Storm Atiyah Sunday - Monday, 8th - 9th Dec 2019

lcasey90 wrote: »

Seen about the jet stream comming from Canada going to be 300kts, what does that mean?

It won't be 300 knots, more like 220-230. A strong jet stream can give strong forcing for the development of surface lows.

sryanbruen wrote: »

Apologies Snow Garden, I remembered for Lorenzo's update that I added Storm Brian (and Hergen from Dec 2011) to the table but for some reason it didn't save in the file. However, I have updated the table now to include both again in the original post. I also fixed some of the provisional gusts for Atiyah.

Correct. Many of them were randomly picked by me because I felt they were notably deep depressions whilst recent ones since Ali have all been added per event.

sryanbruen - remind me what's does the green on the tables denote?

lcasey90 wrote: »

Is it a regular occurrence

300 knots is not a regular occurence. I'm not sure it's ever been recorded.

Perhaps it would be interesting to construct a Storm Index which takes the data compiled by sryanbruen, and assigns 5 points per red, 4 points per orange 120+, 3 points per orange <120, 2 points for yellow and 1 point for greens that break 80. As there are 19 stations, the highest index value possible would be 95, so to bring it to 100 I would go with 6 points for any 140+ red as it would be pretty unlikely that more than five locations would record that. On that basis, these are the totals I get (in order of severity) ... I have estimated Debbie (1961) and the famous storm of Feb 27, 1903 although not the same observation network for them. The "big wind" of Jan 1839 might not have beaten Debbie or Darwin with the spread of stations being what it is, but would have been at least 60 and perhaps over 70. So it should be kept in mind that this is an index for overall impact on the country and not maximum localized severity of any given storm. A better index would probably factor in how long the gusts persisted, perhaps time of year for leaf loading on trees, and maybe population affected although in terms of a natural phenomenon being rated, that doesn't enter into it (the grid probably tends to introduce a population impact variable to some extent although there are a number of isolated coastal locations in the list).

Debbie ____ 74 (est)
Darwin ____ 72
Feb27 1903_68 (est)
Ulli _______ 51
Ophelia ____49
Doris ______49
Erich ______49
Eleanor ____47
Rachel _____41
Atiyah _____39
Hergen ____ 39
Erik _______38
Gareth ____ 37
Hannah ____36
Bawbag ____36
Callum ____ 34
Diana _____ 33
N/A 2011 __ 33
Dirk ______ 28
Brian _____ 25
Deirdre ____22
Lorenzo ___ 15

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There are groups that you could call powerful storms, significant storms, average storms, and non-events here.

Atiyah would rank as a high end average storm a little ahead of the pack of those, by this index ranking system.

Very interesting M.T.C, though I would add that there have been many 'unnamed' significant storms in the fairly recent past (70s, 80s, 90s etc) also that would make that list and which would put recent efforts to shame. How these would be measured for the index I do not know, but perhaps if a few of us on here who might hold an interest in maybe delving into the stats were each assigned a 5 year period or decade to assess and compare.

That Christmas Eve storm was severe here in Cork.

Oneiric 3 wrote: »

Very interesting M.T.C, though I would add that there have been many 'unnamed' significant storms in the fairly recent past (70s, 80s, 90s etc) also that would make that list and which would put recent efforts to shame. How these would be measured for the index I do not know, but perhaps if a few of us on here who might hold an interest in maybe delving into the stats were each assigned a 5 year period or decade to assess and compare.

What one could do for historical storms would be to take whatever data are available, take the index total and inflate it by the factor of (N/n) where N is 19 and n is the number of data points you can find. However, if it appears that the older data are more proportionately located in windy locations, reduce by whatever factor you think that represents (so let's say for some storm with 12 data points and half rather than a third in windy locations, the equation for a derived total of 40 would be

40 x (19/12) x (2/3) = 1520/36 = 42

However, another valid approach would be to take the data available, inspect maps and make a reasonable estimate of what that data field would imply for the 19 locations now in use. For the Big Wind, I came up with my estimate from these points assigned simply on the basis of anecdotal evidence and maps that were reconstructed. However, I was pretty conservative with those assumptions and limited the 5 and 6 point stations to coastal locations. The total could have easily been as high as 80 to 85 if all 19 locations reached orange warning at least.

Another historical windstorm that is often overlooked was Dec 8, 1886 but that affected Ulster and north Leinster, probably their strongest storm on record. It also set a barometric low record for the island of Ireland (922 mbs IIRC in east Ulster either in Armagh or Down, not sure where the reading was taken). :eek:

Danno wrote: »

It was very severe, IIRC Kilkenny had it's strongest ever 10 minute mean windspeed of 54mph (87kph) during that storm, the top gust was 86mph (139kph). Considering Kilkenny's location being sheltered in the southeast in the Nore Valley, this was impressive.

EDIT: That storm was the fourth strongest in Kilkenny's recorded history:

January 1974 (the Kilkenny record gust of 143 km/hr)
January 1976, (141 km/hr)
November 1959 (141 km/hr)
February 2014 (133km/hr) comes in fifth place.

Source: https://www.kilkennyweather.com/index.php/2014-the-great-february-storm

Those were the days when storms were storms!

Just had a quick glance at data from Mullingar from the Met Eireann data set and to date, its 10 min mean of 45 knots back on January 12th 1974 still stands as its highest, as does its gust of 76 knots on the same day.

What I found interesting from this data set is that of all the days that a 10 minute mean speed of 34 knots (Gale 8) or more was recorded, none have occurred in the 2000s which tells me storms over Ireland were fiercer when the N. Atlantic, Arctic, and global temps were lower.

@M.T.C, I do recall that years ago I extracted wind data from the 'ERA' reanalysis for the 5 inland stations (or locations) used in the 'IMT' series I'll have a look for that later on and if I find it, I'll post the data file up on here. Always going to be imperfect, but might give a good general view regarding the ebbs of flows of wind over time (I think that data goes back to 1958 or 1961 or something like that)

I think also there's a 10% "blanding down" factor at work in this warmed up climate, at least for temperate zone storms, the same may not be true for other climate regions. And I agree with Oneiric that the reason is probably a reduced temperature gradient (the colder air masses are being warmed faster than the warmer ones).

At the same time, we have to be alert to the singularity phenomenon. One storm can come along and be more than marginally stronger than previous ones. I think the 1703 storm in southern England was an example, as was the 1839 storm in Ireland. They just seem a bit off the scale even compared to the extreme events otherwise. I could say the same about that 1978 Great Lakes storm, the only other one that I might say was in its league was the November 1913 gale that sank many ships on Lake Huron. Lots of notable storms between them and since, but these seem more than a rank ahead.

What can we look for as a precursor for such a storm? As much research as I've done into it, nothing really jumps off the page. Rather bland weather patterns often precede these mega storms. There was nothing very unusual about the weather from autumn 1977 to the date of the Great Lakes superstorm, many other years had more interesting weather in that stretch of time. The 1839 storm probably came in a decade of somewhat enhanced storminess in general. I have access to a fascinating weather diary from Providence RI 1831 to 1860, in fact here's a link to it, this guy was a weather weenie of epic proportions a century before anyone else even thought to become one. And he was equally interested in astronomy and geomagnetism. If you've heard of the "Carrington event" read his journal notes for the evening of Sept 2, 1859. He was lucky to live in a time of high solar activity, numerous bright aurorae and before street lighting in what was then a rural setting (probably mid-city North Providence now).

https://books.google.ca/books?id=oYY_AAAAcAAJ&pg=PA165&source=gbs_toc_r&cad=4#v=onepage&q&f=false

What's interesting is that he never (as far as I have read through) makes a predictive comment of any kind. I even wonder if he had any concepts of weather prediction beyond what the average seafarer of those times would have known about sky signs. But he was obviously trying to log what it might take to understand weather better in a time when there was no such animal as meteorology.

My interest in his work is for several reasons. I know of no other detailed observations before 1840 when Toronto started its weather station. I wanted to check the lag time of weather events in those colder climatic times from Toronto to the New England coast (worked it out to be about what it is now, 0.5 days for regular progressive frontal systems). Of course more than one of his big storms shows up as a blank or a marginal snowstorm perhaps that far west. (Toronto is barely north of Providence, mostly west). Also, I am finishing a major project on updating weather records set at Toronto's downtown station which has continued to record for 180 years now, more or less continuously. I will discuss those findings here some time later this winter. Sample finding, the biggest climate shift took place in the 1890s rather than the 1990s. There is an urban heat island effect to filter out, but record low max data are least affected since they tend to occur on rather windy days (in daytime). The frequency dropped almost to its modern low frequency as early as 1897 to 1910 before stabilizing and it has actually picked up somewhat after a minimum in the period 2006-12. So I think there's some fine tuning of climate change potential in this long record.

I also like the correlations with astronomy. The frequency of major storms at Providence at the new moon closest to the winter solstice is remarkable. He has detailed pressure readings and I have a preliminary finding of a pressure minimum of 15 mbs around that time. That's three to five times as strong as what I found for Malin Head or the other pressure grid point (54N 6W) as discussed elsewhere. Similar but stronger. This was at a time when the North Magnetic Pole was located over the North American mainland a lot closer to New England than it would be today.

Jpmarn wrote: »

The frequency and the severeness of bad weather events throughout history and nowadays is debatable especially with climate change concerns. There was a lot of bad weather events in the past there will be bad weather events in the future.

One issue with using severe weather as an indicator of change is that the severeness is often measured in impact to human life or monetary costs.

M.T. Cranium wrote: »

I don't perceive that the frequency of severe weather events is increasing in recent years and I suspect it is decreasing slightly. One question that would need to be resolved is, what normal period is being used as the benchmark? There may have been another relatively bland period around the 1940s to 1960s so if it were 1941-70 used as the benchmark, perhaps even 1991-2020 would equal it.
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One could also ask as to which 'normal' is the most normal. the 1961-90 normal for example, is still being used and quoted by the UK Met Office today, yet this was an abnormally cool period in the 20th century relatively speaking. I will use this occasionally myself though, as I will the 1981-2010, and even a more recent, and more relevant, if much smaller 2011-2018 period myself as this is what most of us still have fresh in our memories.