Heat index and wind chill always same as temperature on Fine Offset

[Andrew Milner]

Are heat index and windchill calculated for FO weather stations??  I have noticed that heat index and wind chill are always exactly the same as temperature both in current readings and highs and lows.  I am recording humidity and wind with no problems as far as I can tell, together with a dewpoint (which could be being calculated, I don't know).  Is there a reason for wind chill and heat index being the same as temperature - down to the decimal point??   Am using metric database if that makes any difference.

Andrew

[Andrew Milner]

Mea culpa - yet again

 

After spending god knows how long noticing the heat index and windchill always seemed to match a high or low temperature blow me down but today, after my posting, I have got values that appear valid!!:

Current temp 28.8, heat index 30.1, humidity 56%, dewpoint 19

and

high temp  29.4, high heat index 30.8, high humidity 62%, high dewpoint, 20.1

And low windchill = low temp = 20.1 at 05:50 when the wind would have been very light anyway

 

So I guess I shouted wolf .....

 

I think

 

Andrew

With apologies

[Paul Farrar]

And yet perhaps not.... I too get the same readings for wind chill and heat index as the out side temp.

I have just this weekend installed the weewx software on a Raspberry Pi, along with lighttpd. I hooked up my Watson WS display via USB and was very pleased to start to see data on the default web page layout. I still have some tinkering to do, and eventually I want to come up with a total replacement for the default site - but I am not a developer or much of a programmer so this is long term, very long term

[George D. Nincehelser]

If find the presentation misleading as it seems to imply there is always a value for "windchill" and "heat index".

The definition I have heard is that windchill only has meaning below 50F and heat index above 80F.  Neither is applicable between temps of 50F and 80F.

Perhaps "apparent temperature" is a better term.  I'd like to see a graph of real vs apparent temperature instead of "windchill  heatindex".  .

George

[Andrew Milner]

Thanks to you both for explaining wind chill and heat index and actually making me look up more info on the web!!

 

Yes, indeed apparent would appear to equal windchill values below a threshold value, heat index above a threshold and ambient temperature at points inbetween - and so I suspect my original "they are the same" were at points in between!!

 

I have a fairly strong suspicion that there are multiple definitions of the threshold values and conditions under which wind chill and heat index are activated - and that these definitions are country dependant - so I shall stick with whatever weewx is producing as I am sure I will never find out what Cyprus uses for heat index (wind chill is unlikely to ever occur here in the sunny Med!!)

[Thomas Keffer]

It would not be hard to write a weewx service to define an "apparent temperature." Heck, using a bit of trick Python, you can do it in the existing StdCalibrate service:

apparentTemp = heatindex if heatindex > outTemp else (windchill if windchill < outTemp else outTemp)

Of course, this ignores 'None' values, so to incorporate those you'd have to add still more logic to the above line. Probably it's easier to write a new service. :-)

-tk

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Tom Keffer

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