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Negative Cloudbase Reading
Posted: Mon 20 Sep 2010 11:11 am
by 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
Re: Negative Cloudbase Reading
Posted: Mon 20 Sep 2010 7:58 pm
by Gina
Cloud base below zero = thick fog!
Re: Negative Cloudbase Reading
Posted: Thu 23 Sep 2010 3:33 pm
by Synewave
I've seen a negative cloudbase figure before too. And it was misty/foggy at the time.
Re: Negative Cloudbase Reading
Posted: Sat 25 Sep 2010 12:44 pm
by 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.
Re: Negative Cloudbase Reading
Posted: Sat 25 Sep 2010 1:07 pm
by 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.