11/10/06

Well the storms last night in Devon gave me a daily 1800-1800 total of 56.4 mm.
This is the highest 24 hour total I have ever recorded since moving here. Last
highest was 51.7 mm on 23/10/04. A very large fall but not exceptional for this
area.

There were 4 separate storm cells. The biggest was around 2340 local which had a
rainfall rate of 128.3 mm/h and a 20 minute total of 8.1 mm. Bar fell by 0.5 mp
in 10 minutes 2340-2350 (wake low of storm). Lots of lightning but thunder was
intermittent. Rainfall, however, was torrential but also came in short bursts.
No problems up here whatsoever (we never do with rain). Now like it has never
happened. Flash flooding elsewhere in Devon though.

Now, the manual total was 56.4 mm but my AWS VP2 read just 42.7 mm, why the big
discrepancy? All I can think of is that the rates were so large that the tipping
mechanism could not cope. A sobering thought for users of AWS I think. Comments
appreciated on this?

I'm chuffed. (a) we had a storm, (b) I got a pretty big rainfall total.

Will.
--
-------------------------------------------------------------------------------
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www: http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
-------------------------------------------------------------------------------

Just found out they got 58.1mm in Tavistock!

Will.
--

"Will Hand" wrote in message
...
11/10/06

Well the storms last night in Devon gave me a daily 1800-1800 total of 56.4
mm.
This is the highest 24 hour total I have ever recorded since moving here. Last
highest was 51.7 mm on 23/10/04. A very large fall but not exceptional for
this
area.

There were 4 separate storm cells. The biggest was around 2340 local which had
a
rainfall rate of 128.3 mm/h and a 20 minute total of 8.1 mm. Bar fell by 0.5
mp
in 10 minutes 2340-2350 (wake low of storm). Lots of lightning but thunder was
intermittent. Rainfall, however, was torrential but also came in short bursts.
No problems up here whatsoever (we never do with rain). Now like it has never
happened. Flash flooding elsewhere in Devon though.

Now, the manual total was 56.4 mm but my AWS VP2 read just 42.7 mm, why the
big
discrepancy? All I can think of is that the rates were so large that the
tipping
mechanism could not cope. A sobering thought for users of AWS I think.
Comments
appreciated on this?

I'm chuffed. (a) we had a storm, (b) I got a pretty big rainfall total.

Will.
--
------------------------------------------------------------------------------
-
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www: http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
------------------------------------------------------------------------------
-

Re your tipping bucket query, Campbell Sci quote an error of 4% at 25 mm/hr,
and 8% at 133 mm/hr, due to losses during the tipping of the bucket. I don't
know if this is a linear effect, but I am installing a TBR at my site in the
next couple of weeks, and I will try to check the error values at higher
rates.
B

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"Will Hand" wrote in message
...
11/10/06

Well the storms last night in Devon gave me a daily 1800-1800 total of
56.4 mm.
This is the highest 24 hour total I have ever recorded since moving here.
Last
highest was 51.7 mm on 23/10/04. A very large fall but not exceptional for
this
area.

There were 4 separate storm cells. The biggest was around 2340 local which
had a
rainfall rate of 128.3 mm/h and a 20 minute total of 8.1 mm. Bar fell by
0.5 mp
in 10 minutes 2340-2350 (wake low of storm). Lots of lightning but thunder
was
intermittent. Rainfall, however, was torrential but also came in short
bursts.
No problems up here whatsoever (we never do with rain). Now like it has
never
happened. Flash flooding elsewhere in Devon though.

Now, the manual total was 56.4 mm but my AWS VP2 read just 42.7 mm, why
the big
discrepancy? All I can think of is that the rates were so large that the
tipping
mechanism could not cope. A sobering thought for users of AWS I think.
Comments
appreciated on this?

I'm chuffed. (a) we had a storm, (b) I got a pretty big rainfall total.

Will.
--
--------------------------------------------------------------------------
-----
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www:
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
--------------------------------------------------------------------------
-----

Thanks Bernard, that would be very useful to know.

I don't have a proper dedicated TBR just a Davis VP2 which works on same
principle and I suspect VP2 errors will be even greater.

Looks like I will be retaining my manual instruments and Stevenson screen for
many years to come given the "issues" I have had with my AWS recently. They are
excellent pieces of kit, but in my view they supplement rather than replace
manual instruments. At least the relatively cheaper (not cheap) ones like Davis.

Will.
--

"Bernard Burton" wrote in message
...
Re your tipping bucket query, Campbell Sci quote an error of 4% at 25 mm/hr,
and 8% at 133 mm/hr, due to losses during the tipping of the bucket. I don't
know if this is a linear effect, but I am installing a TBR at my site in the
next couple of weeks, and I will try to check the error values at higher
rates.
B

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"Will Hand" wrote in message
...
11/10/06

Well the storms last night in Devon gave me a daily 1800-1800 total of
56.4 mm.
This is the highest 24 hour total I have ever recorded since moving here.
Last
highest was 51.7 mm on 23/10/04. A very large fall but not exceptional for
this
area.

There were 4 separate storm cells. The biggest was around 2340 local which
had a
rainfall rate of 128.3 mm/h and a 20 minute total of 8.1 mm. Bar fell by
0.5 mp
in 10 minutes 2340-2350 (wake low of storm). Lots of lightning but thunder
was
intermittent. Rainfall, however, was torrential but also came in short
bursts.
No problems up here whatsoever (we never do with rain). Now like it has
never
happened. Flash flooding elsewhere in Devon though.

Now, the manual total was 56.4 mm but my AWS VP2 read just 42.7 mm, why
the big
discrepancy? All I can think of is that the rates were so large that the
tipping
mechanism could not cope. A sobering thought for users of AWS I think.
Comments
appreciated on this?

I'm chuffed. (a) we had a storm, (b) I got a pretty big rainfall total.

Will.
--
--------------------------------------------------------------------------
-----
A COL BH site in East Dartmoor at Haytor, Devon 310m asl (1017 feet).

mailto:
www:
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm

DISCLAIMER - All views and opinions expressed by myself are personal
and do not necessarily represent those of my employer.
--------------------------------------------------------------------------
-----

Will Hand wrote:

11/10/06

Well the storms last night in Devon gave me a daily 1800-1800 total of 56.4 mm.
This is the highest 24 hour total I have ever recorded since moving here.

Records at my present site start in 1992, but my 4 largest 24 hour
totals are all this century.

84.5mm on 13/11/2002 - the day of the St. Ives flood - 100mm+ on the
moors above St. Ives.
78.9mm on 26/06/2006 - When there was considerable flooding just down
the road
62.8mm on 31/12/2002 - Extensive flooding in & around Pz
62.5mm on 14/09/2000

On the other hand, we missed all the heavy rain the lasr 24 hours, just
13mm overnight.

Graham
Penzance

Will

Here in south-east Devon I only scraped 9.7 mm last night despite a few
torrential downpours and lightning on and off throughout the night. The big
stuff seemed to pass just to our west, i.e., your way!
________________
Nick G
Otter Valley, Devon
80 m amsl
http://www.ottervalley.co.uk

"Will Hand" wrote in message
...
11/10/06

.. Flash flooding elsewhere in Devon though.

Now, the manual total was 56.4 mm but my AWS VP2 read just 42.7 mm, why
the big
discrepancy? All I can think of is that the rates were so large that the
tipping
mechanism could not cope. A sobering thought for users of AWS I think.
Comments
appreciated on this?

This topic crops up from time to time.
Some earlier discussion here http://tinyurl.com/p6nho

After a few months using just the Davis 'Rain Collector' I returned to using
the standard rain gauge alongside it as well, as a check. Invariably there
is a difference following heavy rainfall-but we don't get too much of that
here.

All the best
--
George in Epping, West Essex (107m asl)
www.eppingweather.co.uk
www.winter1947.co.uk

Will Hand wrote:
Just found out they got 58.1mm in Tavistock!

Will.

"Will Hand" wrote in message
...
11/10/06

Well the storms last night in Devon gave me a daily 1800-1800 total
of 56.4 mm. This is the highest 24 hour total I have ever recorded
since moving here. Last highest was 51.7 mm on 23/10/04. A very
large fall but not exceptional for this area.

There were 4 separate storm cells. The biggest was around 2340 local
which had a rainfall rate of 128.3 mm/h and a 20 minute total of 8.1
mm. Bar fell by 0.5 mp in 10 minutes 2340-2350 (wake low of storm).
Lots of lightning but thunder was intermittent. Rainfall, however,
was torrential but also came in short bursts. No problems up here
whatsoever (we never do with rain). Now like it has never happened.
Flash flooding elsewhere in Devon though.

Now, the manual total was 56.4 mm but my AWS VP2 read just 42.7 mm,
why the big discrepancy? All I can think of is that the rates were
so large that the tipping mechanism could not cope. A sobering
thought for users of AWS I think. Comments appreciated on this?

I'm chuffed. (a) we had a storm, (b) I got a pretty big rainfall
total.

Will.
--
I assume that the ISS is around 1m off the ground and the manual gauge is at
ground level. Is there a possibility that the wind was stronger at 1m due to
the boundary layer effect and the rain was blown across the top of the ISS
during the heavy bursts of rain?

I don't have a manual gauge to compare my own readings against but from the
monthly MO contoured maps I definitely think that my Davis station gives low
readings. It is possible to adjust the collector but without an accurate
gauge to work out the adjustment that is not really sensible. Perhaps I
need to think about getting a manual gauge.

I have lost very little data over the 5 years I have had the station so in
other respects the Davis has been excellent value and reliable. I did lose
some wind data when I had to get the anemometer repaired (reed switch
failed) but due to the position those readings are not accurate.


Alan Gardiner
Chiswell Green, St Albans
101m ASL

"Alan Gardiner" wrote in message
...


Will Hand wrote:
Just found out they got 58.1mm in Tavistock!

Will.

"Will Hand" wrote in message
...
11/10/06

Well the storms last night in Devon gave me a daily 1800-1800 total
of 56.4 mm. This is the highest 24 hour total I have ever recorded
since moving here. Last highest was 51.7 mm on 23/10/04. A very
large fall but not exceptional for this area.

There were 4 separate storm cells. The biggest was around 2340 local
which had a rainfall rate of 128.3 mm/h and a 20 minute total of 8.1
mm. Bar fell by 0.5 mp in 10 minutes 2340-2350 (wake low of storm).
Lots of lightning but thunder was intermittent. Rainfall, however,
was torrential but also came in short bursts. No problems up here
whatsoever (we never do with rain). Now like it has never happened.
Flash flooding elsewhere in Devon though.

Now, the manual total was 56.4 mm but my AWS VP2 read just 42.7 mm,
why the big discrepancy? All I can think of is that the rates were
so large that the tipping mechanism could not cope. A sobering
thought for users of AWS I think. Comments appreciated on this?

I'm chuffed. (a) we had a storm, (b) I got a pretty big rainfall
total.

Will.
--
I assume that the ISS is around 1m off the ground and the manual gauge is at
ground level. Is there a possibility that the wind was stronger at 1m due to
the boundary layer effect and the rain was blown across the top of the ISS
during the heavy bursts of rain?


Alan we do get that effect fairly often with slanting rain (or snow) but on this
occasion the rain was coming down like stair rods, vertically.

I don't have a manual gauge to compare my own readings against but from the
monthly MO contoured maps I definitely think that my Davis station gives low
readings. It is possible to adjust the collector but without an accurate
gauge to work out the adjustment that is not really sensible. Perhaps I
need to think about getting a manual gauge.

I have lost very little data over the 5 years I have had the station so in
other respects the Davis has been excellent value and reliable. I did lose
some wind data when I had to get the anemometer repaired (reed switch
failed) but due to the position those readings are not accurate.


Yes they are reliable. Just not as good as a manual gauge. At some stage I'll
investigate the issue but no time yet as I have things like work and other
interests to fit in.

Cheers,

Will.
--