Just to clear up obtaining heatindex and windchill from Davis hardware.
Irrespective of any other settings, the only way you will get hardware
provided heatindex and windchill from a Davis station is if you have WeeWX
use the LOOP2 packet data from the console/logger. This is because
heatindex and windchill are not included in the ARCHIVE record and LOOP
packet provided by the console/logger. To use LOOP2 data the user must make
a change to weewx.conf, a default install will use LOOP packet and ARCHIVE
record data from the console/logger and not LOOP2 data.
Based upon what you have posted so far my guess is the WeeWX is not
receiving heatindex/windchill data from the console/logger and hence WeeWX
is calculating both.
Gary
On Saturday, 7 November 2020 at 07:44:41 UTC+10 Peter Fletcher wrote:
> A further note, from Davis's documentation on their wind chill
> calculations:
> "The formula below was adopted by both Environment Canada and the U.S.
> National Weather Service to ensure a uniform wind chill standard in North
> America. The formula is supposed to more closely emulate the response of
> the human body when exposed to conditions of wind and cold than the previous
> formula did:
> 35.74 + 0.6215T - 35.75 * (V^0.16 ) + 0.4275T * (V^0.16 )
> This relationship takes into account the fact that wind speeds are
> measured "officially" at 10 meters (33 feet) above the ground, but the
> human is typically only 5 to 6 feet (2 meters) above the ground..... This
> newer version of the formula addresses the fact that the latest National
> Weather Service (NWS) formula was not designed for use above 40°F. The
> result of the straight NWS implementation was little or no chilling
> effect at mild temperatures. This updated version provides for reasonable
> chilling effect at mild temperatures based on the effects determined by
> Steadman (1979) (see THSW Index section), but as with the new NWS
> formula, no upper limit where chilling has no additional effect."
>
> On heat index, they say:
> " Heat Index uses temperature and relative humidity to determine how hot
> the air actually “feels.” When humidity is low, the apparent temperature
> will be lower than the air temperature, since perspiration evaporates
> rapidly to cool the body. However, when humidity is high (i.e., the air is
> saturated with water vapor) the apparent temperature “feels” higher than
> the actual air temperature, because perspiration evaporates more slowly.
> Formulas: Heat Index is based upon a lookup table presented by Steadman
> (1979) and loosely derived from the methodology outlined by Steadman
> (1998). Thus, air temperatures below 50°F follow this 1998 procedure. Air
> temperatures above 68°F follow his procedure outlined in 1979 (since the US
> NWS continues to use this). Davis has made a smooth transition between
> the two methods between 50°F and 68°F.
>
> On Friday, November 6, 2020 at 4:33:15 PM UTC-5 Peter Fletcher wrote:
>
>> Responding to both of your messages: You are right that my comments would
>> equally apply to the heat index being different to the actual temperature.
>> A relatively quick scan of the relevant pages on the NWS site found the
>> explicit statement that the wind chill was undefined for air temperatures
>> above 50 ºF but I did not notice the slightly less strongly worded caveats
>> about heat index calculations being unreliable below 80 ºF
>>
>> My console initially showed the same value (60) for Heat index and Wind
>> Chill, with outside temperature 62.0, RH 60, and wind in the low teens. At
>> the same time, the weewx display showed a wind chill of 62.0 and a Heat
>> Index of 60.7. A couple of minutes later, the temperature had dropped to 61
>> 7, the RH had risen to 61, the heat index had risen to 61 (all on the
>> console), with no significant change in the wind. The simultaneous weewx
>> value for heat index was 60.5. It looks, therefore as if weewx is not using
>> the console's calculated values for *either* derived parameter..
>>
>> In terms of definitions, at least as per the US NWS, it is not that (wind
>> chill == temperature) above 50 ºF, but that wind chill is *undefined*
>> above that temperature.They are not quite as clear about heat index, simply
>> saying that "...The Heat Index calculation may produce meaningless results
>> for temperatures and dew points outside of the range depicted on the Heat
>> Index Chart linked below {40<= RH <=100; 80<= ºF <=110)}
>>
>> All my 'derived value" options in weewx.conf are set up
>> "prefer_hardware', so weewx should presumably be using those transmitted by
>> the console. As far as I can see, it isn't - certainly not for Wind Chill,
>> and probably not for heat index, either!
>> On Friday, November 6, 2020 at 3:25:32 PM UTC-5 Greg Troxel wrote:
>>
>>>
>>> Also, check the values in your skin against what is on your console.
>>>
>>
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