Rainfall info 18th/19th November 2009

alanucc

Hi all,

Is it possible to source rainfall data for the 18th / 19th November in the Cork region, such as hourly rainfall, radar images etc? I'm aware that the MET have it available, but I don't want to pay for it :P

Trogdor

Radar images are here anyway but it appears the shannon radar was down at the time and it doesn't seem to be included in the composite images..
http://www.meteox.com/hist.aspx?URL

alanucc

Thanks very much.

Martron

this might help http://www.tulligweather.net/

Redsunset

Well there's savage analysis from Met Eireann,perhaps you have not seen this excellent report.

http://www.met.ie/publications/Rainfall%20November%202009.pdf


November 2009 is notable for the high rainfall recorded and the consequent severe flooding experienced in many parts of the country. Atlantic depressions passing close to Ireland brought wet and windy conditions throughout almost all of November, continuing a pattern of very unsettled weather over Ireland which began in the middle of October. Rainfall totals for November were the highest on record at most stations, including the long-term station at Valentia Observatory, where records extend back over 100 years. Valentia’s total of 360mm was its highest of any month since observations began in the area in 1866. This report contains an analysis of approximately 440 rainfall stations in the Met Éireann rainfall network.

alanucc

No I hadn't come across that report actually thanks!

Does anyone find it odd that the Lee catchment doesnt seem to have been hit too badly by rainfall on the 18th/19th? How is it that a <50 year rainfall translated into a ~800 year flood event?

Su Campu

One thing that really bugs me is the following in bold:

Climatological and rainfall stations: The climatological network is a denser network of stations
(approx 70) which record a more limited selection of data, rainfall and maximum and minimum
temperatures, usually once per day at 0900 UTC. The rainfall station network is of higher density
again (approx 400 in total), where rainfall is recorded once per day at 0900 UTC. Daily totals
recorded each morning at 0900 are attributed to the previous day e.g. a rainfall reading of 20mm
made at 0900 on the 18th is the actual total for a 24hr period beginning at 0900 on the 17th and is
attributed to the 17th.

I know it's because most of these stations are run by volunteers, so are not manned at midnight to record the day's total, but I find it very frustrating that the 24hr total to 9am is all attributed to the previous day.

So say there's been no rainfall today, but it buckets down for 10 minutes from 08:50 tomorrow morning, that rainfall will go down as having fallen today. It's ridiculous. Over the space of a month it doesn't really matter, but for important studies such as the 18th/19th November in Cork, some of these totals are of limited use in trying to piece together a daily rainfall distribution picture. Interpolating between synoptic stations is not much use when localised rainfall rates can change by several orders of magnitude in the space of a few kms or less, and can easily be unresolved by the network.

This is an international standard procedure, so not just a ME thing. But with more and more automatic stations making up this network, this problem should hopefully get better in the future.

Mothman

Su Campu wrote: »

One thing that really bugs me is the following in bold:



I know it's because most of these stations are run by volunteers, so are not manned at midnight to record the day's total, but I find it very frustrating that the 24hr total to 9am is all attributed to the previous day.

So say there's been no rainfall today, but it buckets down for 10 minutes from 08:50 tomorrow morning, that rainfall will go down as having fallen today. It's ridiculous. Over the space of a month it doesn't really matter, but for important studies such as the 18th/19th November in Cork, some of these totals are of limited use in trying to piece together a daily rainfall distribution picture. Interpolating between synoptic stations is not much use when localised rainfall rates can change by several orders of magnitude in the space of a few kms or less, and can easily be unresolved by the network.

This is an international standard procedure, so not just a ME thing. But with more and more automatic stations making up this network, this problem should hopefully get better in the future.

While its clear to me that you needed to get this off your chest, what difference does it make whether the 24 hr obs are done at midnight or 0900.

I don't see a time when most rain gauges will be auto gauges. The logisitcs involved will be too big. Copper gauges are very easy to install and move and are easy to operate and are reliable, and while copper is sought after, I think security is less of an issue. I think for my lifetime, the bulk of the rain gauge network will be copper gauges.

Quail

trogdor wrote: »

Radar images are here anyway but it appears the shannon radar was down at the time and it doesn't seem to be included in the composite images..
http://www.meteox.com/hist.aspx?URL

Most people wrongly assume that if Shannon Radar data does not appear on certain websites then the radar is off air. This is not true. The only site that will definitely show the radar data if available is the www.met.ie site. The radar behaved normally during this period and produced quite impressive data. This information should be available from Met Eireann.

Quail

alanucc wrote: »

No I hadn't come across that report actually thanks!

Does anyone find it odd that the Lee catchment doesnt seem to have been hit too badly by rainfall on the 18th/19th? How is it that a <50 year rainfall translated into a ~800 year flood event?

Rain can fall in different formats e.g. short heavy downpours giving high hourly rates but but not necessarily high daily amount. The other method is continuous steady rain giving low to medium rates per hour but large amounts per day. The same statistics are created for the different rainfall types thus sometimes giving confusing results.

For the case of 18/19 Nov I suspect the rainfall was just continuous over an abnormal long time period, but that the limits in rates or actual daily totals may not on their own have exceeded these limits.

If you spend time thinking this out it may become clearer, but still hard to explain.

Redsunset

Right here is the bbc weather report from this period showing extent of rain on radar etc...by Thomazs s

http://www.youtube.com/watch_popup?v=rBeUxvUBU3o

Deep Easterly

Quail wrote: »

Rain can fall in different formats e.g. short heavy downpours giving high hourly rates but but not necessarily high daily amount. The other method is continuous steady rain giving low to medium rates per hour but large amounts per day. The same statistics are created for the different rainfall types thus sometimes giving confusing results.

For the case of 18/19 Nov I suspect the rainfall was just continuous over an abnormal long time period, but that the limits in rates or actual daily totals may not on their own have exceeded these limits.

If you spend time thinking this out it may become clearer, but still hard to explain.

A good post. Here in Galway, most of the rainfall during that period was mostly moderate in intensity overall, although short-lived heavier bursts, some of which were quite severe, were observed. In general though, the high accumulations I recorded came from the persistence, rather than the intensity of rain at any given time.

Su Campu

Mothman wrote: »

While its clear to me that you needed to get this off your chest, what difference does it make whether the 24 hr obs are done at midnight or 0900.

It makes no difference when compiling monthly rainfall figures (except maybe on the first and last days of the month), but it does make a difference for daily records, ie. how much rain fell on calendar day March 3rd (00-24hr)? As this is the normal and logical way of reporting for synoptic stations, it's a pity all stations can't do the same. I do understand though the reasons for it!

Mothman

Su Campu wrote: »

It makes no difference when compiling monthly rainfall figures (except maybe on the first and last days of the month), but it does make a difference for daily records, ie. how much rain fell on calendar day March 3rd (00-24hr)? As this is the normal and logical way of reporting for synoptic stations, it's a pity all stations can't do the same. I do understand though the reasons for it!

While we see 00-24h values for the synoptic stations, when it comes to the likes of the Monthly Weather Bulletin, the data for extremes and means are 09-09h data.

I'll move on and give an example which somewhat illustrates your point if one wants to tie stats down to calender day. Other issues arise with temperatures and it does make more sense to me for observation day to end at 09z rather than midnight, but this is all rather off topic for thread!

My 4th wettest "Oct" day was 31/10/2009 when 34.9mm fell. All of it fell in November! (ie between 00-09h 01/11/09) Had this fall been actually recorded as being in November, it would have made Nov 2009 my wettest month on record. Instead, Nov 2002 remains as wettest month.

Deep Easterly

Briefly captured the rain here in November while out walking the dog one afternoon. Sorry for appalling quality as it was taken on a cheap digital camera.

A bit sad posting up a video of rain, but it's been so long since we had a proper spell of weather!

octo

alanucc wrote: »

Does anyone find it odd that the Lee catchment doesnt seem to have been hit too badly by rainfall on the 18th/19th? How is it that a <50 year rainfall translated into a ~800 year flood event?

Because the ESB allowed an excessive buildup of water behind their dam at Iniscarra which the had to be suddenly released, and hey presto, Cork gets flooded.

Others have asked the same question and there was a major row between the ESB and Cork City Council about it.

http://www.irishtimes.com/newspaper/sciencetoday/2009/1210/1224260413035.html

Deep Easterly

Found this radar sequence on youtube the other day covering the period between the 17th & 19th of November:

octo

Deep Easterly wrote: »

Found this radar sequence on youtube the other day covering the period between the 17th & 19th of November:

Excellent video. Off topic I know, but check out this video of July's rain by the same person....

https://www.youtube.com/watch?v=LpQC72K3TMw

CoalBucket

alanucc wrote: »

Hi all,

Is it possible to source rainfall data for the 18th / 19th November in the Cork region, such as hourly rainfall, radar images etc? I'm aware that the MET have it available, but I don't want to pay for it :P

I had to do a report on rainfall for my previous job and got all my info from weather underground. wunderground.com just type in location and date and bobs your uncle.

Joe Public

They are great videos, I replayed them a few times and remember every shower.
It's amazing how Donegal seemed to miss a lot of it.

Just a slightly unrelated question - what do you post so the graphic of a youtube caption appears on the post?

Deep Easterly

octo wrote: »

Excellent video. Off topic I know, but check out this video of July's rain by the same person....

He has the entire August 09 radar sequence posted up also:

2nd wettest month of 2009 imby (185.1mm) with some really vicious showers in the closing days of the month.