Yesterday we had a colossal rain storm.

My Davis recorded 0.2mm only.

I think the rain must have been so heavy that the tipping bucket
stayed down for the duration of the storm. When the rain eased off
normal operation resumed.

Any body had this happen before?

I would guess that there was between one and two inches in old units
over a period of 20 minutes.

Jeff

On 26/08/12 08:27, Jeff wrote:
Yesterday we had a colossal rain storm.

My Davis recorded 0.2mm only.

I think the rain must have been so heavy that the tipping bucket
stayed down for the duration of the storm. When the rain eased off
normal operation resumed.

Any body had this happen before?

I would guess that there was between one and two inches in old units
over a period of 20 minutes.

It happened to me the other day, not for the first time, I have to say.
Usually it's because the tipping bucket sticks horizontally with neither
bucket being under the rain gatherer's exit pipe. Then I have to tip it
over to start it again. But of course all the data are lost.

Snow too is a problem, but not generally in August!

Luckily I have a standard raingauge as well.

Hugh

--

Hugh Newbury

www.evershot-weather.org

On 26/08/2012 09:20, Hugh Newbury wrote:
On 26/08/12 08:27, Jeff wrote:
Yesterday we had a colossal rain storm.

My Davis recorded 0.2mm only.

I think the rain must have been so heavy that the tipping bucket
stayed down for the duration of the storm. When the rain eased off
normal operation resumed.

Any body had this happen before?

I would guess that there was between one and two inches in old units
over a period of 20 minutes.

It happened to me the other day, not for the first time, I have to say.
Usually it's because the tipping bucket sticks horizontally with neither
bucket being under the rain gatherer's exit pipe. Then I have to tip it
over to start it again. But of course all the data are lost.

Snow too is a problem, but not generally in August!

Luckily I have a standard raingauge as well.

Hugh

.... yes, to be utterly boring (but *correct*) even with all the fancy
stuff available, it is *essential* in my view to have some sort of check
gauge. Doesn't have to be a 'standard' copper effort - I've got one of
those, but I also have a 'cheapo' 3 inch alongside to double-check. It
needs 'correcting' - roughly uprating whatever value is given by ~10% -
but allowing for that it gives good service (and has done for many years).

In really heavy (torrential) rain (and certainly with hail) you'll lose
some PPN, but at least you'll have some sort of record.

Martin.


--
Martin Rowley
West Moors/East Dorset UK

Martin Rowley wrote:

On 26/08/2012 09:20, Hugh Newbury wrote:
On 26/08/12 08:27, Jeff wrote:
Yesterday we had a colossal rain storm.

My Davis recorded 0.2mm only.

I think the rain must have been so heavy that the tipping bucket
stayed down for the duration of the storm. When the rain eased off
normal operation resumed.

Any body had this happen before?

I would guess that there was between one and two inches in old units
over a period of 20 minutes.

It happened to me the other day, not for the first time, I have to say.
Usually it's because the tipping bucket sticks horizontally with neither
bucket being under the rain gatherer's exit pipe. Then I have to tip it
over to start it again. But of course all the data are lost.

Snow too is a problem, but not generally in August!

Luckily I have a standard raingauge as well.

Hugh

... yes, to be utterly boring (but correct) even with all the fancy stuff
available, it is essential in my view to have some sort of check gauge.
Doesn't have to be a 'standard' copper effort - I've got one of those, but I
also have a 'cheapo' 3 inch alongside to double-check. It needs 'correcting'
- roughly uprating whatever value is given by ~10% - but allowing for that it
gives good service (and has done for many years).


I agree, Martin. My Davis VP consistently measures totals around 15-20% lower
than I measure with a standard 5" copper gauge. Reliance solely on this level
of AWS is unlikely to result in accurate rainfall totals.


--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.

On 26/08/12 11:41, Norman wrote:
Martin Rowley wrote:

....

... yes, to be utterly boring (but correct) even with all the fancy stuff
available, it is essential in my view to have some sort of check gauge.
Doesn't have to be a 'standard' copper effort - I've got one of those, but I
also have a 'cheapo' 3 inch alongside to double-check. It needs 'correcting'
- roughly uprating whatever value is given by ~10% - but allowing for that it
gives good service (and has done for many years).


I agree, Martin. My Davis VP consistently measures totals around 15-20% lower
than I measure with a standard 5" copper gauge. Reliance solely on this level
of AWS is unlikely to result in accurate rainfall totals.

I regularly keep track of the difference between the AWS and the std
gauge. This month so far:

AWS 80.0mm, Std G 108.2mm

This year:

AWS 511.6mm, Std G 678.6mm

Hugh

--

Hugh Newbury

www.evershot-weather.org

A couple of comments:

A VP2 gauge should obviously not stop recording simply because rainfall is
very heavy. There must be some other explanation here. As with most less
expensive RBR's, the gauge will under-record to a limited extent during very
high rainfall rates simply because the tipping mechanism will miss rainfall
for example while it is tipping. The display may also give the impression of
missing rainfall at the time because (i) the console rain reading does not
update instantaneously but is subject to a potential delay of 1-2 minutes;
and (ii) during very heavy rain the signal on a wireless model can drop out
if the signal is relatively weak to start with (but the missing readings
should 'catch up' soon after good reception is restored - provided the down
time is not too long).

A VP2 gauge will typically under-record rainfall by a few % relative to a
reference gauge because eg of the difficulties at very high rainfall rates
mentioned above. But the larger discrepancies sometimes reported are often
not genuine like for like comparisons. Typically the VP2 gauge will be at
least a few feet in the air where it will inevitably under-record by 5-10%
relative to a ground-based gauge because of well-known wind effects. Also
the two gauges are often not exactly side-by-side and so location effects
can also come into play. (If a 0.2mm gauge has been mistakenly configured as
a 0.01" at the console or in software then this can also obviously cause an
apparent under-recording of 20-25%.)

John Dann
www.weatherstations.co.uk

If a 0.2mm gauge has been mistakenly configured as a 0.01" at the console
or in software then this can also obviously cause an apparent
under-recording of 20-25%.

John,

I thought this would be the other way about. If you configure a 0.2mm gauge
as a 0.01" (or 0.254mm) then it should over-record by 20-25%. Each tip is
meant to be recorded as 0.2mm but as it is configured as a 0.01" then it
will record as 0.254mm. So 10 tips in a day should be 2.0mm, but will be
recorded as 2.54mm in a gauge thus configured.
--
Freddie
Bayston Hill
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/#!/BaystonHillWx for hourly reports

I agree, Martin. My Davis VP consistently measures totals around 15-20%
lower
than I measure with a standard 5" copper gauge. Reliance solely on this
level
of AWS is unlikely to result in accurate rainfall totals.

At the moment my Davis VP2 is on 74mm for the month and my R&D is on almost
79.4mm for the month.
I always used my R&D rain gauge for my records.



Graham

On Sun, 26 Aug 2012 08:27:21 +0100, Jeff wrote:

Yesterday we had a colossal rain storm.

My Davis recorded 0.2mm only.

I think the rain must have been so heavy that the tipping bucket
stayed down for the duration of the storm. When the rain eased off
normal operation resumed.

Any body had this happen before?

I would guess that there was between one and two inches in old units
over a period of 20 minutes.

Jeff


I have considered a standard gauge as a refererance, but it would be
difficult to site crear of trees and obstructions, the Davis is in
clear air in the middle of a field.

The storms the other day came from the north to north east and hit us
square on.

'normal' storms from a west/south west nearly always miss us, we get
one hit in about 20years,I cannot remember the last. They often pass
within a 1/4 mile but as I say almost never hit us.

Jeff

On Sunday, August 26, 2012 1:05:52 PM UTC+1, johnd wrote:
A couple of comments:



A VP2 gauge should obviously not stop recording simply because rainfall is

very heavy. There must be some other explanation here. As with most less

expensive RBR's, the gauge will under-record to a limited extent during very

high rainfall rates simply because the tipping mechanism will miss rainfall

for example while it is tipping. The display may also give the impression of

missing rainfall at the time because (i) the console rain reading does not

update instantaneously but is subject to a potential delay of 1-2 minutes;

and (ii) during very heavy rain the signal on a wireless model can drop out

if the signal is relatively weak to start with (but the missing readings

should 'catch up' soon after good reception is restored - provided the down

time is not too long).



A VP2 gauge will typically under-record rainfall by a few % relative to a

reference gauge because eg of the difficulties at very high rainfall rates

mentioned above. But the larger discrepancies sometimes reported are often

not genuine like for like comparisons. Typically the VP2 gauge will be at

least a few feet in the air where it will inevitably under-record by 5-10%

relative to a ground-based gauge because of well-known wind effects. Also

the two gauges are often not exactly side-by-side and so location effects

can also come into play. (If a 0.2mm gauge has been mistakenly configured as

a 0.01" at the console or in software then this can also obviously cause an

apparent under-recording of 20-25%.)



John Dann

www.weatherstations.co.uk

Spot on! I once did a trial of two identical 127mm gauges, installed 15 feet apart which showed a difference of 6%.