Since I couldn't find a source for hygrometric tables, perhaps someone
here knows a formula to calculate dewpoint, given temperature & relative
humidity?

I could then use Excel to calculate my own table.
--
Paul Hyett, Cheltenham, England

Paul,

I believe the following works:-

SVP = 6.11*10^(7.5T/(T+237.3)) where T is in Dec C

With RH you can obviously work out VP......I think you know where I'm
going - I created a table of SVP's in excel - if this doesn't make sense
please give me a shout

Paul
"Paul Hyett" wrote in message
...
Since I couldn't find a source for hygrometric tables, perhaps someone
here knows a formula to calculate dewpoint, given temperature & relative
humidity?

I could then use Excel to calculate my own table.
--
Paul Hyett, Cheltenham, England

T is in DEG C, not DEC C!!!!!
"Paul Freeman" wrote in message
...
Paul,

I believe the following works:-

SVP = 6.11*10^(7.5T/(T+237.3)) where T is in Dec C

With RH you can obviously work out VP......I think you know where I'm
going - I created a table of SVP's in excel - if this doesn't make sense
please give me a shout

Paul
"Paul Hyett" wrote in message
...
Since I couldn't find a source for hygrometric tables, perhaps someone
here knows a formula to calculate dewpoint, given temperature & relative
humidity?

I could then use Excel to calculate my own table.
--
Paul Hyett, Cheltenham, England

In uk.sci.weather on Tue, 19 Aug 2003 at 18:17:49, Bernard Burton wrote
:
Here you are, Paul,

RH = 100e/es(t)
where e = the actual vapour pressure
es(t) = the saturation vapour pressure at ambient temp

es(t) = 6.107*exp[17.38*t/(239+t)]
where t = ambient temp in deg C
e = RH/100*es(t)

Dew point = 239*(ln(e)-ln(6.107)/(17.38-(ln(e)-ln(6.107))

where ln = natural logarithm

Let me know if that suffices

Thanks for this, and to the others who replied.

I will experiment with them formulae to see if they produce the desired
result.
--
Paul Hyett, Cheltenham, England

Jack,

The calculator at the meteoservices site you gave does not produce correct
answers. They are all too high. I give an example:

Dry bulb 20.0 C
Wet bulb 14.0 C
From my own formula (see my post this subject) Dew pt 8.6 C RH 48 %
I also get the same result using the RH humidity slide rule Mk 6A (was
standard use in Met Office before the age of the microchip)

From the meteoservices calculator, Dew pt 9.7 C RH 51 %

Personally, Jack, I would take the meteoservices calculator with a pinch of
salt.
--
Bernard Burton
Wokingham, Berkshire, UK.


Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"Jack Harrison" wrote in message
...
http://www.meteoservices.be/en/forec...a/humidity.php

Jack

"Bernard Burton" wrote in message
...
Jack,

The calculator at the meteoservices site you gave does not produce
correct
answers. They are all too high. I give an example:

Dry bulb 20.0 C
Wet bulb 14.0 C
From my own formula (see my post this subject) Dew pt 8.6 C RH 48 %
I also get the same result using the RH humidity slide rule Mk 6A (was
standard use in Met Office before the age of the microchip)

From the meteoservices calculator, Dew pt 9.7 C RH 51 %


Hi, Bernard and Jack,

It depends if they are using the psychrometer constant for Stevenson
Screens or Whirling Hygrometers (or Assman) at meteoservices.

Dry bulb 20C and wet bulb 14C would give RH 47% and DPt 8.5C in a
screen, but RH 51% and DPt 9.5C with a Whirling Hygrometer, according to
my tables.

There are also further adjustments of the constant if the wet bulb is
below 0C.

HTH,

--
Ken Cook, Copley (5miles north of Barnard Castle), County Durham.
830ft
http://mysite.freeserve.com/copley
(MO climat. site updated before 10Z and 19Z daily)
kencookATcopleydurham.freeserve.co.uk

"Bernard Burton" wrote in message
...
Jack,

Personally, Jack, I would take the meteoservices calculator with a pinch
of
salt.

Wouldn't that then change the freezing point? bg

Howard Neil