The air pressure at sea level was above 1030 hPa everywhere over New Zealand at midday on Thursday. Highest pressures were over inland Otago and Canterbury, peaking at 1039 hPa. Christchurch Airport was reporting 1038.2 hPa … that’s very high indeed.

Here is a sequence of weather maps showing how the anticyclone developed over preceding days (click on the image to view animation). The first map is from midday on Thursday 12 April, and the time steps are six hours until the final map at midday on Thursday 19 April. It’s interesting how the initial anticyclone moved onto the Tasman Sea with a central pressure around 1029 to 1030 hPa, then another system came up from the Tasmania region and joined the initial system, reinforcing it.

Sequence of weather maps, 12 to 19 April 2012.

This anticyclone was bringing clear, sunny weather to many places, just as typical barometers indicate on their dials when the air pressure is high. However, there were many places, particularly along eastern coasts, where the weather was not sunny at all. In fact there was even some light rain about.

Take a look at the satellite image below for details of where cloud was on the late morning of Thursday 19 April.

Image courtesy of MODIS Rapid Response Project, NASA/GSFC.

There was a lot of cloud over eastern regions, especially the east of North Island. The satellite picture showed some beautiful cloud forms over eastern Bay of Plenty… these are low clouds shaped by a combination of waves in the lee of the ranges and orientated perpendicular to the flow, and streets of cloud that are parallel to the flow.

Having looked at the clouds from above, let’s also look at them from below. I took this photo of the clouds over the eastern hills of Wellington in the late afternoon of Thursday 19 April, after a rather grey cloudy day in the capital. The barometer was indicating around 1036 hPa.

Stratocumulus and low-topped cumulus cloud, Wellington, 19 April 2012.

Why is it that not all Highs bring sunny weather? It’s all to do with the upward and downward motions associated with them. Anticyclones generate sinking motion of air, as described in an earlier blog post . As the air sinks it becomes drier, and any cloud in it will generally evaporate. But this sinking air doesn’t make it all the way to the ground and, in the case of the current anticylone over New Zealand, there was a lot of moist air and cloud trapped just above the Earth’s surface.

Most of us live within a few hundred metres of sea level. If we are beneath this anticyclonic cloud, all we see is a cloudy day, even though the skies are blue above. If there’s enough low-level moisture the clouds can generate light rain or drizzle too, though it doesn’t come to much.

Wherever the wind at low levels is blowing from the sea onto the coast, it’s more likely that the air will be moist enough to bring cloud. That was the case for most eastern parts of New Zealand on Thursday 19 April. And there were some patches of drizzle and light rain about too.

Most places in the west were sheltered from the low level flow, and were indeed getting clear sunny weather.

So, with some interpretation, it’s possible to deduce quite a bit from what the barometer is measuring!

First of all, here is a series of weather maps covering the period 1pm Friday 02 March to 1am Sunday 04 March.

Mean sea level analyses from 1pm Friday 02 March 2012 to 1am Sunday 03 March 2012, at six-hourly intervals.

A Bit of Background

Large-scale features on the weather map – that is, those systems which influence the day-to-day weather (highs, lows, fronts) – are driven by processes in the middle and upper parts of the troposphere. Lows become deep and anticyclones become intense when there is strong positive feedback between these processes.

In the case of lows, when the intensification (a change in central pressure) exceeds more than a certain amount over a given time, they are defined as “bombs”. Actually, it’s not quite that simple: if you really want to know more, see “Technical Stuff” at the end of this article.

Between 1am Friday 02 March and 1am Saturday 03 March, the central pressure of this particular low fell from 1002 hPa to 975 hPa: it qualifies.

The term “weather bomb” has come into popular usage in New Zealand to describe dramatic and/or destructive weather events – but very seldom is a “bomb” low the cause. “Bomb” lows aren’t all that common in the New Zealand area.

The Low of Saturday 03 March

Below is the weather map for 1am Saturday 03 March, superimposed on a satellite image. At this stage the low was still west of Taranaki, deepening rapidly and heading more or less straight for Palmerston North (but it never got there). I’ve drawn in some mauve arrowed lines to indicate the axis of strongest winds in the upper troposphere, known as the jet. The relative locations of the low and the jet, and the shape of the jet, strongly favour further deepening of the low and its movement towards the eastsoutheast – which is what happened. Note: this is a simplified explanation ahead of a bit more case work.

Mean sea level analysis 1am Saturday 03 March 2012, together with infra-red satellite image. Satellite image courtesy Japan Meteorological Agency.

A few hours later, at 6am Saturday 03 March, the low had a central pressure of about 971hPa and was not far south of Patea. Below is a portion of the working chart for 6am, drawn by one of MetService’s Severe Weather team. There’s a lot of isobars around the low – and over Taranaki, Wellington and the Marlborough Sounds in particular. The closer together the isobars, the stronger the winds. Also note that there’s a front drawn curling around the low. Tucked in on the southern and western side of this front is a zone of very strong winds, shown by the blue arrow. It’s mostly this zone which did the damage as it moved across the southern part of the North Island.

Hand-drawn mean sea level analysis for 6am Saturday 03 March 2012. This is an internal working chart, drawn by a member of MetService's Severe Weather team. Image copyright Meteorological Service of New Zealand Limited 2012.

Some Interesting Observations

At Hawera, the wind increased quickly during the early morning hours of Saturday 03 March.

No observations were received between 6am and 11am because power to the reporting site was lost.

At Wanganui Airport, the temperature climbed steadily from 12.7 C at midnight Friday 02 March to 17.5 C at 5am Saturday 03 March. (The temperature behaved similarly at Hawera a few hours earlier). This happened because the relatively warm moist air flowing around the northern side of the approaching low was warmed and dried – the Foehn effect - as it passed across the high country to the north of Wanganui.

At Ohakea and Palmerston North, the winds were reasonably strong easterlies for some hours before and after dawn, but blew from the northwest for a while around dawn. Two switch-arounds (not quite 180 degrees) of steady to strong-ish winds in a short time is remarkable.

Between 4am and 3pm Saturday 03 March, the south to southeasterly wind at Brothers Island had a mean speed of 108 km/h. During this time, the highest gust was 142 km/h.

Crossing the Country

I mentioned earlier that at 6am the low was not far south of Patea and heading for Palmerston North but never got there. This is because it didn’t physically cross the North Island. Nevertheless, a graph of mean sea level pressure at Palmerston North (below) for Saturday 03 March 2012 shows that the pressure certainly reached a minimum around dawn before rising steeply again from mid morning.

Mean sea level pressure at Palmerston North.

While lows have distinct structures, they’re best not thought of as rotating solid bodies of air – because they’re not. Rather they are the manifestation, at the Earth’s surface, of processes which have produced a local minimum of pressure. Looking back to the working chart above, we see that there are two lows at 6am: one south of Patea, and another just east of Hawke’s Bay. The low south of Patea came ashore east of Wanganui and then decayed, while the “new” low continued to deepen and move away to the east. This decay/development happens because the “driving” atmospheric processes are largely above the Earth’s surface and moving with the general flow: they left the Patea low behind and powered the development of the “new” low east of the North Island.

Technical Stuff

Finally, the definition of a “bomb” low is technical and not whimsical. As far as I know, the first mention of the term “bomb” was in a paper by two distinguished meteorological researchers, Fred Sanders and John Gyakum, titled “Synoptic-Dynamic Climatology of the “Bomb”", published in the October 1980 issue of Weather and Forecasting, a journal of the American Meteorological Society. Because of their destructive potential, rapidly deepening lows have been the subject of many a research paper.

The temperature trend in New Zealand during the past year can be read from the graph below and tells a story. Last summer was significantly hotter than normal, and several tropical weather systems visited our northern parts in January.

Data taken from NIWA’s monthly climate summaries.

Autumn started normally enough in March and April.  Then blocking led to the dominance of north and northeasterly wind patterns, delaying the onset of winter (and the opening of the ski season) by about three weeks.  This all changed in July – click here for a more detailed explanation from our Chief Forecaster, Peter Kreft - when we experienced the coldest time of the year, with polar outbreaks on 25 July and 14 August to 16 August. Spring started a few weeks late but managed to finish on schedule.  And, of course, there was the deluge that struck Nelson in mid December.

Global temperature measurements currently score 2011 as the tenth highest on record. That data is from the global mean surface land-ocean temperature index. 2011 brought its fair share of global meteorological mayhem. In January Brisbane had its worst floods since 1974, and Brazilian landslides killed 900 people in the mountains just north of Rio de Janeiro. Rain in October eased the drought in the Horn of Africa that had been affecting around 12 million people, but the rain was so intense that it brought crop damage to Kenya. The Monsoon stalled over Thailand in October, taking the lives of 650 people in floods, notably around Bangkok.  On Sunday 18^th December, Tropical Cyclone Washi became the deadliest storm of the year with landslides taking more than 1000 lives in the Philippines.

The World Meteorological Organization reports that 14 weather events, each with upwards of US $1 billion of damage have occured in North America during 2011:  heavy snow in February, the most active tornado season on record in April and May, a drought and wild fires in Texas, and the wettest year on record in the east along the Canadian/US Border, culminating in the late August with severe flooding from Hurricane Irene and Tropical Storm Lee.

 In New Zealand, 2011 started with an intense La Nina episode and large anticyclones over Chatham Islands. In the days between Christmas and New Year, an intense storm passed over the country and brought gale force winds to many areas and flooding to the Rakaia area, Pelorus Bridge camp site, Rai Valley, and Aorere River in Golden Bay.

In January there were many episodes of strong easterly winds as three lows of tropical origin brought torrential rain and gales. Former tropical cyclones Vania and Zelia produced heavy rain on the 18th on the West Coast, resulting in the Fox River bursting its banks. On 22^nd/23^rd, a low which formed near New Caledonia moved towards NZ producing rain that caused slips and road closures over much of the North Island, along with a significant storm surge for Auckland.  Insurance payouts for this flooding were $7NZ million. Also, Tropical Cyclone Wilma moved rapidly across the northeastern North Island on the 28th/29th, and brought severe flooding and slips to northeastern regions of the North Island. Insurance payouts for this were $20NZ million, making it the most expensive weather event in NZ in the past year (insurance payout figures from Insurance Council of NZ: http://www.icnz.org.nz/current/weather/).

MetService Weather Map showing Tropical Cyclone WILMA on 28 January 2011. This was our most damaging storm in the past year.

In February, weather conditions were generally settled.  There was a record-breaking heat wave on Waitangi Day, with Timaru Garden’s 41.3 degrees centigrade topping the list of available temperatures.  It was an extremely dry month in the North Island – the driest February in Dannevirke since records began there in 1951. By way of contrast, central Otago had twice its normal February rainfall.

March was very wet over the North Island and parts of the South. After crossing Raoul Island, Tropical Ccyclone Bune wound down as it passed east of East Cape at the end of the month.

April brought more southeast winds than usual, with wet conditions for eastern areas.  The flooding and slips in Hawke’s Bay on 26-27^th April triggered evacuations and resulted in insurance payouts of $6.4million.

During May and most of June north or northeast flow patterns dominated, bringing record-breaking warmth.  Ash clouds from a South American volcano also challenged air travel. May will be long remembered for the tornado that struck Albany on the 3^rd, taking the life of a worker.  Insurance payouts for this event were $6 million. On 18^th June a landslide took the life of a teenager at Ohope. On 19^th June tornadoes hit Taranaki, triggering an insurance payout of around $2 million.

During July and August stormy west, southwest, and southerly flow patterns dominated; click here for a more detailed explanation from our Chief Forecaster, Peter Kreft.  This was the coldest time of the year, with polar outbreaks on 25 July and 14 August to 16 August.  Snow fell across the lower North Island, with flurries in locations well north in the country.

MetService Weather map at midnight start of Monday 15 Aug showed a blast of southerly air from Antarctica to New Zealand.

September was characterized by southwest flows and October by northeast flows, with winds less than normal and generally settled weather because of dominant anticyclones.  Most of the Rugby World Cup games were not directly affected by the weather.  It is interesting to note that on 11^th September, just 36 hours after calm clear weather for the opening ceremony, a tornado hit within 10 km of Eden Park. Then on 13^th September Wellington was coated with hail (MetService tending on Twitter, such was the intensity of the event), and on 14^th September winds caused damage in Auckland, Waikato and Bay of Plenty.  On 18-19^th October, Dunedin andChristchurch had their wettest day in 18 months.  On Labour Day (24 Oct) wind also caused damage in Southland and central Otago.

During November,anticyclones came south earlier than normal but the frontal systems of spring remained steadfast. As a result, isobars over central New Zealand were squashed closer together than normal, causing many bouts of wind.  This produced drier than normal conditions in the northeast, and cooler and wetter than normal conditions in the southwest. The moisture causing the rainfall that flooded the Grey River in Westland on 21^st came from Australia.

In mid-December a major trough stalled for about two days between a low in the Tasman Sea and a large blocking high east of New Zealand.  This brought a deluge of rain to Nelson.

MetService weather map for 15th December 2011 showing a front stalled over Nelson.

The most significant falls of rain occurred in the hills behind Nelson and in the lowland areas of Takaka and Richmond. The rain gauge trace seen at Kotinga in the Takaka township measured 423 mm/24 hours, a new record for this site – the previous record of 256mm/24hr was measured in August 1990.  The New Zealand record for 24 hour rainfall is held by CroppRiver at its waterfall (inland from Hokitika), at 758 mm in 24 hours ending 0620 hours on 27 Dec 1989.

Rainfall accumulation graph for Takaka (TAN), Kotinga (TSR) and Nelson Airport (NSA). Accumulation of rain is in mm, and timestamps are in UTC (add 13 hours to get NZDT).

The total rainfall over the country from this trough can be seen in the rain map for the 7 days ending 18^th Dec 2011.

MetService rainfall accumulation map for the 7 day period ending 9am on 18th Dec 2011.

The purple areas received more rain than desired, but other parts of the country received enough rain to be useful for filling up water tanks and replenishing pastures and gardens before the holiday break.

In summary, NZ’s weather in 2011 had its ups and downs, and produced some interesting events.

Everyone at MetService takes this opportunity to wish our blog readers a refreshing break at the end of the year, and we look forward to sharing with you our insights into the interesting weather events of 2012.

Temperature traces on 28 November in degrees Celcius. DNA=Dunedin, OUA=Oamaru, TUA=Timaru, CHA=Christchurch and KIA=Kaikoura. Timestamp is in UTC; 27 0000 is 1pm NZDT.

The weather map for 1pm Monday 28 November 2011 showed a typical trough moving across New Zealand. The last of a series of fronts within this trough was the one responsible for this dramatic drop in temperature.

Weather map for 1pm NZDT Monday 28 November

The reasons for temperatures soaring to between 26 and 28 C ahead of this southerly change are:
•    Northwest winds ahead of the trough warmed by around 5 to 10 degrees Celsius as they descended down the eastern slopes of the Southern Alps
•    Sunny conditions in the relatively clear skies over the Canterbury Plains – on a date less than one month ahead of the longest day.

These warm temperatures combined with falling air pressure to produce a zone of relatively low density. Higher density air in the cooler southerly flow that followed this cold front accelerated into this zone of low density air producing a squally “gust front” with the wind change. This “gust front” built in size and intensity during the afternoon as can be seen from the tweets sent from @metservice during the afternoon

• Southwest change arrived Dunedin Airport around 11:50am. Temp dropped from 22 to 14 C , gusts to 50 kph , and its on its way north. ^BM

• Southerly change got to Oamaru about 1:30 pm, temp. dropped from 22 to 14 C, initial gusts were 54 kph . South Canterbury’s next ^BM

• Southwest change arrives in #Timaru just before School’s out, Temperature drops from 28 C at 2:30 pm to 16 C by 3 pm , Gusts to 70 kph ^BM

• Southerly change reached #Ashburton between 3:30 and 3:45 pm, temp. dropped from 26 to 16 C, gusts 70 kph see http://t.co/YhuAEZ4L ^BM

• Southwest reached #Christchurch at 5 pm in time for evening commute, temps 28 C to 17 C in 20 minutes. with wind gusts 75 kph , ^BM

• Hi #Christchurch be quick and look at wind blown dust of that southerly change on MetService radar at http://t.co/lmw4BcYA past hour ^BM

Click here to follow us on Twitter.

September to November is the season for the strongest of these southerly busters (but they can occur at any time of the year).  Spring brings the strongest westerly winds of the year to South Island and it is also a time of relative cold offshore sea temperatures.  The temperature difference between the heated air over the Canterbury Plains and seas in the Canterbury Bight is what feeds the wind gusts of a buster. The coldest sea temperatures of the year occur in early spring, and they only just start rising in November.   You can find the latest reading from metservice.com by clicking on ‘marine’ and then ‘beach’ and selecting a suitable site.  The one shown below is Jack’s Point near Timaru (timestamp is 10am Wed, 30 Nov 2011).

Jack's Point on the metservice.com Marine & Surf section. Wind, Wave ands Sea conditions are now available on metservice.com

The showers with this buster occurred mainly along the coast and at sea.   In the drier air over the Canterbury Plains the southwest wind change picked up dust and dirt, especially over the Rakaia River, and lifted and blew these as a “dust storm” into Christchurch.  This can clearly be seen on the animation below, taken from the high frequency Christchurch rain radar site at metservice.com.

In addition to the existing Auckland forecast on the Towns & Cities page, we’ve divided the greater Auckland region into five sub-regions – each with its own characteristic  rainfall, temperature and wind patterns:

• North Shore
• Waitakere
• Auckland Central
• Manukau
• Hunua

To provide hourly predictions of air temperature, wind speed and rainfall for these sub-regions, we’re using

• Data from our own localised-for-New-Zealand weather modelling and statistical processing systems (for more about this, see the blog on MetService’s Investment in Forecasting)
• Observations of temperature and wind speed from representative weather stations within each of the sub-regions (see next point), which we’re blending with  the modelled data for the first few hours of the forecast.
• The weather stations we’re using are Whangaparaoa (for North Shore), Whenuapai (for Waitakere), Auckland Airport (for Manukau), and Ardmore (for Hunua). For Auckland City we’ve created a “virtual weather station” near the Newton Interchange; this will do the job for now, but we want to replace it with a real station within Auckland City soon.

The index map at the bottom left of the map area links back to the Auckland Towns & Cities page you’re already familiar with, containing the overall Auckland urban forecast and max/min temperatures for the next 10 days.

This initiative was partly motivated by the great feedback we received about the ‘dust graphs’ of wind speed and rainfall added to the Christchurch pages in February, to alert people to the potential dust nuisance in the areas affected by liquefaction and, more recently, demolition of large buildings.

As always, we’re looking forward to hearing what you think! Tweet @MetService or drop us an email at enquiries@metservice.com

So the song goes, but what’s it actually like way up high in the atmosphere? Could we humans live up there if we wanted to, or had to?

I recall David Attenborough doing a great documentary in the series “The Living Planet” (“The Sky Above” episode, BBC) where he ascended beneath a very large hot-air balloon, complete with oxygen mask and equipment for sampling for life specimens. It was surprising to discover that small insects could be whisked up there and freeze, before descending again and reviving.

In this post, let’s take a closer look at what the atmosphere is like above New Zealand.

The outer limit of our weather: 10 km above sea level

This is the cruising height for large jet aircraft, and the top of Mount Everest almost reaches this height. All clouds at this altitude are frozen (that is, they are made up of ice crystals). Clouds composed of ice crystals have a wispy appearance and are known as cirrus. The tropopause, which marks the top of the troposphere, occurs at about this height. The winds are usually very strong at this level.

Air pressure: 250 hPa, one quarter of what we experience at the Earth’s surface
Temperature: about -55 °C (perhaps on a long-haul flight you’ve noted on an in-flight air show similar outside temperatures)
Air density: 400 grams per cubic metre of air
Amount of water vapour: a tenth of a gram of vapour for every kilogram of air

The middle levels: 5 km above sea level

Most of our rainfall is produced in clouds at around this level, where there are often large regions of rising air currents. The deep rainy clouds are nimbostratus, and other shallower types are altostratus and altocumulus. Rain or hail can fall from cumulonimbus clouds, where the air rises strongly but over a smaller area. Clouds may or may not be frozen – they may be composed of ice crystals or super-cooled water droplets (liquid water at temperatures below freezing).

Smaller passenger aircraft connecting cities within NZ often fly at around this altitude. At this height there’s less oxygen in the air, but people in some parts of the world. e.g. Tibet and the Andes, are still able to live in these conditions.

Air pressure: about 500 hPa, half of what we experience at the Earth’s surface
Temperature: about -25 to -15 °C
Air density: 700 grams per cubic metre of air
Amount of water vapour: 1 gram of vapour per kilogram of air

The lower levels: 3 km above sea level

The middle-level clouds can extend down to this level. Large cumulus can bubble upwards to this level too. Because NZ is mountainous, the clouds are often shaped by the air as it flows over the mountains. Clouds are generally not frozen (that is, they are made up of liquid water).

Mount Cook rises to just above this level.

Air pressure: about 700 hPa
Temperature: variable, but usually between -10 and +5 °C
Air density: 900 grams per cubic metre of air
Amount of water vapour: from 1 to 5 grams of vapour per kilogram of air

The Earth’s surface: close to sea level

Air pressure: typically between 980 and 1030 hPa (sometimes there are extremes outside this)
Temperature: highly variable, usually between 0 and 30 °C
(extreme highs are often due to the Foehn wind)
Air density: 1.2 kilograms per cubic metre of air
Amount of water vapour: highly variable, from 5 to 15 grams of vapour per kilogram of air.

The illustration shows two common types of low altitude clouds. You can see more pictures of these and other cloud types in the MetService cloud poster.

You may be wondering what lies above the tropopause. Above this level you’d enter the stratosphere. To give you an idea, at 15 km above sea level the air pressure is about 100 hPa, temperature interestingly remains fairly steady at about -60 °C, and the water vapour content is negligible.

Within the stratosphere is the ozone layer which, fortunately for us, absorbs most of the harmful ultraviolet light from the sun. By the way, note the similarity in the words “stratosphere” and “stratus”. Both originate from the Latin word for “layer” – the stratosphere is resistant to vertical motion so tends to have a layered structure, and stratus cloud has a somewhat layered appearance.

So far I’ve confined this post to NZ. Towards the tropics the temperature obviously rises, but it’s a little known paradox that the coldest of all tropospheric temperatures are in the tropics at about the altitude of the tropopause there (around -80 °C).

I think it’s interesting to compare the conditions at the surface with which we’re familiar, with those higher up. At what altitude do you think you could still function? Going up, up and away in a beautiful balloon is a wonderful thought, but make sure you go prepared for the conditions!

New Zealanders will have a new, easy-to-use tool that tells them when they need to protect their skin from the sun, with specific reference to where in the country they live. Using extensive research as well as audience and media feedback, the HSC has worked with the MetService and NIWA, in consultation with the Cancer Society, to produce a new UV radiation public communications tool – called the Sun Protection Alert to replace the UV Index.

The Sun Protection Alert will be the new UV tool used in New Zealand from November onwards and conveys simple information that’s specific to each area of the country for that day.

The new Sun Protection Alert graphic as displayed on metservice.com

The new approach to an old problem
Name: It’s called the Sun Protection Alert and tells you what to do when the sun is at its strongest.
Time: The Sun Protection Alert advises you of the actual time when you need to protect yourself from the sun. The time can change in 5-minute increments from one day to the next.
Simple: The Sun Protection Alert conveys simple information that is easy to understand and act on.
Relevant: Sun protection times indicate when the UV Index reaches 3 or above. The times and ultraviolet radiation levels will differ up and down the country as they are based mainly on latitude
Sun safety messages: Sun safety messages have been incorporated into the tool e.g. seek shade or reapply sunscreen. These messages will change regularly to maintain interest and in some cases will reflect the forecast weather e.g. if it’s a cool or cloudy day the sun safety message will be “Even on cloudy days” or “even on cooler days”.

Some things NZers ought to know…
The NZ lifestyle, the envy of many other countries, has given us the highest melanoma rates in the world – even higher than our mates across the ditch. In recent years, our melanoma death rates have been on a par with the NZ road toll.

Sunburn is a big concern because it is linked to melanoma, the most deadly form of skin cancer. Skin cancer is largely preventable by taking simple measures to protect ourselves from the sun.

Sun Protection Advice to use from September to April

For more information on Sun Protection go to http://www.sunsmart.org.nz

However, the introduction of night-time rugby gave fog a chance to get on the field for some game time. Especially in the United Kingdom, where evening games sometimes have to be cancelled when fog turns up.

In New Zealand, fog showed us what it could do when it rolled into Christchurch an hour before the kickoff of the Super 14 final between the Hurricanes and the Crusaders on 27 May 2006.

As a television spectacle the event was seriously compromised. The cameras down at ground level sometimes got a reasonable view but those high up were mostly obscured. Nicknamed “gorillas in the mist” the contest was won 19-12 by the Crusaders.

The Hurricanes, who do not have much fog of their own as it is usually too windy in Wellington, also got to suck up some Hamilton fog at the end of the Super 14 semi-final against the Chiefs in May 2009, which they also lost. Situated on a river, with swamps nearby, Hamilton is the most fog prone major city in New Zealand. After Hamilton, Christchurch is the next foggiest because it is close to the sea, so the air is often very humid.

Fog formation is helped when there are a lot of condensation nuclei in the air. Many of these come from tiny plants in the sea known as phytoplankton. When tiny animals, known as zooplankton, nibble phytoplankton the chemical dimethylsulfoniopropionate is released into the water. There it changes to dimethyl sulphide (DMS) which gets into the atmosphere when breaking waves throw small water droplets into the air, where they evaporate.

In the air, DMS changes to four different chemicals, three of which act as cloud condensation nuclei. DMS also helps make the characteristic smell of the air at the beach.

Fog: Photo copyright Pernell Hartly

Smoke particles can also act as condensation nuclei. Indeed, the celebratory fireworks after the Crusaders victory resulted in a temporary thickening of the fog in Christchurch. During the Napoleonic wars so much smoke was produced by the massed cannon-fire that fog would sometimes envelope the battle field giving rise to the term “the fog of battle”.

Before the clean air laws were enacted, smoke from coal fires and industry used to cause the famous pea-soup fog in London. In December 1952, a notorious fog lasting for days was blamed for 4000 fatalities, mostly from bronchitis and pneumonia. Breathing this particular fog actually caused pain as a portion of the 1000 tons of dirt particles suspended in the London air was sulphur dioxide which combined with water droplets and oxygen to form sulphuric acid.

Some playing-fields in Scotland have underground heating to prevent the soil freezing when frost strikes but there is not much you can do to prevent fog. During the Second World War a lot of effort went into discovering a way of clearing fog from airfields.

The only method that worked, and then only temporarily, was burning petrol sprayed from long pipes either side of the runway so that planes landed between walls of flame. But at nearly 30,000 litres of petrol per landing, it was prohibitively expensive.

Fog is just cloud resting on the ground, and clouds are often found resting on the mountains. So even before night rugby came to New Zealand there was one place where fog frequently turned up before game time and that was the coal mining settlement of Denniston, situated on a plateau 600 metres above sea-level on the South Island’s West Coast.

Although good for fog, Denniston was not a particularly good place for soil and grass. The rugby ground had been bulldozed out of rock and was covered in new load of sand brought up from the beach at the beginning of each season.

Rugby in the fog had certain disadvantages. A ball kicked high in the air, for example, would disappear and players have to wait around for the telltale thump to discover where it came back down.

There was, however, some home advantage. Visiting teams found playing in the persistent fog somewhat confusing, and if the game was going badly for the home team an extra player could be slipped on in the backline to stiffen the defence.

Nor was this astute use of local conditions restricted to the rugby team. An excellent soccer team from Millerton was once unable to make headway against Denniston until the fog lifted, revealing that Denniston had four extra players on the pitch.

Tragically, a 12 year old boy drowned on Auckland’s North Shore when he slipped into a flooded stream and was washed into a culvert. Surface flooding occurred in parts of Auckland. A million dollars worth of stock was destroyed when water entered the basement of a Nestlé’s warehouse and an old lake reformed in Remuera which proved suitable for dingy sailors while it lasted.

A tornado struck near Huntly, in the Waikato, knocking over a line of power poles and destroying a hay barn, parts of which flew over the heads of children playing nearby. A service station at Waerenga was ripped apart and a number of houses damaged. Fallen trees cut roads and brought down power and phone lines in many other parts of the country.

Slips and floodwaters cut roads in the Coromandel and some small boats were washed away at Te Kaha when large waves ran up beyond the high tide mark.

Cook Strait ferry sailings were cancelled due to the high winds around Wellington. Waves washed away shingle undercutting the railway line to the Hutt Valley and roads were closed at the northern end of the harbour by seas washing driftwood and seaweed over them.

The railway line between New Plymouth and Wanganui was cut by a washout while a slip closed the main trunk line south of Kaikoura. Slips also blocked the roads through the Buller Gorge and the Kawerau Gorge. Snow fell over inland Canterbury with 18cm accumulating on the road at Porter’s Pass and 46cm at Burke’s Pass.

At Auckland’s Eden Park, around 75mm of rain had fallen by kickoff. The ground had sold out but 10,000 spectators stayed away. Some spectators had to walk through ankle deep water to get to their seats. Consideration was given to postponing the game but conditions were not expected to be a lot better the next day and the Scots were booked to fly home on the Monday.

So the game went ahead although the referee blew up the rucks very quickly to avoid anyone drowning under a crush of bodies. The All Blacks turned on some great wet weather rugby winning 24-0. The first try was the result of a running move but the other three came from the classic tactic of kick and chase exploiting mistakes in the defence’s handling of the wet ball.

The ground held up surprisingly well and did not turn into a quagmire. Although the ball was slippery, it did not become so heavy as to prevent Joe Karam converting all of the All Blacks tries.

In the early days of rugby, wet balls often became hard to kick over the cross-bar. In the famous mud-battle at Athletic Park between the All Blacks and the Anglo-Welsh in 1908 the game finished a 3-3 draw when the visitor’s goal-kicker failed to convert a try between the posts as he barely raised the sodden ball out of the mud.

Wet weather used to be regarded as the great equaliser, giving a lesser team a chance against a stronger team. However, the introduction of synthetic balls in the 1980s restored the advantage. As well as being waterproof these new balls had thousands of dimples on their surface to improve the players grip when the ball was wet.

A classic example of the standard of play now possible on a wet ground was seen in the first tri-nations test played between the All Blacks and the Wallabies at Athletic Park in a wet southerly on 6 July 1996. The All Blacks ran in 6 tries to none winning 43-6 and were denied a chance at 50 points when the referee ended the game 3 minutes early when they were hot on attack.

Rugby’s ability to live with the rain has also improved enormously with modern turf engineering which allows the top test venues to drain water away at a rate undreamt of by previous generations. Nevertheless, extreme rainfalls from a thunderstorm can exceed 100mm in an hour so if a thunderstorm parked itself in just the right place at just the wrong time it could still cause trouble. Except, of course, in Dunedin where they have gone for the ultimate solution and put a roof over the ground.

Part of the crowd shelter from one of the snow showers that fell before the match. Photo courtesy of NZ Observer

The snow eased to sleet as the test teams came onto the field then cleared soon after. However, the ground by this time was quite heavy and slippery making expansive back play difficult. The score was 3-3 going into the last minute. The All Blacks were hot on attack, when Great Britain’s Ivor Jones intercepted a pass and took off downfield. As he was tackled by George Nepia he passed to his winger who scored a spectacular try in the corner bringing the crowd to its feet and secured a 6-3 win for Great Britain.

The snow affected eastern areas of the South Island and was regarded as the heaviest in more than a decade. Southland and south Otago were worst hit with many roads closed, delaying spectators trying to return home after the test. Gore had 15 cm while some places as much as 23 cm. When the train carrying the Great Britain rugby team to Invercargill on the Sunday stopped at Gore, the players started a snowball fight amongst themselves before uniting and bombarding the crowd that had turned out to greet them.

The Great Britain team must have become well acclimatised to snow by the time of their game against Ranfurly Shield holders Southland on the Wednesday. There was a bitterly cold wind and further snow fell but Great Britain won 9-3.

The Southland rugby team were no strangers to snow and famously defeated Manawatu in a Shield defence in 1939 when the ground was covered in 10 cm of snow (see my previous blog).

A previous Great Britain team also had a close encounter with snow when it played Canterbury-South Canterbury-West Coast combined at Lancaster Park on 6 August 1904 in the opening game of its tour. Although the weather for the game was fine, snow had fallen earlier in the week and had to be cleared from the playing field.

Fortunately for the home team the snow had not been completely cleared from the in-goal area. Their only try was scored when a defender tried to kick the ball dead only for it to hit the snow and stop. Future All Black Bob Deans dived on it to score. However, the conversion failed and Great Britain won 5-3.

A year later, Deans scored the controversial try that was disallowed when the 1905 All Blacks suffered their only defeat, losing 0-3 to Wales.

While snow occasionally comes to the house of rugby, rugby sometimes goes to the house of snow. In Antarctica there is an annual rugby match between the scientists at Scott Base and those at McMurdo.  Played on a groomed snow surface on top of two metre thick sea ice the Ross Island Cup has been won by New Zealand for 27 years straight. The New Zealand supporters distribute “Rugby 101” leaflets to the US supporters to help them understand the rules.

Closer to home is the Glacier Country Cup disputed annually by seven aside teams the Cunning Foxes and the Franz Josef Eagles on a pitch 2340 metres above sea level. The players, crowd, goalposts, touch-lines and try-lines are all carried up by helicopters.

As winners of the latest match, The Cunning Foxes, hosted a Spanish women’s team, Unio Esportiva Santboiana from near Barcelona. The visitors carried the day with a running game the locals could not match. However, the Spanish women did not arrive in New Zealand entirely ignorant of our style of rugby as the sporting director of Unio Esportiva Santboiana is the former All Black hooker Bruce Hemera.