Topic: Wet Bulb Globe Temperature (WBGT)

[AthleticTrainerPhil]

Hi Weather Folks,

I'm an athletic trainer at a college in New York's Finger Lakes.  One of my duties is to monitor hazardous weather during practice and competition.  We purchased the Davis Vantage Pro 2 Plus last year to help monitor field conditions remotely.  Wind chill, lightning, and Wet Bulb Globe Temperature (WBGT) can all require us to seek shelter.  The Davis unit has been working great for wind chill, and we use the Weather Underground Storm app with Weatherbug as a backup to monitor lightning, and while it would be more convenient to have everything in one place, this has been working fine.  The missing link is the WBGT.  Because we have the Solar Radiation sensor, it is able to give a Temperature Humidity Sun Wind Index (THSW), however in practice, this number is not close to the measured WBGT using our Extech HT30 handheld unit. 

Does anyone have any suggestions to get a WBGT measurement or approximation from this unit?  If there's a somewhat accurate way to approximate the WBGT using current equipment, that would be optimal.  I also would not be opposed to adding sensors if that would be cost effective and be able to take a WBGT measurement directly.

Thanks in advance for any ideas!

[SLOweather]

Here are some ways to do it. You will need either a Davis leaf wetness/soil moisture/temperature station and 2 temp sensors, or 2 temperature only stations with probes.

Build a black globe sensor similar to this:

http://www.wxforum.net/index.php?topic=32489.msg329326#msg329326

and a wet bulb sensor similar to this:

http://www.wxforum.net/index.php?topic=32682.msg330253#msg330253

or this:

https://www.wxforum.net/index.php?topic=4844.0

You may or may not need the fans.

Then, I guess you'll have to do the calculation by hand.

[SLOweather]

Calculation from https://en.wikipedia.org/wiki/Wet-bulb_globe_temperature

WBGT = 0.7Tw + 0.2Tg + 0.1Td
where

    Tw = Natural wet-bulb temperature (combined with dry-bulb temperature indicates humidity)
    Tg = Globe thermometer temperature (measured with a globe thermometer, also known as a black globe thermometer)
    Td = Dry-bulb temperature (actual air temperature)
    Temperatures may be in either Celsius or Fahrenheit

[SteveFitz1]

AthleticTrainerPhil,

I went through this same exercise a couple of months ago and used the formula SLOweather posted to get WBGT. While I was able to get the dry-bulb temp (Td) and the wet-bulb temp (Tw) from my weather software, the Black Globe temperature (Tg) was a challenge since I didn't have access to that. However, I was finally able to find a formula that gave me a good approximation of black glove temp that I used my weather software to input into:

Td = ((0.01498 * SR) + (1.184 * Td) - (0.0789 * H) - 2.739)

where
SR = Solar Radiation Value
Td = Outside air temp
H = Humidity

I convert all the temps into Celsius first because that's what the Black Globe temp calculation used, then I convert it all back to Fahrenheit.

I've compared my calculated value against the WBGT calculator on the NWS site and am almost always with in a degree or less of it's calculation.

It'll be interesting to see how the calculation compares to your device.

Steve

[AthleticTrainerPhil]

Thanks for the equations and ideas.  I may try to assemble something at some point.  I'd like to try calculating it with what I have first.  Steve, what software do you use that gives a wet bulb temp?  I don't find that on any of mine.  I do have a variety of other data that could be used to calculate the wet bulb temp if I had a good equation.

[CW2274]

gives a wet bulb temp? 

No idea if you're online or not, or even if this helps, but Mesowest supplies the wet bulb temp for you.
https://mesowest.utah.edu/cgi-bin/droman/meso_base.cgi?stn=C2274&unit=0&time=LOCAL&product=&year1=2018&month1=2&day1=15&hour1=12&hours=24&graph=0&past=0

[SteveFitz1]

Thanks for the equations and ideas.  I may try to assemble something at some point.  I'd like to try calculating it with what I have first.  Steve, what software do you use that gives a wet bulb temp?  I don't find that on any of mine.  I do have a variety of other data that could be used to calculate the wet bulb temp if I had a good equation.

I get it from Cumulus. I believe Weather Display also provides a Web Bulb value.

Steve

[AthleticTrainerPhil]

Thanks for the advice everyone.  I've been sending the data to Weather Underground, however I've begun the (somewhat obscure) process of uploading to CWOP so that I can get the information needed via MesoWest.  Once that is done, I'll do a comparison of the calculation to approximate WBGT given and on site measurements.  If that doesn't work, I'll consider building the probes to take more accurate measurements remotely.

[twillrick]

bringing this up to the top again, WBGT, i see weatherlink.com now has WBGT on the Davis website but does not have it on the weatherlink 2.0 app.   Instead it uses the THSW index which is not an exact match.   Has anyone been able to get the WBGT from Davis onto their app?  thanks T