12 UTC Wind Chill

Figure 1 – Wind Chill [JAG]

Not incredibly cold as far as wind chill goes today across the country, generally in the range of 1 to 4°C using the JAG/TI formula, except of course if you find yourself on top of a mountain such as in the Cairngorms, where the wind chill is as low as -15°C at the moment.

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An ex-metman passionate about all things to do with weather, climate and clouds

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5 Responses to 12 UTC Wind Chill

  1. quaesoveritas says:

    The MO seem to have got the forecasted wind speed here seriously wrong today.
    As usual, it seems to be at the lower end that they go wrong.
    The forecast as 12mph with 25 mph gusts at 09:00, and 13/24 now, but it fell to about 2mph at 09:00 and has increased to 16/24 now so while it isn’t much faster than forecasted now the increase is dramatic.

  2. quaesoveritas says:

    Apart from that, I don’t really know whether Cumulus is using that formula.
    I have looked in the “help” files but there is no explanation that I can find.
    It produces interesting results. For example, for most of yesterday until about 01:00 this morning, apparent temp. was higher than wind chill, but now it is lower.
    Nothing major has happened to change this, except that humidity has been rising steadily.
    I suppose I could feed the various factors into a spreadsheet or VB programme I see what effect they have on the AT.

  3. quaesoveritas says:

    Thanks, I don’t know if I have seen that explanation before, but I feel that it is so complicated that I can’t really relate to it or work out what it would mean to me on a daily basis.

  4. xmetman says:

    This is from the Australian Bureau of Meteorology site:-

    About the formula for the apparent temperature
    The formula for the AT used by the Bureau of Meteorology is an approximations of the value provided by a mathematical model of heat balance in the human body. It can include the effects of temperature, humidity, wind-speed and radiation. Two forms are given, one including radiation and one without. On this site we use the non-radiation version.
    Version including the effects of temperature, humidity, and wind:
    AT = Ta + 0.33×e − 0.70×ws − 4.00
    Version including the effects of temperature, humidity, wind, and radiation:
    AT = Ta + 0.348×e − 0.70×ws + 0.70×Q/(ws + 10) − 4.25
    where:
    Ta
    = Dry bulb temperature (°C)
    e
    = Water vapour pressure (hPa) [humidity]
    ws
    = Wind speed (m/s) at an elevation of 10 meters
    Q
    = Net radiation absorbed per unit area of body surface (w/m2)
    The vapour pressure can be calculated from the temperature and relative humidity using the equation:
    e = rh / 100 × 6.105 × exp ( 17.27 × Ta / ( 237.7 + Ta ) )
    where:
    rh
    = Relative Humidity [%]

  5. quaesoveritas says:

    Accorrding to my Cumulus software, wind chill here was about 3.5c here at 12:00 but the “apparent temperature” (which I have never been able to explain) was only about 1c. Around 06:00 the figures were -3c and -2c.