Convective/Thunderstorm Discussion : Spring/Summer 2017

JCX BXC

One thing I've learned over the past few years on this forum.

If you want thunderstorms, cross the border.

MJohnston

The news from the North West ought to be a reminder that you should be careful what you wish for, though

DOCARCH

I see Malin Head recorded 77.2mm yesterday and I suspect most of that was probably in a couple of hours.

ninebeanrows

DOCARCH wrote: »

I see Malin Head recorded 77.2mm yesterday and I suspect most of that was probably in a couple of hours.

Very impressive. The Orange Thunderstorm warning was certainly warranted for Donegal and the six counties

Storm 10

Some brilliant pictures and video on this link from Donegal last night, terrible sad for the people living there thank God there was no loss of life.

http://www.donegaldaily.com/2017/08/23/in-pictures-the-night-donegal-was-devastated-by-floods/

And Here

https://www.rte.ie/news/2017/0823/899334-weather-flooding/

Calibos

Weathercheck wrote: »

Very impressive. The Orange Thunderstorm warning was certainly warranted for Donegal and the six counties

Lets keep politics out of the Weather Forum please!

pad199207

Calibos wrote: »

Lets keep politics out of the Weather Forum please!

I see Londonderry was badly hit

Meteorite58

https://twitter.com/convectivewx/status/900260665969049600

PukkaStukka

FOund this on the RTE news website. What a lucky escape. Looks like a culvert that collapsed near Quigley's Point. :eek:



crash.jpg

Irishweather

What I don't understand is the bizarre localised flooding in the Derry area? I am down the road from Eglinton, I received the same volume of rain and it is bone dry here now.

I'm an Environmental Science student so I should know, but this one is a headscratcher? The only thing I can think of is that the Lough Foyle tides came in as the water came down the hills? Or something to do with soil absorption?

Otherwise I can't fathom why this flooding is so extensive but yet so localised in Derry - an area that is somewhat hilly.

Irishweather

pad199207 wrote: »

I see Londonderry was badly hit

Unnecessary.

Oneiric 3

Irishweather wrote: »

Unnecessary.

Indeed, a stupid comment.

Gaoth Laidir

A Met Éireann voluntary observer in Carndonagh, Inishowen peninsula, reported 81.4 mm of rain up to 0900Z today.

James74

Couple of pics I took last night in Burnfoot, Co. Donegal. Not the heaviest rain I've ever seen, but it was prolonged and heavy. A high spring tide just at the wrong time meant that Burnfoot river had no drainage for several hours... this is the result.

James74

https://www.youtube.com/watch?v=__w71Dgjqa0

https://www.youtube.com/watch?v=LB0biYFvzhg

https://www.youtube.com/watch?v=l7vDODpk3eI

https://www.youtube.com/watch?v=vvUeYDgqK1k

Irishweather

So the tide was the trigger?

pad199207

I'm not dissing or criticising Met Eireann here, but they are saying in the news what happened in the NW last night was a '1 in 100 years event'

With respect though this just isn't true anymore as looked at what happened in Dublin in October 2011.

These are far more frequent than 1 in 100 years

Irishweather

Yes it is. It has been a long time since we've had a proper flood up here.

MJohnston

pad199207 wrote: »

I'm not dissing or criticising Met Eireann here, but they are saying in the news what happened in the NW last night was a '1 in 100 years event'

With respect though this just isn't true anymore as looked at what happened in Dublin in October 2011.

These are far more frequent than 1 in 100 years

It just means it has a 1% chance of occurring in any given year, which is pretty accurate when it doesn't apply to the country as a whole. Dublin might have been flooded in 2011, but was the Northwest?

DOCARCH

pad199207 wrote: »

I'm not dissing or criticising Met Eireann here, but they are saying in the news what happened in the NW last night was a '1 in 100 years event'

With respect though this just isn't true anymore as looked at what happened in Dublin in October 2011.

Generally agreed, but I think they were referring to a 1 in a 100 year event to a specific/given location?

BTW, had 125.3mm here in just over 24 hours on 23/24 of October 2011.

mickmackey1

DOCARCH wrote: »

Generally agreed, but I think they were referring to a 1 in a 100 year event to a specific/given location?

How specific? A town, a city, a county, a province? It's a meaningless stat when thrown around without context.

DOCARCH

mickmackey1 wrote: »

How specific? A town, a city, a county, a province? It's a meaningless stat when thrown around without context.

In many ways it is theoretical and is to any one given location/point.

I do think when Met E start stating on the airwaves, a 1 in 100 year event (without context or further explanation) it does sound a little sensational....and then the media run away with themselves!!!

Edit: Removed link to 1 in 100 flood events.

pad199207

I certainly would have thought that when Met Eireann mention '1 in 100 years' event they are referring to the whole country.

They're hardly saying it's a 1 in 100 year event for each affected location after every event

Akrasia

pad199207 wrote: »

I certainly would have thought that when Met Eireann mention '1 in 100 years' event they are referring to the whole country.

They're hardly saying it's a 1 in 100 year event for each affected location after every event

Why wouldn't they?

Every location is unique

Trebor176

20 years old around this time of the year. . .

Oneiric 3

I would have thought that mountainous regions, and the lowland regions in the vicinity of mountains (inc Dublin) would always be more prone to high rainfall totals than in other places? So I would imagine such totals, as recorded at Malin Head would be much less than 1-100 year events in such places as described above?

James74

Irishweather wrote: »

So the tide was the trigger?

Well I'm not sure if trigger is the correct word. Perhaps contributing factor would be more accurate. As soon as the tide dropped enough for the tidal flood defenses on The Slab (an large area of reclaimed farmland between Burnfoot and Burt) to open the water level dropped very quickly. I think it's more likely to be a cascade of causes including the heavy rain, flood defenses on other parts of the river, a 4.5m spring tide at exactly the wrong time, building houses on existing flood plains.

That area has flooded many time before, last night was just the most extreme case since the estates were built in 2002. I have been told by auld fella here who can remember back many decades before that and he told me that the field that the estate is now built in flooded regularly.

imo this is wasn't so much freak weather, as much as it was inevitable.

Akrasia

James74 wrote: »

Well I'm not sure if trigger is the correct word. Perhaps contributing factor would be more accurate. As soon as the tide dropped enough for the tidal flood defenses on The Slab (an large area of reclaimed farmland between Burnfoot and Burt) to open the water level dropped very quickly. I think it's more likely to be a cascade of causes including the heavy rain, flood defenses on other parts of the river, a 4.5m spring tide at exactly the wrong time, building houses on existing flood plains.

That area has flooded many time before, last night was just the most extreme case since the estates were built in 2002. I have been told by auld fella here who can remember back many decades before that and he told me that the field that the estate is now built in flooded regularly.

imo this is wasn't so much freak weather, as much as it was inevitable.

It was freak weather too. 3cm of rain in 2 hours, 7 cm off rain in 24 hours.. That's gonna cause flash flooding regardless of whether a new estate was built on a flood plain.

For very 1 degree of warming, the atmosphere can hold 7% more moisture. Global warming will cause this kind of weather event to be more common. It already is.

George Sunsnow

You know the phrase's we use in winter 'shower train and fetch'

The northwest and Ulster were uniquely placed to maximise thundryness for that flow the other day to make maximum fetch use of the land track with the mixing and disturbing of the air over land combined with the flows very humid nature/source

By the time the building cb's reached the northern third of the island they'd really built explosively with the feeding they had

PukkaStukka

George Sunsnow wrote: »

You know the phrase's we use in winter 'shower train and fetch'

The northwest and Ulster were uniquely placed to maximise thundryness for that flow the other day to make maximum fetch use of the land track with the mixing and disturbing of the air over land combined with the flows very humid nature/source

By the time the building cb's reached the northern third of the island they'd really built explosively with the feeding they had

That last paragraph is essentially it. And if we look at the lightning map for this event, the sferics extended into the north and west of Scotland from the plume.

In terms of Met Eireann's claim that this was a 1/100 year event, I would say that it applies just to that region affected rather than the island as a whole. But what I would question is whether the probability would be more frequent than 1/100, particular with the propensity for atmospheric warming to make such events more common. I hope I am wrong.