There is no real issue as such, it’s just a case of LOOP and LOOP2
providing slightly different data. The main differences are LOOP provides
data for extraTemps, extraSoilTemps/Wetness and leafTemp/Wetness as well as
a number of rain aggregates and alarms whereas LOOP2 does not, but instead
provides a number of more ‘detailed’ obs related to wind and rain (eg 2
minute average wind speed and last 15 minute rain) as well as heatindex,
windchill, dew point and THSW as well as various other things. This is by
no means an exhaustive list of the differences.
The impetus that caused LOOP2 support to be added to WeeWX was due in part
to being able to access THSW. For the average user THSW is probably the
only real point of difference driving the use of LOOP2.
Gary
On Saturday, 7 November 2020 at 08:11:06 UTC+10 Peter Fletcher wrote:
> @gjr80: I am sure that you are right. I did the fairly obvious check of
> forcing both derived parameters to "hardware" in weewx.conf, upon which
> both show up as "N/A" (and blank on the graph) on the web page. I have a
> vague memory that there are potential issues with having weewx use LOOP2
> packets (otherwise, why not default to this). Can you elucidate?
>
> On Friday, November 6, 2020 at 4:53:58 PM UTC-5 gjr80 wrote:
>
>> 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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