FI Charts (T120+ onwards) Winter 2018 **READ MOD NOTE IN FIRST POST**

Kermit.de.frog

ICON brings in the much colder air slightly earlier. Conditions more conducive to snow showers from Monday particularly in the east.

lucernarian

Slightly more southerly movement to the cold air mass at t+63 hours on GFS.

nacho libre

A low now near Iberia.

A nice kink in the flow = Snowy cold from Mother Russia with love.

We can't ask for much more than this or can we?:)

Kermit.de.frog

12z UKMO 120 hrs

lucernarian

Two notable things, heights/pressure rising a bit more strongly over Newfoundwell than the last run. And again that ever so slightly southwards nudge of the cold air compared to earlier (and slightly slacker Easterlies over us.

t+81

Rebelbrowser

High pressure to north a little bit closer on this gfs run

BLIZZARD7

GFS 120 hrs -

lucernarian

GFS 12z t+141:

High Pressure is a little lower, but also acting as a somewhat better block and the cold air is still advected to us fairly well. Still ~1020 hPA on the new run. Also a reload of cold air from the artic is much closer than on the earlier run.

Iancar29

GFS +144hrs

UKMO +144hrs

ICON +144hrs

lucernarian

Compared to the last t+168, the 12z run gives a somewhat nicer big picture at the same point in the future:

There's also -40 degree air at 500 hPa over Ireland on the current run... :eek:

nacho libre

Good grief. What a chart. 510 line so far south. -16 uppers widely over England. -15 uppers reaching the east coast of Ireland. As someone said records will be broken if this comes to fruition.

patneve2

Most potent cold wave since 1991 if these charts come to pass. GFS 12Z showing days of snow showers with winds alternating ESE to ENE. Let's see what the ECM shows

MJohnston

A question about reading the Geop 500 charts - I know what to look for in the 850hpa temperature charts in terms of snow potential, but what makes a great looking chart for cold/snow on the 500hpa pressure charts?

Are we looking for high pressure systems to bring in the cold, dry air and then rely on incoming but blocked low pressure systems or lake effect convection to produce the snow?

Iancar29

MJohnston wrote: »

A question about reading the Geop 500 charts - I know what to look for in the 850hpa temperature charts in terms of snow potential, but what makes a great looking chart for cold/snow on the 500hpa pressure charts?

Are we looking for high pressure systems to bring in the cold, dry air and then rely on incoming but blocked low pressure systems or lake effect convection to produce the snow?

Cold pool from the north sea with some embedded lows will induce lake effect showers. The fetch /wind direction then being key for how intense they can get for the North and East coast.

nacho libre

lucernarian wrote: »

There's also -40 degree air at 500 hPa over Ireland on the current run... :eek:

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could be some prolonged showers of the snow variety around so:D

Isn't - 40 air at that level conducive to polar lows forming?

Rougies

nacho libre wrote: »

could be some prolonged showers of the snow variety around so:D

Isn't - 40 air at that level conducive to polar lows forming?

But don't you need a very large stretch of ocean for them to form? I don't think one has ever formed in the north sea in an easterly, needs to be a northerly or NNE'rly.

lucernarian

Rougies wrote: »

But don't you need a very large stretch of ocean for them to form? I don't think one has ever formed in the north sea in an easterly, needs to be a northerly or NNE'rly.

I thought so too. Even so, with eddies and decent lapse rates, it might allow for better convection. Heights are quite low in that airmass which helps, too early to say what effect wind shear would have at 700 hPa though.

aidanodr

https://twitter.com/metoffice/status/966726802998571009

lucernarian

ECMWF +96....

The HP is a good bit further south, the cold air pool is a bit more distended from the rest of it in Russia, but it seems like the cold air pool is overall bigger and there's more height rises over Greenland. A mixed bunch, it might offer even more potential post t+144 hours.

nacho libre

She looks scared...:D That would be an utterly epic snowfall for parts of Ireland if it came off.

lucernarian

GFS 18z should be around now...

JCX BXC

lucernarian wrote: »

GFS 18z should be around now...

Latest chart I can see is +99 (21hrs Monday), uppers of -6 and below covering Ireland (slightly sooner than previous run) and a slight shift south so far. No massive changes though, and as it's within the reliable range I can't see much change in the timing of the arrival.

Rebelbrowser

Donegal Storm wrote: »

Any chance of a technical thread for next week mods? The other thread is a mess, impossible to keep up with and any good informative posts are immediately ]

Agree. Other thread is a write off at this stage.

lucernarian

Donegal Storm wrote: »

Any chance of a technical thread for next week mods? The other thread is a mess, impossible to keep up with and any good informative posts are immediately lost..


Not looked at the models since last night but nothing much has changed from what I can see, still expecting a big downgrade every time I have a look but so far so good. The main issue I can still see is the high could sink over us leaving us with a nondescript cold inversion but hopefully hopefully it won't come to that

Latest GFS pretty much as we were, cold from Monday with snow potential from Tuesday evening. Still pointless looking at smaller details

[IM

I would be very surprised if the high sunk over us. All the charts indicate very strongly that the polar frontal jet will be like 1000km too far north for a high to truly sink over us. We'll be south of it. My fear is mainly having the high come close enough to stifle serious precipitation, followed by a Greenland high that's not close enough to block warmer air reaching us 10 days away. Even in that case there would be inevitably an advection of cold air over us if the high builds elsewhere, as the Canadian SSW almost inevitably means. I think it's going to be hard to stop at least one day of very intense cold and snow.

BLIZZARD7

I see a trend appearing...

nacho libre

Donegal Storm wrote: »

The main issue I can still see is the high could sink over us leaving us with a nondescript cold inversion but hopefully hopefully it won't come to that

The cold could get deflected further south, unlikely at this stage, but sinking over us?
I really can't see how the High will sink over us given the jet stream profile and the canadian vortex being all but dead, also once you have a low near Genoa it should help to maintain the high where it is.

ZX7R

In relation to the up coming cold spell, do the more knowledgeable posters here think the upgrades to the gsf a few years ago are starting to work, being that the gsf has picked up the coming cold event quicker than the ecm, or was it just luck. It seems to have picked up a couple of weather events quicker over the last year quicker than the ecm

lucernarian

1st March is a bit far away yet. Were the southern fork of the jet (what little there is) behave a bit differently, it would throw off that avenue of snowfall.

Suppose the high pushed the cold that bit further south as part of the block, then that 7-days-away LP would stick around France.

We've plenty of cold and some snow in the days prior in any case

nacho libre

lucernarian wrote: »

ollowed by a Greenland high that's not close enough to block warmer air reaching us 10 days away. Even in that case there would be inevitably an advection of cold air over us if the high builds elsewhere, as the Canadian SSW almost inevitably means. I think it's going to be hard to stop at least one day of very intense cold and snow.

You maybe right about the Greenland high going too far west eventually which alows milder air back in, but as you say looks what on offer before hand. I'd say a lot of people will be glad to get their five days of snowy nrivana or so, and after that won't be distraught if it should go awry there after.

Donegal Storm

lucernarian wrote: »

I would be very surprised if the high sunk over us. All the charts indicate very strongly that the polar frontal jet will be like 1000km too far north for a high to truly sink over us. We'll be south of it. My fear is mainly having the high come close enough to stifle serious precipitation, followed by a Greenland high that's not close enough to block warmer air reaching us 10 days away. Even in that case there would be inevitably an advection of cold air over us if the high builds elsewhere, as the Canadian SSW almost inevitably means. I think it's going to be hard to stop at least one day of very intense cold and snow.

Yeah that's what I meant, the south eastern flank of the high will always be nearby early next week so a slight shift southeastward and we'd just see a few dry and frosty days.

Still on track for now though and cold is all but certain, I reckon by Saturday evenings runs we should have a fairly accurate picture of Tuesday/Wednesday