Negative Cloudbase Reading

[captzero]

Hi Team,

Knowing that the calculation for the cloud base figure is for the lowest height that cumulus type clouds may or may not occur, how is it possible that I had a figure of -12 meters?? Station height is 15m and we have had a day of rotten wet weather.

Cheers

[Gina]

Cloud base below zero = thick fog!

[Synewave]

I've seen a negative cloudbase figure before too. And it was misty/foggy at the time.

[steve]

It's probably a rounding error. the cloud base calculation is based on the difference between the ambient temperature and the (Cumulus calculated) dew point temperature. Dew point can actually be higher than ambient temperature in certain conditions (supersaturated air, i.e. RH above 100%), but I suspect that isn't what's happening here, and it's simply the way the calculation is coming out. I should put a check in to make sure cloud base can never be negative, as that doesn't make sense.

[beteljuice]

I should put a check in to make sure cloud base can never be negative, as that doesn't make sense.

Yes and No

It would mean You are fog bound and probably those below you too.

Some people don't like it being relative to station altitude and use code to change to Sea Level.