Do you believe the weatherman's temperature readings?

During a recent bitterly cold snap in Auckland, I was astounded to head to the Metservice website to be told the current temp in Auckland was sitting at 13 degrees C ... it felt distinctly more like 5 or 6!

Peeved, I shot off an email to them asking for an explanation of their readings, and got this response in reply:

Hi Gayle and thanks for your enquiry.

The temperature for Auckland on the main webpage is taken at the airport. If you head into the “3 hourly temperatures” tab around the middle of the main webpage, you get a list of the locations around New Zealand with the latest 3 hourly measurements. We also have stations taking measurements at Whangaparoa and Whenuapai for Auckland as well.

Air temperatures are measured at a height of approximately 1.3m above a flat surface which is covered with short grass. The thermometers are housed in a white painted wooden louvered shelter known as a Stevenson Screen. The use of a standard screen allows temperatures to be compared accurately with those measured in earlier years and at different places. The screen is designed to allow the temperature probe to reach equilibrium with the air temperature inside – shielding against rain and warming/cooling by radiation (that is out of direct sunlight) and allows free air flow. This is to give a more accurate reading of the “ambient” or “drybulb” temperature of the atmosphere at that particular location – the temperature measured by a thermometer exposed to the airstream but shielded from radiation and moisture. Indeed, it can be warmer or colder than what you feel depending on the sun’s rays or wind chill but it is the accepted form of temperature measurement by National Weather Services across the globe. It should also be noted than WMO guidelines force consideration that the weather station be placed away from artificial heat sources such as parking lots and buildings. A parking lot, for example poses a threat to temperature interference, not just because of the heat generated from the cars, but also from the black bitumen which is used to cover car parking lots attracting sunlight, thereby increasing the ambient temperature.

You are indeed correct though, it can sometimes feels an awful lot colder/hotter than the temperature recorded depending on factors such a wind chill and direct sunlight. A detailed description of the factors which influence how temperature “feels” is available in the blog area of our website - Bob McDavitt’s “Feels like” post dating from the 13th of January 2010.

I trust that this answers your query.

Well, it answered my query, but I am still rather dubious - the day in question, there was very little wind. Right, am off to read Bob's blog post to see if that helps!

www.metservice.co.nz