Storm Barra: December 7/8th 2021 **Technical Discussion Only**

Gaoth Laidir

Max gusts yesterday (7 December), from met.ie

malinheader

https://www.boards.ie/discussion/comment/118288860#Comment_118288860

What would the reason for the sea swells to have moved more south and storms.

Would this be jet stream related or is it just a cycle.

sryanbruen

Here is the storm comparison table for maximum wind gusts updated to include Storm Barra considering data as of 0900 this morning on the 8th of December. 3 of the stations considered reached red level warranted wind gusts and if we were to include Sligo Airport too, that makes 4. This is the most amount of red warranted gusts since Storm Eleanor in January 2018. The average wind gust based on this table for Barra with 105 kph was the highest since Ali in September 2018 which had an average of 106 kph.

On a side note, 5 stations achieved red warranted sustained winds (10-minute mean speeds) including 111 kph at Sherkin Island which is 4 kph short of category 1 hurricane status and is the highest at Sherkin Island since Darwin in February 2014 - 2nd highest in its 17 year record. This was also the most amount of red warranted sustained winds in an individual storm since Darwin. I will be giving a 10-minute mean wind speeds table next month when the full data comes in as I have them only for a select number of stations at the moment from the Met Twitter.

All in all, a decent storm by recent standards (which have been largely weak) with sustained winds at Sherkin Island pretty notable but doesn't stand out amongst those storms seen from 1957 to 2009. I have reposted the table showing such storms' maximum wind gusts also below for context. Mind that some of the stations are different in this one and includes stations which closed in 2008/09. A sustained winds version of this table continues to be in the works which should hopefully be ready for when the data for Barra comes in.

Brief_Lives

https://www.boards.ie/discussion/comment/118289063#Comment_118289063

Great tables, thanks for sharing.

The storms on 9th Feb 1988 and 11th-12th Jan 1974, really took over the country.

pauldry

Yup the day after I was born the country was plunged into darkness. I was destined to be obsessed with weather.

Those tables are great work sryan. You've made them such a staple part of storms that they are now added to the Bingo card.

Still roaring away in Sligo but "only" 100kph now not 139kph. (Beat that Sherkin!!)

malinheader

https://www.boards.ie/discussion/comment/118289063#Comment_118289063

These tables are brilliant. Really shows how weather patterns have changed. Thanks.

prunudo

While Barra is starting to fade away but still gusting here in Wicklow, I just want to say thank you to the usual suspects that go to the effort of sharing their data filled posts. Some invaluable information on this thread the last couple of days. It makes it so much easier to keep track of the storm than getting lost in noise on the other thread. Much appreciated 👏

Gaoth Laidir

A sequence of satellite-derived wind measurement maps for Barra's approach yesterday. Purple means knots and the swathe time (the time the satellite passed over and scanned the ocean) is on the bottom of the image. One image can be made up of more than one swathe.

02:25 (right), 04:03 (left)

10:41

11:29

13:34

22:11 (left, 20:30 (right)

03:08 (8th Dec)

M.T. Cranium

https://www.boards.ie/discussion/comment/118289526#Comment_118289526

You were born in 1839? Wow.

RobertKK

I think its fair to say that Storm Darwin can still be regarded as the most violent and damaging storm we had this century.

M.T. Cranium

Worth preserving the observation that around 06z to 09z as this storm was consolidating its rapid gains off the Clare coastline, there appeared to be three meso-vortices as you sometimes see in hurricanes, one was about level with the Aran Islands and the other two were closer to the latitude of Loop Head. Watching them over the next three hours I thought the northern one eventually gained the primary position which is why the centre appeared to head north-northeast then due east. Probably some weighted mean of centres would have been more of a steady northeast to east-northeast glide.

The exercise involving the 72h model positions showed anecdotally for this storm what most forecasters would think to be generally true, your best guidance is the weighted mean of all guidance, and far outliers at any point can usually be discarded rather than factored in. The three major outliers were JMA timing (too slow), UKMO track and intensity (too far south, too weak) and Arpege timing (too fast). Almost any other model taken in isolation would have been reasonably good but the weighted mean was even better.

This helped us to give people specific answers to their timing and intensity questions which I think worked out reasonably well in most cases.

The biggest "surprise" of the storm was probably the strength of the northerly flow into Sligo last night. It was not a big surprise, just a surprise in terms of degree (like 75 kt instead of maybe 60-65). Most other things that happened were within the bounds of what the models were generally showing. Most of the specific wind speed guidance of almost all the models seems a bit over-amped and probably refers to the most exposed locations at grid points rather than forming a reliable grid sector average. I would always take those numbers as being 10-20 per cent high especially over land where they start getting up into 40-50 per cent high ranges.

Another notable feature of the storm was that very strong gust reported near County Down during the early phases after quite a strong gust at Dun Laoghaire -- don't have the numbers at hand but something like 90 kt after 70 kt. Not much of that materialized on land, hence the very long (and eventually tedious) discussion in the other thread.

If it wasn't on the Bingo card, it should be -- Dublin never gets these winds. One day it will, I suppose.

As somebody who used weather models in the 1970s and is familiar with how forecasting was done with those primitive models and before they existed too (based on what older colleagues at the time told me), I have to wonder what if any advance warning would have been possible for storm Barra, no doubt some sort of lower pressure would have been suggested but the ability of these current models to construct a system like that from what is essentially just raw materials at hand is impressive to me. People keep wondering why such technology cannot then be designed to keep going for very long intervals of time to give accurate long range forecasts, but I keep saying the main reason is the existence of 10-15 day energy cycles that come and go, and have left no hint of their existence in today's data, only perhaps in an analysis of all historical data. Then that exercise gets frustrated by the shifting of background grids where that analysis might be valid for a time, and the contamination of the recent warming which resets everything slightly. But just as an academic exercise related to that, there will be a powerful set of energy peaks around 3-6 January which of course cannot be detected from the data collected today (but perhaps faintly within two weeks or so). Will be interesting to see if there is a named storm situation around that time frame.

Gaoth Laidir

Refering back to the difference in windspeeds between Casement and Dublin Airport (17 km apart), below are the hourly gust reports for Barra, with the general direction roughly shown in arrows underneath (both stations' directions were very similar each hour).

There is a general pattern (which I've noticed before) that Casement's gusts are stronger when the wind has a southerly component (most likely due to the nearby Dublin "mountains"), whereas Dublin Airport tends to overtake it once the wind goes more westerly or northwesterly. Note that the directions shown are the mean wind directions, which will always backed relative to the gust direction (if you're facing straight into the mean wind, the gusts normally come from your right).

M.T. Cranium

Had a look back at historical weather maps for 9 Feb 1988, that storm was basically much like a lot of recent ones in track, from its formation south of Nova Scotia on 7th, track from the WSW and into Donegal Bay, but had a lower central pressure than most, the map has a closed 945 contour (which implies around 942 mb). Historical reconstruction of the 1839 storm looks similar for track only another 10 mb lower than that. Some of the older wetterzentrale maps are not as intense looking as they should be since they seem to lose some of the central isobars (e.g. 8 Dec 1886, 7 Jan 1839). But I would imagine the more recent maps are more accurate with more data points available.

Every hour since noon today,my Davis station in Arklow has recorded gusts above 80kmh

90.2kmh at 7pm

Thats impressive for day 2 on the East Coast

All NW

At one stage this evening I had to climb a vertical outdoor ladder welded to a platform bolted to a wall very exposed to the NW to enter a feed loft

I was under pressure to stay on the ladder

jammiedodgers

@M.T. Cranium

there will be a powerful set of energy peaks around 3-6 January

What does this mean?

M.T. Cranium

It's a research finding, the comment is part of a discussion of why computer models despite their obvious improvement in short-range forecasting may not be able to crack longer term forecasting -- energy peaks that drive weather systems have relatively short life cycles of 10-20 days -- so to illustrate that, I have identified an energy peak that I would expect to see translated into another stormy interval around 3-6 January. My interest will be first to see when this energy peak shows up (if at all) on forecast models (none of them reach out that far yet anyway) and then how intense (if at all) will this energy peak be in the sector of the eastern Atlantic and three other key sectors that often display energy peaks in phase, namely eastern North America, the Pacific coast of North America, and south of Kamchatka, east of Japan in the western Pacific.

I may make a separate thread just to detail those investigations -- would not call them predictions as the theory is not that far along to be making predictions, more at the data collection and theorization stage.

---------------------

Separate item, based on the charts posted by sryanbruen, it appears to me that Mullingar as the most inland of stations has seen a relative reduction not only in peak wind speeds during storms, but also in terms of percentage of coastal wind speed. In other words, while the entire data set is showing some tendency to less extreme winds, this inland location is showing a larger tendency. So since we already had a discussion elsewhere about Mullingar's site aspects not changing very much as one possible explanation, I was wondering if perhaps a reason for this would be one of these two things:

(a) The transfer inland of strong coastal winds drops off at an accelerated rate per unit of wind speed at the coast as a direct result of atmospheric processes including friction, or

(b) Perhaps the widespread planting of trees in rural areas of Ireland over the period has created more overall friction in the boundary layer (which strikes me as being a good thing for all interests except maybe weather weenies during storms) and that has its impacts at inland weather stations even if there is no apparent change in the environment within 1-2 km of the site.

I don't have any statistics at hand to support (b) so I don't know if such a thing has happened or not, would anyone have any insights into that possibility? I can't think of any other environmental change on a widespread basis that could have happened to reduce the percentage of coastal wind reaching an inland site. It is quite noticeable that the further back you go in those tables, the less differential you find with Mullingar gusts and the highest coastal gusts. And then those coastal gusts are generally a bit higher on average too.

dmc17

https://www.boards.ie/discussion/comment/118289063#Comment_118289063

Added your data for Barra to a map I had created earlier

Tyrone212

French met office did a piece on Storm Barra.

https://meteofrance.com/actualites-et-dossiers/actualites/planete/la-tempete-barra-frappe-lirlande

konman

https://www.boards.ie/discussion/comment/118296127#Comment_118296127

Great work, love it. You should put it in the useful weather links thread.

Danno

https://www.boards.ie/discussion/comment/118296127#Comment_118296127

Superb work! That really is something! Well done.

Gaoth Laidir

https://www.boards.ie/discussion/comment/118297695#Comment_118297695

And also the Germans. They named it Harry (every depression and anticyclone gets a name sponsored by members of the public through the Wetterpate scheme of the Freie University of Berlin).

https://www.dwd.de/DE/wetter/thema_des_tages/2021/12/7.html

CrowdedHouse

https://www.boards.ie/discussion/comment/118296127#Comment_118296127

As a Tipp man I take exception to Gurteen missing 😀

dmc17

https://www.boards.ie/discussion/comment/118299339#Comment_118299339

I think Darwin blew it off the map 😄 I must add it in though. I don't think it was in the table I had started from originally.

dmc17

https://www.boards.ie/discussion/comment/118299115#Comment_118299115

Could do. If he'd be so kind as to share the data it would make it easier as I had transcribed the existing ones from one of the images he posts 😅

TTTT

https://twitter.com/CopernicusEU/status/1469272238318927872?t=Wuimzo-EMY9kLbX6iyu6Dw&s=19

Tyrone212

https://www.boards.ie/discussion/comment/118296127#Comment_118296127

That's handy. Storm arwen I believe Malin head recorded a gust of 130kmh and had mean winds above 80kmh (red criteria) for 10 hours.

sryanbruen

https://www.boards.ie/discussion/comment/118296127#Comment_118296127

(Monthly delayed response)

Such a great resource @dmc17, we need more like it around. Visualising the data in a straightforward way is of utmost importance to me as somebody who works with statistics daily. I have planned for a while to build a massive database of Irish station data on all kinds of parameters from something as niche as daily records to ice days.

As great as it is of Met Éireann providing all the data in the historical data section of their site, it is in need of a redesign or makeover. It is clunky to work around and can take a little while to get all the files needed when say data.gov.ie is much faster and I am done downloading in like half the time. There should also be some way to do custom queries without having to use a third party software like Excel such as looking for something as basic as temperature records in a given month or season at a selection of stations etc. Despite the data rescue, there continues to be no digitised records on stations like Kilkenny Castle or Mostrim, both of which still hold national records to present.

But that's irrelevant to the thread at hand, I just thought I'd mention it. I continue to work on the storm comparison table for max. 10-minute mean wind speeds (also known as sustained winds) and it is still nowhere near finished. However, now the data for Storm Barra has all come in so I can give the values.

Here's the max gusts and max sustained wind values for the Irish stations in the original storm comparison table I shared compared and colour coded in line with their respective warning criteria. There were twice as many red warranted sustained winds as there were red warranted wind gusts and same is true for orange warranted wind values. Mace Head's 104 km/h sustained wind value is the highest since 111 km/h at Roches Point during Storm Ellen in August 2020.

Danno

Fantastic work @sryanbruen

Totally agree about the need for a searchable database of all Irish weather records.