Between 17:30 and 20:30 this evening we had around 40mm of rain according to
my automatic (LaCrosse WS-3600) weather station. According to my manual
cone-shaped gauge, which is fairly close by, we had around 18mm.

The automatic gauge is around 1 metre above ground level, and the manual
gauge is stuck into the soil.

The automatic seems to correspond well with the manual in normal conditions.

So, what's wrong? Maybe I need to replace my gauge ... again!

Also TS around 19:00. Graph of today's rain (if you read this today!) from the
automatic at http://users.aber.ac.uk/ais/weather/...hp?data=rtoday

Adrian

--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais/weather/ uk

"Adrian D. Shaw" wrote in message
...
Between 17:30 and 20:30 this evening we had around 40mm of rain
according to
my automatic (LaCrosse WS-3600) weather station. According to my
manual
cone-shaped gauge, which is fairly close by, we had around 18mm.
The automatic gauge is around 1 metre above ground level, and the
manual
gauge is stuck into the soil.
The automatic seems to correspond well with the manual in normal
conditions.

.... If you have had readings that have corresponded well in the past
(over a long period), then I would suspect a 'one-off' problem with one
or other of the gauges: the declared rainfall from the LaCrosse sounds
high to me - the showers etc., yesterday were pretty heavy, but I'm not
sure we had anything quite that perky.

Try doing a test with the auto by putting a measured amount of rainfall
through it. As you had a thunderstorm, would there be any lightning
interference with the system?

Even with high-end professional kit, things can go wrong (witness
Heathrow/03772 last couple of days), so don't necessarily go out and
replace the gauge / electronics etc., just yet: might have been a
one-off 'glitch'.

Martin.

--
FAQ & Glossary for uk.sci.weather at:-
http://homepage.ntlworld.com/booty.weather/uswfaqfr.htm
and
http://booty.org.uk/booty.weather/metindex.htm

Martin Rowley wrote:

Even with high-end professional kit, things can go wrong ...

'Bucket-bounce' even on the best TBRs can be a problem, particularly in
high rainfall rates: the bucket is filling and tipping so quickly, it
can 'bounce' part-way past the reed switch, counting two tips. Some
loggers can be set to refuse two pulses within (say) 500 msec - which
at 0.2 mm tip equates to 1440 mm/hr, which is well above the design
threshold of the instrument itself - which solves the problem.

I have two TBRs and for a while I found one was showing anomalously
high rates during close thunderstorms (one agreed with the checkgauge,
the other didn't - you always need a three-way split to be sure which
is correct) - presumably due to induced currents in the (long) cable
run. Screening the cable run solved this problem. If yours is wireless,
then obviously this won't be directly relevant, but you may find close
'sferics' induce a pulse as Martin suggests.

HTH.

Stephen Burt
Stratfield Mortimer, Berkshire

Thanks Martin and Stephen for your advice, I'll wait a bit before I decide
to replace the gauge.

I don't think the thunderstorm was quite close enough to have had an
effect on the cables, and anyway it happened again later in the evening
when no TS was around.

Adrian
--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais/weather/ uk

On 29 Aug 2006 21:43:02 +0100, Adrian D. Shaw wrote:

I don't think the thunderstorm was quite close enough to have had an
effect on the cables, and anyway it happened again later in the evening
when no TS was around.

My money would be on electromagnetic interference of some sort, be it
from lighting or the chap down the road doing a spot of welding...

The LaCrosse is budget kit like my Oregon. That was very prone to picking
up interference on the rain gauge until I fitted a capacitor and resistor
at the head end. This stops the "bucket bounce" problem either from rapid
tipping or very slow tipping. It also improved the immunity to
interference, thunderstorms within 20 miles would drive it potty, switch
some things on/off in the house would also be registered.

I can't remember the series and/or parrallel capacitor/resistor wiring I
used.

--
Cheers
Dave. pam is missing e-mail