Friday 15th -- flood risk rising, milder

M.T. Cranium · 15-01-2010 8:00am #1

Friday 15th -- flood risk rising, milder
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We need a new focus for the general interest discussion, methinks, as the cold spell ends for the time being in a wave of mild, moist air drawn up from the latitude of the Azores.

I'll just make a brief starting post here, the details can be found in the forecast thread.

The combination of rain today and tonight, with melting snow that is still quite widespread in many areas (central, eastern, northwest especially) seems capable of bringing some moderate or even severe flooding in spots. Any place that streams drain highland areas especially in Wicklow, Dublin, Laois, Carlow, Kilkenny, Tipps, west Cork and Kerry, as well as possibly Mayo and Donegal, need to be closely watched for rapid water level rising.

In other places, the flood situation may be more from waterlogged fields and bogs not releasing standing water but oozing out the excess onto roads and nearby areas. And there could be some flooding in cities and towns in a few spots because water is unable to drain away through clogged drains.

Anyway, if you doubt the potential for flooding, have a look at the photo threads on this forum and realize that there is much more snow available for melting than it may appear in lowland areas. Reports of several feet of snow, some of it already moisture-laden, with rain to come, have me concerned that by tonight or Saturday, there can be some serious flooding.

And add to that dense fog and the odd mudslide, you've got a lot of things to watch out for on the roads today, tonight especially, and through the weekend.

DOCARCH · 15-01-2010 10:27am

Important thread MT - thanks.

With in some places having in execss of 1 metre of snow in the Dublin/Wicklow Mountains at the moment in conjunction with temps now nudging 9.0c here, that 1 metre of snow has the potential to release the equivalent of 100mm of rain (in addittion to what rain may fall today and tonight). Potential for flooding should not be underestimated.

red menace · 15-01-2010 12:31pm

Density of Snow =
Snow, freshly fallen 160 Kg per Cubic metre
Snow, compacted 481 Kg per cubic metre

Snow water equivalent (SWE) is defined as the depth of water (in millimetres) of snow cover on a horizontal surface area if that snow cover is completely melted. SWE is related to snow depth and density by

SWE (millimetres) = depth (metres) x density (kilogram per cubic metre).

I am going to assume 5 Cms of Snow cover coz I am lazy and its easy to multiply

10 cm = .1 of a metre
5 cm = .05 of a metre
Compacted
.05 * 481 = 24 mm

Fresh fall

.05 * 160 = 8 mm

These are some back of envelope calculations I did for a thread I started on this earlier this week...

In short I think it would be wise to be prepared for some water if you live in a prone area

Graces7 · 15-01-2010 12:34pm

Please take care; a few years ago I waded in to rescue 5 ewes and their ten lambs from a sudden flash flood in a different but high situation.

It was a terrifying sight and can happen anywhere there is flowing water; this was a mountain stream suddenly overwhelmed.

Please God that that at least is one thing we are safe from up here. I hope.. the snow is melting gently and we are not in the lee of any great height. The hill opposite us is almost clear now.And drainage seems fine

red menace · 15-01-2010 12:36pm

I am going to guess that the water is not going to be much 1 or 2 degrees so best to stay out of it

maquiladora · 15-01-2010 12:56pm

jenzz · 15-01-2010 2:01pm

Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?

Sponge Bob · 15-01-2010 2:26pm

the nearest one

DOCARCH · 15-01-2010 2:26pm

jenzz wrote: »

Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?

All the riveres that have their sources in the Dublin & Wicklow mountains.

maquiladora · 15-01-2010 2:31pm

Met Eireann has now issued a weather warning for this :

Issued at 15 January 2010 - 13:00

Weather warning

Rain Friday night will produce falls of 20 to 30mm in parts of south Munster and south and east Leinster, with some thawing of mountain snow also. This may cause localised flooding. Strong winds countrywide also, with gusts 80 to 100 km/hr locally.

roryc1 · 15-01-2010 2:55pm

jenzz wrote: »

Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?

The Liffey for one, Watch out strawberry beds

aidan_mc · 15-01-2010 3:13pm

jenzz wrote: »

Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?

The dargle number two

DOCARCH · 15-01-2010 3:28pm

aidan_mc wrote: »

The dargle number two

The Dodder number three.

Kippure · 15-01-2010 4:29pm

jenzz wrote: »

Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?

The River Dodder starts at the foot of kippure, will flow into bournabreena and on through dublin, So does the liffy start at the other side of kippure and on into kildare and dublin.

Elmer Blooker · 15-01-2010 4:34pm

I hope they're filling the sand bags in Carlow Town and Enniscorthy, with deep snow melting in Wicklow feeding the Slaney and Barrow you can throw in heavy rain and southerly gales piling the tides up against the south coast.
I made this point elsewhere on some other thread about a week ago maybe.

DOCARCH · 15-01-2010 4:37pm

Snowline retreating fast on the Dublin Mountains I can see from here (2 and 3 Rock Mountains) and even getting patchy on top.

10.0c now after reaching high of 11.5c - we've had summer days here that 'warm'!

Graces7 · 15-01-2010 4:45pm

The snowline here has marched across the back field and will soon reach the snowless areas around the tree-sheltered house

Inexpressibly lovely to see the greens and browns in all their varied glory again; I missed them.

Joe Public · 15-01-2010 5:03pm

jenzz wrote: »

Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?

The Dodder rises on the northern slopes of Kippure in the Wicklow Mountains, and is formed from several streams.
The river flows for some 20 km through the Dublin suburbs of Tallaght, Rathfarnham, Templeogue, Rathgar, Milltown, Clonskeagh, Donnybrook, and Ballsbridge before entering the Liffey at Ringsend, near where the Grand Canal meets the Liffey at Grand Canal Dock.
There is a weir just above the bridge at Ballsbridge and the river becomes tidal roughly where the bridge at Lansdowne Road crosses it.
The Dodder and the River Tolka are Dublin's second largest rivers, after the River Liffey. The river floods some surrounding areas from time to time.

The River Camac (sometimes spelled Cammock, or, historically, Cammoge) is a river in Dublin, Ireland.
The Camac rises to the south and west of the city and flows through Clondalkin, Inchicore and Kilmainham before entering the Liffey just downstream from Heuston Station.
The Camac is sourced from streams from the Dublin Mountains and County Kildare, which join together in Corcaigh Park, just south of Clondalkin village, and has three major tributaries, the Brownsbarn Stream (rural) and the Robinhood and Walkinstown Streams (urban).

The Liffey rises in the Liffey Head Bog between Kippure and Tonduff in the Wicklow mountains, forming from many streamlets. It flows for around 125 km (78 mi) through counties Wicklow, Kildare and Dublin before entering the Irish Sea at its mouth at the mid-point of Dublin Bay, on a line extending from the Baily lighthouse to the Muglin Rocks.

The Poddle begins as the Tymon River in the Dublin Mountains. Additional ponds were added to its course when Tymon Park was formed in the 1980s and 1990s. It flows from the greater Tallaght area through Templeogue, where its volume was increased for over 700 years by a significant input of water diverted from the River Dodder by the three kilometre first section of the City Watercourse.
The river is split at "The Tongue" at Mount Argus, Kimmage, with one third of the flow forming the second section of the City Watercourse, heading for Dolphin's Barn, and two thirds continuing in the original river bed. In the 1990s, changes were made in the Kimmage area, including the addition of a large fountain to the river.

onq · 15-01-2010 5:05pm

We have a Minister of hte Environment who cannot deal with Water.

First - Too Much Water - and we had the flooding, people's dream houses destroyed, local authorities running for cover as corrupt incompetent planning decisions came to light. - the recent Prime Time exposé showed there is no co-ordination on the Shannon water levels, never mind flooding in the country as a whole. Our beloved minister comforted the masses by explaining how double the money had been allocated to deal with flood issues - "allocated" doesn't mean "spent" and the fools in the ESB whose actions flooded Cork are still not brought to account any more than the geniuses in Kildare Co Co whose inadequate pipe size and stupidity allowed a new housing estate to become flooded.

Second - The Wrong Type of Water - frozen water, and too much of it, showing our utterly inadequate emergency service response time and lack of preparedness for a relatively light fall of snow. hardly any snowploughs in rural regions that I could see and a nasssty habit of ignoring home grown help from quarries and contractors alike, with Noel "tough neck" Dempsey taking his much needed Winter Break - would that we could all afford to do so. Again, the recent Prime Time programme exposed the fact that there is nor real co-ordination beyond what looked like a hastily cobbled together collection of rumbpled suits styling themselves as the Emergency Committee or whatever - how utterly lame.

Third - Not Enough Water - Dun Laoghaire Rathdown has issued the immortal words "water is turned off to allow the engineers to trace a significant water leak in the Bal;lybrack Killiney area" - and exactly HOW are they tracing a leak with the water turned off? Anyone? Beats me. The real agenda all over the country seems to be that they are castigating people in areas where taps were left on to prevent pipes freezing overnight, because its costing them a fortune to treat potable tapwater that we're sending straight down the drain without the courtesy of letting it pass through our digestive systems and kidneys first. No emergency response here, just tanker actions to provide water and unnannounced and stupid breaks in the water supply in many parts of the country. A disgraceful show of incompetence at all levels for which we're expected to be thankful.

Next - Importing Water From Saudi Arabian Swimming Pools To Save Ireland - this mess is what the Mean Green Machine is presiding over - and its not over yet - expect a heatwave in February 2010 to properly finish out the reservoir water. Meanwhile Gormless smiles his beatific smile on Green and non-believer alike, peddling his global warming political agenda and looking forward to getting re-elected. Perish the thought that anyone might hold the Minister to account for not building new reservoirs to cater for Dublin's burgeoning population over the past 10 years. Last week Environment was fronting for Noel Dempsey Absentee Traffic Warden, this week its reversed with helmet head giving us the full depth of his knowledge about burst pipes and water supplies.

They're all the same:
5-year-old Carr Communications grooming, bad hair, slightly rumpled shiny suits and the ministerial driver and car.
Sure it doesn't matter who tells us what anymore.

13 degrees today!
Rock on boys!

Feel free to move this if required Mods.

FWIW

ONQ.

isle of man · 15-01-2010 5:55pm

onq wrote: »

Third - Not Enough Water - Dun Laoghaire Rathdown has issued the immortal words "water is turned off to allow the engineers to trace a significant water leak in the Bal;lybrack Killiney area" - and exactly HOW are they tracing a leak with the water turned off? Anyone? Beats me.

They use cameras to go up inside the pipe which will inspect inside the pipe and show the cracks,
so cant be done when theres water in it

onq · 15-01-2010 6:21pm

isle of man wrote: »

They use cameras to go up inside the pipe which will inspect inside the pipe and show the cracks,
so cant be done when theres water in it

Thansk for the reply.

They're calling this a significant burst.
Working the camera through miles of pipe is onerous.
I would have thought zeroing in on the location would be obvious.
Turn the water back on, find all the houses without supply and work upstream.

ONQ.

maquiladora · 15-01-2010 6:38pm

15 January 2010 16:20

Today

It will become wet and very windy everywhere during this evening and early night. Heavy falls of rain in parts of the south and east, combined with melting snow from the mountains, may cause some flooding. Clearer weather will spread from the west overnight and winds will moderate. It will very mild at first with temperatures between 9 and 11 degrees, but temperatures will fall later to between 4 and 7 degrees

http://www.met.ie/forecasts/

owenc · 15-01-2010 6:40pm

oh my godddd!!!!! we had a high of 10c here today and its 9.4c omg! all the snow is melting on the mountains but there is still a couple of inches of it left on the top it looks all horrible seeing a brown mountain all the grass here is a dirty brown now!

greysides · 15-01-2010 6:47pm

What was the figure quoted recently on the RTE news for the loss of water between treatment and use?

45%, I think.:eek::eek::eek:

And the person who said it was quite blase about it being the average!

It's not cheap to produce potable water either.

If this disgrace were corrected, it would probably end the recession!!!

snaps · 15-01-2010 7:28pm

yes its great not to have the heating on all day today! Just have the fire going since this afternoon and thats keeping the house warm enough! 11.1 c outside now in a huge SW storm!

Welcome back Atlantic!

maquiladora · 15-01-2010 7:49pm

Wet and windy here in Waterford now.

rhonin · 15-01-2010 7:55pm

Very windy and heavy rain here now.

maquiladora · 15-01-2010 7:57pm

9pm precip chart...looks like Cork/Kerry are in for a drenching...

jambofc · 15-01-2010 8:31pm

maquiladora wrote: »

9pm precip chart...looks like Cork/Kerry are in for a drenching...

jeez,are we under all that :eek:

imagine if it was white stuff going to fall out of it :pac:

M.T. Cranium · 15-01-2010 9:39pm

I'm not sure what the local authorities are saying or doing, but I see all the elements required for severe flooding to develop overnight and hit during Saturday morning anywhere that rivers flow out of high ground (and let's face it, they all do to some extent). The 24-hour rainfall equivalent for the Dublin-Wicklow region is nearing 75 mms considering rain and snowmelt.

maquiladora · 15-01-2010 9:44pm

100kmph gust recorded on Marathon.

maquiladora · 15-01-2010 9:45pm

Haven't heard any reports of flooding anywhere yet but there was a good bit of surface water on the roads on the way home from work.

dogpaw · 15-01-2010 9:52pm

This exact time last Friday I took a photo of my car thermometer reading
-10 degrees now it is saying +10. Isn't it amazing the difference a week makes :eek:

owenc · 15-01-2010 9:56pm

dogpaw wrote: »

This exact time last Friday I took a photo of my car thermometer reading
-10 degrees now it is saying +10. Isn't it amazing the difference a week makes :eek:

That reminds me tomorrow night this time last week we were at -13c and we will probably be like 3c or something but at like 7c at day thats real warm thank god today is the highest we will get!:eek::eek::eek::eek:

Scubadevils · 15-01-2010 10:29pm

Really hotting up out there tonight... serious wind and rain now battering off the windows.

Anyone know if it will turn to snow and how deep?

Actually enjoyed the warmer temps today, in Dublin city earlier and quite pleasant before the drizzle kicked in.

Tom Cruises Left Nut · 15-01-2010 10:34pm

Really starting to get windy and rainy here now.

I hope the people accross the road from me in the Waterways in Sallins don't get flooded again, they only finished gutting and drying out their houses from last time !!!!

Su Campu · 15-01-2010 11:34pm

M.T. Cranium wrote: »

I'm not sure what the local authorities are saying or doing, but I see all the elements required for severe flooding to develop overnight and hit during Saturday morning anywhere that rivers flow out of high ground (and let's face it, they all do to some extent). The 24-hour rainfall equivalent for the Dublin-Wicklow region is nearing 75 mms considering rain and snowmelt.

You know, you're dead right MT. This could be a repeat of a month ago when towns like Sallins were ruined. Newbridge, here in Celbridge could get it too, not to mention further downstream in Lucan, Strawberry Beds, etc. This is one that could come up and bite people in the ass, and I haven't seen or heard any official warnings yet...:(

I'm sure there are many more ssimilar situations around the country too.

greysides · 15-01-2010 11:43pm

I read about the rain and the flood risk but we're on top of a hill (400' ASL, North Wexford- no flood worries) and while the rain is heavy and lashing the windows, it's the wind that is the dominant feature.
Very gusty and booming around the house.

mike65 · 15-01-2010 11:51pm

Nasty out there and quiet in here, people only love the snow.

Su Campu · 15-01-2010 11:56pm

Here's the vertical windprofile from the 18Z Valentia sounding, showing a rise in windspeed from 19kts at the surface to 49kts just 144m (472ft) above! Serious gusting from that!

greysides · 16-01-2010 12:03am

Is there a simple (-ish) answer to why do winds gust?

I'm aware that wind speed is determined by pressure differences but what causes the gusting and how are gust speeds predicted?

irish1967 · 16-01-2010 12:11am

Wind really strong here. Gusts are extreme. Temp now 9.6c.

Su Campu · 16-01-2010 12:19am

MT mentioned some beefy showers on developing to our south. They're racing northwards across the country now and giving several positive lightning strikes off the south and southeast coasts

Su Campu · 16-01-2010 12:32am

greysides wrote: »

Is there a simple (-ish) answer to why do winds gust?

I'm aware that wind speed is determined by pressure differences but what causes the gusting and how are gust speeds predicted?

Windspeeds are related to the pressure gradient, ie. the distance between the isobars. At the surface, land friction greatly decreases windspeed, but higher up, where the wind doesn't directly feel the effects of friction, the windspeed remains high. It is this difference in windspeed with height, ie. wind shear, that causes turbulent mixing of higher speeds down towards the surface. There is a general rule for predicting gusts but I can't for the life of me remember it.... :mad:

greysides · 16-01-2010 12:40am

Su Campu, thanks.

Did I understand correctly that its the mixing of the faster upper layers with the slower lower layers that causes the gusting?
If this is so, does that mean that over a flat surface where there would be no geographical impediment to the lower layers (other than surface friction) there would be virtually no gusting?

M.T. Cranium · 16-01-2010 12:58am

I predict gusts partly from climate pattern analogues, in other words, different stability profiles or wind directions give different ranges of wind speeds.

Normally gusts will be about 1.6 times the sustained wind (a sustained wind is the highest 2-minute or whatever time used average in the recent time before a report, and the gust is the highest wind speed recorded instantaneously in the hour before). This tells you that wind speed can also fall below the reported wind speed.

Anyway, an example of the general rule would be 30 mph gusting to 48, or 50 gusting to 80.

I might consider narrowing that range if the air is expected to be stable near the surface because then it won't mix down the higher wind speeds as much. In continuous warm advection sometimes you see a report like 40 G 48 which would be 20% and that's unusually small for a gust increase over sustained.

Winds don't gust very much when they fall off below about 15 mph in stable conditions.

As you say, terrain influences gustiness, it can push up the ratio to about double in some cases (as in 30 G 60). If you ever see a report that gives a very high ratio, like 20 G 80, this is because a squall has occurred in the past hour and winds are already decreasing considerably.

irish1967 · 16-01-2010 1:01am

Just a question for those in the know. When was the last time it was 10c at midnight in January in Ireland??

snowstreams · 16-01-2010 1:10am

Ive seen it at 12c on Dun Laoghaire Pier at 11pm in January before. After the last few wks i never thought it could get this warm again!

K-9 · 16-01-2010 4:06am

irish1967 wrote: »

Just a question for those in the know. When was the last time it was 10c at midnight in January in Ireland??

Wondering that myself!

Mothman · 16-01-2010 4:39am

I've just checked my stream and its very high. I don't have a measure on it but I think highest since 2002 and the catchment area for the stream had little or no lying snow.
24hr total 35mm, 17.5mm since midnight (3.5hrs)

Mothman · 16-01-2010 4:43am

irish1967 wrote: »

Just a question for those in the know. When was the last time it was 10c at midnight in January in Ireland??

This is very common during winter. Sunshine makes very little difference to temperature at this time of year and temperature is more determined by the air mass.
Jan 09 was the coldest month in my records, yet the max temp of month was recorded just before midnight on the 11th. Temp was 12.0C with 11.9C at midnight

Friday 15th -- flood risk rising, milder

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