Cloud height as reported by WD

[oldun]

I have some misgivings about the veracity of the cloud height as reported by WD it rarely agrees with the Meta from Auckland airport or visual evaluation, particularly under conditions of high humidity e.g. >60% Rel..
Would appreciate comments on this from others using this feature

[Weather Display]

it relies on your weather stations humdiity and then dew point reading being correct, and then it assumes the environmental adiabatic elapse rate is standard, which it might not be, and its just as a guide as to where, if any, clouds will start forming at, but unstable conditions and a whole host of other factors means the actual cloud height will be different in practice...and so just use it as a guide....also have you set your stations altitude in the units setup?

[oldun]

Hi Brian,

Thanks for the info, yes the altitude is set at the height above MSL  ( from GPS data) of the main sensor (temp,hum,pressure) head of the weather station.
I'll put a note of explanation on my website.
Robert

[Weather Display]

mine currently says 3500 feet
and i would say at a guess the cloud BASE height is not too far from that, of the cumulus clouds

[Weather Display]

mine currently says 3500 feet
and i would say at a guess the cloud BASE height is not too far from that, of the cumulus clouds
in fact the airport metar says cloudy with clear patches at 3500
so for me here, not all that far from you, WD is spot on!

[41South]

Brian,

Do you use the "standard" lapse rate, or the more correct wet/dry lapse rates?

[oldun]

Mine is currently showing 2077m whis is about 6814 feet a big difference
R

[Weather Display]

its a simple formula, but for me today, is surprisingly accurate
  temp:=((temperature-dewpoint)*412)+heightabovesealevel

for feet

[niko]

Hi Brian,

Thanks for the info, yes the altitude is set at the height above MSL  ( from GPS data) of the main sensor (temp,hum,pressure) head of the weather station.
I'll put a note of explanation on my website.
Robert

The cloud height is above MSL too.

[Weather Display]

as i said, its dependent on how accurate your dew point is
my dew point is 10.6oC, which ,matches exactly auckland airport, 18km from me in a straight line
my temperature is 20oC

[Weather Display]

checking your web site, your dew point is only 7.4oC, which is too low, and hence thats why the cloud base is being reported as too high

i have a davis VP, which is giving me real good dew point readings 

[41South]

This calculator lines up pretty well with WD 

http://www.csgnetwork.com/estcloudbasecalc.html

[Weather Display]

yes, if i put in my current numbers, and my height, 280 feet, then it matches wd (which is now saying 4100 feet )

[oldun]

Time 0700 wd reports cloud height 320 meters ( temp9.4C , dew point 7.0C Height ASL=21m)
Visual zero cloud, Auckland airport concurs.????????

[NorCal Dan]

Time 0700 wd reports cloud height 320 meters ( temp9.4C , dew point 7.0C Height ASL=21m)
Visual zero cloud, Auckland airport concurs.????????

The calculator gives me 313m for cloud height, matches up with your station report of 320m.

it relies on your weather stations humdiity and then dew point reading being correct, and then it assumes the environmental adiabatic elapse rate is standard, which it might not be, and its just as a guide as to where, if any, clouds will start forming at, but unstable conditions and a whole host of other factors means the actual cloud height will be different in practice...and so just use it as a guide....also have you set your stations altitude in the units setup?

It doesn't mean there are clouds present, just that if there were clouds the expected base would be as reported.