I received a lot of interesting information regarding THSW. Normally I wouldn’t refer to the following board with the exception that I think that with the addition of the solar input on the WD software this might be a better option than windchill for those units that have solar sensors.

Perhaps it might be an option to add to the weather table along with the solar or sunshine readings, if it wouldn’t complicate the program :smiley:

What is the formula for that index?


but it involves the temperature, solar radiation, wind and humidity. I wrote an email today to Davis tech for the formula. We will see what shakes loose.

it would be a good thing to add to WD me thinks
the heat index forumal seems to work backwards
i.e lower humdity gives a higher heat index
why is that?

I am not certain. Davis refers to the Steadman 1979 formula, but all I can find out is that any references refers to Davis. I did write them twice and they are supposed to send me the calculation. When it shows, I will post if it is not long or email it to you if it is gobs of stuff.

Look at it this way, Brian, Beats being in the garden.

Steadman’s 1979 work refers to heat index. No mention of the other things. Davis must have their own formula. HI is easy to calc.


Here’s his postulate:

Heat index (HI), or apparent temperature (AI) = -42.379 + 2.04901523(Tf) + 10.14333127(RH) - 0.22475541(Tf)(RH) - ((6.83783 x 10-3)(Tf2) - ((5.481717 x 10-2)(RH2) + ((1.22874 x 10-3)(Tf2)(RH)) + ((8.5282 x 10-4)(Tf)(RH2)) - ((1.99 x 10-6)(Tf2)(RH2))

(Note: RH expressed as a whole number, not %)


that is fine, as it brings in the temperature and RH. Now somehow Davis added the wind speed and solar values into the formula that brings in the cooling 0r heating effect of wind and the solar radiation . It is this portion of the equation, I am waiting for.

After that is available and along with your formula can the TSWH be produced.

Ah trade secrets. Should be a good addition, should it ever get warm.

I have Davis’ calculations for all their variables that require a formula. It’s a .pdf file that’s 45 pages long and includes the THSW Index. The THSW computation is very complex and I’m afraid is beyond my capabilities. Unfortunately the software I’m running for my webpage is Ambient’s Virtual Weather Station and it doesn’t recognize the THSW Index from the console. If anyone has any ideas I’d appreciate their thoughts on writing the code for my weather page.
Write me a personal email at [email protected] and I’ll send you the file with all their formulas if you’re interested.
Thanks for any help with my problem.

Marsh Wren

could you email me the caclulations?
note that the apararent solar temperature, as calculated by WD, and which is avalilable as a cutom tag,and which can be displayed on the main screen, and is aslo available on the web table, is very similar if not the same as the davis THSW

Any updates on implementing THSW as a variable for those with Davis VP2 stations?

some one just sent me the formula for this, and so I will try and add i to WD over the next few days

That was more than likely my dad. He’s really itchy to get the THSW index on his website (which wrote the ASP for -, since it varies so much from the standard “heat index” value. For instance, today the air temp is 88F, but the humidity is really low (25%) and full sunshine. The generic heat index shows 84F, but the THSW index is around 97F.

Anyway, I’m surprised you’d have to do the THSW calc in WD, since THSW can be displayed on the Vantage Pro console. Isn’t it just a variable you can request from the console?

Thanks for your efforts! We’ve tried Weather Link and Virtual Weather Station… but WD looks like a far superior product… I’m really looking forward to using it!-

hi, ah, LOL
its not part of the normal data stream from the console
note that WD does have an apparent solar temperature (which takes into account windspeed and humidity and solar), which most likely will be a similar reading…but we will be able to find out :slight_smile:

Ahh, very interesting. I figured it would be part of the data stream that is spit out by the console. I know that I wasn’t looking forward to trying to recreate the Davis THSW formula in VBScrip/ASP :lol:

actualy, if you could give me a example of a thsw reading for a particular temp/hum/wind/solar
then i will know if i have the formula working correct :wink:

Currently in Webster, NY at 4:00pm the conditions are Temp 82.2, Hum 27%, solar radiation 738 W/m and the winds are light 6-7 mph. The resulting THSW is 93.

I just put your readings into WD’s exising apparent temperature solar,and that calculation comes up with the exac same reading
so the THSW is already availble in WD as the apparent temperature solar reading
(and you can have that show on the main screen instead of wet bulb temperature (see in the extra/misc setup in WD), and it also shows up on the extra dials screen too (see on the view panel)
I iwll put a note in WD that its actualy the THSW

Thanks Brian! That means I’ll be downloading and playing with WD tonight then!

Do you think if the winds were higher that the THSW would be lower due to the wind component?