MetService: Challenges in forecasting severe weather

Flood waters cover farm land and Parewanui Road at Scott's Ferry, near Bulls. Photo / Mark Mitchell

The severe weather in various parts of the country over the last week or so has presented a significant challenge to some communities - and to staff at MetService as well.

Getting the message out about severe weather, particularly when it involves rapid changes, requires excellent communication with the New Zealand public and many organisations managing weather-related risks. The message needs to be relevant and clear - not always an easy task, given that users of weather information have such diverse needs.

Last Thursday saw the beginning of a memorable outbreak of west to southwest winds over the country. Indeed, this event still has some days to run.

In the days leading up to this event, well before any weather watches or warnings were issued, while monitoring the upcoming southwest outbreak MetService's Severe Weather team recognised that severe weather was likely in some areas. By the afternoon of Sunday 12 September there was sufficient concern for MetService to mention the southwest outbreak in the Severe Weather Outlook, which is issued daily to media, the public, regional councils, outdoor leisure companies, etc.

Over the next few days, as the picture became clearer, various outlooks and forecasts issued by MetService contained more detail about what to expect.

The projected severity of the event prompted MetService to issue a media release on the afternoon of Wednesday September 15, several days before anything much had actually happened.

MetService advised that "the westerlies are likely to be strong or gale force in many places ... possibly reaching severe gale around central New Zealand late in the week," and that "a gradual change to bitterly cold conditions is likely to spread onto southern New Zealand from late Friday and this may bring appreciable amounts of snow to low levels."

This sequence of events reflects a typical approach that MetService takes to achieve the right level of public attention in the lead-up to a major weather event. Severe Weather Outlooks and press releases act as a "heads-up" that significant weather is on the way. As the event draws closer, Severe Weather Warnings are issued, targeted at specific regions, to ensure that people in affected areas get more detailed advice about what to expect.

The timing of these steps, and the language used in the various bulletins, are chosen carefully to ensure that the message is pitched appropriately for the level of severity of the weather, and is delivered with an appropriate lead time.

If the message is under-stated, or arrives too late, people may get caught out; if it's over-stated, or comes too early, people may not listen the next time. In some ways, the challenge of getting the communication right is even more difficult than getting the meteorology right.

During this particular event, shortly after the MetService press release on Wednesday, this communication process was thrown off kilter by a media article about "the largest storm on the planet". The article was based in part on the MetService press release but included information from other sources as well as a measure of journalistic licence.

Within a matter of hours, MetService was fielding calls from people concerned about the "massive storm heading for New Zealand" and asking for clarification on various statements that MetService had apparently made. It was clear early on that people were confused about the source of the information they were receiving, and had been misled into thinking that the whole country was in for serious weather.

The article "went viral" overnight on Wednesday September 15 and by the following morning had generated an unusually high level of concern in the community and interest from the media, both local and international. From Thursday 16 September to today,

MetService has fielded a huge number of enquiries - primarily from media organisations, but also from worried farmers and business people, and frightened members of the public. Organisations responsible for public safety, such as the New Zealand Transport Agency, have also contacted MetService concerned about the confusing information in the media and seeking clarification.

Over the last few days there has indeed been some very severe weather in several parts of the country, as had been predicted in MetService's forecasts and warnings. Unfortunately, MetService's ability to get weather information to those who really needed to know was significantly hampered by media articles over-stating the area affected by the storm.

The effects of this event on those communities that bore the brunt of the severe weather were and are substantial, with widespread flooding, slips and damage to property in some areas, stock losses and disruption to transport.

However, it is important to remember that many parts of the country have experienced benign weather at the same time, leaving many people wondering what all the fuss was about. The danger this raises is that some of those may simply ignore the next Severe Weather Warning they receive.

To date, this cold, wet, windy, and snowy outbreak has progressed pretty much as MetService's Severe Weather Team thought it would.

As well as issuing forecasts and warnings for various areas and monitoring the weather, the MetService team has stayed in close touch with hydrologists and emergency managers at territorial authorities and the Ministry of Civil Defence & Emergency Management.

At the same time, it has dealt with a large number of media interviews and public queries to try and clarify the situation as much as possible.

Like many others, the team at MetService will be relieved when recent events finally draw to a close and spring resumes its progress towards summer.

- Article provided by MetService