I'm looking for a wind chill formula that will work from -10 °C to +50 °C and uses wind speed in km/h so that I can use this formula to add this element to a weather station I am programming. I don't need it in code, just the normal math formula will work. I couldn't find this exact formula on google, and I am hoping someone here will know.
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$\begingroup$ Not sure it exists at the range you're looking for. "Windchill temperature is defined only for temperatures at or below 10 °C (50 °F) and wind speeds above 4.8 kilometres per hour (3.0 mph)." From en.wikipedia.org/wiki/… $\endgroup$– Jean-Marie PrivalCommented Aug 2, 2022 at 11:02
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$\begingroup$ weather.gov/media/epz/wxcalc/windChill.pdf has the formula the US govt uses. As others have noted, wind chill doesn't really apply above 10C. Quoting the site that links to the PDF, weather.gov/epz/wxcalc_windchill "The wind chill calculator only works for temperatures at or below 50 ° F and wind speeds above 3 mph." $\endgroup$– Barry CarterCommented Aug 2, 2022 at 12:51
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$\begingroup$ Having lived in Montreal (where -10 °C is a pleasant winter day) and Dallas, (where the average high temperature in July 2022 was just over 39 °C), I can tell you that a windy day when it's 40 °C "feels like" oven, not chill $\endgroup$– Flydog57Commented Aug 2, 2022 at 20:00
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1 Answer
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Wind chill is only relevant for cold temperatures. During hot temperatures, the affect of wind is to increase the felt temperatures.
What would be more appropriate would be apparent temperature, also known as the "feels like" temperature. This calculated temperature considers the effect of the dry bulb temperature, humidity and wind speed.
$ {\displaystyle \mathrm {AT} =T_{\mathrm {a} }+0.33e-0.7v-4.00}$
where:
Ta = dry bulb temperature (°C)
e = water vapour pressure (hPa)
v = wind speed (m/s) at an elevation of 10 m
The vapour pressure can be calculated from the temperature and relative humidity using the equation:
$e = \frac{R H}{100} ⋅ 6.105 ⋅ exp ( \frac{17.27 ⋅ T a}{ 237.7 + T a} ) $
Where:
Ta = dry bulb temperature (°C)
RH = Relative humidity (%)
$exp$ represents the exponential function
The Australian formula includes the important factor of humidity and is somewhat more involved than the simpler North American model.
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1$\begingroup$ Related: bom.gov.au/jshess/docs/1994/steadman.pdf $\endgroup$ Commented Aug 2, 2022 at 14:26
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$\begingroup$ @Fred Is this formula the same as the heat index formula? Also, is this going to work considering that I don't live at an altitude of ten meters? I live at an altitude of 44 meters. $\endgroup$ Commented Aug 2, 2022 at 22:19
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$\begingroup$ I presume this means the data to support this formula were collected with an anemometer 10 feet off the ground. The wind speed at ground level would probably be slower and more variable. $\endgroup$ Commented Aug 2, 2022 at 23:04
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$\begingroup$ @DanielVanNattan: The Heat Index, used in the USA, is a similar measure, based in the Steadman Apparent Temperature, but the equation has a lot more terms. The Heat Index measures the effect of humidity on the perception of temperatures above +27 °C (81 °F). In humid conditions, the air feels much hotter, because less perspiration evaporates from the skin. $\endgroup$– FredCommented Aug 3, 2022 at 1:45
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$\begingroup$ @cowboydaniel: The elevation of 10 m for the wind speed, is not elevation above sea level. It is the height above the ground. "A common anemometer height for meteorological measurements is 10m" . $\endgroup$– FredCommented Aug 3, 2022 at 18:03