Author Topic: How to calculate WBGT, Dew Point and Wind Chill  (Read 606 times)

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Offline john.chartkoff

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How to calculate WBGT, Dew Point and Wind Chill
« on: February 25, 2023, 06:56:49 PM »
I am working on building a weather station that connects to Ecowitt WS90 using a native Java class. It is for another software package that displays weather information on a Raspberry Pi 7” screen. It also reads NASA DONKI alerts and updates my APRS node.

I am still trying to figure out the best way to calculate WBGT without actually using a separate thermometer wrapped in a wet towel. I found some plots on the NWS site but I would like to do it pragmatically in the software. I have all the necessary parameters: dry bulb temperature, humidity and air pressure and altitude.

I just can’t figure out how to write a formula.

Any help would be most appreciated

Thanks in advance.


Offline Mattk

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Re: How to calculate WBGT, Dew Point and Wind Chill
« Reply #1 on: February 25, 2023, 07:23:28 PM »
Davis derived variable formula, Dew Point and Wind Chill can be found here

Offline Cutty Sark Sailor

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Re: How to calculate WBGT, Dew Point and Wind Chill
« Reply #2 on: February 25, 2023, 10:58:39 PM »
found this.
enjoy :twisted:   

Wet-bulb globe temperature (in Fahrenheit) is calculated with the following equation:
 WBGT = (0.7 * Tw) + (0.2 * Tg) + (0.1 * T) 

In this formula, there are three important variables to note:
T = Temperature in Celsius
Tg = Globe Thermometer Temperature (in Celsius) – this is measured by a thermometer placed in a special black globe to estimate solar radiation without the effects of the light itself
Tw = Wet-bulb Temperature (in Celsius)

The wet-bulb temperature is the lowest possible temperature that air can be cooled down to by the evaporation of water alone, given constant pressure.
This is represented by a rather complex formula:

Tw = T * arctan[0.151977 * (rh% + 8.313659)^(1/2)] + arctan(T + rh%) – arctan(rh% – 1.676331) + 0.00391838 *(rh%)^(3/2) * arctan(0.023101 * rh%) – 4.686035

Here, “T” is the temperature in celsius and “rh” represents the relative humidity.
With this final calculation, you can calculate WBGT completely. :roll:   
  it says at

I guess the black globe thermo replaces sun angle, cloud cover parameters...
But, for me, this is "Too Much Information"...  :D
« Last Edit: February 25, 2023, 11:01:27 PM by Cutty Sark Sailor »

Offline john.chartkoff

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Re: How to calculate WBGT, Dew Point and Wind Chill
« Reply #3 on: February 26, 2023, 09:39:31 PM »
Thank you to Matt and The Cutty Sark!
This is very helpful info...

That math for the Tw is crazy!!!
... I think I will include it in my Dew Point calculation method, just so I can display it down to 6 decimal places... just to impress people  :twisted:

So far I have the Ecowitt WS90 working through the GW2000B, as well as Honeywell MPRLS, Bosch BME280 and the DHT11. Also a Peet emulator to present the data as a Peet weather station for APRS. And a GUI... I will share the project as open source as soon as I figure out how to use the GIT sharing web site.