Why does it feel so cold? A guide to ‘feels like’ temperatures

24 02 2013

With bitterly cold conditions across parts of the UK just now, have you been asking yourself why it can feel so much colder in the wind?

The temperatures that you normally see on our website represent the temperature of the air, but this takes no account of how we actually experience the temperature. It is our ‘feels like’ temperature that gives you a better idea about how the weather will actually feel when you step outdoors.

Our ‘feels like’ temperature takes into account wind speeds and humidity to assess how the human body actually feels temperature.  For example in winter a strong wind can feel much colder than the measured temperature would indicate. The impacts of the temperature and wind combined can be much greater  than each on their own and the feels like temperature allows users to make a better assessment of conditions outdoors.

But how do you actually calculate the ‘feels like’ temperature?

We calculate a ‘feels like temperature by taking into account the expected air temperature, relative humidity and the strength of the wind at around 5 feet (the typical height of an human face) combined with our understanding of how heat is lost from the human body during cold and windy days.

On windy days the speed of moisture evaporation from your skin increases and serves to move heat away from your body making it feel colder than it actually is. The exception to this rule, however, is when higher temperatures are concerned. At higher temperatures, wind chill is considered far less significant. Instead humidity plays a greater role. When a human being perspires, the water in his or her sweat evaporates. This results in the cooling of the body as heat is carried away from it. When humidity is high, the rate of evaporation and cooling is reduced, resulting in it feeling hotter than it actually is.

Using these facts we use a formula to adjust the air temperature based on our understanding of wind chill at lower temperatures, heat index at higher temperatures and a combination of the two in between.

You can get ‘feels like’ temperatures on our five day forecast and on our Android, iPhone and Windows Phone apps.


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4 responses

24 02 2013
Goaty's News

Reblogged this on Goaty's News.

25 02 2013
Neil King

What is the formula used to calculate the “Feels Like” temperature?

25 02 2013
Dave Britton

The wind chill (WC) is dependent on the ambient dry bulb temperature (T) and the wind speed (V). Here is the formula: WC = 35.74 + 0.6215*T – 35.75*(V^(0.16)) + 0.4275*T*(V^(0.16))
The Heat Index (HI) is dependent on the ambient dry bulb temperature (T) and the relative humidity (R). Here is the formula: HI = -42.379 + 2.04901523*T + 10.14333127*R – 0.22475541*T*R – (6.83783*10^-3)*(T^2) – (5.481717*10^-2)*(R^2) + (1.22874*10^-3)*(T^2)*R + (8.5282*10^-4)*T*(R^2) – (1.99*10^-6)*(T^2)*(R^2)

In these instances T is in deg F, V is in mph, R is a %age

26 02 2013
Neil King

Dave,

Thanks for the reply giving the Wind Chill and Heat Index formula. I had the impression that there was a specific formula for working out the “Feels Like” temperature?

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