Cloudbase Calculation

[Synewave]

Steve,

Just a quick question, does your cloudbase tag value incorporate the station's set altitude/elevation value? Or do I need to add the altitude to get a more accurate reading?

I have had 19m cloudbase today, but to my eye it seems higher.

[daj]

This should help

https://cumulus.hosiene.co.uk/viewtopic.p ... 81&p=24124

[steve]

The calculation gives height above ground level (AGL), which is the usual way that cloud base is quoted (e.g. in METARs).

If you have high humidity, the calculation will give a correspondingly low figure; for example at 100% it will give zero, even though it may not be foggy, because basically that's all the calculation does - it works out the theoretical height at which the humidity reaches 100%.

[Synewave]

Steve and David,

Many thanks for a super fast reply!

So, presenting data on my website, should I add the altitude value to the calculated cloudbase to give a more accurate reading? If I did that I guess my reading would never go below my altitude value though?

[steve]

The only way to get a more accurate reading is to actually measure/estimate the height. If you add the station altitude to the calculated figure, you're not getting a more accurate figure, you're getting height above sea level (ASL) rather than AGL, which is more usual. So if you really want to do that, you should probably make it clear on your web site that your figure is ASL.

The calculation makes a number of assumptions about the atmospheric conditions, and really only applies to the formation of Cumulus clouds anyway.

[Synewave]

Many thanks Steve, it's all much clearer now. Thanks also for the quick responses.