According to my Davis VP there was no precipitation today before 1230z.
From that time it then shows steady moderate rain up to the present time
at a rate of about 1 mm/hr. Of course, what happened is that snow
collected in the funnel this morning while the temperature was below
freezing. It has then steadily melted through the afternoon and is being
measured as ongoing precipitation.

Does anyone know how this problem is dealt with in the automatic weather
stations in the Met Office synoptic network? Is the rain gauge heated so
that snow is melted as it falls? Or do these stations suffer from the
same problem that I have had with mine today?

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles 85m a.s.l.
England

I believe they are heat assisted Norman, however, don't quote me on this.

Mike
www.dudleyweather.co.uk

"Norman Lynagh" wrote in
message ...
According to my Davis VP there was no precipitation today before 1230z.
From that time it then shows steady moderate rain up to the present time
at a rate of about 1 mm/hr. Of course, what happened is that snow
collected in the funnel this morning while the temperature was below
freezing. It has then steadily melted through the afternoon and is being
measured as ongoing precipitation.

Does anyone know how this problem is dealt with in the automatic weather
stations in the Met Office synoptic network? Is the rain gauge heated so
that snow is melted as it falls? Or do these stations suffer from the same
problem that I have had with mine today?

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles 85m a.s.l.
England

"Norman Lynagh" wrote

According to my Davis VP there was no precipitation today before
1230z. From that time it then shows steady moderate rain up to the
present time at a rate of about 1 mm/hr. Of course, what happened is
that snow collected in the funnel this morning while the temperature
was below freezing. It has then steadily melted through the afternoon
and is being measured as ongoing precipitation.

Does anyone know how this problem is dealt with in the automatic
weather stations in the Met Office synoptic network? Is the rain
gauge heated so that snow is melted as it falls? Or do these stations
suffer from the same problem that I have had with mine today?

I believe that the gauges are supplied with low-level heating elements
.... this is what the 'official' word is from the document which relates
to Automatic Weather Stations (AWS), which you can find on the Met
Office web site (see link below) ....
" The gauge can be heated to ensure that it functions when the air
temperature falls below freezing. Although this does enable snow to be
melted, only

approximate values of frozen precipitation can be obtained in this way.
The low terminal velocity of snowflakes and the risk of lying snow being
blown into the

gauge make snow measurements unreliable. If the gauge is not heated it
can become frozen, giving a spurious reading of nil when in fact rain or
snow has

fallen. In these periods the CAWS missing data indicator (88888) should
be used. Snow should be cleared from the funnel each day. "

(Begs the question about what happens when the station, as so many
nowadays, is unmanned.)

http://www.metoffice.gov.uk/publicat...ons/index.html

(follow the link from 'More information on automatic weather
measurements', but beware, it is a large PDF document.)

Martin.


--
Martin Rowley
Bracknell

In message , Martin Rowley
m writes
"Norman Lynagh" wrote

According to my Davis VP there was no precipitation today before
1230z. From that time it then shows steady moderate rain up to the
present time at a rate of about 1 mm/hr. Of course, what happened is
that snow collected in the funnel this morning while the temperature
was below freezing. It has then steadily melted through the afternoon
and is being measured as ongoing precipitation.

Does anyone know how this problem is dealt with in the automatic
weather stations in the Met Office synoptic network? Is the rain
gauge heated so that snow is melted as it falls? Or do these stations
suffer from the same problem that I have had with mine today?

I believe that the gauges are supplied with low-level heating elements
... this is what the 'official' word is from the document which relates
to Automatic Weather Stations (AWS), which you can find on the Met
Office web site (see link below) ....
" The gauge can be heated to ensure that it functions when the air
temperature falls below freezing. Although this does enable snow to be
melted, only

approximate values of frozen precipitation can be obtained in this way.
The low terminal velocity of snowflakes and the risk of lying snow being
blown into the

gauge make snow measurements unreliable. If the gauge is not heated it
can become frozen, giving a spurious reading of nil when in fact rain or
snow has

fallen. In these periods the CAWS missing data indicator (88888) should
be used. Snow should be cleared from the funnel each day. "

(Begs the question about what happens when the station, as so many
nowadays, is unmanned.)

http://www.metoffice.gov.uk/publicat...ons/index.html

(follow the link from 'More information on automatic weather
measurements', but beware, it is a large PDF document.)

Martin.

Thanks for that Martin. I've downloaded the document. I note that it
says the gauge "can" be heated. It doesn't say that all are heated.
Indeed it implies that not all are heated.

The reason why I asked the question is that measurements from AWS are
included in the archived national meteorological database on an equal
basis to observations from a manned site. If a rain gauge is not heated
the precipitation from a snow event could easily be assigned to the
wrong time period, as would be the case with my Davis VP measurements
today. This could be of great significance if the archived data were to
be used in litigation or in investigation of an iinsurance claim several
years after the event. By that time it might not easily be identified
that there could be a problem with the reliability of the rainfall
measurements.

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles 85m a.s.l.
England

On 8 Feb, 17:24, Norman Lynagh normanthis...@thisbitweather-
consultancy.com wrote:
Does anyone know how this problem is dealt with in the automatic weather
stations in the Met Office synoptic network? Is the rain gauge heated so
that snow is melted as it falls? Or do these stations suffer from the
same problem that I have had with mine today?

Although we are a Met Office climatological station, rather than a
synoptic station, our rain gauge is heated primarily as a precaution
against frost damge, though the snow has quite efficiently melted
today as it fell from 0520hr onwards. Its readings tally very well
with the standard gauge with snow melted in the more traditional
method!

Steve Jackson
Bablake Weather Station
Coventry UK
www.bablakeweather.co.uk

My Snowden guage ,which resembled an igloo by 0800 this morning ,produced
12.3mm of melt water by this evening ,Patently that must be wrong but what
can one do to ignore the way it melted into the can ?
There was very little drifting..

RonB...
"Steve J" wrote in message
ups.com...
On 8 Feb, 17:24, Norman Lynagh normanthis...@thisbitweather-
consultancy.com wrote:
Does anyone know how this problem is dealt with in the automatic weather
stations in the Met Office synoptic network? Is the rain gauge heated so
that snow is melted as it falls? Or do these stations suffer from the
same problem that I have had with mine today?

Although we are a Met Office climatological station, rather than a
synoptic station, our rain gauge is heated primarily as a precaution
against frost damge, though the snow has quite efficiently melted
today as it fell from 0520hr onwards. Its readings tally very well
with the standard gauge with snow melted in the more traditional
method!

Steve Jackson
Bablake Weather Station
Coventry UK
www.bablakeweather.co.uk

"Ron Button" wrote in message
...
My Snowden guage ,which resembled an igloo by 0800 this morning ,produced
12.3mm of melt water by this evening ,Patently that must be wrong but what
can one do to ignore the way it melted into the can ?
There was very little drifting..

RonB...
"Steve J" wrote in message
ups.com...
On 8 Feb, 17:24, Norman Lynagh normanthis...@thisbitweather-
consultancy.com wrote:
Does anyone know how this problem is dealt with in the automatic weather
stations in the Met Office synoptic network? Is the rain gauge heated so
that snow is melted as it falls? Or do these stations suffer from the
same problem that I have had with mine today?

Although we are a Met Office climatological station, rather than a
synoptic station, our rain gauge is heated primarily as a precaution
against frost damge, though the snow has quite efficiently melted
today as it fell from 0520hr onwards. Its readings tally very well
with the standard gauge with snow melted in the more traditional
method!

Steve Jackson
Bablake Weather Station
Coventry UK
www.bablakeweather.co.uk



To my knowledge none of the synoptic stations ie RAF stations with tipping
bucket rain guages have heaters in them. Many, most of these are on
automatic over the weekend so collect snow in the funnel waiting for an
observer to melt it with a balloon filled with hot water or the like!

Colin Lush