA (National Institute of Water and Atmospheric Research) has mean monthly temperature records and a seasonal climate outlook.
- An excellent resource for mountain weather information is provided by Sunrockice mountain guides.
Department of Conservation field centres
Up-to-date weather forecasts can be obtained at Department of Conservation (DoC) field centres.
Metservice has an extensive range of phone forecasts. Charges may apply for 0900 calls.
Mountain forecast numbers are:
- 0900 999 24 Brief Mountain (National)
- 0900 999 15 Central North Island
- 0900 999 02 Nelson Lakes
- 0900 999 26 Canterbury Region
- 0900 999 81 Southern Lakes
Radio New Zealand National has a mountain forecast after the 4.00pm news every day. A five-day forecast is after the 12:30pm news weekdays and after the 1pm news on weekends.
Television forecasts are generally too brief to be useful for climbers, but will quickly show you a situation map.
Teletext weather: page 103
All local and national daily newspapers carry a detailed forecast with a situation map, often including mountain forecasts.
Search and rescue
Sunrise and sunset times
Times listed are sunrise and sunset at Christchurch. Times given are New Zealand Standard Time (NZST). Add one hour to obtain New Zealand Daylight Time (NZDT).
Auckland has 40 minutes less daylight during summer than Christchurch, while during winter the opposite applies. Sunrise and sunset times can also be obtained from the Carter Observatory in Wellington, ph (04) 472 8167.
These notes are intended only as a brief guide to New Zealand's weather conditions.
New Zealand is surrounded by sea, creating a temperate but changeable climate.
More stable weather patterns usually occur during late summer and late winter. Spring tends to be dominated by unstable westerly conditions.
Rainfall is concentrated on the western sides of both islands. The North Island receives most of its rainfall during winter
Rock climbing and tramping are year-round activities, but are more popular during summer.
Summer is the peak time for alpine climbing, especially the Christmas–New Year period when most New Zealanders take their summer holiday. However, more stable weather usually develops during February and March.
August and September are commonly regarded as the best months for winter climbing, but stable fine spells can develop at any time during winter months.
Significant factors for alpine climbing in New Zealand are crevasses and rockfall. By late summer, although the weather improves, many climbs become more difficult as crevasses are open up, and more dangerous as warm conditions loosen rocks. For this reason some people regard August to November as the best time for climbing in the high Southern Alps.
The Darrans are less glaciated and the rock is more solid, so late summer generally gives the best conditions there.
New Zealand straddles the “roaring forties”, a band of strong westerly winds that circulate around the southern ocean. New Zealand's weather patterns are dominated by these westerly winds.
Moisture collected over the ocean cools as it rises over the alps and falls as rain and snow. Emptied of precipitation, the air descends over the eastern lowlands as often very warm, dry winds.
A typical New Zealand mountain weather pattern may follow an approximately 6–10 day cycle. A westerly airflow, caused by a low pressure system passing to the south of the country, brings a warm front and northwesterly winds, followed by colder west to southwest fronts. A clearance from the south marks the entry of a high pressure system, bringing light winds and generally fine weather.
That said, the only real certainty about New Zealand weather is its uncertainty. Lengthy storms are possible: Two climbers were trapped on the summit ridge of Mt Cook for 14 days in November 1982.
The South Island's free air freezing level is usually about 1650m in winter and 3200m in summer, but in alpine regions it is usually lower.
At Mt Cook village, the average winter temperature is 2°C (Celsius), while in summer it will average 14°C. As a general rule, temperature declines by approximately 6.5°C every 1000 metres altitude gained. In Christchurch, 30°C is not uncommon during summer.
In the North Island, weather patterns are less pronounced and temperatures are generally a few degrees warmer than in the South Island.
Common weather patterns
A northwesterly airflow over the South Island will bring rain to the West Coast and Main Divide, with high winds in the mountains. Further east, skies clear and winds are strong, warm and dry.
Head to the east coast crags. Take sunblock and swimming gear.
A southerly quarter storm usually progresses up the east coast (more southwest conditions can affect the West Coast), bringing a big drop in termperatures and cool rain (summer), or snow (winter). Winter southeast snowfalls can affect the low country to the east and alpine roads may close.
Southerlies bring good news for climbers. If in a hut, find a good book. Otherwise, make preparations for a trip and start walking in during the tail end of the bad weather.
After the southerly front passes, patches of blue sky increase on the southern horizon. This is good news. The clouds will be moved away by the cool southerly airflow and a period of fine weather will follow, initially cool but warming as the air flow moves into the westerly quarter.
Go climbing. Rock routes may take a day or two to clear of snow.
A light westerly brings some cloud cover on the western side of the Divide, often referred to as “West Coast Crud”. Early mornings may bring clear weather but, as the day develops, white fluffy cloud builds up at about 1200m. By about midday, anybody east of the divide will see the "crud" flowing over low points of the Divide at its low points. The cloud will disperse during the evening, leaving a clear night.
Go climbing. On the western side of the Divide you may be engulfed by cloud, but don't panic, just make sure you can navigate back to the hut in poor visibility.
West Coast cloud thickens and does not retreat during the evening. High cloud moves in from the west and intensifies. Air temperature rises, particularly noticeable at night. Lenticular clouds, known as “hogs backs”, appear in the sky or sitting over major summits and indicate high winds at altitude.
Abandon high camps, and head for reliable shelter while you can. Last-minute ascents may be sneaked in on more easterly mountains such the Malte Brun Range at Mt Cook, the Remarkables, or the Arrowsmiths.
Usually the result of a tropical depression travelling southeast across northern New Zealand, bringing extremely heavy rain to the north and east of the North Island.
Go to the Darrans. It will most likely have stopped raining there.
Often the residual effects of a northeasterly system bring warm rain with little wind to the east coast, and sometimes as far inland as the alpine regions. In winter these systems can bring heavy snow to eastern ski fields.
The West Coast remains fine in all but the strongest easterly weather.
New Zealand’s clear air, and the residual effect of the breakup of the ozone hole that develops over Antarctica each winter, means sunburn can be a major problem. In spring and summer, weather forecasts often include a “burn factor” which estimates the number of minutes before unprotected skin will suffer sunburn. This can be as short as 12 minutes, and even shorter times should be expected at altitude or in the snow.