My memories as an observer on a wet day or night shift, were of hourly observations where I reported total hourly rainfall typically in the range 0.2 to 2 mm per hour. Admittedly my memory isn't fantastic, but nowadays if it rains (and I know I live in Devon now) it pours!

I do have an automatic weather station to watch rainfall intensities which might skew things, but as an observer we always had the tipping bucket gauge that gave off an audible click in the office as the counter updated, so it's not that I'm any more attentive than I was back then. Don't get me wrong, there were many occasions in showers or thunderstorms when you could report closer to 10 mm in a single hour, and I don't think the frequency of those events has changed. It's the other slow-moving frontal events I am thinking of, when instead of reporting several hours of slight (0.6 mm/hr) occasionally moderate rain (0.6 to 3.9 mm/hr), and perhaps an hour of heavier rain (=4.0 mm/hr) as the front passed through, but in recent years all you just seem to get is a succession of hours of heavy rain.

Perhaps it's that I'm finally coming to terms (after 12 years) with how rain falls in this part of the country and it's just taken me a long time to notice it!

Anyway here is my best guess of rainfall accumulations across the UK for yesterday 0700 and today at 0645 UTC (13/14 August 2015). I must say the total is spot on for here in mid-Devon. There is a sharp line running down through the British Isles marking the extent of the rain, and it also captures a number of drier pockets in East Anglia, West Wales and Central southern England. see http://wp.me/p3yVic-1hS

Teignmouth 51.8mm midnight to 9am http://www.teignmouth-nci.org.uk/live-weather.html

That's exeptional for Teignmouth, & one of the wettest days on record for the resort!

"xmetman" wrote in message
...
My memories as an observer on a wet day or night shift, were of hourly
observations where I reported total hourly rainfall typically in the range
0.2 to 2 mm per hour. Admittedly my memory isn't fantastic, but nowadays if
it rains (and I know I live in Devon now) it pours!

I do have an automatic weather station to watch rainfall intensities which
might skew things, but as an observer we always had the tipping bucket
gauge that gave off an audible click in the office as the counter updated,
so it's not that I'm any more attentive than I was back then. Don't get me
wrong, there were many occasions in showers or thunderstorms when you could
report closer to 10 mm in a single hour, and I don't think the frequency of
those events has changed. It's the other slow-moving frontal events I am
thinking of, when instead of reporting several hours of slight (0.6 mm/hr)
occasionally moderate rain (0.6 to 3.9 mm/hr), and perhaps an hour of
heavier rain (=4.0 mm/hr) as the front passed through, but in recent years
all you just seem to get is a succession of hours of heavy rain.

Perhaps it's that I'm finally coming to terms (after 12 years) with how
rain falls in this part of the country and it's just taken me a long time
to notice it!
================================

Yes you must be.

===================
Anyway here is my best guess of rainfall accumulations across the UK for
yesterday 0700 and today at 0645 UTC (13/14 August 2015). I must say the
total is spot on for here in mid-Devon. There is a sharp line running down
through the British Isles marking the extent of the rain, and it also
captures a number of drier pockets in East Anglia, West Wales and Central
southern England. see http://wp.me/p3yVic-1hS
===================

Haytor is 51mm. How are you estimating your totals Bruce. Surely you are not
assuming dwell times for the whole of the radar return? E.g if you have
quarterly reports then if you use a dwell time of 0.25 hours then you will
normally over-estimate. We found that out in the Nowcasting department way
back in the 90s when you were in the Office. Better to use 5 minute or even
1 minute radar data but there are more sophisticated algorithms that look at
the standard deviation of returns over the whole period and essentially fit
an accumulation model to the data. Yours is an excellent poor man's
representation of the data and does give a quick overview but I'm worried
that your readers wil take it as gospel when it could be so much better? Do
you reference your methodology anywhere?

Will
--
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

"Dave" wrote in message
...
Teignmouth 51.8mm midnight to 9am
http://www.teignmouth-nci.org.uk/live-weather.html

That's exeptional for Teignmouth, & one of the wettest days on record for
the resort!

Hi David, yes indeed, many thanks. Beats Haytor by a mile which is very
unusual.

Will
--
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

On Friday, August 14, 2015 at 9:15:22 AM UTC+1, Dave wrote:
Teignmouth 51.8mm midnight to 9am http://www.teignmouth-nci.org.uk/live-weather.html

That's exeptional for Teignmouth, & one of the wettest days on record for the resort!

Ant Veal has 32mm for Teignmouth for yesterday and then an amazing 42mm since midnight. Quite a difference from the Coastguard lookout, but still exceptional for Teignmouth. Still raining, but only light stuff. One hell of a slow clearance!!

http://www.teignmouthweather.co.uk/current.html

Will, I'll check the official Met Station 24hrs 10am-10am on the seafront by the Pier once I've finished work.

On Friday, August 14, 2015 at 9:47:20 AM UTC+1, Dave wrote:
Will, I'll check the official Met Station 24hrs 10am-10am on the seafront by the Pier once I've finished work.

Will be good to compare all three. TY.

Official Teignmouth Met Office Station rainfall 24hrs to 10am 14-Aug-15 was 50.1 mm or 1.972 inches in old money.

I can only remember one or two other occasions when 50mm has been exceeded.

On Friday, August 14, 2015 at 7:29:21 PM UTC+1, Dave wrote:
Official Teignmouth Met Office Station rainfall 24hrs to 10am 14-Aug-15 was 50.1 mm or 1.972 inches in old money.

I can only remember one or two other occasions when 50mm has been exceeded.

Ant Veal has 42.4mm. East Cliff station has 52.6mm. An amazingly wet day!

On Friday, 14 August 2015 09:25:32 UTC+1, wrote:
"xmetman" wrote in message
...
My memories as an observer on a wet day or night shift, were of hourly
observations where I reported total hourly rainfall typically in the range
0.2 to 2 mm per hour. Admittedly my memory isn't fantastic, but nowadays if
it rains (and I know I live in Devon now) it pours!

I do have an automatic weather station to watch rainfall intensities which
might skew things, but as an observer we always had the tipping bucket
gauge that gave off an audible click in the office as the counter updated,
so it's not that I'm any more attentive than I was back then. Don't get me
wrong, there were many occasions in showers or thunderstorms when you could
report closer to 10 mm in a single hour, and I don't think the frequency of
those events has changed. It's the other slow-moving frontal events I am
thinking of, when instead of reporting several hours of slight (0.6 mm/hr)
occasionally moderate rain (0.6 to 3.9 mm/hr), and perhaps an hour of
heavier rain (=4.0 mm/hr) as the front passed through, but in recent years
all you just seem to get is a succession of hours of heavy rain.

Perhaps it's that I'm finally coming to terms (after 12 years) with how
rain falls in this part of the country and it's just taken me a long time
to notice it!
================================

Yes you must be.

===================
Anyway here is my best guess of rainfall accumulations across the UK for
yesterday 0700 and today at 0645 UTC (13/14 August 2015). I must say the
total is spot on for here in mid-Devon. There is a sharp line running down
through the British Isles marking the extent of the rain, and it also
captures a number of drier pockets in East Anglia, West Wales and Central
southern England. see http://wp.me/p3yVic-1hS
===================

Haytor is 51mm. How are you estimating your totals Bruce. Surely you are not
assuming dwell times for the whole of the radar return? E.g if you have
quarterly reports then if you use a dwell time of 0.25 hours then you will
normally over-estimate. We found that out in the Nowcasting department way
back in the 90s when you were in the Office. Better to use 5 minute or even
1 minute radar data but there are more sophisticated algorithms that look at
the standard deviation of returns over the whole period and essentially fit
an accumulation model to the data. Yours is an excellent poor man's
representation of the data and does give a quick overview but I'm worried
that your readers wil take it as gospel when it could be so much better? Do
you reference your methodology anywhere?

Will
--
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

Will

I have a very simple approach - I keep three arrays of intensities to match the rainfall intensities low/medium/high:

TIntensitiesLow : array[0..8] of double = (0, 0.01, 0.5 , 1 , 2, 4, 8, 16, 32);
TIntensitiesMid : array[0..8] of double = (0, 0.25, 0.75, 1.5, 3, 6, 12, 24, 48);
TIntensitiesHigh : array[0..8] of double = (0, 0.5, 1, 2 , 4, 8, 16, 32, 64);

As you can see the high intensity array matches the lower of the seven mm/hr values displayed on the weather radar page. I suppose I could have added another couple of arrays to cover the mean and the max of the range as well..
By default I use the medium setting which as you can see I've reduced from the lower range value by around 25%. This is what I normally use when running the accumulation, I look up the pixel colour and take a quarter of the 60 minute intensity and add it to my running accumulation for each pixel.

As you point out if we had more frequent weather radar images estimates would be more exact. Increasing the size of the image would enable to show more detail, but to be realistic this is not a big issue, because an 18 hour accumulation takes about 25 seconds to run and create a tabulated list of accumulations for 3100 places across the British Isles, which makes it a usable tool. The big pain is that the Met Office don't produce a single weather radar image (they do in the DataPoint service but the last time I looked it was not hi-res and has a weird projection), so I have to stitch a grid of tiles together before I can even display an image in a viewer.

As for fooling the user, I always make it clear in my blog or in the images that I generate the accumulation is an estimate. I see it as being no more misleading than an original image, which at times can be very misleading, with precipitation from medium level cloud that never reaches the surface, bright banding in winter, and 'spoking' from numerous sites especially Chenies caused by nearby trees (which I have blogged about).

I noticed recently that Weather Online are doing a similar thing to what I'm doing with accumulations, they may have beat me to it, but they can't match my tabulated list of 3,100 wettest places (although it may be in the premium version) which as far as I know is unique, and all generated from what is after all a very simple application.

What beats me is the Met Office have accumulations from the Weather Radar that they generate all the time. I asked for them to be released so we could display them in NAMIS and Nimbus but hit a blank wall. They may have been available on Horace or as far as I know Visual Weather but one hopes that must have changed by now. In my opinion they would make an invaluable resource for the Wet Bench team. Just before I left I did some work for that team and proposed that we combine estimated hourly accumulations gleaned from weather radar, with observational SREW reports (either 60 minute or even more frequent ones because they are available) from SAMOS sites, climate stations and all the hundreds of automatic gauges the Environment Agency have, it never happened. Perhaps it has now. If you've got the data you have to visualise it to make the best sense of it.

Bruce.

PS If anyone from the old firm is reading this, and would like a Rainfall TDA similar to what I've outlined above, please let the relevant people know that I am available, reasonably cheap, and a lot better programmer than when I left over three years ago!