Cloudbase

[Stigian]

Hi,

What am I doing wrong here when calculating cloud base. It gives me a different result than CMX. This is the formula I am using

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Cloudbase EVAL [ ((Temperature - Dewpoint ) / 4.5 ) * 1000 + 15 

[EDIT]

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2024-01-10 16:12:11.321 Information CeckAllVariablesInThisSetOfCharts (found: False): Keyword: Dewpoint; Plotvar: dew; Datafile: tempdata.json
2024-01-10 16:12:11.321 Information CeckAllVariablesInThisSetOfCharts (found: False): Keyword: Temperature; Plotvar: temp; Datafile: tempdata.json

[HansR]

Hi,

I am not sure what you are showing me here I am anyway missing the closing square bracket at the end of the EVAL.

Could you post the CutilsCharts.def please (change the extension to .txt to be able to attach it).
Could you also post the full logfile for this run (CompileOnly would be enough I guess)

[Stigian]

Hi,

Sorry for not being clearer

CutilsCharts.txt

2401101833cumulusutils.log

[HansR]

I use:

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CloudBase EVAL [ (Temperature - DewPoint) / 10*1247 ] 

but I can't find the reference anymore

You use:

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Cloudbase EVAL [ ((Temperature - Dewpoint ) / 4.5 ) * 1000 + 15 

which comes from the wiki (I presume).

The point is that your temperatures are in Celsius but the formula expects Fahrenheit (and I think that is where my equation differs) so you have to convert the temperature and dewpoint to fahrenheit or (as the wiki says):

For metric divide the spread in °C by 8 and multiply by 1000 and get the cloud base in meters.

Hope this helps.

[Stigian]

I've changed the formula into;

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        Cloudbase EVAL [ ((Temperature - DewPoint ) / 8 ) * 1000 + 15 ]

The result is now correct. Thanks again for your help.