Winter | The Meteorological Society of New Zealand

Winter

Winter 2012

A season of two halves: cold and dry, then wet and warm

Temperature

The first half of winter was colder than usual; the second half of winter was unusually mild. Overall, winter temperatures were above average in the west and south of the South Island, as well as in Nelson, parts of Northland and around Ohakune. Elsewhere, winter temperatures were generally near average. 

Rainfall 

An extremely wet winter in the north and east of the South Island; unusually dry in the west and south of the South Island. Rainfall generally near normal in the North Island, except western Bay of Plenty and the Wairarapa coast, which were wetter than usual.

Sunshine

An unusually cloudy winter for Otago, south Canterbury, Nelson, Marlborough, and Wellington.  Extremely sunny in the west and south of the South Island. It was also a rather sunny winter for western parts of the North Island.

Soil moisture

As at the end of winter, below normal soil moisture levels for the southwest South Island. Above normal levels for the Kaikoura Coast and south Canterbury.

Overview

Winter was characterised by much higher pressures than normal to the southeast of New Zealand, and extending across the South Island. However, the season started off with frequent southwest winds over the country, resulting in a cooler and drier than normal start to the winter. In the middle of July, a change to more frequent northeast winds brought relatively mild and rather wet weather to many areas.

Winter was a season of two halves – it started colder than usual but ended unusually warm. Overall, it was a relatively mild winter in the west and south of the South Island, as well as in Nelson, parts of Northland, and around Ohakune (with winter temperatures between 0.5°C and 1.2°C above winter average). The change in pressure patterns mid-season meant that in all other regions winter temperatures were near average (within 0.5°C of the winter average). The nation-wide average temperature in winter 2012 was 8.7°C (0.4°C above the 1971-2000 winter average), using NIWA’s seven-station temperature series which begins in 1909.

It was an extremely wet winter for the north and east of the South Island, being the wettest winter on record for Timaru, and one of the wettest winters on record in the Nelson region. In contrast, it was one of the driest winters recorded in the west and south of the South Island. For the North Island, most regions recorded near normal winter rainfall (between 80 and 120 percent of winter normal rainfall total). Exceptions to this were the western Bay of Plenty and the Wairarapa coast, which were both much wetter than usual.

As at the end of winter, below normal soil moisture levels were evident across the southwest South Island. In contrast, above normal soil moisture levels were observed on the Kaikoura Coast and in south Canterbury.

It was an unusually cloudy winter for Otago, south Canterbury, Nelson, Marlborough, and Wellington. It was the cloudiest winter on record for Takaka. In contrast, it was an extremely sunny winter for the west and south of the South Island. It was also rather sunny over western parts of the North Island.  Record-breaking winter sunshine was experienced at Taumarunui, Cheviot, and Queenstown.

Further Highlights:

  • The highest temperature was 22.7°C, observed at Christchurch on 26 August.
  • The lowest temperature was -11.8°C, at Darfield on 7 June.
  • The highest 1-day rainfall experienced was 358 mm at North Egmont on 16 July.
  • The highest gust recorded was 161 km/hr at Taiaroa Head on 28 June.
  • Of the six main centres in winter 2012, Auckland was the warmest and sunniest, Tauranga the wettest, Christchurch the coolest, Dunedin the driest, and Wellington the cloudiest.

For further information, please contact:

Ms Georgina Griffiths

Climate Scientist– NIWA National Climate Centre, Auckland

Tel. 09 375 4506 (office) or 027 293 6545 (mobile)

Dr Mike Revell

Principal Scientist, Meteorology and Remote Sensing, NIWA Wellington

Tel. 04 386 0328

 

NOTABLE WEATHER IN NZ - WINTER 2012

 

This season saw a great variety of weather patterns, with it being a winter of two halves temperature wise - cold during the first half, but then unusually mild in the second. The most significant events of the month involved deep low pressure systems crossing NZ - one resulting in a severe snowstorm in Canterbury in early June, and a series of lows from the end of July to mid-August bringing persistent wet weather, especially in the east of the South Island.

 

JUNE

  • 2nd - Only 3C maximum in Alexandra, as the town lies under persistent low cloud and fog.
  • 3rd - Warm 20C maximum in Kaikoura.
  • 4th - Frosty morning in inland South Island, eg -6C minimums in Middlemarch and Pukaki. By contrast, considerably milder in the north, with a 20C maximum in Leigh.
  • 5th-7th - Deep low pressure system crosses NZ with stormy weather, including severe snowstorm in Canterbury. (see details below)
  • 8th - Severe morning frosts again in snow covered Canterbury, eg -10C minimum in Culverden (new June record) and -5C in Cheviot.
  • 9th -7C minimum at Molesworth.
  • 11th - Cold south to southwest flow spreads over country, with snow showers on some high country areas.
  • 12th - Severe frosts in central North Island, under clear skies in a light southerly flow. -5C minimum in Taumaranui.
  • 12th - Cold, showery southerly flow in eastern areas; only 6C maximums in Masterton, Dunedin, and Queenstown. Snow showers to low levels about Dunedin and Banks Peninsula, also non-settling flurries at Rimutake Hill Road summit.
  • 14th - Cold southerlies strengthen again over South Island, with snow showers lowering on the high country.
  • 15th - Very cold southerly flow, with snow showers to low levels in some eastern parts of South Island. Roads closed on Christchurch’s Port Hills, plus sleet in city. Only 2C maximum in Hanmer.
  • 16th - Very cold southerlies with snow on central and southern North Island high country, falling as low as Taihape. Desert and Napier-Taupo roads closed by snow and ice. Continuing very cold in South Island, with -6C minimum in Manapouri and only 1C maximum in Lumsden
  • 17th - Severe frosts in South Island and parts of North Island, in wake of southerly, eg -9C minimum at Pukaki, -4C in Palmerston North, and -3C in Dunedin. High cloud following the frosts keeps maximums low in places, eg only 3C in Murchison, Culverden, and Gore.
  • 18th - Freezing rain, sleet, and some snow in inland areas of South Island, as moist air in a northerly flow from approaching low in Tasman Sea arrives while very cold air persists in valleys and basins. Only 2C maximum in Alexandra; 4C in Invercargill; 5C in Queenstown and Ashburton. Heavy rain in Nelson region results in some flooding and slips. 87mm recorded in Appleby and 66mm in Nelson.
  • 19th - Only 1C maximum in Alexandra; 4C in Queenstown. Black ice makes many Central Otago roads hazardous, with school buses delayed until after 10am.Thick fog disrupts operations at Christchurch Airport. Thunderstorm in Nelson sets off property alarms.
  • 20th/21st - Fog causes problems at Queenstown Airport. SH8 between Alexandra and Roxburgh closed be ice until grit is layed on road. 4C maximum in Alexandra.
  • 23rd- Severe northwesterly gales from inland Canterbury to Wairarapa. (133 km/hr gust recorded on Mt Kaukau) Heavy rain about and west of the Southern Alps. Warm in several eastern areas, eg 22C maximum in Kaikoura and 20C at Christchurch Airport and Cheviot. However, a change to colder southerlies later in South Island with snow on the high country overnight 23rd/24th.
  • 25th - Chilly 5C maximum at Milford Sound, as snow closed SH94 between there and Te Anau. Other South Island high country roads also affected by snow.
  • 26th/27th - Strong, disturbed west to southwest flow over NZ, with gales in exposed areas. (96 km/hr gust recorded in Hawera on 27th). Becoming very cold and showery with hail and snow to near sea-level in the far south on 26th and falls affecting roads further north about the South Island high country. Milford Sound’s 2C maximum on 26th is a new June record. Unusually low-level snowfalls extend along West Coast by morning of 27th, with 15cm settling in Reefton and snow even lying on beaches in South Westland. Reefton only reaches 1C during the day, with St Arnaud only climbing as high as 2C.
  • 28th - South to southwest gales in exposed southern and eastern parts of South Island. Campervan blown off road near Balclutha.
  • 30th - Severe frosts in many areas. Minimums include -7C in Lumsden, -4C in Motueka, -3C in Te Kuiti, and -1C in Te Puke.

 

JULY

  • 1st - Very frosty in areas away from eastern coasts. (where there is cloud and an onshore airflow) Minimums include -9C at Tekapo, and -7C in Queenstown.
  • 2nd - Severe frosts again in many sheltered areas. Minimums include -11C in Ranfurly, -9C in Alexandra, -8C at Dunedin Airport and Lumsden, -6C in Timaru and Turangi, -4C in Paraparaumu, and -1C in Wanganui.
  • 3rd - Thunderstorms with heavy downpours in north of North Island. A particularly heavy storm lashes eastern and central parts of Auckland (especially the Hauraki Gulf islands), with flooding and power outages. Wind gusts lift a roof in Hobson Street. SH2 closed by flooding north of Katikati. Hailstorm leaves a white blanketing on Waihi Beach. The East Cape area also is deluged, with a new July record of 96mm at Hicks Bay. Another very frosty start to the day in inland areas of South Island, eg -12C minimum in Ophir, Central Otago. Alexandra rises to only -1C under freezing fog.
  • 4th - Heavy rain in Gisborne/Hawkes Bay areas. Flooding about Gisborne. Snow on Canterbury high country, with Porters Pass closed to towing vehicles. Icy and frosty conditions further south, with water freezing in pipes in some areas.
  • 5th - Foggy about South Auckland and the Waikato. Thick fog closes Auckland Airport, and makes driving hazardous elsewhere around the city. Hamilton only reaches a 6C maximum under the fog cover. Alexandra rises to an icy -2C under freezing fog, which clears later, only to be replaced by high cloud.
  • 6th - Foggy in many areas of the country. Auckland Airport disrupted again, as are  Hamilton and Christchurch airports. Recent heavy rain results in flooding of Manawatu River, closing SH56 in two places.
  • 7th - Some more fog in scattered areas of NZ, but little disruption. -7C minimum in Queenstown.
  • 8th-11th - Frosty in many areas, eg -7 minimums at Tekapo (8th) and Taumaranui (10th), -5C in Waiouru (5th), and -4C in Cambridge. (10th) Freezing fogs in Central Otago, with 2C maximum in Alexandra on 8th and 9th, and 1C in Wanaka on 9th. Frankton Marina on Lake Wakatipu frozen on 9th, and jet boats can’t be used on Shotover River due to ice on same day.
  • 12th-17th - Heavy rain, especially in Buller. (see details below)
  • 18th - Anticyclonic northwesterly flow over South Island, with daytime maximums well above normal in many northern and eastern places, eg 20C in Motueka (new July record), 18C in Dunedin, 17C in Lauder, and 16C at Nugget Point.
  • 19th - Northerly flow with milder than normal temperatures again in parts of South Island, eg 18C maximum at Mt Cook Village.
  • 22nd/23rd - Heavy rain in some northern North Island areas. Flooding and slips cause disruption in Hauraki, Coromadel Peninsula, and western Bay of Plenty, with Waihi Beach isolated on the 23rd.
  • 24th - Dowmpour causes flash flooding in Cambridge, with a large slip blocking off several properties.
  • 24th/25th - Heavy rain in east of North Island. Flooding forces kaiti School in Gisborne to close, while the Clive River in Hawkes Bay breaks its banks, resulting in damage to properties and land. By contrast, unusally mild in many western areas
  • 26th - Unseasonably mild in some western parts of North Island under a light southeasterly flow. Port Taharoa records a new July record maximum of 20C.
  • 29th July-15th August - Depressions bring heavy rain, especially in east of South Island. (see details below)

 

AUGUST

  • 16th-19th - Foggy about Dunedin area, thanks to a weak ridge with light winds and lingering ground moisture from recent wet weather. Dunedin Airport disrupted at times, while the fog prevents a container ship entering Dunedin Harbour on 19th.
  • 18th - Thunderstorms in Taranaki, plus a band crosses northern North island areas. Mild in northern areas, eg 20C maximum at Leigh.
  • 19th - Some thunderstorms in north of North Island. Also, an evening thunderstorm in Wellington with heavy hail in some southern and eastern parts of city, eg marble-sized stones in Miramar. (some surface flooding reported)
  • 20th - Rain causes more flooding in eastern Otago. Falls not as heavy as earlier rain events, but saturated ground means not much rain needed to cause flooding. Some heavy rain in southwest of North Island; surface flooding closes all sports grounds in Palmerston North, and a slips affect Taranaki. Tornado reported in Bell Block, New Plymouth.
  • 21st - Two slips reported in Hamilton after persistent overnight rain.
  • 25th - Warm 20C maximum at Christchurch Airport. Heavy rain in southwest of South Island, with northwesterly gales. (Puysegur Point gusts to 135 km/hr) However,  record high August minimums at Southwest Cape, Stewart Island (10C)  and Puysegur Point. (12C)
  • 26th - Unseasonably warm in east of South Island, eg 22C maximum in Kaikoura and Christchurch Airport, plus 20C-21C maximums in other eastern South Island places.
  • 27th - Unusually warm overnight minimums in north of South Island. Takaka and Nelson record new August records of 12C. Warm 20C maximum in Motueka. However, colder southwesterlies in Fiordland, with chains required due to snow on SH94 near Homer Tunnel.
  • 28th - Thunder and hail in some central and eastern parts of North Island. Snow showers on ranges, as low as Desert Road for a time.
  • 31st - Above normal temperatures in many areas due to a north to northeast flow. 19C maximums in Port Taharoa and Alexandra; 18C in Ranfurly.

 

MAJOR EVENTS

 

5th-7th June - Deep low pressure system crosses NZ with stormy weather, including severe snowstorm in Canterbury

A deep low crossed the country during this period, with heavy rain, severe gales and snow causing disruption to many areas. The most significant aspect of this storm was a heavy snowfall to sea-level in Mid and North Canterbury, including Christchurch, on the 6th.

A low, which had been developing over and just to the east of Australia during the previous few days, deepened significantly as it crossed the Tasman Sea during the 5th. A north to northwest flow strengthened over northern and central NZ as fronts linked to the low moved onto the area later in the day. Rain spread to northern and western areas, and became very heavy in the northwest of the South Island. Slips and flooding caused significant disruption to the area. High totals included 151mm in Greymouth (a new June record) and 95mm in Reefton. Heavy rain in the Wellington area also resulted in trains running late.

Meanwhile, very cold air spread onto the lower South Island via cold fronts to the south of the low, bringing a southerly flow with snow showers to low levels. A clash between the warmer, moist air from the low and the southerly occurred over the upper South Island overnight 5th/6th. This resulted in heavy snow falling to sea-level in Mid and North Canterbury from the early hours of the 6th. The snow then continued for most of the day as the low established itself over central NZ, with heavy accumulations down to sea-level, including Christchurch. Many roads were closed, schools shut, power cut to (mostly rural) places, and trees and branches felled. In Christchurch, bus services were also halted and Airport operations disrupted. In the city, snow depths varied from about 5cm by the sea to 15cm in the western outskirts. Inland, the snow acumulated to 20-30cm, but Hanmer received about 45cm and some high country areas (such as Arthurs Pass) recorded as much as one metre.

Consequently, daytime temperatures struggled to get much above freezing, with Christchurch Airport’s 0.4C being a new all-time record. Elsewhere in the area, Waipara West (2C), and Cheviot (1C) also set new records for any month, while Arthur Pass’s -1C was a June record.

The cold also spread to other northern areas of the South Island, with snow falling to low levels on the West Coast, Kaikoura, Central Marlborough, and some southern parts of the Nelson region. These areas were also lashed by severe gales, causing some damage. In Westland, some 200 cattle were were killed by a wind-chill combination of easterly gales and temperatures in the low single figures. Both Greymouth and Hokitika shivered in June record low maximums of 5C, while Blenheim (where light snow settled in the evening) also recorded an equal record low June maximum of 5C, with Kaikoura only reaching 4C.

Overnight 6th/7th, the low moved across the North Island, allowing a cold southerly to cover the island by early 7th. (but with only light snowfalls on the high country). During the day, a weak ridge crossed NZ, with milder westerlies later developing in the far south. Despite the more settled weather, conditions remained icy where the snow still lay thickly and conditions remained hazardous on the roads. Darfield and Arthurs Pass recorded overnight lows of -11C (June record at latter location), Christchurch Airport -5C, and Le Bons Bay 0C.

Mean sea-level analyses for midday NZST 5th June to midday NZST 7th June in 24 hour steps are shown here.

 

13th-17th July - Heavy rain, especially in Buller

A moist onshore airflow and frontal systems affected western areas during this period, with heavy rain at times. This especially affected the South Island West Coast, with the Buller region being worst hit by flooding.

A moist northwesterly flow developed over the lower South Island on the 12th and spread north to cover southern and central NZ on the 13th/14th. This was linked to a complex low pressure system in the South Tasman Sea, which extended onto the far south from later on the 13th. At the same time, ridging from an anticyclone well to the east was slow in leaving the northern North Island. The fronts in the moist northwesterly flow dumped heavy rain, which began in Fiordland on 12th and spread further north along the West Coast on the 13th.

On the 15th, the fronts began to move onto the lower North Island, with torrential rain concentrated in the northwest of the South Island. This resulted in flooding affecting Buller and Nelson regions on 15th/16th.  Many roads were closed throughout the area, with Westport being isolated on 16th. (there was surface flooding in the town as well) Rainfall totals during this period included 204mm in Takaka (14th - new July record), 74mm in Reefton (14th), 89mm in Greymouth (14th), 96mm in Hokitika (13th), and 114mm in Haast. (13th)

The heavy rain also spread to North Island areas exposed tot he north and west on the 15th and persisted into the 16th as further fronts moved in from the Tasman Sea, with flooding and slips causing problems (such as road closures) around Lake Taupo, King Country and the Wellington area. North Egmont was deluged by 336mm on the 15th, with other high totals on that day including 86mm in Te Puke, 62mm in Turangi, and 48mm in Levin.

Rain cleared the North Island on 17th, as a ridge spread onto central NZ.

By contrast, it was warm in many eastern areas during this period, ending the prolonged cold weather which had prevailed for most of the winter so far. Christchurch Airport, Rangiora, and Cheviot recorded 22C maximums on the 15th, with Napier rising to 21C the next day. Temperatures reached the high teens in other eastern places during this period.

Mean sea-level analyses for midday NZST 13th July to midday NZST 17th July in 12 hour steps are shown here.

 

29th July-15th August - Depressions bring heavy rain events, especially in east of South Island

Three significant depressions affected NZ during this period, with heavy rain in several areas, especially the east of the South Island, causing much damage in several areas.

The first depression, which developed in the Tasman Sea over the previous two days, had deepened significantly by late on the 29th July when it parked itself to the west of the North Island. It remained there without losing intensity until the 2nd August. Frontal disturbances on its eastern side delivered periods of often heavy rain to northern and central North Island areas. Flooding and slips resulted in road closures on the 30th, especially about the western Bay of Plenty and Hauraki areas, where (in combination with strong winds) the rain caused trees and power-line to fall and the Tauranga sewer system to leak into an estuary. From the 2nd-4th August, heavy rain caused flooding in parts of the Gisborne area.

Meanwhile persistent high pressure to the south of NZ resulted in a persistent easterly flow over the South Island. Rain set in there late on the 30th, with heavy falls in some areas until the 3rd. The heaviest falls were in North Otago, South Canterbury, and eastern Marlborough/Kaikoura with slips and flooding closing many roads. Rain in Christchurch on 30th/31st caused the Heathcoate River to break its banks. By contrast, a fohn easterly flow brought unusually warm temperatures to the West Coast, including 18C in Westport and 17C at Secretary Island on the 1st.

On the 4th/5th August weak ridging meant somewhat more settled conditions in many areas with lighter airflows over most of NZ. However, low pressure to the north and west allowed wet weather to continue in the northern North Island, and on the South Island West Coast.

During the 6th, a weak ridged covered NZ, but a new low pressure system moved into the South Tasman. Fog disrupted operations at Invercargill Airport on the 6th/7th.

This new system morphed into a large depression which became centred to the west of the South Island during the 7th, slowly moving northeast to lie to the east of the North Island by the 9th. Heavy rain again affected the eastern South Island areas previously deluged by the previous wet spell, with more flooding and slips. The rain caused a sewerage leak in Blenheim on the 8th, while some Marlborough schools closed early. Heavy snow fell on the high country of South Canterbury, disrupting traffic on SH8 between Tekapo and Fairlie. However, South Island ski-fields welcomed these snowfalls. Heavy rain also caused some flooding and slips in the Wellington region on the 9th.

A weak ridge covered the South Island on the 9th, and the rest of NZ the next day, but yet another low formed in the Tasman Sea during this time and became a large system as it gradually moved onto the country later on the 11th. From then it became slow moving over NZ on the 12th, remaining there until the 14th. Yet again, moist easterlies brought significant rain to many eastern areas of the South Island. Eastern Otago was deluged again, as well as Christchurch and Banks Peninsula. Both areas were plagued by flooding and slips with many closed, including SH75 from Christchurch-Akaroa (Little River township flooded), SH1 in several places, and some other Otago highways, not to mention numerous smaller roads. Several streets in Christchurch experienced surface flooding, while a mudslide forced the evacuation of several properties in Lyttelton on the 14th. Meanwhile, heavy snow fell again in the alpine areas, with many people trapped at Mt Cheeseman ski-field due to the access road being blocked by snow.

Meanwhile heavy falls of rain and thunderstorms affected several North Island areas, with slips and flooding reported in the Bay of Plenty (including Taurangi and Rotorua) and the Wairarapa. A tornado damaged some trees and property near Taipa, Northland on the 12th. A hailstorm struck Pamerston North on the 13th, resulting in some surface flooding.

The low weakened on the 15th, with rain easing in the affected areas, though the effects of the wet weather were to last much longer, with many slips having to be cleared.

While no rainfall records were broken during this whole period, there still some very high totals. The highest was 198mm in Akaroa on the 12th August, while other high totals during that event included 73mm in Lyttelton, 64mm in Ashburton, and 46mm at Christchurch Airport. Geraldine Forest recorded 168mm over the 30th/31st July.

Mean sea-level analyses for midday NZST 29th July to midday NZST 15th August in 24 hour steps are shown here.

 

MONTHLY WEATHER NOTES FOR CHRISTCHURCH

WINTER 2012

 

JUNE

Winter arrived with a bang this year, with a major snowstorm early in the month, and much colder than normal conditions in general. This was thanks to more southerly and southwesterly flows than normal. After relatively settled weather for the first few days, a deep low approached from the Tasman Sea on the 5th, while a very cold southerly airmass moved onto the lower South island later in the day. Rain set in over Christchurch in the evening, and had turned by snow by about dawn. The snow continued for most of the day, causing significant disruption and keeping the temperatures to only just above 0C. The coldest day in the city on record. As the snow cleared in the evening, it became very icy. A fine day on the 7th, failed to melt much snow, so conditions remained hazardous with freezing temperatures and black ice returning as soon as it got dark.

A period of cold southerlies from the 11th-16th brought showers to the city and snow to higher Banks Peninsula hills. At its coldest on the 15th, snow fell to low levels, with some sleet and snow reported in parts of Christchurch, though only settling on the Port Hills this time. A third very cold outbreak affected the South Island on the 26th/27th, but this airflow was southwesterly this time, and Canterbury remaining mostly fine, while snow fell to near sea-level in the far south and (unusually) on the West Coast.

 

JULY

Anticyclones were more predominant this month, but these were interspersed with some depressions crossing over, especially towards the end of the month. The month began with a cloudy (and at times drizzly) week under onshore flows. Anticyclonic conditions then brought fine, frosty weather until the 11th when a northwesterly flow became established over the South Island until the 16th and temperatures rose significantly. Indeed, the 15th was one of the warmest July days ever recorded in Christchurch, with a 22C maximum at the Airport.

Conditions became anticyclonic from the 17th, but there was taste of things to come from the 22nd-25th when a deep low over the north of the North Island brought some drizzle as far south as the city. However, another even deeper depression moved to the west of central NZ during the last two days of the month, with a moist easterly flow over the South Island bringing some heavy rain in Christchurch.

 

AUGUST

Continuing the pattern that began in the last few days of July, a series of depressions crossing the North Island during the first two-thirds of the month maintained damp easterly flows over the South Island. Consequently, it was a very damp, cloudy month for Christchurch, with well above normal rainfall and much less sunshine than usual. Two further periods of significant rain affected Canterbury during this period. The first of these, on the 7th/8th, brought only some briefly heavy rain in the city midday on the 8th. However, the second event on the 12th/13th saw a secondary low forming off the Canterbury coast. This time, Christchurch and Banks Peninsula were deluged by heavy rain, which resulted in flooding and slips causing road closures and property damage in places.

The 20th was also a wet day in the city, but the rain wasn’t heavy. From then on the weather patterns changed, as conditions became more anticyclonic. While some light frosts occurred, several days became mild, with a northwesterly flow on the 26th/27th pushing temperatures into the high teens.

 

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