Wind Chill value not the same as station value..

[jon_iz]

I run a VP2 with CMX 3.8.4b3094
There's a bit of chill in the air today, and while toggling between the "Other temps" today, I have noticed that CMX appears to be reporting the chill figure the same as the outside temp, in this instance, outside temp is 13.4°C, VP2 reads Chill as 11°C and CMX say 13.4°C
In the CMX options, the calculate Windchill box is unchecked.
Checking the calculate Windchill box in options, also returns the same value. Apparent and Feels like are shown as 9.4°C & 11.4°C respectively, with a windspeed of 12mph.
Is this expected, or is CMX incorrectly reporting the Chill value?

[freddie]

Yes, it is expected as wind chill is calculated only when the temperature is 10 Celsius or less. This is because the formula used to calculate wind chill is only valid for temperatures of 10 Celsius or less.

[jon_iz]

Yep, I understand that theory and there are various methods for calculating windchill (and no agreed standard?)
However, the point is that CMX appears to be calculating, (confirmed by the sudden drop in the trend graphs at 10°C)
rather than taking the station value irrespective of the setting in options.

[freddie]

Possibly CMX is ignoring the station's value as the temperature is above 10 Celsius?

[jon_iz]

Thats one for Mark I guess?

[mcrossley]

I'll take a look tomorrow. It should use the station value if that is what is selected regardless of the 10C norm.

[jon_iz]

Let me know if you need any logs....

[mcrossley]

OK, Cumulus has never used the station wind chill value for Davis VP2 stations.

There are two reasons for this...

1. The standard LOOP data does not contain the wind chill value.
2. The LOOP2 data does contain the wind chill value, but it is only provided in whole degrees Fahrenheit.

For completeness I could change the code so that you *could* use the station value, but only if you have LOOP2 enabled (obviously), and Cumulus is set to NOT calculate the value.

[jon_iz]

Tnx Mark,

I think it would make sense to include it if the user wants CMX to reflect the VP2 station displays?
I run the VP2 in °C. It only displays wind chill in integers.

I'm assuming you would calculate the °C from the °F value?

Lastly - is CMX still using loop2 by default unless UseDavisLoop2=0 is added to the cumulus.ini file, as I couldn't find any other options for it in the settings of the web interface?

[mcrossley]

Cumulus does use loop2 default. And therein lies the problem. If I altered the code, the default would become to use the station value which is not what most users would want I expect.

[jon_iz]

No worries - leave as is then.