FI CHARTS AUTUMN/WINTER 2014/15 **Mod Note Post #1**

lucernarian

BLIZZARD7 wrote: »

That 2009 new years eve chart actually delivered 2-3 inches of dry powdery snow via an Irish Sea streamer to the south Dublin area- that snow lay on the ground with little or no melt until it was topped up 4 or 5 days later.

I wish I was alive to experience that 1982 event... Hopefully a repeat is to come early next week

Check the times of the charts. It's 00z 31/12/09, not 23z 31/12/09 I wasn't in Dublin at the time but I saw plenty of photos of the New Years' Streamer. Seemed to mainly deliver graupel if I remember correctly.

But all that's got nothing to do with the incursion of cold air meeting an Atlantic front that happened earlier that day. It was cold enough to snow only away from where the atlantic front actually was. People in the likes of Galway and Roscommon did manage to get some snow out of it before it turned to sleet.

John.Icy

Where on earth did the 18z GFS ensembles come from? Run after Run of developing easterly. You struggle to find one run that doesn't develop blocking with an Easterly or else be tediously close to a very cold outcome. Some absolute humdingers, best set of FI ensembles I've ever went through possibly, irrespective of how 'cold' the uppers are, talking synoptics here or else developing synoptics (ie high pressure a little too close to our North etc but we have everything moving in the right direction) that would see the real cold arrive. Blocking just doesn't quit from the post Tuesday mark, ala GEM 0Z yesterday.

Gonna go mad and stick my neck out and say the 0z are going to see some big upgrades.

(Or else the 18z is playing games with overtired me and I'm falling for it)

EDIT: I should have known better than to fall for the 18z

Redsunset

Wow. Could we be in for Snowmagedden early next week. 0z juicy for whiteout conditions. Fingers crossed.

maquiladora

Tuesday's low looks extremely weak on the 0Z ECM. Precip amounts are really poor. Looks more like a dusting than a dumping. Hopefully it'll be more interesting than this...




And as for Monday, that one barely brushes the far southwest coast on the ECM.

munsterlegend

maquiladora wrote: »

Tuesday's low looks extremely weak on the 0Z ECM. Precip amounts are really poor. Looks more like a dusting than a dumping. Hopefully it'll be more interesting than this...


typical of course we get plenty precipitation most of the time! how are temps and dp looking?

Nabber

Wicklow mountains is the Place to be begining of next week.

WheatenBriar

I honestly don't see where Cork city would see snow from this front, it is not cold enough.
Less precipitation makes it worse
Even in the great Jan 1982 blizzard, rain fell at times in cork city and there was a rain snow mix in Rosslare
The air mass that was bumping into was much much colder surface flow off GB and Europe

I think the further north you get up the western corridor, you'd want to be looking at the front 2 weeks ago that widely fell as snow but fizzled out as it travelled east for guidance
This doesn't look like heavier precipitation

Thirdly will the front traverse the country at all,where will it stall,thats what could make things interesting alright

Fourthly is this evening going to be the solution at all,what with models struggling 36hrs out,they'd have had none of yesterday's snow in Dublin for example at that range even
Forecasting needs intuition now and braveness

Fifthly I think the lack of strong modeled precipitation is symptomatic of the cold air a front is hitting not being cold enough, that's a bad sign.

Sorry these comments might be better suited in an event thread,however my thinking is professional forecasters are being very cagey on any details 48hrs plus
In any of the great cold spells I remember they never were,there was enough certainty because the air mass was colder
I guess I'm cautioning here against losing the run of ourselves but I'm not saying this cold spell won't get colder and cross that threshold of no return(in terms of an event ) regarding marginality ,I think it can

maquiladora

munsterlegend wrote: »

typical of course we get plenty precipitation most of the time! how are temps and dp looking?

At the moment, temps/dp look ok snow at most times Monday/Tuesday apart from the far southwest Monday morning.

Rebelbrowser

WheatenBriar wrote: »

I honestly don't see where Cork city would see snow from this front, it is not cold enough.
Less precipitation makes it worse
Even in the great Jan 1982 blizzard, rain fell at times in cork city and there was a rain snow mix in Rosslare
The air mass that was bumping into was much much colder surface flow off GB and Europe

I think the further north you get up the western corridor, you'd want to be looking at the front 2 weeks ago that widely fell as snow but fizzled out as it travelled east for guidance
This doesn't look like heavier precipitation

Thirdly will the front traverse the country at all,where will it stall,thats what could make things interesting alright

Fourthly is this evening going to be the solution at all,what with models struggling 36hrs out,they'd have had none of yesterday's snow in Dublin for example at that range even
Forecasting needs intuition now and braveness

Fifthly I think the lack of strong modeled precipitation is symptomatic of the cold air a front is hitting not being cold enough, that's a bad sign.

Sorry these comments might be better suited in an event thread,however my thinking is professional forecasters are being very cagey on any details 48hrs plus
In any of the great cold spells I remember they never were,there was enough certainty because the air mass was colder
I guess I'm cautioning here against losing the run of ourselves but I'm not saying this cold spell won't get colder and cross that threshold of no return(in terms of an event ) regarding marginality ,I think it can

Sure if snow was certain in this country we would all have lives rather than wasting our time posting to fellow deranged people about possible dew points in 4 day's time and the like......

Reckless Abandonment

6z gfs has Mondays low just clipping the south west. Tuesday still looks good. But a little far out to be getting excited. Sorry on mobile can post charts

maquiladora

Reckless Abandonment wrote: »

6z gfs has Mondays low just clipping the south west. Tuesday still looks good. But a little far out to be getting excited. Sorry on mobile can post charts

Tuesdays low is still there on the 06Z, but it's about 5mb weaker than the 0Z. So seems to be trending towards the weaker ECM solution. Still looking snowy at the moment but this could get downgraded further the closer we get to Tuesday.

typhoony

what happens after mid-week is interesting, can the High Pressure properly retrogress towards Greenland, all models give a weak attempt but ultimately fail with too much energy riding over the top to allow it to happen. still worth keeping an eye on. the most likely solution is High pressure dominated over Ireland and UK.

Kermit.de.frog

maquiladora wrote: »

Tuesdays low is still there on the 06Z, but it's about 5mb weaker than the 0Z.

That is what we want. We don't want it to deepen so much that it develops a larger independent circulation, we want it to remain shallow to avoid excessive mixing of the air mass.

Musicman2000

From the UKMO a Snow Warning. For Sunday and Monday

Reckless Abandonment

looks snowy

Rebelbrowser

Reckless Abandonment wrote: »

looks snowy

Yup...

maquiladora

12Z GFS still looking snowy for Tuesday, but will need to see what the ECM does later as the 0Z run has the low weaker than this.

1-3cm widely, a bit more in the north and on high ground elsewhere.

JanuarySnowstor

maquiladora wrote: »

12Z GFS still looking snowy for Tuesday, but will need to see what the ECM does later as the 0Z run has the low weaker than this.

1-3cm widely, a bit more in the north and on high ground elsewhere.

looks more like 5 - 10 cm to me maq
Uppers are bitter so everything that falls should lie and stick.
Possibly the snowiest day for a long long time
Here's hoping

maquiladora

JanuarySnowstor wrote: »

looks more like 5 - 10 cm to me maq
Uppers are bitter so everything that falls should lie and stick.
Possibly the snowiest day for a long long time
Here's hoping

Maybe, only showing what the GFS shows, and the majority of it is 1cm there. And the ECM had less than that for most of the country (still waiting on 12Z ECM). I think a lot will depend on the amount of precip rather than whether it will fall as snow or rain. Some areas will obviously be luckier than others too, but we won't know that until the day itself.

Kermit.de.frog

maquiladora wrote: »

Maybe, only showing what the GFS shows, and the majority of it is 1cm there.

I'd take that with a very large pinch of salt. Snow accumulation charts are still on the experimental side of what is generally accepted as a reasonable barometer with which to forecast even now.

Timing is most important here. It's moving down over the country during the early hours - temperatures will be well below freezing at that stage and any wet roads will be icy.

If it occurred as currently progged there should be no issue with snow settling on most if not all surfaces and certainly more than 1 cm should be expected.

That assumes of course the synoptic evolution remains as is which is by no means guaranteed.

Reckless Abandonment

Any snow depth chart 4 days out may as well be drawn by my dog . They are notoriously unreliable

maquiladora

Reckless Abandonment wrote: »

Any snow depth chart 4 days out may as well be drawn by my dog . They are notoriously unreliable

It just gives a rough estimation of what to expect. Radar on the day trumps everything. If anything these charts usually overdo the amount of snow over a broad area but underdo localised amounts.

Yesterday, for example, 90+% of the country should have had snow accumulations looking at this, but we know that wasn't the case.

Strangegravy

maquiladora wrote: »

If anything these charts usually overdo the amount of snow over a broad area but underdo localised amount.

This.

Watching the radar and satellite images on the day is the only way to know for certain. I see these charts as rough guides really, as in, "Your area should get X amount, but that's no means guaranteed etc"

Reckless Abandonment

http://www.meteociel.fr/modeles/ecmwf/runs/2015013012/ECM1-96.GIF?30-0
ecm looking good for Tuesday

Kermit.de.frog

ECM has another feature worth watching for Wednesday too from the northwest

Easterly Beasterly

For a novice, what does the above ECM chart show? chart show? Cold NE'ly? I always find ECM more difficult to follow because there can be big changes in the 24 Hour Frames. Does this differ from what GFS and UKMO is showing or is there broad agreement?

Kermit.de.frog

Easterly Beasterly wrote: »

For a novice, what does the above ECM chart show? chart show? Cold NE'ly? I always find ECM more difficult to follow because there can be big changes in the 24 Hour Frames. Does this differ from what GFS and UKMO is showing or is there broad agreement?

There is a trough to the north west coming down over the country. This is what happens when Atlantic air tries to break a cold block. The milder air becomes trapped in a sort of wedge between the cold air which is what the 850 temp chart shows but it can't get through and so pushes south giving snow particularly on it's eastern flank.

Interesting in that we could be dealing with 3 different potential snow falls over just 3 days.

rickdangerouss

Kermit.de.frog wrote: »

There is a trough to the north west coming down over the country. This is what happens when Atlantic air tries to break a cold block. The milder air becomes trapped in a sort of wedge between the cold air which is what the 850 temp chart shows but it can't get through and so pushes south giving snow particularly on it's eastern flank.

Interesting in that we could be dealing with 3 different potential snow falls over just 3 days.

Yes, however none of them will turn out like what they are tonight. Which might be a good thing.

Its FI, anyway.

Gonzo

JanuarySnowstor wrote: »

looks more like 5 - 10 cm to me maq
Uppers are bitter so everything that falls should lie and stick.
Possibly the snowiest day for a long long time
Here's hoping

those charts are useless, the same type of chart posted 2 days ago showed 1-3cm across most of the country with little to nothing in the east and some parts of the east ended up with 10-25cm! (mostly Cavan, Monaghan).

typhoony

my thoughts on post wednesday haven't changed from last night, High Pressure does seem like it wants to set it's stall out, and from past experience once established can be very difficult to shift without a major upstream pattern change. a week or 2 could not be discounted. hopefully it stays a little bit north and where I am on the west coast will benefit from bright clear cold but pleasant weather. midlands and east though would suffer with cold frosty and foggy weather