We all look out the window to see what the weather is up to. In a similar way, MetService meteorologists are always checking to make sure what they have predicted is actually happening.

The forecasters may not be examining the skies themselves every few minutes, but they are monitoring a network of instruments across Aotearoa New Zealand, including those sited on our sub-tropical and sub-Antarctic islands, which are constantly feeding back crucial information to the National Forecasting Centre.

Wind direction, wind speed, air temperature, humidity, rainfall, air pressure, cloud, and visibility, etc. – all these observations and data help build a picture of what is going on. But they can’t just be measured from anywhere.

For example, temperature readings taken above or next to a concrete or asphalt surface in a confined space will read several degrees higher than those taken in a grassy location which is better ventilated. While those exaggerated temperatures may be a true reflection of that super-heated spot, they do not represent those of the entire neighbourhood.

Accurate and reliable weather observations that are consistent with the standards of the World Meteorological Organization from around the motu are the bedrock on which good forecasts are based. MetService has a dedicated team who ensure that all our automatic weather stations operate to world standards, and that the observations from our observing network are quality controlled and delivered reliably to the forecasters. 

Precise observations do more than tell meteorologists if the weather is unfolding as they had forecast in a certain situation. They are essential as an input to start the computer models which use complex mathematical equations to predict how weather systems will move, form and decay. In other words, the observations are critical to describe the weather now so that models can accurately step forward in time providing our forecasts and warnings. Most importantly the data keeps the computer weather models ‘true’ and in line with what is actually happening with the weather.

Thinking in 3D

We know the Earth’s atmosphere is not two-dimensional, which means observations of temperature, wind and air pressure are not just needed from the surface of the Earth but also right up through the lowest slice of the atmosphere, known as the troposphere, which contains nearly all of our weather.

At Aotearoa New Zealand’s latitude, the troposphere reaches an altitude of about 12km above the surface. Within this layer, large weather balloons carrying radiosonde equipment take regular measurements during their ascent. MetService operates four upper-air sounding stations, at Invercargill, Paraparaumu, and Auckland and one in the Kermadec Islands 1000km northeast of Auckland where these balloons are released once or twice a day.

Pilots flying aircraft at high altitude also pass on observations of wind, temperature, and turbulence to assist meteorologists with their predictions.

Even higher up, weather satellites provide important measurements of moisture and temperature in the atmosphere. MetService meteorologists have access to data from the Japanese geostationary satellite Himawari-8 which effectively provides a photo from space every 10 minutes, so they can see how weather systems develop and move.

On the ground and at sea

MetService has an extensive weather radar network of 10 radars, from Kerikeri in the north to Invercargill in the south. Radars are extremely useful tools for monitoring the movement and intensity of rain, hail, and snow, and are particularly valuable when lives are at risk from severe thunderstorms or for immediate information of rainfall rates in an area with no surface observation. Radars are also vital when tracking a severe thunderstorm cell when the heavy downpours from it could cause flooding.

To complement radar information, forecasters use observations from Transpower’s National Lightning Detection Network to pinpoint where lightning from the severe thunderstorms reaches the ground.

It’s not only the land and the sky which MetService has covered. Ships which travel around our coasts and to and from Aotearoa send through useful observations of the weather conditions out at sea. And a network of drifting buoys in the Tasman Sea provides vital data on developing systems before they reach our shores.

Our observations

Until a few decades ago, surface observations were made manually by people around the country, on farms, at airports, in lighthouses and the like. Some of MetService’s stations have been in operation for more than 100 years – the longer a consistent record the better from a climatological perspective.

Now, most observations come from more than 220 automatic weather stations (AWS) in all corners of Aotearoa New Zealand, which provide data every 60 seconds and are extremely efficient, operating more than 99% of the time. In addition to being used by weather forecasters, data from these stations also feed into the National Climate Database.

As well as operating its own AWS network MetService also partners with other organisations that have networks of stations.  MetService also has more than 50 AWS units monitoring road conditions for Waka Kotahi on our state highways and provides Airways Corporation with airport weather conditions at airport control towers across the country.

As well as the observations keeping meteorologists up to date with what they are dealing with, they assess how well the global computer models are performing in the Aotearoa New Zealand region.

We need you!

There’s one other source of weather observations we haven’t covered yet – you! Public feedback and photos via social media and the WOW observations, where members of the public with weather stations can add the information to the WOW map on the MetService website, are extremely helpful.

MetService also calls for snow observers each year and asks for photos and videos from the public to help verify the strength of tornadoes and to share the impacts that severe weather has on our nation.

Keep looking out your window and let MetService know what is happening in your own backyard.

Accurate weather forecasting requires three key ingredients – trustworthy observations, reliable computer models and experienced meteorologists.

Before the computer age and the satellite era, forecasters were reliant on weather observations from land stations, ships, and balloon soundings from which they could predict the movement of high and low-pressure systems and fronts.

Computer modelling has completely changed the forecasting game during the past three or four decades. Most of the MetService forecasts you read on the website or see elsewhere are the result of highly trained meteorologists studying a range of different models and deciding which ones, or which combination of them, are picking the most likely future weather outcomes.

These computer models have an endless appetite for crunching mind-blowing amounts of data.

(Above: One of the many equations used to help model the atmosphere)

How do they do it?

Observations are taken from as many sources as possible, right across the planet. All these figures are fed into the models, which use complex mathematical equations reflecting the physics of the atmosphere to produce simulations of its possible future evolution.

Each model has its own personality, its own strengths, and weaknesses in covering our part of the world. This is where the experience of the forecasters and their geographical knowledge comes in, determining which weather situation from which model is the most likely to come true and how it will be influenced by local conditions and features such as Cook Strait and the Southern Alps.

At MetService, we use several of the most-respected global weather models to aid our forecasting.

Probably the most consistent is the European Centre for Medium-Range Weather Forecasts (ECMWF) model, generally recognised as the best-performing of the global models. As well, we consider runs of the UK Met Office model, which is very good when it comes to predicting the development and movement of mid-latitude weather systems.

The GFS model, generated by the National Centers for Environmental Prediction (NCEP) in the United States, is also consulted, although this is perhaps not as steady and reliable in this part of the Pacific as the ECMWF model. On top of that, we get modelling from meteorological services in Canada and Japan, and from the Bureau of Meteorology in Australia.

We also run our own in-house models to simulate the turmoil of the atmosphere and can operate these at much higher resolutions to reflect the idiosyncrasies of Aotearoa New Zealand’s landscape. We can run these with data points just 200 metres apart, which takes into account the different terrain of an area and whether it is forested or urban, which can make a significant difference to temperature and winds across a short distance.

Are they any good though?

The models themselves are constantly being tweaked by their operators to reflect the latest research findings and to keep up with new technology. The users of the models are also changing what they require from them.

In recent months there has been some discussion about whether climate change may be affecting the running of the models and especially their outcomes. Is it possible that an increasing number of more extreme events are pushing the models beyond their comfort zones into unknown territory?

The jury is still out on this. One thing that is for certain is that the basic physics of the atmosphere, on which the models are constructed, has not changed.

What has changed, though, is how often the conditions that lead to extreme weather are now occurring in our warming world. So, the models which are really good at picking bog-standard weather are being asked to deal with potentially severe weather situations more often.

What about Artificial Intelligence?

Like in any other industry, it is hard to predict just how machine-learning and artificial intelligence will affect weather forecasting.

AI-informed weather models have recently been found comparable to, or have even out-performed, physics-based models. But these AI-informed weather models aren’t coming in cold – they are first ‘trained’ on the physical models and then add a layer of prediction on top.

Then of course there remains the task of interpreting what the output of such a system might mean for the activities or safety of end-users.

At MetService we continue to work with the operators of modelling systems to ensure we get the best from them, while continuing to develop our in-house models. We have a keen eye on developments in the AI field and the opportunities it will bring. At the same time, we continually improve our forecasting expertise, which includes an understanding of the strengths and weaknesses of any modelling system.

By doing so, we will be in the best position to identify the risks future weather may bring, and how these are best communicated to those concerned.

Some may think it’s one of those jobs which anyone might turn their hand to, but the difficulties of weather forecasting are hugely underrated.

After all, there aren’t many jobs where you’re expected to predict the future. Economists are also required to make forecasts, but at least they have some control over the system they are foretelling. When it comes to weather, meteorologists have no such influence.

The best weather forecasting is a mixture of science, geography, and experience.

The science of meteorology is extremely complex, involving difficult atmospheric physics and chemistry, and convoluted mathematical equations. As well as having a higher degree in physics or maths, a meteorologist must know a great deal about the geography of Aotearoa New Zealand and how the prevailing westerly winds at our latitude push over and around mountains and through narrow sea straits, influencing our weather.

There is no substitute for experience in forecasting and for having seen how a certain weather pattern has affected the country in the past. This base of knowledge and skills builds insight that comes naturally after years in the job and cannot easily be taught.

(Above: Metservice meteorologists working at the National Forecasting Centre)

Simplifying the complicated

MetService forecasters work every hour of every day of the year to interpret the complexities of the atmosphere above Aotearoa New Zealand and communicate this clearly and simply to different audiences.

Our highly trained staff work tirelessly to ensure New Zealanders are kept safe and that communities can be as resilient as possible in the face of severe weather. People need to be able to trust the weather information they receive to enable them to make the best decisions they can.

One of the biggest tasks for meteorologists these days is analysing which of the suite of computer models they receive from around the world is producing the most likely weather map on which to base their forecasts.

Technology may be crucial to our operation but the forecasts themselves are still the result of a great deal of human effort and acumen. Our meteorologists interpret the models and all the observations made around the country, and apply their knowledge of a region’s topography, aspect and broader physical characteristics before settling on a forecast.

Knowing when to trust the models

There are curve-ball occasions when the models appear to go rogue, predicting tropical cyclones or icy southerlies with snow right across the motu / land. This is when meteorologists have to be at the top of their game – knowledgeable and confident enough to ignore such over-the-top predictions. After all, the models are just a guide from which forecasts are made.

The MetService forecasting team meets for about half an hour every morning online, just before 10am, to discuss the weather situation and which of the global models seem to be going down the right track. Another briefing is held about 10.30pm for the night-shift forecasters.

The weather briefings were known as “nodding”, a tradition which started more than 60 years ago. In those days, the chief forecaster’s views were unchallengeable, and everyone else would just “nod” in agreement.

These days, the meetings in the National Forecasting Centre in Wellington are called “map discussion” and are much more democratic. One of the senior meteorologists will choose which model is telling the most likely story or, if there is no clear guidance, will consider which mix of models appear to work. This is where observations, backed up by radar and satellite imagery, are vital.

Discussions follow and, from those, teams of meteorologists then write forecasts for different customers.

Tailoring our forecasts

The aviation team provides forecasts for airlines, general pilots and airports around New Zealand, and also acts as the Volcanic Ash Advisory Centre, should a volcano erupt.

Marine forecasters warn of high winds and bad weather in our inshore areas and across a huge area of oceans around the country.

Specialised severe weather meteorologists focus on heavy rain and snow, high winds, and thunderstorms which could cause damage and threaten life and livelihoods. During the tropical cyclone season (November to March), they also monitor the development of such storms. These forecasters work closely with emergency management and local and regional council staff when the worst weather is on the way.

Meteorologists working on the public and weather communications sections make the day-to-day predictions and generate the forecasts and weather graphics most of us see on the MetService website, or on the app on our phone, or on the television and elsewhere in the media.

To be a MetService meteorologist, you need a degree in either maths or physics and then to have completed a post-graduate meteorology programme which aligns with the World Meteorological Organisation’s Basic Instruction Package for Meteorologists. This ensures all meteorologists around the globe are adequately skilled.

In Aotearoa New Zealand, the meteorology programme is run in conjunction with Te Herenga Waka Victoria University as a Master of Meteorology degree.

Next time there’s rain threatening, a storm is on the way, the wind is picking up, or it’s just a lovely sunny day, you can have confidence that highly trained MetService meteorologists are providing the best possible forecasts to keep you safe and in the picture.