We've probably all thought it at some point, and especially this summer.

The highs and lows reported on the TV news just didn't gel with what you felt outside that day.

There's a good chance you were right.

While weather forecasting is indeed a science, that doesn't mean the MetService figures reported each night in your city were the same at your house - or even your part of town.


If you're checking TVNZ's website, you'll find today's high and low in Auckland is 24C and 19C, yet it's 25C and 20C on nzherald.co.nz.

Take a look at the official MetService website and you'll see Auckland Central is forecast to hit a high of 24C - but it's going to be slightly cooler at North Shore (23C) and slightly hotter at Waitakere (25C).

"Each media outlet has their own approach, depending on how focused they are on urban versus regional areas, observations versus forecasts, what timeframe constitutes a day," MetService forecaster Lisa Murray said.

That included choosing which sites they focused on, and what they did when an "outlier" site recorded the highest value.

In other cases, it came down to timing.

"The daily maximum temperatures on TV are the highest temperatures so far that day, up to the time we send the information to the media outlets," Murray said.

"There may be occasions when the highest temperature occurs later in the evening, so that would not be captured."

And as for how those temperatures were actually captured, most figures for most towns and cities - including Auckland, Wellington and Christchurch - were recorded at airports.

This was to offer the most accurate current conditions for aviation, but also meant sea breezes could make for cooler temperatures that might be otherwise slightly higher in the middle of the city.

Regardless, our diverse landscape and the simple fact we're surrounded by ocean meant there would always be variations in temperature on any given day or night.

"It is very possible that there are other places in a city or region who would experience higher or lower temperature," Murray said.

"This is can be due to topography, being close to the sea, direction of slope and other influencers like the built or natural micro-environment."

Or it could just reflect the set-up of your home thermometer, which would record higher temperatures if fitted to the side of a brick house in direct sunlight, or set too close to the ground.

Ideally, thermometers needed to be about 1.3m above ground; protected from direct sunlight, rain and snow; and placed in a well exposed position, preferably four times its height away from obstructions like trees and buildings.

In most cases, where people did notice variations in temperature compared to their home thermometer, they could adjust the readings compared to what they see on metservice.com.

All temperatures measured by MetService were recorded on highly sensitive instruments in ideal locations, out of direct sunlight and away from heat sources, housed in Stephenson's screens.

But good recording spots for official stations were hard to find.

Along with the other requirements, sites had to be secure from vandalism, with reliable access to power and communication, and few obstructions - something most urban and suburban areas couldn't offer.

Large parks and sports fields tended to be the best prospects - the weather station at Lumsden in Southland was located on the local high school grounds.

Finally, all recordings were made in line with international best practice, Murray said.

"Our observation network is set up in occurrence to the World Meteorological Organisation recommendations, where standard enclosures and a standard exposure are used, so temperatures are comparable from place to place and from day to day," she said.

"Basically put: so, you can compare apples to apples."