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Latest Cumulus MX release 3.10.5 (build 3122) - 06 April 2021 (please see announcement regarding releases since 3.5.0)
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Apparent Vs Feels Like

From build 3044 the development baton passed to Mark Crossley. Mark has been responsible for all the Builds since. He has made the code available on GitHub. It is Mark's hope that others will join in this development, but at the very least he welcomes your ideas for future developments (see Cumulus MX Development suggestions).

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Big Daddy
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Apparent Vs Feels Like

Post by Big Daddy »

Trying to find if these 2 values are related, just a different calculation, whats the difference etc.

This evening there is a 2.4 degree difference in these 2 figures, so is it apparantley 1.5 but feels like 3.9. I understand that this calcualation takes in to account a few factors. Current temperature is 4.8.

Is there a preference which to use.

Andy

Mapantz
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Re: Apparent Vs Feels Like

Post by Mapantz »

Big Daddy wrote:
Wed 07 Apr 2021 8:34 pm
Trying to find if these 2 values are related, just a different calculation, whats the difference etc.

This evening there is a 2.4 degree difference in these 2 figures, so is it apparantley 1.5 but feels like 3.9. I understand that this calcualation takes in to account a few factors. Current temperature is 4.8.

Is there a preference which to use.

Andy
The Met Office use 'Feels Like'

That's what I have stuck to for a long time. Mark has improved the calculation of this, significantly.
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sfws
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Re: Apparent Vs Feels Like

Post by sfws »

Big Daddy wrote:
Wed 07 Apr 2021 8:34 pm
This evening there is a 2.4 degree difference in these 2 figures, so apparent reports 1.5, but feels like reports 3.9.
I understand that this calculation takes into account a few factors.
Current temperature is 4.8
BCJKiwi asked a similar question based on comparing chart plots, you can search for that topic if you like.
That was answered by posts from Mark, and me.
Don't forget there is documentation in the Wiki, but it is easier if I explain again.

When the current temperature is 4.8 oCelsius, the difference is purely because of the humidity in Lincolnshire at that time.
Big Daddy wrote:
Wed 07 Apr 2021 8:34 pm
Trying to find if these 2 values are related, just a different calculation, what is the difference etc.
Apparent temperature for both flavours of Cumulus is based on a formula specified by BOM in Australia, see Cumulus documentation at https://cumuluswiki.org/a/Apparent_temperature for the relevant link. It involves humidity, as well as what wind chill uses (temperature and wind speed).

Cumulus optionally calculates wind chill, see Cumulus documentation at https://cumuluswiki.org/a/Wind_chill

When air temperature is below 10, Feels Like temperature Cumulus reports is exactly the same as it optionally calculates for Wind Chill. It thus uses temperature (lower temperature makes wind chill greater) and wind speed (higher speed means wind chill greater) , but not humidity. That is the basis for my explanation earlier.

When air temperature is above 20, Feels Like temperature Cumulus (from release 3.6.10 build 3086) reports is exactly the same as it calculates for Apparent Temperature (see above reference to BOM).

The previous answer to your post mentioned the formula had changed. The Cumulus documentation at https://cumuluswiki.org/a/Feels_Like indicates which releases changed the formula. The reason why Mark kept changing the Feels Like temperature formula, was simply that he could not find any documentation that indicated what formula the Met Office actually uses! So he experimented with different apparent temperature formulae for feels like, effectively until it "seemed right", this actually made Cumulus simpler as Feels Like at higher temperatures could share the code used for pparent temperature calculation.


For in-between temperature a modified wind chill formula (one not having a 10oCelsius cut-off) is blended (as Mark's earlier answer put it) with apparent temperature.

As previous answer, feels like is used by UK Met Office, so this should normally be the UK derivative of preference.

One advantage of using MX is that it reports Feels Like. The original Cumulus software did not!

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