Cold Snap, T0-180Hours Only

yorlum11

pistolpetes11 wrote: »

Hard to show off that chart ,

But we dont want the high pressure to sink into Europe ,

Ideally it would place over Scandinavia or move towards Iceland.

On most of the tonights models there is too much energy in the northern arm of the jet stream , which in turns send a low pressure system toppling over our high and pushing our the HP into Euro which in turn allows the atlantic /milder air to come across us.

Tha makes sense PP thank you lets hope for a better run shortly.

nacho libre

pistolpetes11 wrote: »

Hard to show off that chart ,

But we dont want the high pressure to sink into Europe ,

Ideally it would place over Scandinavia or move towards Iceland.

On most of the tonights models there is too much energy in the northern arm of the jet stream , which in turns send a low pressure system toppling over our high and pushing our the HP into Euro which in turn allows the atlantic /milder air to come across us.

Yes. It's really the absence of a Greenland high or even a mid atlantic high that's the problem. Relying on a Scandi high alone is nearly always big a risk, because quite often the highs don't come quite far enough west to prevent the Atlantic pushing the cold air away. Let's just hope the ecm holds on to the idea of a possible reload from the north west a bit further down the line!

Tom Cruises Left Nut

Looks like the HP keeping the LP a bit further west on this run

sdanseo

Quick question.

None of these models for the next few days are showing dm readings lower than about 540. Thought we needed <528dm for snow?

Also, GFS 850 temps are very high for any type of snow on Tuesday. All between 0 and -5.

cherryghost

Looks like the cold air mass is making a wee push further westwards this time round.

Su Campu

sdeire wrote: »

Quick question.

None of these models for the next few days are showing dm readings lower than about 540. Thought we needed <528dm for snow?

I think you may be making the common mistake of taking the heights shown on the charts above as being 500-1000 thickness. Those show 500 hPa geopotential, and also happen to use dam as units (1 dam = 10 metres).

Here are actual thickness charts (use the coloured contours). Also shows sea level pressure (white lines) and 500 hPa geopotential (black lines)

http://www.wetter3.de/animation.html

TheMilkyPirate

sdeire wrote: »

Quick question.

None of these models for the next few days are showing dm readings lower than about 540. Thought we needed <528dm for snow?

Also, GFS 850 temps are very high for any type of snow on Tuesday. All between 0 and -5.

Current GFS is showing 528dm over the east coast by wednesday afternoon

nacho libre

Update from GP:
"sharp increase in momentum transport across 30N which has triggered some of the NWP into the kind of response we've seen a lot recently, that is to bounce the NAO from negative to strongly positive in a short period of time.

However, broad signals remain good for a robust mean ridge over Scandinavia as the trend in angular momentum is still downward and GEFS (P) 00z and 12z are indicative of neutral or weakly negative NAO. Interestingly, the GEFS (P) suite is starting to depict another strongly negative AO developing mid month which ties in with recent stratospheric warmings. If the AO is negative, watch the NAO follow suit.



sharp increase in momentum transport across 30N which has triggered some of the NWP into the kind of response we've seen a lot recently, that is to bounce the NAO from negative to strongly positive in a short period of time.

However, broad signals remain good for a robust mean ridge over Scandinavia as the trend in angular momentum is still downward and GEFS (P) 00z and 12z are indicative of neutral or weakly negative NAO. Interestingly, the GEFS (P) suite is starting to depict another strongly negative AO developing mid month which ties in with recent stratospheric warmings. If the AO is negative, watch the NAO follow suit.

"Models are invariably too progressive in removing blocking signals and even more progressive in removing surface cold, so not sure how much change we're really looking at here. ECM 12z mean, operational ECM 12z and GEM/BOM all still keen on the Scandinavian ridge but undergoing some subtle redistribution of energy - that poleward movement of the cold uppers aroud the western flank of the ridge causing short and mid term uncertainties. The ECM quite interesting in opening up a potential below average temperature / above average rainfall signal.

Long term, still looking for mean ridge over Scandinavia shifting north-west from mid month on. "

sdanseo

Su Campu wrote: »

I think you may be making the common mistake of taking the heights shown on the charts above as being 500-1000 thickness. Those show 500 hPa geopotential, and also happen to use dam as units (1 dam = 10 metres).

Here are actual thickness charts (use the coloured contours). Also shows sea level pressure (white lines) and 500 hPa geopotential (black lines)

http://www.wetter3.de/animation.html

Mystery solved. Cheers.

Makes the world of difference when you combine different sources for this forcasting lar, it's juts not all available in one place :P

BEASTERLY

Another slight downgrade so far?

Musicman2000

BEASTERLY wrote: »

Another slight downgrade so far?

No not much difference between the 12z

rc28

BEASTERLY wrote: »

Another slight downgrade so far?

Nope seems broadly in line with earlier 12z GFS. In fact, the cold is slightly further west over Ireland up until Friday than the 12z - at that point it again shows the atlantic trying to make inroads.

Musicman2000

People need to remember out to 96/102hrs is the reliable time frame at the moment.

Deep Easterly

nacho libre wrote: »

I can't even remember things from a couple of years:o

While the entrenched cold air helped no end, the track sw- ne over the country was crucial. Had it been west - east, things could have been different..

A SE or E flow ahead of an Atlantic front (under the right conditions) is a favored option for frontal snow in the midlands, west and north of Ireland as this 'cuts off' a directed Atlantic air stream which helps to lowers humidity, thus dew points over the region due to the (relatively) long land track of the flow.

This chart from Jan 84' is a good example of that.



This brought true blizzard conditions over much of the northern half of the country and cut off parts of Donegal, Sligo, Mayo and Galway for days.

aurora 527

rc28 wrote: »

Nope seems broadly in line with earlier 12z GFS. In fact, the cold is slightly further west over Ireland up until Friday than the 12z - at that point it again shows the atlantic trying to make inroads.

I thought so too. Also the cold seems to progress towards us quicker than the earlier run.

BEASTERLY

Musicman2000 wrote: »

People need to remember out to 96/102hrs is the reliable time frame at the moment.

Well anything that was progged around 144hrs over the last couple of days has safely made into ''reliable timeframe''. It seems that FI creeps closer along with unfavorable solutions. I said earlier on that this downgrade was coming and that prediction was cast aside. Reality check tonight. I hope but highly doubt things will be different in the morning!

Sponge Bob

That reminded me.

Deep Easterly wrote: »

track of the flow.

This chart from Jan 84' is a good example of that.



This brought true blizzard conditions over much of the northern half of the country and cut off parts of Donegal, Sligo, Mayo and Galway for days.

The February 1933 Blizzard in resulted from a slightly more forward but broadly similar setup. It affected Leinster/Wales rather than Ulster and North Connacht.

pistolpetes11

To me it looks like the cold arrives earlier and leaves later .

A comparison vid for you all, prob best viewed in full screen and at 480p

https://www.youtube.com/watch?v=X-SOnrpyRJ4

davidsr20

All theses great posts about what's to come and now a big downgrade again , I really do give up at this stage, come on guys like this is what it's been like the last 2 months,it's like the roller coaster from hell ;(

BEASTERLY

So what we're looking at is a 36 hour dry cold snap. All the excitement I had yesterday is well gone.

pistolpetes11

BEASTERLY wrote: »

Well anything that was progged around 144hrs over the last couple of days has safely made into ''reliable timeframe''. It seems that FI creeps closer along with unfavorable solutions. I said earlier on that this downgrade was coming and that prediction was cast aside. Reality check tonight. I hope but highly doubt things will be different in the morning!

Is there any where to actually check verification stats on this ?


Was only thinking about it today , the models have to get a handle and FI should be after 144 at this stage but I dont know of any way to get the actual stats on it.

Trotter

BEASTERLY wrote: »

So what we're looking at is a 36 hour dry cold snap. All the excitement I had yesterday is well gone.

This offers some hope no?

BEASTERLY

Trotter wrote: »

This offers some hope no?

All melted by the next morning even if it comes off.

mcriot29

BEASTERLY wrote: »

So what we're looking at is a 36 hour dry cold snap. All the excitement I had yesterday is well gone.

Lol that what it looks like i can see us getting -4 at night at best if where lucky ,maybe mid feb is a better chance

pistolpetes11

Block not sinking ,

Polar Vortex splitting,

What so sad Beasterly ?

darkman2

A good GFS run IMO. I think we may see over the next couple of days us being teed for for some "battleground" snow. It just depends on how far west the cold air propagates. The GFS is very cold next week as a whole, mostly dry, severe frosts and ice but offers some snowy solutions by next weekend.

Redsunset

BEASTERLY I think your suffering from snow withdrawal. What ever will be, will be. But compared to the last 2 months this is a great chase. Just be glad its not progged to be 10c and mild south westerlies for the time being.

Spoilt last year we were.

ninebeanrows

18z has brought some hope back.

Some ENS 4/20 go for an actual easterly at 120 from 0/20 at 12z.

The morning runs huge again as usual. Lets hope the 12z, jumped on some new data and will bactrack in the morning.

Wouldn't put it past the bounds of possibility.

We also have the potential snowfall at as early as T48 to watch.

ninebeanrows

Just a note, this thread is turning very scatty and a lot of posts are lacking any depth of content.

Can people please use the CHAT thread for this type of talk and leave detailed discussion of the charts in here. Also one word questions etc are not helpful.

I propose this thread to have content filled posts so people can just come and browse through some quality posts to understand what is going on.

Thanks.

Trogdor

Just to note how uncertain things are and how hard the models are finding it, here are the gfs ensembles from the 18z:


The range of scenarios for tomorrow night just T+24 already shows a range of different situations with upper temperatures varying from +1C to -4C, a huge spread for just one day out. By midnight next saturday (T+120) there is no consensus at all with outcomes varying from +2C to -13C! The models don't handle this kind of setup well at all so expect many more changes to the output, with some at quite short notice too.