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

BLIZZARD7 · 23-02-2018 11:37am

Slack low pressure by the end of the week and deep cold over snowfields - lows of -8c to -15c possible under those conditions. I await the 12z's with Interest.

Rebelbrowser · 23-02-2018 11:53am

The evolution keeps getting quicker and in fairness MT flagged that this might happen as did an Austrian meteorologist who posts on NW. I reckon the cold could arrive on Sunday evening ultimately.

Larbre34 · 23-02-2018 1:13pm

BLIZZARD7 wrote: »

Slack low pressure by the end of the week and deep cold over snowfields - lows of -8c to -15c possible under those conditions. I await the 12z's with Interest.

My personal record was -15.4C over snow on Christmas morning 2010 at around 8.30am, semi-rural site on Dublin/Meath/Kildare border. Frankly I'd expect to see that broken at my loc by Sunday 4th March

Oscar Bravo · 23-02-2018 1:36pm

STATUS YELLOW

Weather Advisory for Ireland
Exceptionally cold weather is forecast for next week with significant wind chill and severe frosts. Disruptive snow showers are expected from Tuesday onwards, particularly in the east and southeast.

Issued:Friday 23 February 2018 12:00
Valid:Friday 23 February 2018 12:07 to Friday 02 March 2018 12:00

patneve2 · 23-02-2018 1:51pm

Gaoth Laidir wrote: »

It's totalling all of the precipitation falling as snow, not the accumulated depth on the ground.

I would add too that the ECM may slightly underplay the amount of snow showers extending inland as it tends to kill them off too quickly over cold land.

This. Winds are looking strong so I wouldn't be surprised if ppn peaks may occur somewhat inland, like the first spell of 2010 (the one at the end of Nov). Could be seriously nasty on the coast next week, 50 km/h winds and snow squalls coming in off the Irish sea

patneve2 · 23-02-2018 2:09pm

Great, 4/5 days of excellent snow potential. Should be some windows when sst to 850 hpha differences go over 20 degrees C. Hoping for more runs backing all of this up

Mullaghteelin · 23-02-2018 2:23pm

BLIZZARD7 wrote: »

EC Snow accumulation chart in inches by Friday 00z - From Nick L on netweather - Dublin in the firing line

That gap in the heaviest precipitation downwind of the Isle of Man is aiming straight at me. Hopefully wind direction varies about enough so that all of us get a decent share.
Nothing worse than having to endure the high temperatures from the sea, but without the compensation of decent shower activity.

Gonzo · 23-02-2018 2:55pm

Mullaghteelin wrote: »

That gap in the heaviest precipitation downwind of the Isle of Man is aiming straight at me. Hopefully wind direction varies about enough so that all of us get a decent share.
Nothing worse than having to endure the high temperatures from the sea, but without the compensation of decent shower activity.

going by that I could be in the firing line for the IOM shadow.

Calibos · 23-02-2018 3:00pm

Gonzo wrote: »

going by that I could be in the firing line for the IOM shadow.

While I am giddy with excitement. An ENE gives me in Bray the longest Sea Fetch possible.

Kermit.de.frog · 23-02-2018 3:43pm

NMM progging light to moderate snow showers in to eastern and some southern fringes overnight Tuesday

nmm-1-120-0.png?23-13

davidsr20 · 23-02-2018 3:53pm

In regards to your comment earlier about a possible downgrade. How’s it looking since ?

TheMilkyPirate · 23-02-2018 3:55pm

davidsr20 wrote: »

In regards to your comment earlier about a possible downgrade. How’s it looking since ?

12Zs rolling out over the next two hours. Nothing to worry about anyway

Kermit.de.frog · 23-02-2018 3:57pm

davidsr20 wrote: »

In regards to your comment earlier about a possible downgrade. How’s it looking since ?

No change. It's a possibility. No more than that. Favored outcome is still the severe end of the spectrum.

We'll know more shortly.

pad199207 · 23-02-2018 3:59pm

Kermit.de.frog wrote: »

No change. It's a possibility. No more than that. Favored outcome is still the severe end of the spectrum.

We'll know more shortly.

Is this the ICON your talking about Kermit?

bogman_bass · 23-02-2018 4:04pm

Excuse my ignorance but what do you mean by a sea fetch

And while we're at it what is a streamer?

Rebelbrowser · 23-02-2018 4:08pm

bogman_bass wrote: »

Excuse my ignorance but what do you mean by a sea fetch

And while we're at it what is a streamer?

Just google "lake effect snow" and think of the Irish sea as your lake and you will get all your answers

RobertKK · 23-02-2018 4:08pm

bogman_bass wrote: »

Excuse my ignorance but what do you mean by a sea fetch

And while we're at it what is a streamer?

Sea fetch is the length of sea the air mass travels over, the longer it is the greater for lake effect snow when it comes to the Irish sea in our case.

A streamer is like a continuous line of showers generated from the same spot, caused by the lake effect snow scenario.

Kermit.de.frog · 23-02-2018 4:08pm

pad199207 wrote: »

Is this the ICON your talking about Kermit?

ICON and NAVGEM.

Both picked up sudden more progressive retrogression of high pressure toward Greenland this morning. Still a cold outcome, no doubt about that, but not quite as severe and more marginal overall.

derekon · 23-02-2018 4:32pm

Kermit.de.frog wrote: »

ICON and NAVGEM.

Both picked up sudden more progressive retrogression of high pressure toward Greenland this morning. Still a cold outcome, no doubt about that, but not quite as severe and more marginal overall.

Now we don't really want to be hearing the word "marginal" here with a severely cold easterly. If we don't get snow out of this on the east coast next week, I will really give up!!!! However glad you are referring to NAVGEM and ICON models!!!

For a moment there I thought you were talking about the ECM, GFS and the UKMO! Phew!!!!!

D

lucernarian · 23-02-2018 4:36pm

Not that the ICON is worth all that much, but that still depicts a very snowy outcome. Some of the big 3 model runs had hinted at that also yesterday but since 00z they seem more on board with more prolonged cold and windy conditions over a week from now.

We have the GFS 12z coming out currently too

Rebelbrowser · 23-02-2018 4:41pm

lucernarian wrote: »

Not that the ICON is worth all that much, but that still depicts a very snowy outcome. Some of the big 3 model runs had hinted at that also yesterday but since 00z they seem more on board with more prolonged cold and windy conditions over a week from now.

We have the GFS 12z coming out currently too

And in fact the 12z ICON is looking much better for cold too

Akrasia · 23-02-2018 4:41pm

RobertKK wrote: »

Sea fetch is the length of sea the air mass travels over, the longer it is the greater for lake effect snow when it comes to the Irish sea in our case.

A streamer is like a continuous line of showers generated from the same spot, caused by the lake effect snow scenario.

With the lake effect in operation over the irish sea, is there any chance of more localised lake effect snow to the west of places like Lough Derg, Lough Corrib, Lough Ree etc or are they all much too small in Ireland for that kind of thing?

Gaoth Laidir · 23-02-2018 4:48pm

Akrasia wrote: »

With the lake effect in operation over the irish sea, is there any chance of more localised lake effect snow to the west of places like Lough Derg, Lough Corrib, Lough Ree etc or are they all much too small in Ireland for that kind of thing?

The're too small. I reckon we'll need a fetch of at least 50 km to get showers properly going.

lucernarian · 23-02-2018 4:51pm

-10 850 hPa air is reaching Ireland at 6am on Monday going by the latest run:

pad199207 · 23-02-2018 4:53pm

I think kermits little worry could be fixed on this run!

lucernarian · 23-02-2018 5:00pm

The trend from GFS 12z seems to be an upgrade, I can't really believe how quickly the air is being sent westwards from Russia though. Also heights a built up a little more north from Sunday onwards, and leaves us with a strong and slightly further away Scandi High by t+96.

TheMilkyPirate · 23-02-2018 5:03pm

UKMO is fantastic. ICON again has a different development but still cold and snowy

patneve2 · 23-02-2018 5:03pm

To close the topic on the air source of this airmass, its clearly an arctic continental hybrid. Arctic air cooling down over western siberia, then west of the urals before moving towards scandi while retaining a lot of its frigid characteristics. As it stands looks like the most potent easterly/north easterly in decades. Let's see what effects it will bring to the ground.

111 hrs GFS 12Z

LEIN · 23-02-2018 5:04pm

pad199207 wrote: »

I think kermits little worry could be fixed on this run!

Excellent!

Rebelbrowser · 23-02-2018 5:13pm

First snow to Louth and Cork at 1pm on Monday!

72-574UK.GIF?23-12

patneve2 · 23-02-2018 5:14pm

Ridiculous at 144 hrs. Going to take a good 10 hour break from model watching I think

BLIZZARD7 · 23-02-2018 5:14pm

-15c 850's in even faster on this GFS run, ICON is a marginal improvement and is still very cold but also very different to the other models.

12_120_ukthickness850.png?cb=13

Iancar29 · 23-02-2018 5:17pm

12z is perfect. Cold air entrenched over Ireland by Monday. Showers possible from Monday night, increasing into tuesday and wednesday with some nice kinks in the flow, leading to good instability. Thundersnow anyone? :pac:

Kermit.de.frog · 23-02-2018 5:18pm

Quite severe runs from the UKMO and GFS. Plenty of snow particularly in the eastern half of the country, really piling up there. Lake effect, relentless.

If the ECM is equally severe this evening I'll draw up the forecast for the other thread. Proviso is the 12z ICON model is consistent so there is some uncertainty there.

gfs-0-126.png?12

Surinam · 23-02-2018 5:20pm

Kermit.de.frog wrote: »

Quite severe runs from the UKMO and GFS. Plenty of snow particularly in the eastern half of the country, really piling up there. Lake effect, relentless.

If the ECM is equally severe this evening I'll draw up the forecast for the other thread. Proviso is the 12z ICON model is consistent so there is some uncertainty there.

Agree with cautious approach but honest question: when have we ever cared about what the ICON is showing? I don't recall it getting so much consideration before.

pauldry · 23-02-2018 5:24pm

That second chart is the most wonderful thing I have seen on boards.

Theres purples near us

Its a day after tomorrow scenario except...

Its the day after the day after the day after the day after tomorrow

nacho libre · 23-02-2018 5:30pm

Why are people getting hung up on the ICON. Kermit the frog is just suffering late stage nerves.:P The Icon is cannon fodder compared to the big three- which all show snow heaven for a few days. As someone said we may not see charts like these again for a long, long, time. For those who drink, if the ECM show what we want this evening(which i think it will), then it's time to open the champagne.

BLIZZARD7 · 23-02-2018 5:38pm

ARPEGE is on board too-

arpegeeur-0-114.png?12

BLIZZARD7 · 23-02-2018 5:46pm

503 DAM, wow that is some depth of cold.

12_138_ukthickness.png?cb=44

nacho libre · 23-02-2018 5:49pm

BLIZZARD7 wrote: »

503 DAM, wow that is some depth of cold.

My God to think we were marvelling at the depth of cold over Canada a few weeks ago, we are not that far off it ourselves. it's really incredible stuff.

BLIZZARD7 · 23-02-2018 6:17pm

GEM has us buried midweek

gem-0-126.png?12

BLIZZARD7 · 23-02-2018 6:22pm

GFS control run, likewise. Something tells me we are going to remember this week for a longtime.

vizualpics · 23-02-2018 6:54pm

Akrasia wrote: »

With the lake effect in operation over the irish sea, is there any chance of more localised lake effect snow to the west of places like Lough Derg, Lough Corrib, Lough Ree etc or are they all much too small in Ireland for that kind of thing?

There was streamers off Lough Neagh from a NE in 2010 also around Sligo Bay into Mayo.