Model output discussion - 5th December 2016 - Into Winter we go

[Man With Beard]

It's increasingly likely, to me, that we are looking at not one but two potential cold snaps to begin the new year. 

The first arrives on 1st Jan with high confidence for snow-supporting conditions over 24-48 hours. This period was very well picked up by ECM ensembles at T240-T360, with very clear cold clustering evident around this time last week.

The second potential period is sometime between 6-10 Jan, where it currently looks as if a new ridge will edge towards Greenland and another cold front may move down through the UK. The ECM ensemble 850hpa mean for 8 Jan shows the potential for this - probably all of England/Wales/Scotland at minus 4C or below:

 

And bear in mind this is a mean chart - main clustering is bound to be a couple of degrees lower as any major mild outliers will skew the average.

And where it goes afterwards - if it gets that far - is of immense interest. We're starting to see some real icy runs on the ensembles at D15 and if heights build further north, we have some bringing the house down options open. But I suppose we should keep our focus on the next 7 days for starters!!

 

[Rocheydub]

Better amplification out west on the 12z (78hrs) compared to the like for like from the 6z (84hrs) 130mb as opposed to 125 and its further up into Greenland slightly. Doesn't mean it won't topple over us later on, but should be slightly stronger.

[bluearmy]

It's the mobility from the west that ms important rather than just the amplification achieved

imo, the sharper  the Pacific ridge into the pole the slower the speed of the troughing upstream. the shallower Pacific ridges tend to drive a chunk of vortex around them into n America which is obviously bad for us on two levels 

[Iceberg]

Some interest changes on the gfs out to 96z the meto 96z is good and interesting as well. 

Its difficult to get the head around some of these and the implication but I am struggling to believe the models for our bit of the world from t144 Onwards 

[Rocheydub]

GFS out to 120 has better amplification and more west/north than the 6z. Happy with that. That's all I want to see so far. Everything after that is so open to change and conjecture it's not worth studying too much!

[Kieran]

Back edge snow for most parts (except for the far south) on New Years Day shown on the GFS. Something to keep an eye on....

                 

 

 

Edited December 27, 2016 by Kieran

[radiohead]

The evolution on the 12Z GFS within the reliable time-frame is the same as the 06Z, only difference being a slight timing difference. 

UKMO is further West than the GFS at T120. So still possible we could see some "upgrades" with this initial cold shot.

[Banbury]

I wonder where that HP is off to

[PersianPaladin]

10 minutes ago, Rocheydub said:

GFS out to 120 has better amplification and more west/north than the 6z. Happy with that. That's all I want to see so far. Everything after that is so open to change and conjecture it's not worth studying too much!

Yup...the words  dogs' + dinner came to mind.

 

 

Edited December 27, 2016 by PersianPaladin

[Iceberg]

Meto and gfs have very different set ups and consequences for us at t144 hence the very low confidence. Meto I think is very good at t144. Very good indeed with a push down of energy from the north. 

Low pressure systems to the west and north of the high are both different on the meto. 

Edited December 27, 2016 by Iceberg

[Snowman.]

Just now, Iceberg said:

Meto and gfs have very different set ups and consequences for us at t144 hence the very low confidence. Meto I think is very good at t144. Very good indeed with a push down of energy from the north. 

Low pressure systems to the east and north are both different on the meto. 

Indeed UKMO is looking to go for another shot.

[booferking]

1 minute ago, SN0WM4N said:

Indeed UKMO is looking to go for another shot.

Will be interesting to see what the ECM thinks later.

[Banbury]

7 minutes ago, Iceberg said:

Meto and gfs have very different set ups and consequences for us at t144 hence the very low confidence. Meto I think is very good at t144. Very good indeed with a push down of energy from the north. 

Low pressure systems to the west and north of the high are both different on the meto. 

I also think the 144 for Met o is good , could get all that cold air across us in a 168 chart

[tight isobar]

Quite' nice placement of deep cell hp (west)..

This being good in terms going forward for retrogression nw-Greenland. .thus forward march of notable cold incur/prolongement. 

Also again of note is establishment of large lobe vortex to eastern migration! !!..

Things looking v-favorable for decen cold as alignment start to resolve! !

[Daniel*]

1 minute ago, booferking said:

Will be interesting to see what the ECM thinks later.

The UKMO is intriguing looks like it might retrogress on t168 and open the gates to the north again. However I've never seen it be a lone wolf at that range and get it right. Of course we await EC.

[northwestsnow]

Well lets hope ecm is better because gfs is pretty appalling for cold fans, shortwaves everywhere ruining any hope of long lasting cold..

[Dorsetbred]

28 minutes ago, Kieran said:

Back edge snow for most parts (except for the far south) on New Years Day shown on the GFS. Something to keep an eye on....

                 

 

 

You might well be right it's only a rain maker over the extreme south given the synoptics, it appears to lack the cold strength behind it to reinforce it.

 

Edited December 27, 2016 by Dorsetbred

[Banbury]

4 minutes ago, northwestsnow said:

Well lets hope ecm is better because gfs is pretty appalling for cold fans, shortwaves everywhere ruining any hope of long lasting cold..

That's not the language I would have used, Id have associated that with the 14c and winds we had on Xmas day

what you mean is it could be better but chilly / dry weather is ok

[Dorsetbred]

19 minutes ago, Iceberg said:

Meto and gfs have very different set ups and consequences for us at t144 hence the very low confidence. Meto I think is very good at t144. Very good indeed with a push down of energy from the north. 

Low pressure systems to the west and north of the high are both different on the meto. 

You right Northern surges do not really hold much by the time they reach the south coast. Again this one lacks presence it needs more oomph behind it which right now it lacks.

[Singularity]

 

Here's UKMO on the left and ARPEGE on the right. The latter has a slight negative tilt to the Canadian trough while UKMO has a neutral - direct north - orientation.

Around 24 hours later, this slight difference grows exponentially, with dramatic results:

 

While UKMO is progressing to a surprisingly quick dive down of a shortwave low from the northwest - with nice separation from the Canadian/NW Atlantic trough it has to be said - the ARPEGE solution sees an omega block established to the west which is going nowhere fast. The UK is in an increasingly unstable northerly as the jet angles NE to SW on the east flank of the OB. A rare and valuable setup and nice to see that the option remains on the table, especially coming from a high-resolution model, albeit not a particularly reliable one at such range.

[Norrona2015]

I've been taking a keener interest in the model thread today ever since snow started to appear in the Mets forecasts for New years eve/day. Aviemore, Braemar and my own location, to name a few, are in the firing line........at this time.

Edited December 27, 2016 by Norrona2015

[tight isobar]

Short-waving' in such hp west based dominate will come down to +24/36 hr windows. .

Again. .it expansion/placement that stand out..bigger picture and suite compare...not micro scale prognosis. .

[Banbury]

2 minutes ago, tight isobar said:

Short-waving' in such hp west based dominate will come down to +24/36 hr windows. .

Again. .it expansion/placement that stand out..bigger picture and suite compare...not micro scale prognosis. .

I agree , up to 120 /144 is where we look, just for amusement and perhaps possible trends thereafter

[radiohead]

Let's hope the ECM follows the ARPEGE as it does look the most promising at this point. Since ARPEGE was co-developed with ECMWF we might see something similar 

[Mucka]

let's hope ECM backs UKMO rather than GFS which is pretty much a worse case scenario for snow chances through 1st week of January from where we are.

If we can just back the pattern West a few hundred miles it will make all the difference in lowering pressure to our S/SE, raising pressure to our NW and of course opening the gate to an Arctic flow which even with toppler scenarios would give much better depth of cold and snow chances between ridges and better Easterly chances further down the line.

It is on a knife edge between a standard cold/frosty spell with short milder interludes and a prolonged cold spell with better snow chances IMO.