Does anyone have a formula for calculating relative humidity using
temperature and dew-point as input data? I have a large number of these
calculations to do and using Excel is a much more attractive proposition
than using look-up tables.

Norman
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles
England

================================================== ==================
This posting expresses the personal view and opinions of the author.
Something which everyone on this planet should be able to do.
================================================== ==================

Norman, I use Teten's formula in my excel spreadsheets to derive dewpoint from
T/RH
http://www.paroscientific.com/dewpoint.htm

You'll have to a little bit of schoolboy maths to transpose the equation to get
RH from T/Td !

Will.
--

" A cup is most useful when empty "
-------------------------------------------------------------------------------
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www: http://www.lyneside.demon.co.uk

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
-------------------------------------------------------------------------------

Norman Lynagh wrote in message ...
Does anyone have a formula for calculating relative humidity using
temperature and dew-point as input data? I have a large number of these
calculations to do and using Excel is a much more attractive proposition
than using look-up tables.

Norman
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles
England

In message , Will
writes

================================================= ===================
This posting expresses the personal view and opinions of the author.
Something which everyone on this planet should be able to do.
================================================= ===================

Norman, I use Teten's formula in my excel spreadsheets to derive dewpoint from
T/RH
http://www.paroscientific.com/dewpoint.htm

You'll have to a little bit of schoolboy maths to transpose the equation to get
RH from T/Td !

Will.

Many thanks, Will. That takes me part of the way but it doesn't cope
with dew points below 0c. Many of the values I am dealing with are below
0c.

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles
England

Norman Lynagh wrote in message ...
In message , Will
writes

================================================ ====================
This posting expresses the personal view and opinions of the author.
Something which everyone on this planet should be able to do.
================================================ ====================

Norman, I use Teten's formula in my excel spreadsheets to derive dewpoint from
T/RH
http://www.paroscientific.com/dewpoint.htm

You'll have to a little bit of schoolboy maths to transpose the equation to
get
RH from T/Td !

Will.

Many thanks, Will. That takes me part of the way but it doesn't cope
with dew points below 0c. Many of the values I am dealing with are below
0c.

Norman.
(delete "thisbit" twice to e-mail)
--

OK Norman. back to basics.

If you want high accuracy for -35 to +35 C
use our old friend Clausius Clapeyron for calculating saturated and vapour
pressu

Es = 0.6112 x exp(17.67T/(T+243.5)) T in deg C
E = 0.6112 x exp(17.67Td/(Td+243.5)) Td in deg C
RH = E/Es

Will.
--

" A cup is most useful when empty "
-------------------------------------------------------------------------------
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www: http://www.lyneside.demon.co.uk

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
-------------------------------------------------------------------------------

In message , Will
writes

Norman Lynagh wrote in message ...
In message , Will
writes

=============================================== =====================
This posting expresses the personal view and opinions of the author.
Something which everyone on this planet should be able to do.
=============================================== =====================

Norman, I use Teten's formula in my excel spreadsheets to derive
dewpoint from
T/RH
http://www.paroscientific.com/dewpoint.htm

You'll have to a little bit of schoolboy maths to transpose the equation to
get
RH from T/Td !

Will.

Many thanks, Will. That takes me part of the way but it doesn't cope
with dew points below 0c. Many of the values I am dealing with are below
0c.

Norman.
(delete "thisbit" twice to e-mail)
--

OK Norman. back to basics.

If you want high accuracy for -35 to +35 C
use our old friend Clausius Clapeyron for calculating saturated and vapour
pressu

Es = 0.6112 x exp(17.67T/(T+243.5)) T in deg C
E = 0.6112 x exp(17.67Td/(Td+243.5)) Td in deg C
RH = E/Es

Will.

Excellent, Will. Many thanks.

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles
England