Why the weather's always better at your place: How we record temperature

Monday, 29 January 2018

The weather station of Albert Chan, 70, of Henderson, west Auckland. The slats visible with gaps between them are called a Stevenson screen.

If you think the weather's hotter at your place, well, there's a good chance you're right.

But for the record's sake, that doesn't matter unless you have an official, verified weather station that meets World Meteorological Organisation (WMO) standards.

Kahu Hunter-Brown of Nelson jumps in to Lake Rotoiti at St Arnaud during the hot weather.

What's the temperature doing at your place? Send your recordings, images and location to newstips@stuff.co.nz.

MetService meteorologist Brian Mercer says the forecasting agency is 'frequently' bombarded by people claiming the temperature is hotter - or colder - than the official reading where they are.

Correct positioning for a weather station at your home.

'People always want to win. They want their town, specifically, to win. And quite often, some of our stations tend to be on the coast, because that's where our airports are, and you will get sea breezes which cool things down,' Mercer said.

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'So you get legitimate cases where you would assume the temperatures would be a little bit warmer inland. But unless we have a verified and checked thermometer we can't actually take that as a record.

'Basically, with our weather stations there are specific standards which the WMO set for where you can place a weather station and how exactly you can take the temperature.'

Stations need to be:

- Out of direct sunlight

- Have have good clearance around them.

- Be 1.4 metres above the ground

- Be inside what's called a Stevenson Screen, so they are protected from the sunlight but allow good flow of air around the actual thermometer to give it a correct temperature that isn't going to be influenced.

If you have a weather station at home that's giving you a hotter temperature than the official one, there are a range of factors that could be causing that.

Leaving a thermometer directly in the sun, on or near a black roof or near anything made of cement or away from the ocean can play a part.

Thermometers in cars record very high temperatures that aren't the 'actual' temperature.

'Where you situate your thermometer can give you quite different temperatures so we (MetService) have to abide by these regulations,' Mercer said.

A lot of weather station in New Zealand are near airports.

'[That's] because they are actually quite expensive things to run and it is critical for airlines to have accurate and up-to-date data. So that's where you will have a lot of good reports from the airports.'

MetService has a large network of automated weather stations and finding suitable locations can be hard to do.

They need to be secure from vandalism, have good unobstructed exposure for wind, rain and temperature and access to power and communications needs to be reliable.

MetServiceAWS Network by stuffnewsroom on Scribd

MetService aren't the only ones with a network of stations.

'There are quite a few on the mountains, the New Zealand Transport Agency (NZTA) have their own series of stations which we can access the data from which are along the road network,' Mercer said.

The NZTA uses those for situations like identifying if it's freezing on the Desert Road.

Climate agency Niwa also had its own observation system and so did many councils around the country, all recording from slightly different locations.

WHAT SORT OF GEAR DOES METSERVICE USE?

MetService meteorologist Lisa Murray said its stations were 'not the bog standard'.

'Depending on where our automatic stations are set-up - they they are near an airport, they need to be the highest calibre type ones because obviously it's a life and death situation… Aviation standard ones can run from $10,000 to $100,000… so this is pretty flash equipment.'

Those stations had recording devices like ceilometers for measuring cloud height and anemometers for wind speed.

'We use digital thermometers to WMO standards. So they have really specific standards for how they measure it down to the number of decimal places, the accuracy involved in it…

'We have a team of engineers that work at Paraparaumu at a workshop out there and their job is calibrating, maintaining the network throughout the country.'

MISSING THE MAX

Mercer said it was absolutely possible the highest - and lowest - temperatures experienced had been missed by MetService weather stations.

In any given city, temperatures could vary. Geographical features, shelter from wind and proximity to the coast were all factors which could influence temperature differences.

'If you imagine the topography of New Zealand there's lots of hills and valleys and each one is going to have a different temperature profile. We try to cover as much of the country as possible but there are certain commercial aspects - they (weather stations) are quite expensive to maintain.

'It would be utterly impossible to covered the entire country with thermometers and there are certain places that will be warmer and colder than the mean.'

If you're convinced the weather is always hotter or colder at your place, you can contribute your own weather station readings to MetService.

But Mercer said to be wary of any recordings that had distinct highs or lows.