Cloud Height

[Oz Greg]

All,

Looking for some suggestions here..  We are currently calculating cloud height from the following formula but I am noticing that the (cloud) height value on Weather WU is almost double the cloud calculation (which looking out the window is closer to what I am seeing).. 

The formula is $cloudHeight = int(($current.outTemp.raw - $current.dewpoint.raw) / 4.4 * 1000) + $station.altitude.raw which equals 497M  however I am seeing 914M on WU..

Any suggestions?

Thanks :)

[Andrew Milner]

As you did not give any of the input numbers am not sure what the inputs actually were - but doesnt the formula assume temps in F and give the height in feet and so require a station altitude in feet - whilst you are giving the results in meters so I am confused.

[gjr80]

Not wanting to be picky but I understand we are really talking cloud base (nominally distance from mean sea level to the bottom of the clouds) not cloud height (distance from bottom of cloud to top of cloud).

The formula was taken from Wikipedia

Quote

The cloud base in feet can be calculated as follows:

1. Find the difference between the surface temperature and the dew point. This value is known as the "spread".
2. Divide the spread by 4.4 (if temperatures are in °F) or 2.5 (if temperatures are in °C), then multiply by 1000. This will give you cloud base in feet AGL (Above Ground Level). A shortcut to the above method when temperatures is measured in °C is to simply multiply the spread by 400.
3. Add the results from step (2) to the Field Elevation (ft) to get cloud base ASL (Above Sea Level)

Unquote

I have noted our calculated value does seem rather low but had not gotten around to doing anything more.

Gary

[gjr80]

Greg,

Having just had another look I think your 4.4 should be a 2.5 since you will be defaulting to C not F. Probably safest to force your temp/dewpoint to either C or F and use either 2.5 or 4.4 respectively. Have at look at around line 400 in testtags.

Gary