In article ,
"Mark Chamberlain (Southend)" writes:
On Tue, 29 Dec 2009 06:47:31 -0800 (PST), MahFL
wrote:

Keith..what do you mean by the crucial 3 C dew point ?


I believe that the dew point needs to drop below 0 C as a snow
indicator. I'm sure I will be put right shortly if i'm wrong

I think that the wet-bulb temperature is the critical one. IIRC that
lies in between the ordinary "dry bulb" temperature and the dew point,
Knowing any two of the three temps, I imagine one could calculate the
third id one knew how.
--
John Hall "[It was] so steep that at intervals the street broke into steps,
like a person breaking into giggles or hiccups, and then resumed
its sober climb, until it had another fit of steps."
Ursula K Le Guin "The Beginning Place"

John Hall wrote:
In article ,
"Mark Chamberlain (Southend)" writes:
On Tue, 29 Dec 2009 06:47:31 -0800 (PST), MahFL
wrote:

Keith..what do you mean by the crucial 3 C dew point ?

I believe that the dew point needs to drop below 0 C as a snow
indicator. I'm sure I will be put right shortly if i'm wrong

I think that the wet-bulb temperature is the critical one. IIRC that
lies in between the ordinary "dry bulb" temperature and the dew point,
Knowing any two of the three temps, I imagine one could calculate the
third id one knew how.

+3.3 Dew Point here atm :-(
4.4°C Dry bulb.
Wind NNE 5mph
991.3mb steady.

--
Keith (Southend)
http://www.southendweather.net
e-mail: kreh at southendweather dot net

I think that the wet-bulb temperature is the critical one. IIRC
that
lies in between the ordinary "dry bulb" temperature and the dew
point,
Knowing any two of the three temps, I imagine one could calculate
the
third id one knew how.


.... the Internet is awash with these calculators: the problem is
knowing which ones are right!

This one *appears* to do a good job, but I haven't checked it across a
broad range of readings ....

http://www.srh.noaa.gov/epz/?n=wxcalc_dewpoint

Martin.



--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

In article ,
Martin Rowley writes:
I think that the wet-bulb temperature is the critical one. IIRC
that
lies in between the ordinary "dry bulb" temperature and the dew
point,
Knowing any two of the three temps, I imagine one could calculate
the
third id one knew how.


... the Internet is awash with these calculators: the problem is
knowing which ones are right!

This one *appears* to do a good job, but I haven't checked it across a
broad range of readings ....

http://www.srh.noaa.gov/epz/?n=wxcalc_dewpoint

Martin.


Thanks. As it's on NOAA's site, one would hope that it was right!
--
John Hall "[It was] so steep that at intervals the street broke into steps,
like a person breaking into giggles or hiccups, and then resumed
its sober climb, until it had another fit of steps."
Ursula K Le Guin "The Beginning Place"

On Tue, 29 Dec 2009 21:33:28 -0000, Martin Rowley wrote:

.... the Internet is awash with these calculators: the problem is
knowing which ones are right!

This one *appears* to do a good job, but I haven't checked it across a
broad range of readings ....

http://www.srh.noaa.gov/epz/?n=wxcalc_dewpoint

I can't get that to work, keeps asking me to enter the dewpoint temp
and units (which is a radio button with one enabled anyway). Isn't it
supposed to be working out the dewpoint given the pressure,
temperature, wet bulb and RH?

Yersterday I found:

http://www.decatur.de/javascript/dew/index.html

Feed it temperature and RH and it returns dew point, probably not
100% accurate but close enough? The "about" page explains it. Not
that I understand any of it but it looks convincing. B-)

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.

On Tue, 29 Dec 2009 21:33:28 -0000, Martin Rowley wrote:
This one *appears* to do a good job, but I haven't checked it
across a
broad range of readings ....

http://www.srh.noaa.gov/epz/?n=wxcalc_dewpoint

[and]

"Dave Liquorice" wrote ...

I can't get that to work, keeps asking me to enter the dewpoint temp
and units (which is a radio button with one enabled anyway). Isn't
it
supposed to be working out the dewpoint given the pressure,
temperature, wet bulb and RH?

.... As the question earlier in the thread was how to work out the *wet
bulb*, given the dry bulb and dew point, then this is the appropriate
link. However, for other requirements, you need to choose from this
list ....

http://www.srh.noaa.gov/epz/?n=wxcalc

for practical meteorologists like what I am, this is the 'wrong' way
round of course, because we usually start with the dry bulb and wet
bulb, then require the other parameters which is probably what you
were expecting.

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

On Wed, 30 Dec 2009 10:52:34 -0000, Martin Rowley wrote:

I can't get that to work, keeps asking me to enter the dewpoint
temp
and units (which is a radio button with one enabled anyway). Isn't

it supposed to be working out the dewpoint given the pressure,
temperature, wet bulb and RH?

.... As the question earlier in the thread was how to work out the *wet
bulb*, given the dry bulb and dew point, then this is the appropriate
link.

Whoops, must have missed the slight change in thread direction. B-)

for practical meteorologists like what I am, this is the 'wrong' way
round of course, because we usually start with the dry bulb and wet
bulb, then require the other parameters which is probably what you
were expecting.

For those with AWS's though you have don't have the wet bulb temp
just temp, RH and pressure. My AWS goes "out of range" when the
(calculated) dewpoint drops below freezing. Having something I can
plug the temp and RH into that produces negative dew points is
useful. The link I gave before agrees with the NOAA site.

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.