Cloud base calculation

Reading 32.5 temp and 32.5 dew point and yet have 1600 ft. close base calculated. Seems it would be closer to 0 (which we are having dense fog right now). I remember you mentioning a new equation. Anyway, just some feedback.

There’s a whole other thread on this subject recently. What elevation do you have in your setup? The formula adds in your elevation to give an estimate in ASL.

I have 1200 ft. entered. Wow, I did not know it was given in altitude above SEA LEVEL. I may have to “fudge” my altitude to yield altitude above ground level, which is the standard useage. I’ll go look for that thread. Thanks!

UPDATE-Found the thread. I agree with person who says it seem to ADD your altitude to AGL cloud base to give ASL. My solution is to just put 0 feet in altitude to get AGL base, but I wonder if that affects anything else in WD.

The elevation setting may affect the barometric correction.

i am slowly getting the wind back in my sails…

the cloud base is based on the dew point, which is based on the humidity and temperature from the station.

and it is based on a assumed adiabatic environmental elapse rate…(dry air assumption), and so the height at which the temperature reaches the dew point due to cooling as you increase in altitude, is the estimated cloud height.
by setting a alitutude, under units, this then creates an offset for the cloud height formula.
if you live at altitude, your temperature will be lower …and there fore the dew point depression will be lower…and this then creates a lower cloud height estimate
the formula is simply the dew point depression*412 (estimated cloud height in feet)

but this is from assumed sea level…
so you do need to have your altitude set…

which is need for QFE barometer option as well…


I think I get the idea now.

Am I correct in thinking that the estimated cloud height is reported AMSL and not above ground level?

If this is the case, is there any way of making it report above ground level using ground level as the setting under units?


look at this way
say someone at sea level has a dew point of 10oC (and a temperature of 15pC), and so a dew point depression of 5oC
that gives 2060 feet for cloud base height

now, if someone lived at 2000 feet in the same location, then there humiditwill be 100%, the dew point is still 10oC, but there temperature will be 10oC, and the dew point depression is then zero, and so zero * 412 gives zero for cloud base height
well, thats not correct, unless you refer to it as height above ground
so you need to add the stations altitude
which is 2000 feet

so to add that option, it would need to be specified :slight_smile:

Hi Brian

Thank you for your reply, it makes sense now.

Im back to the old QFE, QNH senario. Now I understand that when the reported cloudbase is around 620 feet at my elevation of 525 feet Im in mist or cloud.

I will amend the website.



those numbers would mean the cloud base will be only 100 feet above you…

the cloud base really does need to be based from sea level…as its aerolanes/gliders that use the info mostly, and they work from an altitude corrected to sea level :slight_smile:
just my thoughts!