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

piuswal

https://www.ecmwf.int/en/forecasts/charts/catalogue/medium-mslp-wind850?facets=Range,Medium%20(15%20days)&time=2018022712,72,2018030212&projection=classical_europe

latest ECMWF has EMMA literally on the west Kerry coast at 1200 UTC Friday. If that pans out then its likely that the milder air south of its associated trough line will have made some progress up over the country, so rain likely at least into southern and southeastern areas.

Gaoth Laidir

I'm not seeing very impressively-cold cloudtops upstream over the North Sea, the source of tonight's action. Granted the sea there is 2-3 degrees colder than the Irish Sea, but I would have expected to see more than the 5000-metre tops there at the moment.

Tops are cooling just west of Denmark, where the core of the cold is just moving out over the North Sea. Hopefully this will turn things around a bit for later tomorrow, cos to be frank, this evening is nothing near orange level and has been a big disappointment so far, a bit less than I was expecting.

Weather BOFH

policy75 wrote: »

is there a post to explain stratosphere, troposphere, arctic temperatures being out of sync, jet stream gone to sleep as a description of how we come to witness this weather event to help our TV3 weather 'experts'? Or is that an essay?

Met Eireann have a good summary here:

http://www.met.ie/news/display.asp?ID=498

dacogawa

I Think the Irish sea heard you Gaoth Laidir, you gave it a wake up call

George Sunsnow

I’ve just one small request of the streamer machine please thank you




150+ miles

sdanseo

Gaoth Laidir wrote: »

I'm not seeing very impressively-cold cloudtops upstream over the North Sea, the source of tonight's action. Granted the sea there is 2-3 degrees colder than the Irish Sea, but I would have expected to see more than the 5000-metre tops there at the moment.

Tops are cooling just west of Denmark, where the core of the cold is just moving out over the North Sea. Hopefully this will turn things around a bit for later tomorrow, cos to be frank, this evening is nothing near orange level and has been a big disappointment so far, a bit less than I was expecting.

I did people a favour and didn't quote the pic (pls resize :pac: )

Much lower uppers projected over the next 8-10hrs though. Surely this will increase convective potential significantly (as indicated in the EIDW TAF which forecast an increase in intensity after midnight).

JanuarySnowstor

Tomorrow looks very snowy to me and I think with so much (almost non sensical) attention on Thursday night....
@ Gaoth laidir the ppn isn't due to get going until after midnight

Re Cork further showers through the night on and off and tomorrow looks quite snowy here too.

My punt a red issued in the morning for tomorrow!! 😆

SleetAndSnow

JanuarySnowstor wrote: »

Tomorrow looks very snowy to me and I think with so much (almost non sensical) attention on Thursday night....
@ Gaoth laidir the ppn isn't due to get going until after midnight

Re Cork further showers through the night on and off and tomorrow looks quite snowy here too.

My punt a red issued in the morning for tomorrow!! ��

Ay thats great, I am seeing the same. Quite a few snow showers for us in Cork and looking at the latest ECM is looks like a red guranteed for Cork, Waterford and the east coast.

Gaoth Laidir

Gaoth Laidir wrote: »

I'm not seeing very impressively-cold cloudtops upstream over the North Sea, the source of tonight's action. Granted the sea there is 2-3 degrees colder than the Irish Sea, but I would have expected to see more than the 5000-metre tops there at the moment.

Tops are cooling just west of Denmark, where the core of the cold is just moving out over the North Sea. Hopefully this will turn things around a bit for later tomorrow, cos to be frank, this evening is nothing near orange level and has been a big disappointment so far, a bit less than I was expecting.

Its amazing looking at that image how much the normal weather patterns are out of kilter currently. Look at the Canary Islands, there a front approaching them from the NW with a westerly flow cutting in behind. Pretty rare for that latitude I would imagine. They had terrible weather on Sunday with flight cancellations etc.

Gaoth Laidir

sdanseo wrote: »

I did people a favour and didn't quote the pic (pls resize :pac: )

Much lower uppers projected over the next 8-10hrs though. Surely this will increase convective potential significantly (as indicated in the EIDW TAF which forecast an increase in intensity after midnight).

On my screen the image seems normal width

Yes, but what we get after midnight, the UK or at least the North Sea should be getting now. It's not happening, and snow depths in the UK are sporadic and struggling to reach more than 1 cm. We should be seeing 8 or 9 there already, according to models. They were higher earlier but has been a lot of melt there this evening, despite wbt a few degrees below zero. Ground temperature is still a problem, and here too. We need some continuous heavy showers to lay a base for further accumulations, but right now it's not happening.

Anyway, I hope I did give things a kick up the arse a bit but there's still an awful way to go to reach some of the depths forecasted (up 15 cm by me in Dublin by Thursday).

ninebeanrows

Gaoth Laidir wrote: »

I'm not seeing very impressively-cold cloudtops upstream over the North Sea, the source of tonight's action. Granted the sea there is 2-3 degrees colder than the Irish Sea, but I would have expected to see more than the 5000-metre tops there at the moment.

Tops are cooling just west of Denmark, where the core of the cold is just moving out over the North Sea. Hopefully this will turn things around a bit for later tomorrow, cos to be frank, this evening is nothing near orange level and has been a big disappointment so far, a bit less than I was expecting.

I don't understand your final statement about big disappointment?

We always new the beefier showers were going to kick off after midnight?

500hPa temps this evening and at 9am posted,




-42 over the Irish Sea!!

Gaoth Laidir

Met Éireann aviation have warnings out now for 3-5 cm snow at Dublin and Casement from 2330Z tonight to 1200Z tomorrow.

Did anyone take a look at the 12Z Euro 4 charts by any chance? They looked ok for the early morning period, but looked pretty poor for the afternoon tomorrow.

sdanseo

Gaoth Laidir wrote: »

On my screen the image seems normal width

Yes, but what we get after midnight, the UK or at least the North Sea should be getting now. It's not happening, and snow depths in the UK are sporadic and struggling to reach more than 1 cm.

Not really, the higher level temps are farther out in the north sea (-38 line at 500hpa not even at the east coast of UK yet)

Gaoth Laidir wrote: »

We should be seeing 8 or 9 there already, according to models.

Most models are going for the biggest increase in precip in the early hours though?

Gaoth Laidir wrote: »

Anyway, I hope I did give things a kick up the arse a bit but there's still an awful way to go to reach some of the depths forecasted (up 15 cm by me in Dublin by Thursday).

I hope so too! You remain probably the most knowledgeable person here and the voice of reason and managed expectations - but speaking light heartedly optimism from you is much more fun

Weathercheck wrote: »

I don't understand your final statement about big disappointment?

We always new the beefier showers were going to kick off after midnight?

500hPa temps this evening and at 9am posted

-42 over the Irish Sea!!

This is what I was getting at, you've summarised better.

Gaoth Laidir

Weathercheck wrote: »

I don't understand your final statement about big disappointment?

We always new the beefier showers were going to kick off after midnight?

500hPa temps this evening and at 9am posted,


-42 over the Irish Sea!!

Yes I know that, but for example the -41 isotherm is now on the east coast of England and we're not seeing the deep convection I would expect from such instability. Should be seeing cloudtops of around -45 to -50 with that, however they're not even below -30 yet in that area. If it's not happening upstream, how will it happen here?

Larbre34

2045 radar return showing Irish sea streamer pattern picking up

Gaoth Laidir

Gaoth Laidir wrote: »

Yes I know that, but for example the -41 isotherm is now on the east coast of England and we're not seeing the deep convection I would expect from such instability. Should be seeing cloudtops of around -45 to -50 with that, however they're not even below -30 yet in that area. If it's not happening upstream, how will it happen here?

If the Irish sea temps were a bit warmer than the North sea, would this provide the contrast needed?

Gaoth Laidir

sdanseo wrote: »

Not really, the higher level temps are farther out in the north sea (-38 line at 500hpa not even at the east coast of UK yet)

Yes it is, as is the -41 line.




Anyway, we'll keep on trucking...

Gaoth Laidir

Deleted User wrote: »

If the Irish sea temps were a bit warmer than the North sea, would this provide the contrast needed?

A little bit, yes, but the difference is only 2-3 degrees, and the sea fetch over the North Sea is about 3 times more.

MJohnston

Gaoth Laidir wrote: »

Yes I know that, but for example the -41 isotherm is now on the east coast of England and we're not seeing the deep convection I would expect from such instability. Should be seeing cloudtops of around -45 to -50 with that, however they're not even below -30 yet in that area. If it's not happening upstream, how will it happen here?

Won't the higher Irish sea temps make a difference for that?

Low pressure centre is on a more eastward track by +66 hrs on the 18Z GFS run.

JanuarySnowstor

@ Cork fans

I made a comment this morning that snow along the coast(thursday)would turn to rain later.
At the moment following slight upgrades with every run I'm more enclined to think it will remain as snow. This is an epic event for the South and a red warning isn't a doubt I'm

Also, and a big also are we ignoring the wind?
It looks storm force ten or worse accompanied with high tides. Folks this is serious and it's not a case of will schools shut rather a case of how do we keep frontline staff going!

glightning

Airmass is just too dry. This is the type of airmass you’d get over the continental US with crisp, cold, and dry weather. We need a proper battleground where moisture is injected from the south (like they do in the US).

Difference between there and here though is that they are a huge continent and where the cold air doesn’t get modified at low level and can truely win the battle out.

This spell has surprised me and brought me back down to Earth when it comes to temps to expect from cold air sources. If we were living on a continent where this air actually came from then we shouldn’t be seeing daytime maxes of +4 to +6 today with uppers as they were. Also, with the -15c uppers knocking our door tomorrow we should really be seeing maxes more like -7c and lows of -15c. The fact we are not a continent and the air is travelling over relatively warm water greatly modifies it at the lowest levels and stops true true cold at the surface. This I also believe (the fact the air is relatively warm at the surface) is part of the reason not a lot of water is evaporating from the sea into the air above. If it was -7c at the surface, the sea would readily evaporate.

GFS appears a lot less aggresive than the ECM for Friday. Doesn't seem to want to push alot of precipitation northwards at all.

SleetAndSnow

JanuarySnowstor wrote: »

@ Cork fans

I made a comment this morning that snow along the coast(thursday)would turn to rain later.
At the moment following slight upgrades with every run I'm more enclined to think it will remain as snow. This is an epic event for the South and a red warning isn't a doubt I'm

Also, and a big also are we ignoring the wind?
It looks storm force ten or worse accompanied with high tides. Folks this is serious and it's not a case of will schools shut rather a case of how do we keep frontline staff going!

indeed its pretty bad going by the ECM, but the GFZ 18z isn't the best for any part of the country so far. I have a feeling its just general pub run shenanigans though but that depends on UKMO 0z and ECM 0z later on The uncertainty this close is scary

munsterlegend

JanuarySnowstor wrote: »

@ Cork fans

I made a comment this morning that snow along the coast(thursday)would turn to rain later.
At the moment following slight upgrades with every run I'm more enclined to think it will remain as snow. This is an epic event for the South and a red warning isn't a doubt I'm

Also, and a big also are we ignoring the wind?
It looks storm force ten or worse accompanied with high tides. Folks this is serious and it's not a case of will schools shut rather a case of how do we keep frontline staff going!

Do precipitation amounts not look rather patchy though? nothing too heavy per the models. the heavier stuff stays off shore.

JanuarySnowstor

@ Cork fans

I made a comment earlier today that it might be bordeline for the South coast on Thurs night...I no longer think this after upgrades today.
Looks serious and epic!!
If I had to pick a sweet spot would go with Carlow

Also, and a big also, are we forgetting the wind issue?
Looks storm force to me coinciding with high tides

Red warning a certainty

JanuarySnowstor

@ Cork fans

I made a comment earlier today that it might be bordeline for the South coast on Thurs night...I no longer think this after upgrades today.
Looks serious and epic!!
If I had to pick a sweet spot would go with Carlow

Also, and a big also, are we forgetting the wind issue?
Looks storm force to me coinciding with high tides

Red warning a certainty

downwiththatsor

JanuarySnowstor wrote: »

@ Cork fans

I made a comment earlier today that it might be bordeline for the South coast on Thurs night...I no longer think this after upgrades today.
Looks serious and epic!!
If I had to pick a sweet spot would go with Carlow

Also, and a big also, are we forgetting the wind issue?
Looks storm force to me coinciding with high tides

Red warning a certainty

I cant see any gusts higher than 60mph, but that would be epic in heavy snow i guess

SleetAndSnow

This GFS has taken a very weird turn of events. Last run it was basically saying all cold gone by friday evening. Now its showing snow well off the cork coast still on Monday evening. Its either an outlier or else it has copped onto something.