Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

Artane2002

The operational runs at a higher resolution with different starting data to the ensemble members. Then the control is basically the operational (has the same starting data) but it is run at a lower resolution. The perturbations are all fed different starting data and are compared to the operational (I like to shorten it to OP). Then, a mean is extracted from the 20 perturbations. I think that is how it works, I could be wrong though.

Gaoth Laidir

Latest snow-depth chart. It was getting crowded now into its fifth day so had to take out the data labels.

kilkenny31

Hi guys. I have been following the threads on here for the past few days and I think it's been great. Two weeks ago I was telling people about the cold spell that was on its way thanks to you guys. I was just doing a bit of reading online and I came across a article from Canada which I think would put what we had in context and maybe quiten people complaining about the red warning. This shows that the totals we received on Thursday into Friday would be considered a lot even if it fell in Canada. Here's the link https://www.google.ie/amp/s/www.cbc.ca/amp/1.1370387

patneve2

Looks to me that snowfall wise this storm dumped a lot more snow than the 1982 event in many areas and was superior to 1982 in this regard. However, i think that 1982 was superior from a synoptic point of view - it looks like it packed a stronger punch even though it lasted for a shorter amount of time. Also, i bet that dew points were lower during that event with drier snow even on coasts throughout the storm. The 2018 storm occurred when the colder air had already passed over ireland. The 82 one had a perfect max cold - atlantic interaction making it the rarest set up possible in irish weather imo.

George Sunsnow

Villain wrote: »

Seeing loads of these types of reports, confusing IMBY with a general view. I’ve spoken with many farmers who had said it was worse than 82 with drifts much higher and thaw is slow enough.

It depends on where you are when comparing to 1982
By Friday night here we had drifts 10ft high which certainly was on a par with 82
Despite the rain there’s still a foot or more of snow in the fields here

As you know I had two shed roofs collapse with the weight of snow on top
That didn’t happen in 82
The snow drifts were peculiar in the fields they rippled into drifts well away from ditches like frozen waves and then a big one at the ditch
Lug must be insane

Elmer Blooker

Gaoth Laidir wrote: »

@Elmer, yes, air temperature does affect snow melt, but so does daytime insolation, even in the overcast conditions we had. Daylight is almost 4 hours longer now than at the beginning of January and insolation almost 50% more. I noted during the day on Friday that my a layer on my car was turning liquid despite the temperature being -2 °C. This insolation also accelerates sublimation.

Just after the big fall in '82 the sun was out but there was little melt. Yes, this then let temperatures nosedive at night, but you can't negate the increased effect the sun and length of day has at this time of the year compared to 2 months ago.

And at night? In the early hours of Sat morning the snow stopped and immediately the temperature started to creep above freezing, game over I thought and went to bed.
In Jan 1987 the same happened, the snow stopped and an immediate thaw began at night.
If some posters (not you G.L.) think I'm a moaner they're probably right but what good is a snowfall without a few days of blue skies, dazzling sunshine and hard frost at night? Thats why the St Stephen's Day thaw in 2010 didn't bother me, we had what was a long cold spell by Irish standards and got a glorious sunny Xmas Day out of it. Couldn't complain!

Seeing loads of these types of reports, confusing IMBY with a general view.

IMBYism? Can you imagine if today was sunny? (the thaw would be no quicker than now, Johnstown Castle now 7c, no sun) The WHOLE country would be enjoying themselves with toboggans or even a plastic bag would do! Instead we have had our three days and today is so vile few want to venture out. I know we don't live in Canada but to have a decent fall lie for just a few days and not a complete waste would be pleasant.

hatrickpatrick

I cannot for the life of me understand how so many folks out there don't understand that weather forecasting is ridiculously far from an exact science, and that therefore the decision to issue a red alert or similar is not based on "these specific areas will experience life threatening conditions and these others will not", instead it's "all of these areas have a significant potential to experience life threatening conditions, and the alert is designed to take the worst realistic possible scenario and take action accordingly".

It's like during Ophelia when people talked about how their specific area was under a red alert and didn't see much dangerous action from the storm - the track shifted at literally the eleventh hour and all the experts and computers in the world simply couldn't have predicted that. The warning was for what was significantly possible, not for what was set in stone.

I guess maybe it's a sign of how far we've come in the last couple of decades regarding forecasting, that people now have enough confidence in it to assume that it is an exact science. But still seems bizarre that the simple concepts of forecasting uncertainty and "prepare for the worst, hope for the best" are lost on so many people.

This forum has been quite the breath of fresh air compared with some of the ridiculous Met bashing I've seen in some places.

Casualsingby

sryanbruen wrote: »

March 3 2018, another day of snow covered ground across the board.

How accurate is that? Seems the whole country is white to my beady eyes when that isn't the case.

wakka12

Casualsingby wrote: »

How accurate is that? Seems the whole country is white to my beady eyes when that isn't the case.

Each little white pixel is like 20 square kilometres I don't think its that accurate

I would have loved to have seen a NASA image of the country !

sryanbruen

Casualsingby wrote: »

How accurate is that? Seems the whole country is white to my beady eyes when that isn't the case.

Well for one, Ireland looks very tiny on that so you can't really make out parts having snowfall specifically. Two, not highly accurate is my guess because you could only imagine how difficult making these charts would be. Here's the link for yourself:

http://www.natice.noaa.gov/ims/

Irish Steve

The last time we had easterly snow, it was very educational to watch how a narrow band of heavy snow meandered up and down the east coast as the wind direction changed by just a degree or two, and the Isle of Man streamer moved accordingly. There was and is no way to give wind forecasts to the degree of accuracy that would be needed to allow people to know where was going to be affected, as an example, the intensity of the snow in the streamers meant that the airport was massively affected if the streamer was over them, and not at all troubled if it moved literally a mile north or south.

In the same way this last week, when the snow first started, we had next to nothing in Ashbourne, as the Isle of Man shadow meant the streamers came on shore south of us, if the wind had been just a bit more east than north, we'd have had a lot more snow in the early stages of the event. That can't be forecast with the precision that would mean the difference between a yellow or red alert, so the only option is to say that a wider area is at red risk.

The same applies to geographical areas local to the Wicklow mountains, and other high ground, a few miles can make a huge difference, but the next day, a few degrees wind shift will change the areas affected, or not affected, and that's without other changes in the structure and temperatures of the air masses causing the weather.

With each weather event that happens, the historic data enlarges, so the models (in theory) have more history to draw on and refine the results, but even then, we have to recognise that minute variations of a huge number of possible parameters can mean that today's results will not be the same as they were the last time there were similar parameters.

The Met office have to then make a call based on all the information they have to hand, and based on the possible variances that may occur, and they have to do it with enough lead time to allow affected parties to respond accordingly. A Red alert 1 hour before massive snow fall will occur is too late, a red alert 4 days before the event is too early, and transport and distribution organisations realistically need at least 24 hours notice in order to put appropriate close down or modification plans into place.

OK, some of the country didn't get the worst possible scenario, but the forecast was indicating that there was the strong possibility of needing it, and the balance of probability was that it would happen. Be glad it didn't, rather than beating up on the relevant decision makers, their main priority was public safety, and for most of the country, they got it right. The very low death toll and lack of massive pressure on already stretched emergency services was a huge benefit of the way the situation was managed.

We only get to see what the media chooses to report from the "public coverage" of things like the Emergency response meetings, we don't get to know about the many minor detail decisions made to ensure food got out of storage locations, or power was restored to water treatment plants, or critical staff were moved by civil defence, or put into hotels because they couldn't get home, or all of the other issues that affected every aspect of life for a few days.

I'm also sure that once things are back to normal, all concerned will look at how it worked out, and next time round, the plan will be better, or if not better, it will have been tweaked a little where needed to improve the end result.

If people are not happy with how it all worked out, complaining on the net won't change it, making positive suggestions on how to improve the plan to the relevant people may mean a better outcome next time round.

brookers

patneve2 wrote: »

Looks to me that snowfall wise this storm dumped a lot more snow than the 1982 event in many areas and was superior to 1982 in this regard. However, i think that 1982 was superior from a synoptic point of view - it looks like it packed a stronger punch even though it lasted for a shorter amount of time. Also, i bet that dew points were lower during that event with drier snow even on coasts throughout the storm. The 2018 storm occurred when the colder air had already passed over ireland. The 82 one had a perfect max cold - atlantic interaction making it the rarest set up possible in irish weather imo.

I was on a farm when 1982 happened and a snow drift didnt thaw until march, it was on a lane, what happened then was that people were not that really well prepared, kinda waking up from a sleepy christmas, I think there was way more snow this time but people whilst isolated have more contact with the outside world, social media, farmers coming with jcbs diggers etc, wasnt as much of that around in 1982, we were much more backward....

Gonzo

snow is almost melted here now except for compacted snow and slushy snow mounds. Half my garden is green again and most of the driveway is clear. All side roads were cleared this morning by a JCB and are fine for driving again.

I have noticed that Dunshaughlin village itself had a heavier snow layer compared to where I live 2km to the east of the town. There is a noticeable difference in the amount of snow piles and lying snow between Dunshaughlin village and my area which is half way to Ratoath.

lucernarian

@Irish Steve some good points there, especially how our preparation for it goes.

In 1982 there was the serious issue of diesel clumping up from a lack of antifreeze in the fuel. That was since dealt with by law.

In 2001 the significant power losses led to the ESB doing some network changes to help prevent so many areas being vulnerable to 20kV lines getting downed in a blizzard.

2010 had the country flatfooted when it came to salt supplies and equipment to clear roads and runways. Since that, salt and grit stockpiles are more available and used when freezing temperatures are forecast.

2018 was handled fairly well by all national agencies and pretty good macroscopic weather modelling to help us prepare.

What I'd like to see change is an acceptance in this country that we need to have winter tyres on vehicles more often. An adoption of graphical weather warnings like by the UKMO which covers areas rather than simple county boundaries. Finally, some more sophisticated radar and a third base located in the NW of the country. The radar this time around was a mess for all the hardest-hit areas, something a better upgrade than the one a few years ago might fix.

Finally, shout-out to Weathercheck for calling the prolonged and at times heavy snow on Friday evening which added well over 10cm in much of the Dublin area. It was flagged in different ways by the models, and M.T Cranium called the trend too earlier on Friday. But the intensity of the snow and the way air temps clung on below zero throughout the day was something I didn't expect at Friday lunchtime based on the existing guidance.

nacho libre

Elmer Blooker wrote: »

.
PS. I think in future we'll have to look to Greenland for a prolonged cold spell as Scand highs only last a couple of days.

The scandi high was not helped by a west based nao setting up, that means any high there usually goes too far west when it retrogresses. If we had an east based nao, the high when it retrogressed would have been further east, but then the attack from the south may not have happened at all, thus no snowstorm

If your preference, which yours seems to be, is a prolonged cold spell then that would have been a positive thing. However we had a set of charts last Thursday that we will not likely see again in our life time. I think we will see cold outbreaks in the future, but i'll eat my socks if we witness last weeks snowfall again within the next 35 years .

Casualsingby

gozunda wrote: »

Many of the existing weather stations are located along or adjacent to the coastline - there are significant inland areas which have little or no coverage with the result that weather variables are under reported imo.




Most notable block imo is Limerick Mid / South Tipperary Kilkenny Waterford with existing weather stations being outliers outside this area. There is also a huge block of Kerry and Cork which has no significant coverage. Given the varied terrain and topography of these areas I believe a dearth of weather stations is a significant issue with recording weather data.

Yes there is poor representation country wide. Agree with areas you mentioned. Three in Ulster and two of those are on the coast. I believe the all Ireland temperature record could, emphasis could have been broken in December 2010.

Northern Ireland has a lot more representation. Some attachments below from met office showing how cold it was in the west of Northern Ireland. - 7 or more minimum temperature anomaly. A shot of the wide difference of minimum temperature on one night,-18 to -3.3. And "Hourly air temperature at Castlederg, 49m amsl, from 24 November to 27 December 2010. Between 0500 utc on 18 December and 2300 utc on 25 December (187 hours) the air temperature was continuously below –5°C (denoted by the blue arrow), falling below –15°C on 6 nights and briefly reaching –15°C again at 1900 utc on the 25th. The record minimum of –18.7°C is also marked. Note the sudden thaw on Boxing Day, the temperature rising 18 degC in 18 hours“ Castlederg is 1 to 2km away from the Donegal border.

Met Éireann “The Cold Spell in Historical Context
There is no single figure which classifies a spell of cold weather and allows fully objective comparison
with previous events. Important factors are the duration of the cold weather, how cold it was and
how much snow. This particular cold spell was notable for being the earliest spell of significant
duration (started in November). It was also notable for the sustained extreme low temperatures. We would characterise December 2010 as the most extreme cold spell in terms of
the “depth of cold” but the cold spell of 1963 was significantly longer.“


Most extreme recorded in terms of depth of cold. It really was amazing when you think about it.

sdanseo

wakka12 wrote: »

Each little white pixel is like 20 square kilometres I don't think its that accurate

I would have loved to have seen a NASA image of the country !

You can here, they take an image every day but there's too much cloud to see any snow. https://worldview.earthdata.nasa.gov/?p=geographic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels,Reference_Features,Coastlines&t=2018-02-28&z=3&v=-9.667321277630757,50.90035277224669,-1.2298212776307569,55.07076292849669

nacho libre

gabeeg wrote: »

3 weeks ago I was f5-ing the GFS's FI charts looking for signs of impact from the SSW. An easterly was depicted, and eventually made its way here.
.

When the UKMO is steadfast about a a cold outbreak a couple of weeks in advance it's always a good sign too. It was that way in 2010 too. And speaking of the gfs, as you point out, whatever about over doing low temperatures and sometimes being too progressive with breakdowns, it is good at picking up on a new signal well out in FI.

Casualsingby

What was the lowest max temperature for Thursday? Surely the march record was broken?

lucernarian

nacho libre wrote: »

When the UKMO is steadfast about a a cold outbreak a couple of weeks in advance it's always a good sign too. It was that way in 2010 too. And speaking of the gfs, as you point out, whatever about over doing low temperatures and sometimes being too progressive with breakdowns, it is good at picking up on a new signal well out in FI.

Very true, though to GFS' credit, it was one of the first to flag Storm Emma in the first place last weekend, and in a rather similar form to how it actually verified.

sdanseo

Casualsingby wrote: »

What was the lowest max temperature for Thursday? Surely the march record was broken?

Edit: misread your post, thought it was the minimum you were after. I'll leave the below anyway.

-7.0 in Cork Airport. We didn't get any long clear nights but the 1947 record for March is -17.2 which was always going to be a hard one to beat.

It did beat the Cork record for March though which was -6.1 (source below, only up to 2010 so unless they got any lower since then)
http://www.met.ie/climate-ireland/extreme-mintemps.pdf

Casualsingby

sdanseo wrote: »

Edit: misread your post, thought it was the minimum you were after. I'll leave the below anyway.

-7.0 in Cork Airport. We didn't get any long clear nights but the 1947 record for March is -17.2 which was always going to be a hard one to beat.

It did beat the Cork record for March though which was -6.1 (source below, only up to 2010 so unless they got any lower since then)
http://www.met.ie/climate-ireland/extreme-mintemps.pdf

Looks like the record for Northern Ireland was broken. -1.2 twice, I think I saw somewhere in the east of northern ireland with a high of -2 on Thursday.

Casualsingby

Yeah NI march record for lowest maximum temperature was broken on Thursday.

mickger844posts

nacho libre wrote: »

The scandi high was not helped by a west based nao setting up, that means any high there usually goes too far west when it retrogresses. If we had an east based nao, the high when it retrogressed would have been further east, but then the attack from the south may not have happened at all, thus no snowstorm

If your preference, which yours seems to be, is a prolonged cold spell then that would have been a positive thing. However we had a set of charts last Thursday that we will not likely see again in our life time. I think we will see cold outbreaks in the future, but i'll eat my socks if we witness last weeks snowfall again within the next 35 years .

I think you are right Nacho. The majority of us in here will never see the likes of it again. As snow storms go it was the perfect storm. Endless snow with massive drifts. Did we ever think we would get a chance to witness such an event.
Model wise the signs were there 10 days out but we had so many disappointments in the past we just couldn't believe. So we had 2010 for unbelievable cold and longevity and 2018 for massive snow amounts so is that it for us now? Can we ever reach these highs again? Well we just have to believe we can as thats what we strive for.
Models in general performed really well but for me Icon has put itself up there to rival the big three and maybe can we now say we have a big four?

JCX BXC

mickger844posts wrote: »

Models in general performed really well but for me Icon has put itself up there to rival the big three and maybe can we now say we have a big four?

One swallow does not a summer make.

M.T. Cranium

That map with the 25 or so stations just shows the daily reporting sites. The met service have a second order group of stations from which they can pull in reports, for example the report of the maximum snow depth at Glencullen, not on the list of daily sites. Also not on the list would be various co-op stations which I believe includes Danno's station in Laois, and Kerry airport, Waterford airport and Donegal airport. You can often see Kerry and Donegal airport reports on meteociel maps and occasionally Waterford airport too.

BLIZZARD7

JCX BXC wrote: »

One swallow does not a summer make.

Indeed, the ICON model has had its moments but for me GEM is closer to if not better than some of the others (thinking GFS mainly here). All of this can be settled with verification stats anyway although they don't really show the true picture for how accurate the models are locally over Ireland.

M.T. Cranium

Good job everyone who contributed to this thread. It helped me a lot, you can imagine how much extra work I might have been forced to do, had there not been a steady supply of useful and timely map and data captures. Also the opinions and outlooks that you shared went into my forecasts more than you might imagine, I have learned over these past ten years to search out the consensus of the more knowledgeable posters on the forum and if there's a range, that helps me too because then I know what range of possible outcomes might be reasonable.

So whenever people thank me in particular, you should understand that I know if they don't know, that it's a group effort (not a highly organized one like Net-weather employs) and not just me flying solo. However when I mess up, that's all on me.

Unrelated second item -- I posted an interesting table of monthly temperatures (from the CET) for the Dalton and overlapping decades, to show how cold it can get when the Sun goes fairly quiet. That's in the general chat thread for this event, around 10:20 p.m. today just ending.

Gaoth Laidir

Elmer Blooker wrote: »

And at night? In the early hours of Sat morning the snow stopped and immediately the temperature started to creep above freezing, game over I thought and went to bed.
In Jan 1987 the same happened, the snow stopped and an immediate thaw began at night.
If some posters (not you G.L.) think I'm a moaner they're probably right but what good is a snowfall without a few days of blue skies, dazzling sunshine and hard frost at night? Thats why the St Stephen's Day thaw in 2010 didn't bother me, we had what was a long cold spell by Irish standards and got a glorious sunny Xmas Day out of it. Couldn't complain!
IMBYism? Can you imagine if today was sunny? (the thaw would be no quicker than now, Johnstown Castle now 7c, no sun) The WHOLE country would be enjoying themselves with toboggans or even a plastic bag would do! Instead we have had our three days and today is so vile few want to venture out. I know we don't live in Canada but to have a decent fall lie for just a few days and not a complete waste would be pleasant.

The air at 1.5 metres can be very different to the air right at the snow or the temperature of the surface underneath. Depending on factors such as snow depth, age, contamination, type of underlying surface, ground temperature, etc., what goes on in the snow cover may be unrelated to the air above. Solar radiation can heat up the underlying surface (e.g. pavement, roof) and cause melting while having little ffect on the reported air temperature. This is a well-studied scientific fact. Add almost 50% stronger radiation and 50% longer daylight for a March snowfall and it's not surprising to see quicker melt than the same fall in January. That's why I don't get why the thaw would be no quicker now if it was completely sunny.

Gaoth Laidir

Latest snow depths at 6 am this morning. Still some sizeable figures in the UK. Little Rissington (215 m) still 42 cm.