An analysis of the 2009/2010 cold spell

Su Campu

It's interesting to see where the recent cold spell came from - what caused the pattern change, and why it hung around for so long.

November was a record month for rainfall, with widespread flooding in the western half of the country later on in the month. Ireland was bombarded day after day by low pressure systems fed in on a persistent southwesterly airflow. This was the result of a vast area of low pressure near Iceland, causing the jetstream to position itself over northwestern Europe, ensuring that we were in the firing line for anything it produced.



The constant feed of warm southwesterlies eventually led to the formation of an anticyclone over southern Europe early in December, which moved northwestwards towards Iceland towards mid month. This shoved the Iceland low westwards towards northern Canada, and at the same time fed a cold Russian airmass southwestwards over Iberia, leading to the formation of a cut-off low near the Azores. This flip in the pattern (Icelandic High, Azores Low, ie. Negative NAO (North Atlantic Oscillation)) led to the start of the northeasterly feed of cold Arctic airmass towards northwestern Europe. It was consolidated by the strong southerly flow in the western Atlantic feeding high geopotentials to the Icelandic high, strengthening it and expanding it over Greenland.




In the week before Christmas, the first taste of winter hit the northwestern half of the country, as an Artcic blast from the Norwegian Sea fed snow showers to many areas, marking the start of several weeks of hardship for the likes of Graces7, and many like her.



Then we had the famous "Wet-bulb Wednesday" on the 29th, when thousands of boardies followed the movement of a low pressure system moving up from our south, hoping in vain for it to dump a load of snow over the whole country. While there were decent falls in western parts (Galway, Clare, Tipp) and in many other areas on higher ground, for most on low ground it turned into nothing more than a wet, windy mess. :rolleyes:




Two days later and the winds turned northesterly, giving revellers the chance of a drunken New Years snowball fight with several cms of snow falling in Dublin and the east coast.




In the days that followed the cold northeasterlies continued, with the occasional idiot predicting the formation if a polar low or two near Norway. It never happened of course, but as H850 and H500 temperatures reached rare low values, the unstable northeasterly generated a potent Irish Sea trof on the 7th, which crippled Dublin city, and dumped several cms of snow on the majority of Leinster and on into eastern Munster.




With the fresh snow cover, temperatures in the east fell to rare low values, with Villain's station in Tullow recording a low of -17.7°C on the morning of the 9th, and many other areas falling below -10°C on the 9th and 10th. Maxima were well below zero for much of the east

With the Greenland High joining forces with the Scandi High by the end of the week, a cold easterly fed the last blast of frigid airmass westwards towards northwestern Europe for the weekend, cutting off a low over the Mediterranean. A shortwave trof on this cutoff low pushed a line of snow showers westwards across the country on Saturday, and hung around to feed energy to the upper warm front on Sunday, generating widespread snowfall to many areas, apart from the east and southeast coastal counties, where a warming was beginning to take place, signalling the first signs of a thaw late Sunday and Monday.

A rapidly deepening storm system passed to the west of the country on Tuesday, bringing with it strong southerly winds and widespread precipitation, falling as sleet and snow above around 400ft. Cork Airport had 17 hours of continuous snowfall, which closed it for several hours. The occluded front from this system dragged it heels as it came up against the cold air to the east, and has only really cleared the country this evening, officially signing off a memorable spell of both weather and hardship.

We're now back in a more recognisable Atlantic setup, with the Scandi High still not a million miles away, but with strong baroclinicity in the Atlantic and the Iceland Low/Azores High pattern back in place, it's possible we could be in this regime for a while to come.

That is unless we get fed something cold, from Russia with love

greysides

Would an analysis of the performance of the different models be useful for the future?

opr

Awesome post. Thanks for taking the time to do this.

Opr

WolfeIRE

opr wrote: »

Awesome post. Thanks for taking the time to do this.

Opr

+1 well done Su. Nice one for the archives so we can contrast and compare for future events.

Great suggestion from greysides too. Would be a hell of a lot of work to do a definitive analysis of all models over four weeks though.

nacho libre

An excellent analysis overall, but I think it should be pointed out that yesterday's system gave prolonged snowfall to several areas well below 400ft. Sorry if that seems like i'm nitpicking. It's not my intention.

snow ghost

nacho libre wrote: »

An excellent analysis overall, but I think it should be pointed out that yesterday's system gave prolonged snowfall to several areas well below 400ft. Sorry if that seems like i'm nitpicking. It's not my intention.

Good point Nacho... and not just below 400ft, but at sea level on the Atlantic coast (well a bay off the Atlantic, but ye know what I mean)... not something many, if any, foresaw.

M.T. Cranium

A really useful summary of a very unusual stretch of weather (in recent years, anyway).

I felt that the models did quite well with some of the changes and details, but I didn't keep detailed notes on that. I've noticed that the GEM seems to be improving, and I'm not saying that for patriotic reasons, the GEM in previous winters tended to be too progressive (eastward moving of systems) against the consensus of all models, but occasionally would be odd man out, and right as well (very rarely). This winter it seems to have done as well as the two or three most consulted models in Europe.

Most people who forecast regularly seem to prefer ECM over GFS and either rate UKMO equal to GFS or a bit higher or lower, but in the past three months I think I've come to see them all as a blur together with the GEM, if you took the consensus of all four of them, it might be optimal.

As the ground in Ireland and the UK became snow-covered and frozen to a fairly wide extent, the usual rules about thickness and snowfall started to change a bit towards the higher thickness parameters normally used in more continental climates. In other words, the maritime influence weakened somewhat. But not enough to prevent the Sunday-Monday situation from being very closely connected to slight changes in thickness, as higher values were advected from east to west, pushing the coldest air and snow into western Ireland. For future reference, be wary of snowfall forecasts when thicknesses fail to "go blue" or "stay blue" or hit sub-528 dm. (Some readers will know this, but I should mention, it's common to find some people confusing height and thickness, heights only correlate weakly with precip phase, thickness correlates much better). Normally over snow-free Ireland or UK winter surfaces, 528 dm thickness isn't nearly good enough for snow, you like to see sub-522 dm and even then the nearby ocean can spoil things.

However, in continental climates like say Kansas or such, the rain-snow dividing line can often be well up around 534 dm and in a rapidly developing east coast storm it can go up over 540 dm briefly. That "grey zone" on the GEM maps is meant to show the "thickness ribbon" of transition, 534-540 dm, that's the second green contour on the GFS outside the blues. It's the one you've been in for a couple of days recently. As you can see, when all is set up to perfection, it can snow at these higher thickness values, especially at any significant elevation.

There are a lot of system-specific rules or guidelines that I could get into in some other thread, if people are into it.

Su Campu

snow ghost wrote: »

Good point Nacho... and not just below 400ft, but at sea level on the Atlantic coast (well a bay off the Atlantic, but ye know what I mean)... not something many, if any, foresaw.

Fair enough, maybe there was, but going on the official synop reports for Tuesday it was pretty much rain or sleet for all Met Eireann stations, with just the odd brief flurry between the rain at some stations.

http://www.ogimet.com/cgi-bin/gsynres?lang=en&state=Irel&osum=no&fmt=html&ord=REV&ano=2010&mes=01&day=12&hora=23&ndays=1&Send=send

Not exactly a widespread snow event going on that data!

For reference:
Gurteen (71m/232ft)
Sherkin Island (near sea level??)
Oak Park - 63m (203ft)
Casement Aerodrome (97m/325ft)
Mullingar (101m/331ft)
Connaugt Airport (203m/665ft)

Regarding the performace of the models, I don't have any proper comparison, though I did notice that the GFS overdid the snow forecasts more than the NAE. It's a good idea though, and one we should try to get a handle on the next time....whenever that will be

nacho libre

Su Campu wrote: »

Fair enough, maybe there was, but going on the official synop reports for Tuesday it was pretty much rain or sleet for all Met Eireann stations, with just the odd brief flurry between the rain at some stations.

http://www.ogimet.com/cgi-bin/gsynres?lang=en&state=Irel&osum=no&fmt=html&ord=REV&ano=2010&mes=01&day=12&hora=23&ndays=1&Send=send

Not exactly a widespread snow event going on that data!

For reference:
Gurteen (71m/232ft)
Sherkin Island (near sea level??)
Oak Park - 63m (203ft)
Casement Aerodrome (97m/325ft)
Mullingar (101m/331ft)
Connaugt Airport (203m/665ft)

)

No one is suggesting it was a widespread snow event, just that snow fell in several places, in the midlands and further west, that were well below 400ft.
Tuesday's rather localised snowfall also demonstrates that the data from the met eireann stations doesn't always reveal the full story of the weather conditions on a particular day. It also shows how tricky a nationwide forecast can be in these situations . Met Eireann got it wrong on tuesday when they said it would be snow and sleet that would turn back to rain. However, the eagle was spot on, on Monday, when he said it would get less cold as the week went on and by Friday it would be much milder.

Deep Easterly

nacho libre wrote: »

No one is suggesting it was a widespread snow event, just that snow fell in several places, in the midlands and further west, that were well below 400ft.
Tuesday's rather localised snowfall also demonstrates that the data from the met eireann stations doesn't always reveal the full story of the weather conditions on a particular day. It also shows how tricky a nationwide forecast can be in these situations . Met Eireann got it wrong on tuesday when they said it would be snow and sleet that would turn back to rain. However, the eagle was spot on, on Monday, when he said it would get less cold as the week went on and by Friday it would be much milder.

Indeed Nacho. Looking at the satellites today it would seem there was a good and widespread covering in parts of the west/NW and parts of the midlands/Ulster due to tuesday's event. I agree, met eireann "official" reports don't suggest this as stations are sparsely located, esp in the regions that did get the snow. (ie, the NW, but sure what do they matter)

Are events like this to be discounted simply because they are not officially recorded? Who decides what is official in the first place? Is officialdom the preserve of the those who decide what it is?

snow ghost

Deep Easterly wrote: »

Indeed Nacho. Looking at the satellites today it would seem there was a good and widespread covering in parts of the west/NW and parts of the midlands/Ulster due to tuesday's event. I agree, met eireann "official" reports don't suggest this as stations are sparsely located, esp in the regions that did get the snow. (ie, the NW, but sure what do they matter)

Are events like this to be discounted simply because they are not officially recorded? Who decides what is official in the first place? Is officialdom the preserve of the those who decide what it is?

I agree with you Deep Easterly and Nacho on these points.

One of my biggest gripes is that - and correct me if I'm wrong - here in Mayo the weather stations are in Belmullet and at Knock Airport... both of which have distincitive micro climates very different from the rest of the county and they are certainly not representative of the rest of the county.

1) Belmullet is located on a penninsula which is essentially almost an island in the Atlantic and is influenced much more by the Atlantic than a few miles away or most of the county.

2) Knock AIrport is essentially built on a bog "on the side of a mountain" as many locals say, and is equally not representative.

Anyone who knows these locations are very aware of the different weather that affects them compared to much of the rest of the county.

I've lost count of times I've driven from pure cloudless sky & bright sunshine Westport to a rainy and windy Belmullet. Belmullet's weather is probably only representative for the weater on Achill island which is very similar. Likewise ask anyone about the fog at Knock airport.

I'm certain that Met Eireann give much of the weather - especially in the summer - for Mayo based on analysis from Belmullet.

In the summer when Met Eireann predict rain for Mayo it is often pure sunshine all day... not in Belmullet though where it is probably raining.

Deep Easterly

snow ghost wrote: »

I agree with you Deep Easterly and Nacho on these points.

One of my biggest gripes is that - and correct me if I'm wrong - here in Mayo the weather stations are in Belmullet and at Knock Airport... both of which have distincitive micro climates very different from the rest of the county and they are certainly not representative of the rest of the county.

1) Belmullet is located on a penninsula which is essentially almost an island in the Atlantic and is influenced much more by the Atlantic than a few miles away or most of the county.

2) Knock AIrport is essentially built on a bog "on the side of a mountain" as many locals say, and is equally not representative.

Anyone who knows these locations are very aware of the different weather that affects them compared to much of the rest of the county.

I've lost count of times I've driven from pure cloudless sky & bright sunshine Westport to a rainy and windy Belmullet. Belmullet's weather is probably only representative for the weater on Achill island which is very similar. Likewise ask anyone about the fog at Knock airport.

I'm certain that Met Eireann give much of the weather - especially in the summer - for Mayo based on analysis from Belmullet.

In the summer when Met Eireann predict rain for Mayo it is often pure sunshine all day... not in Belmullet though where it is probably raining.

Yep Snow Ghost. They do also have a station in Claremorris which represents the inland Mayo and north Galway climate better, but of course it is one of the stations that does not report or record weather conditions. "N/A" is what we get here.

snow ghost

Su Campu wrote: »

Fair enough, maybe there was, but going on the official synop reports for Tuesday it was pretty much rain or sleet for all Met Eireann stations, with just the odd brief flurry between the rain at some stations.

http://www.ogimet.com/cgi-bin/gsynres?lang=en&state=Irel&osum=no&fmt=html&ord=REV&ano=2010&mes=01&day=12&hora=23&ndays=1&Send=send

Not exactly a widespread snow event going on that data!

For reference:
Gurteen (71m/232ft)
Sherkin Island (near sea level??)
Oak Park - 63m (203ft)
Casement Aerodrome (97m/325ft)
Mullingar (101m/331ft)
Connaugt Airport (203m/665ft)

Regarding the performace of the models, I don't have any proper comparison, though I did notice that the GFS overdid the snow forecasts more than the NAE. It's a good idea though, and one we should try to get a handle on the next time....whenever that will be

Su Campu,

Knock Airport reported 'moderate snow' for many of its hourly reports on Tuesday.

That aside there was persistant snow here at sea level for hours on end on Tuesday.

Btw Thank you for your overall analysis of the cold spell - it's very interesting.

nacho libre

snow ghost wrote: »

I agree with you Deep Easterly and Nacho on these points.

One of my biggest gripes is that - and correct me if I'm wrong - here in Mayo the weather stations are in Belmullet and at Knock Airport... both of which have distincitive micro climates very different from the rest of the county and they are certainly not representative of the rest of the county.

1) Belmullet is located on a penninsula which is essentially almost an island in the Atlantic and is influenced much more by the Atlantic than a few miles away or most of the county.

2) Knock AIrport is essentially built on a bog "on the side of a mountain" as many locals say, and is equally not representative.

Anyone who knows these locations are very aware of the different weather that affects them compared to much of the rest of the county.

I've lost count of times I've driven from pure cloudless sky & bright sunshine Westport to a rainy and windy Belmullet. Belmullet's weather is probably only representative for the weater on Achill island which is very similar. Likewise ask anyone about the fog at Knock airport.

I'm certain that Met Eireann give much of the weather - especially in the summer - for Mayo based on analysis from Belmullet.

In the summer when Met Eireann predict rain for Mayo it is often pure sunshine all day... not in Belmullet though where it is probably raining.

heh very true about Belmullet. Although i do remember a couple of years ago being there when it was raining everywhere else in Mayo and in Ireland. Belmullet, as it said on the met eireann broadcast that night, was the only place in the country that was fine and it recorded a temperature of 25c. it was interesting to be there that day because the sky overhead was clear, yet a couple of miles further to the west there was sea fog, then just 10- 20 miles further east it was raining. Belmullet stayed in a rain shield all that day.

nacho libre

Deep Easterly wrote: »

Indeed Nacho. Looking at the satellites today it would seem there was a good and widespread covering in parts of the west/NW and parts of the midlands/Ulster due to tuesday's event. I agree, met eireann "official" reports don't suggest this as stations are sparsely located, esp in the regions that did get the snow. (ie, the NW, but sure what do they matter)

Are events like this to be discounted simply because they are not officially recorded? Who decides what is official in the first place? Is officialdom the preserve of the those who decide what it is?

indeed.
naturally a noteworthy event in your own area will bring out a bit of tribalism..;) but seriously much like villian's low temperature value, it's a pity that if isn't officially recorded it doesn't then exist as official data for people to look back on when studying this cold spell.

snow ghost

nacho libre wrote: »

heh very true about Belmullet. Although i do remember a couple of years ago being there when it was raining everywhere else in Mayo and in Ireland. Belmullet, as it said on the met eireann broadcast that night, was the only place in the country that was fine and it recorded a temperature of 25c. it was interesting to be there that day because the sky overhead was clear, yet a couple of miles further to the west there was sea fog, then just 10- 20 miles further east it was raining. Belmullet stayed in a rain shield all that day.

That'd be about right Nacho, for Belmullet, I've only been there once when it was pure sunshine and it was dull, overcast and raining in Westport all day at the same time. Usually if it is wet and windy in Westport, it will be a hurricane in Belmullet.

The best one ever I heard from Met Eireann was a few years back when they infamously forecast the heavy snow for Mayo and Donegal that never came. I drove up to Belmullet that day and back and on one of the main national radio stations - that presumably got its weather info from Met Eireann (?) -they were constantly reporting that there was 2 foot of snow in Mayo... there hadn't even been a snowflake, there wasn't even a bit of white on any of the North Mayo Mountains.

I can't even blame Belmullet for that one as there was no snow there either... but admittedly I didn't go further than the town, so there could have been a blizzard just over the weather station, but I doubt it!

Su Campu

snow ghost wrote: »

Su Campu,

Knock Airport reported 'moderate snow' for many of its hourly reports on Tuesday.

Of course, but it's at 665ft!

I agree about the coverage of the stations, they don't tell the whole story, but to listen to some people (not necessarily on here) you'd think the whole country had been blanketed.

Deep Easterly

Su Campu wrote: »

to listen to some people (not necessarily on here) you'd think the whole country had been blanketed.

No one is suggesting it was a countrywide event, but many parts of the country did see many hours of snow on Tuesday. Even here in Galway it snowed for about 6 hours, with even longer spells reported further north and east. A little bit more than can be classed as 'fleeting'.

Mobhi1

M.T. Cranium wrote: »

There are a lot of system-specific rules or guidelines that I could get into in some other thread, if people are into it.

I'd be into it for one, M.T. I'd be surprised if there weren't a lot of others on here interested as well.

Mobhi1

snow ghost wrote: »

I agree with you Deep Easterly and Nacho on these points.

One of my biggest gripes is that - and correct me if I'm wrong - here in Mayo the weather stations are in Belmullet and at Knock Airport... both of which have distincitive micro climates very different from the rest of the county and they are certainly not representative of the rest of the county.

1) Belmullet is located on a penninsula which is essentially almost an island in the Atlantic and is influenced much more by the Atlantic than a few miles away or most of the county.

2) Knock AIrport is essentially built on a bog "on the side of a mountain" as many locals say, and is equally not representative.

Anyone who knows these locations are very aware of the different weather that affects them compared to much of the rest of the county.

I've lost count of times I've driven from pure cloudless sky & bright sunshine Westport to a rainy and windy Belmullet. Belmullet's weather is probably only representative for the weater on Achill island which is very similar. Likewise ask anyone about the fog at Knock airport.

I'm certain that Met Eireann give much of the weather - especially in the summer - for Mayo based on analysis from Belmullet.

In the summer when Met Eireann predict rain for Mayo it is often pure sunshine all day... not in Belmullet though where it is probably raining.

At least you have 2 (or 3 if you include Claremorris) - there's not many counties can claim that - although thinking about it, Cork has 3 - Cork AP, Sherkin and Roches Pt - but none of them particularly representative of most of County Cork either, and Dublin has Casement and Dublin AP.

snow ghost

Su Campu wrote: »

Fair enough, maybe there was, but going on the official synop reports for Tuesday it was pretty much rain or sleet for all Met Eireann stations, with just the odd brief flurry between the rain at some stations.

http://www.ogimet.com/cgi-bin/gsynres?lang=en&state=Irel&osum=no&fmt=html&ord=REV&ano=2010&mes=01&day=12&hora=23&ndays=1&Send=send

Not exactly a widespread snow event going on that data!

For reference:
Gurteen (71m/232ft)
Sherkin Island (near sea level??)
Oak Park - 63m (203ft)
Casement Aerodrome (97m/325ft)
Mullingar (101m/331ft)
Connaugt Airport (203m/665ft)

Regarding the performace of the models, I don't have any proper comparison, though I did notice that the GFS overdid the snow forecasts more than the NAE. It's a good idea though, and one we should try to get a handle on the next time....whenever that will be

Su Campu,

I'm aware of Knock Airport's elevation, as I mentioned earlier it was built 'on the side of a mountain' as some locals say.

The reason I mentioned the regular moderate snow reports there on Tusday was because you used it as an example - as can be seen in your post above for connaught airport and you said "it was pretty much rain or sleet for all Met Eireann stations".

You're right in that it wasn't a wide spread snow event, countrywide, however on a regional basis it was fairly widespread.

The crux of all this is just how unrepresentative Met Eireanns stations are and if you are in a different part of the country, you mightn't be aware of what is actually happening - or has happened - in other parts, going on Met Eireann data.

snow ghost

Mobhi1 wrote: »

At least you have 2 (or 3 if you include Claremorris) - there's not many counties can claim that - although thinking about it, Cork has 3 - Cork AP, Sherkin and Roches Pt - but none of them particularly representative of most of County Cork either, and Dublin has Casement and Dublin AP.

Mobhi,

True, perhaps it's because it's the third largest county by area (Cork is the largest). In Comparison Dublin is the thrid smallest county by area, it's approx. a sixth of the size of Mayo.

Deep Easterly

snow ghost wrote: »

Mobhi,

True, perhaps it's because it's the third largest county by area (Cork is the largest). In Comparison Dublin is the thrid smallest county by area, it's approx. a sixth of the size of Mayo.

Just reading this make me feel even more hard done by!

Galway is the 2nd biggest county in the country and has only one station (which is just a recent addition) representing it on the daily reports. Mace Head, on the far west coast. Certainly does not represent the climate here in East Galway which is way different on a daily, monthly and yearly basis. I agree for the size of Dublin (county) it has a disproportionate high representation synoptic station wise.

I have noticed that it is not only the west and northwest that is poorly represented, but also the SE, areas such as Waterford, Wexford and Wicklow. The hourly reports on the met.ie web represent very little of what is going on weatherwise in the country.

snow ghost

Deep Easterly wrote: »

Just reading this make me feel even more hard done by!

Galway is the 2nd biggest county in the country and has only one station (which is just a recent addition) representing it on the daily reports. Mace Head, on the far west coast. Certainly does not represent the climate here in East Galway which is way different on a daily, monthly and yearly basis. I agree for the size of Dublin (county) it has a disproportionate high representation synoptic station wise.

I have noticed that it is not only the west and northwest that is poorly represented, but also the SE, areas such as Waterford, Wexford and Wicklow. The hourly reports on the met.ie web represent very little of what is going on weatherwise in the country.

Deep,

I think that one in Galway should be moved to Westport.

On a serious note, it would be good if Met Eireann had regional centres, in the main cities of the provinces analysing the provincial weather. I.e Galway for the West. Obviously resource wise this may not be viable, but it would be good.

Deep Easterly

snow ghost wrote: »

Deep,

I think that one in Galway should be moved to Westport.

On a serious note, it would be good if Met Eireann had regional centres, in the main cities of the provinces analysing the provincial weather. I.e Galway for the West. Obviously resource wise this may not be viable, but it would be good.

I agree. It is a good idea. Resourse wise as you say would be a problem but given that they are the national met service, I am sure they could speak up to the relevant departments for more dosh!

Good analysis there su campu!

Meanwhile during the spell it was a bit artic up at mount leinster aswell on the carlow wexford border!

http://www.boards.ie/vbulletin/showpost.php?p=64032582&postcount=30

octo

nacho libre wrote: »

indeed.
naturally a noteworthy event in your own area will bring out a bit of tribalism..;) but seriously much like villian's low temperature value, it's a pity that if isn't officially recorded it doesn't then exist as official data for people to look back on when studying this cold spell.

Current Climatalogical stations:



Rainfall Stations:

nacho libre

octo wrote: »

Current Climatalogical stations:



Rainfall Stations:

so villian's temperature will be officially recognised, then.
is that what you're trying to tell me?
or you are disputing my assertion that met eireann stations do not always reveal the full picture weather-wise. i presume that's your motivation in posting those two charts.

to repeat it once more for you octo: snow fell at sea level in several areas in the midlands and west last Tuesday. su campu was suggesting snow fell only at 400ft and then referenced met eireann stations to back up his assertion that snow was not widespread. In other words if met eireann stations didn't record snow then it can't have snowed in too many areas.
yet as was pointed out to him several times no one was claiming that snowfall was widespread, rather that snow fell at sea level in the west and the midlands despite what the met eireann stations recorded.

so basicially their stations around the country did not tell the full story of that day's weather.

Deep Easterly

Would be great if all those stations on the maps posted above were reporting hourly on the met eireann site with daily assessments on the "Yesterday's Weather page". Even still, looks like my area is probably the most unrepresented area in the country regarding both the climatological and rainfall station distribution. I wonder is there a reason the east Galway region is left out?

octo

nacho libre wrote: »

so villian's temperature will be officially recognised, then.
is that what you're trying to tell me?
or you are disputing my assertion that met eireann stations do not always reveal the full picture weather-wise. i presume that's your motivation in posting those two charts.

to repeat it once more for you octo: snow fell at sea level in several areas in the midlands and west last Tuesday. su campu was suggesting snow fell only at 400ft and then referenced met eireann stations to back up his assertion that snow was not widespread. In other words if met eireann stations didn't record snow then it can't have snowed in too many areas.
yet as was pointed out to him several times no one was claiming that snowfall was widespread, rather that snow fell at sea level in the west and the midlands despite what the met eireann stations recorded.

so basicially their stations around the country did not tell the full story of that day's weather.

Sorry, I should have explained. I`m saying that there`s much more to the official record, particularly with regard to max and min temperatures and rainfall, than the hourly reports on the website. But the point about snow is a good one. Now that the manned stations are closing, there are very few ways of recording snowfalls (the snow reports from automatic stations are unreliable).

Deep Easterly wrote: »

Would be great if all those stations on the maps posted above were reporting hourly on the met eireann site with daily assessments on the "Yesterday's Weather page". Even still, looks like my area is probably the most unrepresented area in the country regarding both the climatological and rainfall station distribution. I wonder is there a reason the east Galway region is left out?

I`d say they just don`t have any volunteers to do it. AFAIK, they`re grateful for anyone who`ll help out. It needs someone who can make a long-term commitment to go out every day 365 at 9 UTC and take rainfall and max/min readings.

snow ghost

octo wrote: »

Now that the manned stations are closing, there are very few ways of recording snowfalls (the snow reports from automatic stations are unreliable).

Octo,

When you say that the manned stations are closing, do you mean they are closing or they are going to be automated?

Is that all manned stations or just some of them?

I presume this is as a result of recent government cut backs?

octo

snow ghost wrote: »

Octo,

When you say that the manned stations are closing, do you mean they are closing or they are going to be automated?

Is that all manned stations or just some of them?

I presume this is as a result of recent government cut backs?

Pretty soon, the only manned stations left will be the airports and Valentia. A 24/7 station requires nearly 6 people to fill the roster.

snow ghost

octo wrote: »

Pretty soon, the only manned stations left will be the airports and Valentia. A 24/7 station requires nearly 6 people to fill the roster.

I find that quite disappointing, as I presume with things like snow, etc, human input is necessary?

Obviously a manned station is quite resource heavy if it takes 6 people, and technology is obviously improving, still it's dispappointing.

Redsunset

It's so Cold, there can't be Global Warming video, below:

It's So Cold There Can't be Global Warming

http://www.youtube.com/watch?v=yDTUuckNHgc&feature=player_embedded



Causes of the Unusually Cold & Snowy 2009~2010 Winter

During the winter of 2009-2010 a rare confluence of known factors in earth’s major climate variability systems (the Arctic Oscillation, El Nino and the Pacific Decadal Oscillation in the Pacific, the Indian Ocean dipole) have influenced the Northern Hemisphere winter from North America across to eastern Eurasia, as far east as China and Korea.

The major protagonist in producing the cold winter conditions of 2009/2010 was the Arctic Oscillation; as the Arctic Oscillation's effects fade then El Nino will come to the fore later in 2010, until that too fades away.

The AO refers to the changes in the strength of the atmospheric pressure (measured at sea level) in the Arctic and the mid-latitudes. It is currently in an extreme negative phase; above-normal pressure over the polar region and below-normal pressure over the mid-latitudes. This results in smaller pressure differences, and these weaker systems allow cold air to flow south, displacing the Jet Stream and resulting in wintry weather across Northern Europe, Northern America and Eurasia.

This confluence of climate variability systems, and the strength of the Arctic Oscillation, resulted in extremely harsh, cold winter conditions with heavy snowfall in many regions across the northern hemisphere. (Scroll down to Why the 2019-2010 winter was unusually cold and snowy below for explanation.)
January 5th 2010. Yorkshire From The Air.






The most dominant features have been regions of high pressure - anticyclones or Highs - over Greenland, Scandinavia and Siberia. These anticyclones forced colder air away from the Arctic and down into northern America, western Europe and parts of central and eastern Asia. The Greenland anticyclone blocked the usual path of the Jet Stream, forcing it to swerve well away from its usual course. (See graphic below.)

Image fromTechnorati's Lynn Voedisch blog: Used under fair use/educational/non commercial terms.

The cold many of us experienced was a weather phenomenon, not a climate phenomenon. It is not connected to climate change but is part of earth's natural climate variability. In fact we appear to be experiencing a repeat of the same factors that produced extremely cold winters in 1963 and 1978 (See below). Source.

When thinking of the vast area that forms the northern hemisphere bear in mind that cities and towns in America share one important thing with cities and towns in Europe and Asia - the same line-of-latitude.
e.g. Denver [Colorado] & Philadelphia [between New Jersey and New York] in the USA, Madrid in Spain, Ankara in Turkey, Baku in Azerbaijan, Beijing in China and Hamhung in North Korea are all situated approximately* along latitude 40 degrees north. (* Within onedegree [plus/minus] latitude of the 40 degrees north line-of-latitude. NB: All these countries [and India] are in the northern hemisphere.)
When cold air from the Arctic circle spreads out southwards then all the places named above above can be equally affected; particularly as during this winter they found themselves to the north (cold) side of the Jet Stream as it moved to the south.

In N. America the Arctic air reached as far south as Florida which suffered unaccustomed cold and frosts. This was later followed by the cold air mixing with air coming from the Gulf of Mexico carrying moisture that resulted in snow and ice coating Florida's roadways and fields. (See graphic below.)

Graphic from Accuweather. Used under fair-use/educational/non-commercial terms.

According to records going back to 1950, this is one of the the strongest El Nino combined with the most negative Arctic Oscillation yet seen during a winter. The northern polar region is colder than usual, but the equatorial Pacific is warmer than usual. (see below). Both of those helped produce colder conditions.

Bear in mind it wasn't cold worldwide: The town of Exmouth, in Western Australia, for example recorded record heat of 48.9 degrees C (121.82 degrees F)on the 2nd January 2010. Source.
[FONT=arial,sans-serif]The Australian city of Melbourne sweltered through its hottest night since 1902 on 11th January 2010, with temperatures topping 34 degrees Celsius (93 degrees Fahrenheit). [/FONT](Unsurprising its hot, as it's summer in the summer hemisphere.)
In the northern hemisphere north-east America and Canada, in North Africa, across the Mediterranean through to south-west Asia temperatures are very much above normal in early January 2010 - in many places by more than 5 degrees C (9 degrees F), and in parts of northern Canada by more than 10 degrees C (18 degrees F).

On 8th January 2010 parts of coastal Alaska were warmer than Florida.
[FONT=arial,sans-serif]The anticyclones (high pressure) resulted in an unusually warm Arctic, with air temperatures locally at 5.6 to 8.4 degrees C (10 to 15 degrees F) warmer than they should be in certain areas. [/FONT]
[FONT=arial,sans-serif]If you look at the Greenland region on the two images below - towards the centre of each - that is where the high pressure is. Cold air is being displaced away either side and down towards the mid latitudes.[/FONT]

[FONT=arial,sans-serif]Image above: NASA Earth Observatory. (+ Google Cached)[/FONT]

At Goose Bay in Newfoundland on January 7th 2010, temperatures were barely getting below zero, the average minimum for January there should be minus 23 degrees C. (Minus 9.4 degrees F.).
In Canada unseasonably warm weather and heavy rain led to the closure of one of Vancouver's Olympic premier ski venues (January 13th 2010), one month before the 2010 Winter Olympics are scheduled to start, in an attempt to conserve the snow for the games. (See also here.) Vancouver, Seattle and Portland all experienced a winter of rain and wind, but much warmer than usual with temperatures around the 10°C mark.
Bulgaria also experienced record warm temperatures. The thermometer reached 17 degrees C in many places with temperatures in Sofia on January 7th, 2010, soaring up to 14 degrees C (57.2 degrees F); at a time when the country should be blanketed by snow and temperatures be well below freezing.

In Crete on New Year's Day the temperature reached 30°C (86F), a new all-time record for Europe in January.

Although there has been freezing weather in places as far afield as Mexico, Florida, China and the UK; the Arctic, Greenland, much of the Mediterranean and southern Asia have been warmer than usual.

Overall the northern hemisphere winter may turn out to be no colder than in previous years, it's just that the heat is being distributed differently.

All this points to a major reorganisation of atmospheric conditions: particularly over the northern hemisphere, caused by the current positions of anticyclones (high pressure areas) and Lows (low pressure areas) across the northern Atlantic and Arctic. During the coldest part of winter it also altered the path of the Jet Stream that crosses the north Atlantic; it was well to the south of its normal track over western Europe for late December and early January. (See below.)

See also: Washington Post Capital Weather Gang. A virtual tour of the cold (and not so cold).
See also: If It’s That Warm, How Come It’s So Damned Cold? Hansen et al.
See also: New Scientist. Errors and Lies Thrive in Cold Weather.
See also:WeatherOnline: The 'Big' Freeze, 2009-10 - Unprecedented, or What?

Some Quick Facts to Bear in Mind

Warm air carries moisture and comes from the tropics/equator. Cold air is denser and carries much less moisture and originates from our planet's poles. In a high-pressure area air is denser than in areas of lower pressure. The result is that air will move from the high-pressure area to an area of lower density, or lower pressure. Winds usually blow from areas of high air pressure towards areas of low air pressure.


Whenever cold, dry air moves away from the poles it eventually encounters warmer, wetter air moving away from the equator. When warm, moist air meets cold air condensation occurs and precipitation results. If the temperature is at-or-below zero then the precipitation falls as snow.
Why the 2009-2010 Winter Was Unusually Cold and Snowy

An atmospheric pattern developed over the Arctic Circle region that flushed cold air away from the North Pole towards the mid-latitudes, where many of us in the N. Hemisphere live.

This pattern, known as ‘high-latitude blocking’ (caused by the negative phase of the Arctic Oscillation, or -AO) is essentially a large area of high pressure (anticyclone) in the atmosphere over far northern latitudes.

[FONT=arial,sans-serif]Saturday 9th January 2010. A large area of high pressure stretches from Northern Ireland across northern Britain[/FONT]
[FONT=arial,sans-serif]and the North Sea to Scandinavia. [/FONT]
[FONT=arial,sans-serif]High pressure also stretches over Greenland, Baffin Bay and NW Canada.[/FONT]
[FONT=arial,sans-serif]The thicker back lines across the UK indicate the main areas of snow showers. More are over the Atlantic.[/FONT]
[FONT=arial,sans-serif]On this day low pressure in the Mediterranean is spreading active weather fronts northwards across Europe & towards south-east England. [/FONT]
[FONT=arial,sans-serif]Met Office Synoptic Chart. 07.30 on Saturday 9th January 2010.[/FONT]

[FONT=arial,sans-serif]Below: AO Index (updated daily). January 12th 2010 [/FONT]

[FONT=arial,sans-serif]Image from US National Weather Service Climate Prediction Centre. Used under fair-use/educational/non-commercial terms.[/FONT]

[FONT=arial,sans-serif]The Arctic Oscillation is part of the North Atlantic Oscillation (NAO), also now in its negative phase.[/FONT]

When the NAO is in its positivephase the storm-track doesn’t bring down the intensely cold air from the Arctic. Instead, it drops into Quebec and the Canadian maritimes; a large subtropical high is set up in the Atlantic which keeps the south-eastern United States warmer than normal.


[FONT=arial,sans-serif]When in NAO is in its negative phase (as during the cold winter spell), the main branch of the jet stream brings the cold, Arctic air down into the Central United States, then down to its south-east. The only warm spots on the continent would be the Canadian Maritimes and [/FONT]Newfoundland [FONT=arial,sans-serif]over to [/FONT][FONT=arial,sans-serif]Greenland.[/FONT]

Images from: Wrex.com 13WeatherAuthority blog. Used under fair use/educational/non commercial terms.


High pressure pushes cold air downwards; as that air gets nearer the Earth's surface it's forced outwards and away, sending cold air toward us.
This high-latitude blocking pattern (-AO) was the strongest on record for a December in 2009 - and is continued into January 2010. The pattern consisted of two blocking anti-cyclones:
The first was over Greenland and it prevented (blocking) the usual warmer, damper westerly winds from reaching Europe across the Atlantic, by steering the high-altitude jet stream far to the south of Britain, leaving the country and north-western Europe exposed to winds from Russia, Scandinavia and the Arctic Ocean. This anticyclone also pushed large amounts of cold, Arctic air from the north, southwards, towards the United States. e.g. Below.

Charts above from weatherunderground.com. Image [FONT=arial,sans-serif]used under fair-use/educational/non-commercial terms.[/FONT]

The second anti-cyclone was the Siberian anti-cyclone (Siberian High) that was over much of northern Eurasia (during the coldest spell high pressure also stretched from above Northern Ireland, across northern Britain and the North Sea to Scandinavia) and also supplied much cold air to areas further south and east such as eastern regions of the USA, as well as to western Europe and across to China. The Siberian High is an intense, cold anticyclone that forms over eastern Siberia in winter; lasting from late November to early March and is associated with cold air and winters over East Asia.
(NB: during any winter a number of High pressure zones (anti-cyclones) form over high latitude areas.)

Negative Arctic Oscillation (AO) conditions allows Arctic air to spill southwards into eastern North America more readily.
Negative AO winters tend to bring cold winters to Europe (winds were from the north and east) whilst the prevailing storm-track (Jet Stream) moved south towards the Mediterranean Sea.
This brought increased storm activity and rainfall to southern Europe and North Africa.
North Western Europe's prevailing winds generally bring weather from the south-west and west; but during the coldest period the wind blew from the north and east.
This led to increased snowy conditions and also brought sub-zero temperatures to North Western Europe from the Arctic, Scandinavia and Siberia.

Image of the UK covered in snow below taken by Nasa's Terra satellite on 7th Jan. 2010. Photo: NASA. Click here to go to much larger version.

The weather that north-western Europe normally gets (brought by the Jet Stream) was diverted south towards Spain and the Mediterranean, where it was unseasonably wet for this time of year. e.g. See chart below.

Screenshot from weatheronline.co.ukImage [FONT=arial,sans-serif]used under fair-use/educational/non-commercial terms. Arrows added by site administrator.[/FONT]

The Jet Stream was over the Mediterranean & N. Africa, hundreds of miles south of its normal position, for a January.
The North Atlantic Oscillation and the Historic Record
The Arctic Oscillation forms part of the larger North Atlantic Oscillation (NAO). It also was in a negative phase (above-normal pressure over Iceland; below-normal pressure over the Azores; in Northern Europe this is usually associated with below-normal temperatures).

The NAO index for the month of December 2009 was -1.93, which is the third lowest NAO index since 1950 for a winter month (December, January, or February).

[FONT=arial,sans-serif]Above: NAO Index. January 17th 2010 [/FONT]

[FONT=arial,sans-serif]Image from US National Weather Service Climate Prediction Centre. Used under fair-use/educational/non-commercial terms.[/FONT]

The only winter months with a lower NAO index were February 1978 (-2.20) and January 1963 (-2.12). January 1963 was one of the coldest months on record in the both United Kingdom and the eastern regions of the USA. Source plus US National Weather Service.

In 1963 anticyclones to the North and East of the UK, brought bitterly cold air over Britain. A depression tracked to the South, and brought heavy snowfalls to England, Wales, and Scotland.


The mean maximum temperatures for January 1963 was more than 5 degrees C (9 degrees F) below average over most of Wales, the Midlands and Southern England, and in some places 7 degrees C below average (12.6 degrees F).
1963 was the coldest winter in the UK for 200 years.


We don't have sufficient records (to my knowledge) to demonstrate that these are similar conditions to those that produced the extremely harsh winter of 1946/47, but it I believe it likely to be the case.

That winter was followed by a summer with temperatures well above average, so there may be something to look forward to.
Looking back, it seems that strong and weak jet streams tend to cluster in groups: a series of mild and stormy winters, followed by three or four cold and snowy ones. We can identify the cold clusters in the past half-century: 1962-65, 1968-70, 1978-82, 1985-87 and 1994-97.
What we can't yet tell is whether the conditions experienced this winter will just be for 2009-10, or will prove to be part of a cluster that extends through winters from to 2009 to 2012? Only time will tell.

Some newspaper reports at the time predicted 30 years of cooling or of such winters, this I believe to be erroneous, if not active disinformation.

See also: What’s Causing the Cold Weather?

See also:WeatherOnline: The 'Big' Freeze, 2009-10 - Unprecedented, or What?

Deep Easterly

Epic & interesting analysis Redsunset.

Su Campu

Thanks for that, where did you get all that info from?

octo

Su Campu wrote: »

Thanks for that, where did you get all that info from?

I suspect from UCAR Magazine

Turtwig

octo wrote: »

I suspect from UCAR Magazine

Nope here.
Unless of course they're the same person.

skittles16

Hi just wondering if some can help me doing a project for collage on the big freeze of 2009/2010 and i just wana no if the siberian high cause it or if the atlantic oscillation. Thanks guys :o