Model output discussion - 1st December onwards

[feb1991blizzard]

10 minutes ago, Interitus said:

You tell me lol!

To be serious, it's not totally unusual for it to be colder before an SSW than afterwards, and the precursor set ups are quite vague - though the forcing may be Atlantic or Pacific side or whatever they are large areas. From the data for example it appears there might be a signal for lower AO, NAO and CET roughly between 35 and 25 days prior to SSW give or take a couple of days here and there. There doesn't appear to be much sign of this at the moment and in any case this pretty much amounts to looking for a cold spell with the models regardless of if it is a precursor or not. I will have to look closer at the precursor set ups and include minor warmings to get a better picture.

 

Jan 1987 definitely and didn't Feb1991 cold occur almost at the same time as the 'Near SSW'

[Nick F]

30 minutes ago, Interitus said:

You tell me lol!

To be serious, it's not totally unusual for it to be colder before an SSW than afterwards, and the precursor set ups are quite vague - though the forcing may be Atlantic or Pacific side or whatever they are large areas. From the data for example it appears there might be a signal for lower AO, NAO and CET roughly between 35 and 25 days prior to SSW give or take a couple of days here and there. There doesn't appear to be much sign of this at the moment and in any case this pretty much amounts to looking for a cold spell with the models regardless of if it is a precursor or not. I will have to look closer at the precursor set ups and include minor warmings to get a better picture.

 

As I mentioned in the strat thread earlier this month, some previous strat warming events saw the tropospheric pattern change (i.e. blocking) before the official stratospheric vortex split or displacement. The 1986-87 winter featured a strong El Nino, the strat vortex displacement didn't officially occur until Jan 25th '87' but the infamous brutal cold easterly started early on in the month. Check out this strat loop here:

http://www.meteo.mcgill.ca/~pmartineau/updated_graphs/svw_anim/all_gif/1987_01_25

However, we are long way off seeing any major pattern change for now. The tease of the Scandinavian high with deep cold air developing over NW Russia looks to become increasingly out of reach as very low heights/deep cold over Nern Canada and Greenland drives a strong and flat jet up against the +height anomaly trying to build north to the east. The NWP ops and ens are more weighted to pushing the +height anomaly east out of reach of the UK unfortunately. Though one positive, albeit still verging in unreliable timeframe, is that as the low heights spread east again, we gain a colder Pm westerly flow, with increasing chance of northern snow as we enter the new year. However, that's if the models aren't understimating the block to the east!

Even though no pattern change looks likely for the foreseeable, thanks to the unhindered and strong polar vortex, the ridging to our east does, at least, seem to be punching the Polar Vortex around a bit, as recent ECM lower strat charts have highlighted next week in the geopotential height field.

 

But are the current waves bouncing against the Polar Vortex more like ping-pong balls rather than canon balls? As Mike Ventrice mentions on twitter, time is running out to weaken the behemoth that is the Polar Vortex this winter. Lets hope a SSW occurs in late Jan, as per Judah Cohen's latest update, to bring a cold end to winter. We may even have a trop pattern change before any SSW, as my example above shows. The MJO looks favourable, but there is a great deal of uncertainty whether the wave will be coherent enough once it reaches phase 7 to really make much effect to change the northern hemisphere teleconnections ... certainly the models aren't picking up on it for now.

It's a long waiting game this winter for uncertain reward if any reward.

Edited December 22, 2015 by Nick F

[nick sussex]

GEFS MJO has updated the ensemble mean now has this into a decent amplitude phase 7. The GEFS BC is less bullish about phase 7 and has the signal hanging around in a decent amplitude phase 6. Still waiting for the others to update.

[karlos1983]

Well the GEM wants to play

 

[karlos1983]

BANK!!

 

Shame it is unlikely to verify, but my word that's good viewing. 

Edited December 22, 2015 by karlos1983

[bluearmy]

The GEM showing that it's upgrade won't be making much difference to it's position as a less than reliable model !

[karlos1983]

Not a bad chart out in fl from the GFS either, 

The route to cold wouldn't be to difficult from there I would imagine?

Edited December 22, 2015 by karlos1983

[Mucka]

3 minutes ago, karlos1983 said:

Not a bad chart out in fl from the GFS either, 

The route to cold wouldn't be to difficult from there I would imagine?

Agreed, much improved in FI, especially in regard to the NH profile, but quite chilly at the surface too and much of Northern Europe going into the freezer.

Edited December 22, 2015 by Mucka

[karlos1983]

2 minutes ago, Mucka said:

Agreed, much improved in FI, especially in regard to the NH profile, but quite chilly at the surface too and Europe going into the freezer.

I asked Ian F a couple of questions on twitter yesterday, and he did mention that there is potential for some major trough disruption into January, but stressed tricky detail.

[The PIT]

While everyone is looking deep into FI much uncertainly over the xmas period.  A band of heavy rain needs to be kept an eye at the moment this gets stuck over north wales across the pennines into south yorkshire. A movement further north would not be good at all. Likewise the strong winds forecast in the last runs have also now gone bar the south west late on boxing day. An secondary low brings strong winds across northern england on Xmas eve as well which well worth keeping an eye on as well.

[Daniel*]

The GEM is stunning...

The outer reaches of GFS would give great depths of snow for Scotland & N. England. It is painting a cooling trend with the jet stream wanting to take a more meridonal flow this can only be a good thing! Something is afoot.

Edited December 22, 2015 by Daniel*

[Mucka]

Stunning GEM, unfortunately it is cannon fodder mostly

 

 

Edit:

 

LOL Ninja'd by Daniel, well done sir. 

Edited December 22, 2015 by Mucka

[bobbydog]

more of that please!

that run was like a stick in the spokes for the trop vortex!

strat next.....?

 

[chrisbell-nottheweatherman]

9 minutes ago, Daniel* said:

The GEM is stunning...

The outer reaches of GFS would give great depths of snow for Scotland & N. England. It is painting a cooling trend with the jet stream wanting to take a more meridonal flow this can only be a good thing! Something is afoot.

Come on - I'm no model expert, but even I know that the GEM isn't worth the electricity used to power the computer that produces it.  As a reformed coldie I know you're searching for something more "wintry", but, apparently, it's further-off than ever at present.

[radiohead]

I've sometimes noticed the ECM will often show a similar pattern to the GEM. It may be little more than coincidence but it would bring some festive cheer if it happens again tonight!

 

[booferking]

How do people know the cold weather is further off than ever, i would love to know who can guarantee this as if they can then it would be very easy to do the weather forecast for months  ahead nobody knows and nature does what it likes when it likes.

[Snowy L]

1 minute ago, booferking said:

How do people know the cold weather is further off than ever, i would love to know who can guarantee this as if they can then it would be very easy to do the weather forecast for months  ahead nobody knows and nature does what it likes when it likes.

It was very easy to forecast a mild December and first half of January based on the strength of the vortex at all levels in November.

Edited December 22, 2015 by Snowy L

[mountain shadow]

4 hours ago, radiohead said:

I've sometimes noticed the ECM will often show a similar pattern to the GEM. It may be little more than coincidence but it would bring some festive cheer if it happens again tonight!

 

Here's hoping tonight is one of those times. The lesser models continue to be thrown by the mixed MJO signals. The GEM has taken it to its zenith. 

I fancy the ECM will show a bit more amplification than earlier runs but with the Atlantic winning in the end. 

I think we're seeing signs of a decent North Westerly blast early in the New Year though.

[booferking]

Yea was mild for most but i have had 3 days of lying snow and about 4 snow falls in Dec so not totally mild and not a complete disaster for myself and we might even get some more before Xmas.

[Methuselah]

15 minutes ago, Snowy L said:

It was very easy to forecast a mild December and first half of January based on the strength of the vortex at all levels in November.

If you were 'psychic', of course; the rest of us, however, are unable to predict the strength of the vortex, six-weeks' in advance?

[grca]

A quick question for the more knowledgeable to answer, with the scatter on the pressure for London on the GEFS at 4-5 days does that suggest that the pattern is still not determined correctly ? The GEM seems to be very different in it's evolution from GFS  especially at 120hrs but there are quite a few GEFS with a similar notion on the low the develops over northern Germany which reduces the higher heights in Europe and allows the cold to come in from the East. Just wondered if anyone else had a view on if this was game over and a return to SW / W pattern or could something pop out of the blue so to speak.

Not posted for a very long time so if the link of the GEFS pattern diagram does not link I will try again..

http://www.meteociel.fr/cartes_obs/gens_display.php?x=306&y=141&run=12&ville=Londres&runpara=0&type=1&ext=1

[Snowy L]

6 minutes ago, Ed Stone said:

If you were 'psychic', of course; the rest of us, however, are unable to predict the strength of the vortex, six-weeks' in advance?

That's not what I meant, most winter forecasts went for a mild first half to winter because the vortex was so strong in November. The impossible part is to forecast what happens after the first half of winter.

Edited December 22, 2015 by Snowy L

[Mucka]

10 minutes ago, grca said:

A quick question for the more knowledgeable to answer, with the scatter on the pressure for London on the GEFS at 4-5 days does that suggest that the pattern is still not determined correctly ? The GEM seems to be very different in it's evolution from GFS  especially at 120hrs but there are quite a few GEFS with a similar notion on the low the develops over northern Germany which reduces the higher heights in Europe and allows the cold to come in from the East. Just wondered if anyone else had a view on if this was game over and a return to SW / W pattern or could something pop out of the blue so to speak.

Not posted for a very long time so if the link of the GEFS pattern diagram does not link I will try again..

http://www.meteociel.fr/cartes_obs/gens_display.php?x=306&y=141&run=12&ville=Londres&runpara=0&type=1&ext=1

 

I'm sure nick will tell you all about it but essentially the GEM is down to two things.

first the shortwave exiting East (not unlike this mornings GFS 00z)

Which essentially allows the pattern to set up further West and have a sharper ridge and it then moves South into Europe allowing lower heights there.

 

 

And second having more favourable upstream pattern allowing for trough disruption.

 

GFS ensembles at least showing a good cool off first week of January.

Edited December 22, 2015 by Mucka

[Methuselah]

12 minutes ago, Snowy L said:

That's not what I meant, most winter forecasts went for a mild first half to winter because the vortex was so strong in November. The impossible part is to forecast what happens after the first half of winter.

Sorry Snowy L, my bad; I agree absolutely!

[Daniel*]

25 minutes ago, chrisbell-nottheweatherman said:

Come on - I'm no model expert, but even I know that the GEM isn't worth the electricity used to power the computer that produces it.  As a reformed coldie I know you're searching for something more "wintry", but, apparently, it's further-off than ever at present.

Neither am I, the GEM addresses the possibilities of which is not favoured by a large stretch. However I would not say wholeheartedly it's spouting out crap. I disagree to that, the MJO wants to go in a more favourable phase, I think this is critical in hopefully reconfiguring this pattern perhaps this run is starting to factor these background signals? We're finally getting an assault on the mighty vortex - it doesn't quite seem to be enough for a SSW, albeit it looks disturbed on charts I'm seeing with HLB creeping in, the MJO may be the tipping balance we need in emphasising the assault and then a SSW may initiate - from a rather simple way of looking at it, I sense this pattern is running out of steam, it will not sustain all the way through the winter that's irrational. When and if we get the cold I'm increasingly feeling it will be significant. I still think early Jan is not lost...