Firstly let me apologise if this is not the right group in which to ask this
question.

I am based between Liverool and Manchester and I am about to embark on a
'pet' project which will require the local relative humidity to be below
about 60% and ideally below 50%. Keen to check the r/h, I bought an
inexpensive (or cheap!) digital hygrometer from Maplin:

http://preview.tinyurl.com/ywsspy

The spec claims a 'display' accuracy of +-3%. That would probably be good
enough, but I thought that I'd run a check against the nearest weather
station which appears to be about 20 miles away from me

Comparison with r/h measurements from there might put the claimed accuracy
of my hygrometer in some doubt. For example, the weather station was
reporting an r/h of 75% at the same time that my hygrometer was reading 58%.


If I thought that the distance wasn't an issue, I'd happily monitor the
weather station and use that as a guide. However, since I've been monitoring
it, the r/h value has never been lower than 60%, even on cold, dry days so
I'm left wondering wether it will ever drop.

Hence my questions:
1/ Is this r/h ever likely to improve (i.e, go below 60%)
2/ Does anyone know if the distance of 20% is a likely contributor to the
differences I'm seeing between the weather and my own measurements?
3/ Does anyone know what kind of r/h range we typically see in the n/w uk
across the year?
4/ Does anyone know if there are any online archives of uk r/h to give me a
feel for what time of the year the lowest r/h is likely to be? I've checked
the Met office and can't see any there.

Regards and TIA,
MikeB

In article ,
MikeB wrote:

Firstly let me apologise if this is not the right group in which to ask this
question.

I am based between Liverool and Manchester and I am about to embark on a
'pet' project which will require the local relative humidity to be below
about 60% and ideally below 50%. Keen to check the r/h, I bought an
inexpensive (or cheap!) digital hygrometer from Maplin:

http://preview.tinyurl.com/ywsspy

Just a thought and apologies if a silly question, but is this unit
simply measuring the indoor RH?

--
Bob Cox. Stoke Gifford, near Bristol, UK.

"MikeB" wrote in message ...
2/ Does anyone know if the distance of 20% is a likely contributor to the
differences I'm seeing between the weather and my own measurements?
Hygrometers are weird things. I've got the opposite problem with mine, it
seems to under-read considerably. For example, it's saying 37% RH and an air
temperature of 10.9C at the moment, which gives a dewpoint of around -3C.
Yet nearby stations are reporting a dewpoint of 5C (Manston) and 4C
(Southend).

I don't know *why* the difference should be so marked, as the air
temperature matches Manston and the screen is shaded (and has the wind
whistling through it at the moment!)

The airflow's all wrong at the moment for low humidities by the way. You
need to look out for low dewpoints but with relatively high air
temperatures, which generally occur with a polar flow; clear skies and cold
air aloft are often a recipe for such low dewpoints.

If you use a site like this:

http://wxweb.meteostar.com/sample/sa...html?text=EGGP

you can find out what the forecast for dewpoints is from the GFS. The BBC
5-dayers have a humidity forecast as well, but it's a value for 12 noon on a
day rather than the detail you get from the above:

http://www.bbc.co.uk/weather/5day.shtml?id=2387

(both links for Liverpool)

As for climate tables regarding humidity, they're not really of much use: as
most of our weather is maritime in origin the averages will be quite high.
The best bet would be to look out for the sort of setups which give low
humiditied in your area.

NB - as you're in the NW you'll be looking out for different things than I
would here. For example, a polar NW'ly would give low humidities, yet up
there you'd get more in the way of moisture from the Atlantic. Local
knowledge is the key!

weatheronline has an archive going back a year or so

http://www.weatheronline.co.uk/ukweather.htm

Jack

"Bob Cox" wrote in message
...
Just a thought and apologies if a silly question, but is this unit
simply measuring the indoor RH?

Thanks Bob and no, it's not a silly question. I was originally interested in
the RH in the garage as that's where my pet project will be undertaken.
However, for the purposes of the comparison, I've been leaving it outside.
Having said that, it's situated close to the house but it is sheltered so
that it can't be rained on.

Regards,
MikeB

wrote in message
...
weatheronline has an archive going back a year or so

http://www.weatheronline.co.uk/ukweather.htm

Thanks,

I've had a shutfy and the disappointing news is that RH (very) rarely seems
to drop below 60% where I am!

Regards,
MikeB

"Darren Prescott" wrote in message
...
http://wxweb.meteostar.com/sample/sa...html?text=EGGP
http://www.bbc.co.uk/weather/5day.shtml?id=2387
(both links for Liverpool)

Thanks Darren. These look really useful but I suspect that I'll have to move
to Nevada in order to complete my project!

Regards,
MikeB

I can let you have current and archive RH measurements from my Vantage Pro 2
for locking birchwood, Warrington area if it's any use.

ps. whats the project ?

Mark

"MikeB" wrote in message
...
Firstly let me apologise if this is not the right group in which to ask
this question.

I am based between Liverool and Manchester and I am about to embark on a
'pet' project which will require the local relative humidity to be below
about 60% and ideally below 50%. Keen to check the r/h, I bought an
inexpensive (or cheap!) digital hygrometer from Maplin:

http://preview.tinyurl.com/ywsspy

The spec claims a 'display' accuracy of +-3%. That would probably be good
enough, but I thought that I'd run a check against the nearest weather
station which appears to be about 20 miles away from me

Comparison with r/h measurements from there might put the claimed accuracy
of my hygrometer in some doubt. For example, the weather station was
reporting an r/h of 75% at the same time that my hygrometer was reading
58%.


If I thought that the distance wasn't an issue, I'd happily monitor the
weather station and use that as a guide. However, since I've been
monitoring it, the r/h value has never been lower than 60%, even on cold,
dry days so I'm left wondering wether it will ever drop.

Hence my questions:
1/ Is this r/h ever likely to improve (i.e, go below 60%)
2/ Does anyone know if the distance of 20% is a likely contributor to the
differences I'm seeing between the weather and my own measurements?
3/ Does anyone know what kind of r/h range we typically see in the n/w uk
across the year?
4/ Does anyone know if there are any online archives of uk r/h to give me
a feel for what time of the year the lowest r/h is likely to be? I've
checked the Met office and can't see any there.

Regards and TIA,
MikeB

On Fri, 25 Jan 2008 at 15:25:52, MikeB
wrote in uk.sci.weather :

wrote in message
...
weatheronline has an archive going back a year or so

http://www.weatheronline.co.uk/ukweather.htm

Thanks,

I've had a shutfy and the disappointing news is that RH (very) rarely seems
to drop below 60% where I am!

It is rare for it to do so in winter, certainly.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

"M.John" mDOTjohnATwhichDOTnet wrote in message
...
I can let you have current and archive RH measurements from my Vantage Pro
2 for locking birchwood, Warrington area if it's any use.

Mark,

thanks for that. Are you based in Locking Stumps? My dad lives there! I'm in
Whittle Hall, between Great Sankey and Burtonwood.

From the data that I've looked at today, it seems like we rarely get below
60% around these parts and then it's only for a short time. If that's the
case, I'm going to have to do something to control the environment in my
garage - something that I was hoping to avoid on both cost and convenience
grounds. Anyway, if you have data that contradicts this, I'd really be
interested in it:


ps. whats the project ?

Oh, it's not anything gripping. Well it is to me, but probably not to many
others. I'm hoping to spray-finish a guitar using nitrocellulose lacquer. As
a long-time player, I've always wanted to have a go but the experts tell me
that nitro tends to 'blush' if sprayed above about 60% RH.

It's possible to use wood-stain and then apply something like tung oil to
seal and protect the wood but I'm not as keen on the visual effect of oil
finishes.

I have to admit that this project has been an eye-opener. Up until a few
years ago, I rarely went out of my way to look at a weather forecast. Even
recently, I really only ever looked at the big-picture details when I
venture out: Is it overcast, rainy, windy etc.

However, the project has led me to investigate RH, an aspect of the weather
that I've never really considered. It was on another newsgroup
(rec.music.makers.builders) that I learned that RH can be an issue when
spraying cellulose. So I started to look into that and it led me to here.

This is what I find fascinating and invaluable about newsgroups: Start
looking into something and you never know where you're going to end up.

Regards,
MikeB