Model Output Discussion - cold spell to end Autumn

[frosty ground]

For future runs what should we be looking for in respect the cold air catching up to the precipitation on thursday?

[gottolovethisweather]

What is all this PNA talk about, please? Pacific something I'm guessing. Google doesn't help me much. https://en.wikipedia.org/wiki/PNA

Perhaps, we can have it added to the abbreviations, MODS?

Seems like I nailed it. 

For those left wondering, check out the following.

https://en.wikipedia.org/wiki/Pacific–North_American_teleconnection_pattern

 

 

Edited December 3, 2017 by gottolovethisweather

[Duane S.]

Certainly got a nice old Skool 2-wave feel about this set up. One that drives cold to both the East of the US and the UK. The MJO looks to be almost perfectly positioned to fuel this and then, all things being equal and fair (which they rarely are of course ), the set up looks primed for all eyes to start looking eastwards towards the end of the month.

[bluearmy]

2 minutes ago, frosty ground said:

For future runs what should we be looking for in respect the cold air catching up to the precipitation on thursday?

I think that ship sailed away from elevation some time ago - tbh, it was generally only a gfs thing anyway.  

[shaky]

15 minutes ago, nick sussex said:

NOAA State Forecast for Connecticut explains a bit more as to the differences upstream.

This is the main cause of the UKMO versus the ECM/GFS at T144hrs, also note their overwiew:

 Overview...

From midweek till the foreseeable future we will find ourselves in a
cooler, more active pattern. Fairly apparent and well known, will go
with a short and sweet overview. N Pacific split flow with MJO phase
5-6 implications as energy piles up over the N Atlantic buckles the
flow across N America creating a high amplitude ridge-trof pattern.
Warm air surging towards the pole, both Arctic air and energy are
displaced at times as individual impulses sweep S/E through the H5
trof over Central/E N America, bottling up and slowed over E/SE
Canada as there`s little room to escape across the N Atlantic.
 

The high amplitude trough ridge pattern is the hallmark of the positive PNA.

Now in terms of the differences upstream at T144hrs between the UKMO versus the ECM/GFS below is  part of those in terms of handling of shortwave energy:

2.) Individual disturbances. Apparent that individual waves through
the aforementioned H5 trof will reload colder air S/E. However what
is not well known is how individual waves evolve and respond, how
they modify the H5 trof ( steepness / amplitude / tilt ) and as to
what draw and amplification individually they bring about in respect
to conveyor belt motions / thermal wind response as they rotate thru
the flow. Isn`t with any certainty that we`ll see an east coast snow
storm for those wish-casting. Especially from 120 hours and beyond,
run to run model guidance continues to sway such that little to no
confidence can be gained. Have to wait and see how things evolve
with later forecast guidance.
 

The re-loading is as the shortwave moves through it pulls the colder flow further south again, as that happens the PV is also pulled back nw.  You can correlate in these circumstances cold digging further south over the east USA corresponds with more amplification upstream and which downstream is similar in the UK.

 

Is this a good update for the uk?

[Duane S.]

10 minutes ago, gottolovethisweather said:

What is all this PNA talk about, please? Pacific something I'm guessing. Google doesn't help me much. https://en.wikipedia.org/wiki/PNA

Perhaps, we can have it added to the abbreviations, MODS?

 

Pacific North American. Their equivalent of 'our' NAO. Not a driver as such, just a reflection of pressure anomalies in given areas. A positive PNA, whilst on its own means little, in the context of here and now (and especially against the backdrop of a Nina, albeit it is still weak and early in the winter season) should be viewed, overall, as favourable.

Edited December 3, 2017 by s4lancia

[gottolovethisweather]

3 minutes ago, s4lancia said:

Pacific North American. Their equivalent of 'our' NAO. Not a driver as such, just a reflection of pressure anomalies in given areas. A positive PNA, whilst on its own means little, in the context of here and now (and especially against the backdrop of a Nina, albeit it is still weak and early in the winter season) should be viewed, overall, as favourable.

Thanks, @s4lancia

[Chesil View]

Just now, s4lancia said:

Certainly got a nice old Skool 2-wave feel about this set up. One that drives cold to both the East of the US and the UK. The MJO looks to be almost perfectly positioned to fuel this and then, all things being equal and fair (which they rarely are of course ), the set up looks primed for all eyes to start looking eastwards towards the end of the month.

Quite so S4L. While everyone was looking north and west yesterday. A massive russian high was showing its hand in Scandinavia towards the end of the GFS 12z. This looks lie a classic slow burner build up to an easterly outbreak to me.

[damianslaw]

Keep an eye on developments to our NE, signs heights may build out of siberian and arctic high as we move through the second week of December, any return to slightly milder atlantic westerly air that may occur around the 12-14th as suggested by GFS may just like the current spell be a small blip against what is a predominantly cold background, but by mid December those heights will have greater chance of nosing SW, thanks to a trigger deep shortwave/low pressure feature anchored down and through the UK, thereafter we would be exposed to polar continental air. 

I'm quite bemused that I started a thread titled where have the deep seated northerlies gone, some few weeks back, and since then I've lost count of the number of long-drawn northerlies we've had, end of the week looks like delivering one, and each one more potent than the last.

So what I'm expecting from the models, is a progressive breakdown from the northerly with low barrelling in through northern parts, the south could be quite mild for a few days around the 12-14th, but all the time high pressure will be building strongly to the NE, and then a trigger will be pulled by weekend of 16/17 Dec pulling in the cold air to the NE.

We shall see - all might not happen if we see too much energy go into the northern arm of the split jet, but I don't foresee this. These are my current thoughts as always open to change.

[bluearmy]

We have the main players on stage

alsakan ridge 

east American trough

arctic ridge 

russian ridge

The atlantic ridge and sceuro trough are also present but not as fixed as the other features. 

fitting the pieces into the gaps in between  is proving tricky for the nwp 

 

[nick sussex]

1 minute ago, blizzard81 said:

Knowing our luck and also going by previous painful experiences, the ukmo will be on the money.

I agree its not as good as the ECM/GFS but unless the positive PNA is going to suddenly implode then a return to milder weather is very unlikely.

If you look at the UKMO at T168hrs of what we can see, you can tell by the curvature in the isobars on the eastern flank of the high that pressure is still low to the east,  pressure is still likely to be okay to the ne, the high is likely to shift nw towards that lobe coming out of Newfoundland, the low to the nw of the UK is going to be drawn to lower pressure over central Europe.

 

Of course we'd prefer the UKMO to be wrong with the pattern edged further west and jet track se further west however even with that we might see the troughing over Europe eventually sink south.

I expect the UKMO is too flat and even if we see a halfway house between the outputs that still keeps the UK in the game.

 

[Frosty.]

The GEFS 6z mean is a cracker if you love cold and want it to stay around until mid Dec. Check out these beauties..arctic blast from later in the coming week and then it stays generally cold with plenty of frosts / ice and an on going chance of snow! 

[nick sussex]

19 minutes ago, shaky said:

Is this a good update for the uk?

Yes it keeps the chances for cold and snow there. As long as the positive PNA keeps getting re-loaded as per NOAAs thoughts then this is good for UK coldies.

[blizzard81]

9 minutes ago, nick sussex said:

I agree its not as good as the ECM/GFS but unless the positive PNA is going to suddenly implode then a return to milder weather is very unlikely.

If you look at the UKMO at T168hrs of what we can see, you can tell by the curvature in the isobars on the eastern flank of the high that pressure is still low to the east,  pressure is still likely to be okay to the ne, the high is likely to shift nw towards that lobe coming out of Newfoundland, the low to the nw of the UK is going to be drawn to lower pressure over central Europe.

 

Of course we'd prefer the UKMO to be wrong with the pattern edged further west and jet track se further west however even with that we might see the troughing over Europe eventually sink south.

I expect the UKMO is too flat and even if we see a halfway house between the outputs that still keeps the UK in the game.

 

Cheers Nick. I agree so long as the ukmo is as bad ( or less good lol) as it gets. 

[I remember Atlantic 252]

Clear mild sector moving from the north on GFS, Thursday night, only places to see snow off this are 500m plus, but FI yet, so hope better charts to come, but this is ugly!

[Duane S.]

18 minutes ago, damianslaw said:

Keep an eye on developments to our NE, signs heights may build out of siberian and arctic high as we move through the second week of December, any return to slightly milder atlantic westerly air that may occur around the 12-14th as suggested by GFS may just like the current spell be a small blip against what is a predominantly cold background, but by mid December those heights will have greater chance of nosing SW, thanks to a trigger deep shortwave/low pressure feature anchored down and through the UK, thereafter we would be exposed to polar continental air. 

I'm quite bemused that I started a thread titled where have the deep seated northerlies gone, some few weeks back, and since then I've lost count of the number of long-drawn northerlies we've had, end of the week looks like delivering one, and each one more potent than the last.

So what I'm expecting from the models, is a progressive breakdown from the northerly with low barrelling in through northern parts, the south could be quite mild for a few days around the 12-14th, but all the time high pressure will be building strongly to the NE, and then a trigger will be pulled by weekend of 16/17 Dec pulling in the cold air to the NE.

We shall see - all might not happen if we see too much energy go into the northern arm of the split jet, but I don't foresee this. These are my current thoughts as always open to change.

Good post, pretty much how I see things currently.

Also, may I suggest you start another thread, entitled "Where have all the frigid Easterlies, that last for weeks on end and bury the entire UK in powder snow, gone"??

[Biggin]

24 minutes ago, Frosty. said:

The GEFS 6z mean is a cracker if you love cold and want it to stay around until mid Dec. Check out these beauties..arctic blast from later in the coming week and then it stays generally cold with plenty of frosts / ice and an on going chance of snow! 

Too much green not enough blue there Frosty.

[Iceaxecrampon]

21 minutes ago, Frosty. said:

The GEFS 6z mean is a cracker if you love cold and want it to stay around until mid Dec. Check out these beauties..arctic blast from later in the coming week and then it stays generally cold with plenty of frosts / ice and an on going chance of snow! 

Not to mention the Atlantic well and truly blocked.

[MR EXTREMES]

8 minutes ago, I remember Atlantic 252 said:

Clear mild sector moving from the north on GFS, Thursday night, only places to see snow off this are 500m plus, but FI yet, so hope better charts to come, but this is ugly!

Lol it will be back edge snow and possibly alot of it.

[Frosty.]

9 minutes ago, Biggin said:

Too much green not enough blue there Frosty.

Haha, well at least I'm looking for the good news and not moaning about breakdowns, I like to stay positive ??

Plenty to be positive about too

Edited December 3, 2017 by Frosty.

[Fozfoster]

32 minutes ago, nick sussex said:

I agree its not as good as the ECM/GFS but unless the positive PNA is going to suddenly implode then a return to milder weather is very unlikely.

If you look at the UKMO at T168hrs of what we can see, you can tell by the curvature in the isobars on the eastern flank of the high that pressure is still low to the east,  pressure is still likely to be okay to the ne, the high is likely to shift nw towards that lobe coming out of Newfoundland, the low to the nw of the UK is going to be drawn to lower pressure over central Europe.

 

Of course we'd prefer the UKMO to be wrong with the pattern edged further west and jet track se further west however even with that we might see the troughing over Europe eventually sink south.

I expect the UKMO is too flat and even if we see a halfway house between the outputs that still keeps the UK in the game.

 

Hey Nick thats another post without mentioning short waves....... 

[karlos1983]

Just now, Frosty. said:

Haha, well at least I'm looking for the good news and not moaning about breakdowns, I like to stay positive ??

Breakdown lol no sign of s breakdown from what I see. Rogue UKMO run that’s anout it. Which will be resolved in about 3 hours time 

[MattStoke]

I thought the 6z was an upgrade on the 0z in terms of snow prospects for many, including a strong Cheshire Gap streamer for here, other parts of the Midlands and parts of Wales. Although, finer details will chop and change until very short range, of course. A bit surprised to see some doom and gloom on here. 

Edited December 3, 2017 by MattStoke

[Connor Bailey Degnan]

4 minutes ago, MattStoke said:

I thought the 6z was an upgrade on the 0z in terms of snow prospects for many, including a strong Cheshire Gap streamer for here, other parts of the Midlands and parts of Wales. Although, finer details will chop and change until very short range, of course. A bit surprised to see some doom and gloom on here. 

Agree, completely.  North western areas look prime spot for snow showers. Then, as the winds turn more northerly, Northern and eastern areas are prime spots 

[johnholmes]

45 minutes ago, I remember Atlantic 252 said:

Clear mild sector moving from the north on GFS, Thursday night, only places to see snow off this are 500m plus, but FI yet, so hope better charts to come, but this is ugly!

I find that comment puzzling, can you explain please 'clear mild sector' ?

Perhaps I am missing the tongue in cheek idea?

thanks