The hunt for cold - Model discussion (late November)

[Catacol]

On 18/11/2018 at 22:03, Catacol said:

 

Conclusion? The pattern has to relax: but I'm pretty sure it wont relax all that much. High atmospheric AAM at the equator has to be balanced by a reduction of momentum at higher lats - and this means a weak jet overall, a tendency for blocks to hang around and certainly no signal for an atlantic return. The models are picking up a retrogressive signal in the long wave pattern so the high will drift westwards through the week, but I don't think it will sink. The downside to this descending AAM phase however will be that the trough may struggle to undercut fully - there just isn't the oomph in the supporting pattern to force it through so the EPS signal for 10 days time looks about right and the south may experience much milder air in 7 - 10 days' time than many on here will like.

However - what about mid December? Next surge in GLAAM will occur on a base that is already fairly strongly positive provided the trend for decent westerly windbursts in the pacific  continues. Let's assume the pacific stays lively....what will this mean? Another torque cycle, probable forcing of the jet on a SE axis through the US and a signal for a return of a scandy height rise as the atlantic trough is pushed through. Colder air in place...lower sun....high pressure over Greeny/Canada already in situ - link up possible to scandy? Winter then on its way.

Worth pulling this post out from 11 days ago - because it has proved overoptimistic though not totally incorrect in perceived development. The pattern has in fact "relaxed" a great deal - calculated tendency of AAM has started a sharp fall

Why? The simple answer is that overall Glaam hit such a height (+3SD) that there had to be a reaction....and therefore the downward phase of the to and fro nature of the momentum budget has been strong. I was guilty of not, perhaps, placing enough emphasis on that +3SD peak of the global momentum budget, largely because I didn't expect it to get quite so high.

But - hold on. This is not a post of resignation (from an openly slightly biased snow lover...) - quite the opposite. The pattern was always going to relax at this point, and we have ended up with a trough that appears to have blown away the blocking pattern and led to gloom on here. But remember that these cycles are predictable - and while the current phase has proved to offer more atlantic south westerlies than were hoped for the medium term prognosis is still very good. Note the cyclical nature of momentum budgets...and the certainty that an upwards trend will return before too long.

Key to this will be the MJO. We continue to see forecasts of a strong MJO wave and without doubt the signal for blocking to return under a Nino base state will return:

Meanwhile the very favourable positioning of blocks through November is having the expected impact on the vortex as we enter December - this is a strong wave 1 attack and is sustained for many days

What do these signals therefore suggest? Frictional and then mountain torques will reengage in the next 5 - 10 days and this will initiate a surge in momentum as the pacific jet extends, and poleward wave energy forces a much more meridional pattern to the north atlantic. With increased westerlies over the tropics, sub tropical ridges will be undermined and the signal for falling pressure over the azores and/or Europe will increase. We will see ridging return. Given the pattern at present I will hold to the timetable advertised previously - mid December for the true start to winter, and if we can get engagement with the pool of very cold air that is concentrating over Russia then some snowy fun for some is certainly a possibility.

The extent to which the vortex is impacted will have a bearing on where we then go forward. I don't think we have a serious chance of a full reversal in December - but perhaps we are setting the vortex up for a lethal blow in early to mid January. If the blocking pattern that returns mid month sets a scandy/russian ridge up once again, then this will initiate the second phase of necessary warm air attacks on the vortex, with a lag effect impact into January. So - cold in mid December, and the potential for winter to accelerate into January. There will always be ebb and flow within this broad scale pattern - but right now we are still on course for some great model watching kicking off early next week as NWP picks up on the mid December signal.

Optimism still in place.

[feb1991blizzard]

2 minutes ago, Catacol said:

Worth pulling this post out from 11 days ago - because it has proved overoptimistic though not totally incorrect in perceived development. The pattern has in fact "relaxed" a great deal - calculated tendency of AAM has started a sharp fall

Why? The simple answer is that overall Glaam hit such a height (+3SD) that there had to be a reaction....and therefore the downward phase of the to and fro nature of the momentum budget has been strong. I was guilty of not, perhaps, placing enough emphasis on that +3SD peak of the global momentum budget, largely because I didn't expect it to get quite so high.

But - hold on. This is not a post of resignation (from an openly slightly biased snow lover...) - quite the opposite. The pattern was always going to relax at this point, and we have ended up with a trough that appears to have blown away the blocking pattern and led to gloom on here. But remember that these cycles are predictable - and while the current phase has proved to offer more atlantic south westerlies than were hoped for the medium term prognosis is still very good. Note the cyclical nature of momentum budgets...and the certainty that an upwards trend will return before too long.

Key to this will be the MJO. We continue to see forecasts of a strong MJO wave and without doubt the signal for blocking to return under a Nino base state will return:

If the MJO goes through the Indian Ocean (as per the post above yours) and carries on its mery way at reasonable amplitude and not enter the COD, could an East Asian mountain torque event ensue and trigger a proper major midwinter SSW in late December?

[Catacol]

1 minute ago, feb1991blizzard said:

If the MJO goes through the Indian Ocean (as per the post above yours) and carries on its mery way at reasonable amplitude and not enter the COD, could an East Asian mountain torque event ensue and trigger a proper major midwinter SSW in late December?

Given a pacific pattern that feels more super Nino than weak Nino at the moment - I'd say a substantive torque event is not out of the question, though it requires a bit of luck to get the tropospheric pattern just right. We saw a +1SD east Asian torque event in mid October and another in early November. We ought to see another in about 10 days' time, but it would need to be a bit special to knock the vortex into touch in December. More likely we see a hit that knocks it back a bit further in mid December with the potential then for a more deadly blow in early January. But there is a lot of water to flow under the bridge before then - and there is no guarantee that a knock out blow will be landed at all. 

However a powerful east Asian event would certainly substantially increase the chances. They are, however, fairly rare.

[cheeky_monkey]

1 hour ago, Daniel Smith said:

That depends on where you're looking..

im looking at the GFS and ECM runs..without rose tinted glasses

[Snowman.]

1 hour ago, cheeky_monkey said:

im looking at the GFS and ECM runs..without rose tinted glasses

Because looking at single op runs is a fraction of what is available.

The clusters show a strong positive height rise over Sacndi, 50 percent at that range is significant. May be nothing and we end up in a normal December pattern but the signals are there.

[Met4Cast]

1 hour ago, cheeky_monkey said:

im looking at the GFS and ECM runs..without rose tinted glasses

Maybe if you looked at the ensemble means & Clusters you’d see the Scandi height rises instead of looking at Det runs in isolation

[Seasonality]

I'm still of the opinion a pressure rise over the UK with euro troughing accompanying is the form horse in the medium term. UKMO supportive of this. As always should the evidence swing more convincingly against this I'll change my mind. Maintaining objectivity and overcoming your preferences and resulting confirmation bias is hard work but something we should all aspire to. Apologies for the tl;dr off topic stuff

[blizzard81]

Much better run from the ecm. Look at the 1010mb low forming in the mid Atlantic at t144. Then look at t168 and you will see that it is acting like a cut off low and has actually moved back north westwards. This is what we need to see. The t192 chart then shows the fruits of this. Much more amplified. 

Edited November 30, 2018 by blizzard81

[blizzard81]

This one's for that cheeky monkey

[Duane S.]

Great ECM this morning. The Atlantic is going to have its time over the next 7 days, quite possibly two week but my thoughts remain positive thereafter.

Are we looking at a similar Jan'13 wedge situation perhaps? Here's the chart two weeks before that memorable cold spell kicked off...

 

Hardly the polar opposite to the ECM's take on proceedings at D8...

Food for thought, that's all.

Edited November 30, 2018 by s4lancia

[Paul_1978]

The lows on the overnight GFS and ECM do seem to be tracking a little more southerly than normal, but not quite southerly enough....

[northwestsnow]

Hurrrah!!

UKMO/EC show a bit of Atlantic amplification!

GEM similar to UKMO and goes onto produce a very nice day 10..

Hoping for some momentum towards a pattern change .

Edited November 30, 2018 by northwestsnow

[bluearmy]

Eps extended mean smells of binary clusters again  ..... if not, it’s probably a swing away on the pendulum after yesterday’s 12z promise .......

[ArHu3]

1 hour ago, s4lancia said:

Great ECM this morning. The Atlantic is going to have its time over the next 7 days, quite possibly two week but my thoughts remain positive thereafter.

Are we looking at a similar Jan'13 wedge situation perhaps? Here's the chart two weeks before that memorable cold spell kicked off...

 

Hardly the polar opposite to the ECM's take on proceedings at D8...

Food for thought, that's all.

Yesterday's 12z oper was a warm outlier, today's 00z a cold outlier. 

(click on image if you don't see control and oper being the coldest) 

 

Edited November 30, 2018 by ArHu3

[mulzy]

4 minutes ago, bluearmy said:

Eps extended mean smells of binary clusters again  ..... if not, it’s probably a swing away on the pendulum after yesterday’s 12z promise .......

Atlantic trough and Euro heights the favourite for me. 

[northwestsnow]

Well i'm going to keep the optimistic (tin) hat on this morning..

UKMO pick of the 3 at 144 IMHO, i'm not convinced we will see a euro high longer term, infact, i'm thinking a slow process of Atlantic amplification as the jet drops into Europe..

 

[Summer Sun]

GFS going for the north-south split again this morning over the next week

 

[johnholmes]

I'll do an update with the 500 mb anomaly charts later today, not all gloom and doom for you coldies though!

[northwestsnow]

2 minutes ago, johnholmes said:

I'll do an update with the 500 mb anomaly charts later today, not all gloom and doom for you coldies though!

Thanks John

Phew, i was feeling a bit lonely with my optimism !!

[carinthian]

Morning all. Really excited about the start of the new ski season tomorrow. All piste groomed and ready to go. As every year passes ,I get more excited at the prospect of being in snow and surrounded by beautiful scenery . Right the charts, interesting feature the wave or low development over Southern Britain at 120t. GFS has this passing further north into the North Sea, whereas UK has a more southerly passage , similar position as highlighted below from Winter View chart below. The thought from over here at 120t, much of the UK will be in a Polar Airmass with the track of the low over Southern Britain to move towards the Alps ( hence we have now a snow alert here for next Wednesday) . So there remains some variability in the short range model forecasts but basically all fairly fluid from west to east. Medium term ,picks up high pressure to SW of Ireland with developing longer wave trough over Central Europe. Thereafter, uncertainty remains as to what extend the Atlantic push into Europe, zonal or more meridional . The forecast jet pattern at 300mb seems inconsistent out in medium longer term forecast models but our experts expect more of a wintry theme to development over The British Isles but cannot say whether this will be sustained. All very interesting. Notice the snow spikes increasing over parts of Britain early next week.

C

[ICE COLD]

58 minutes ago, bluearmy said:

Eps extended mean smells of binary clusters again  ..... if not, it’s probably a swing away on the pendulum after yesterday’s 12z promise .......

Are the updated clusters out yet ? Cheers 

[Summer Sun]

Just now, ICE COLD said:

Are the updated clusters out yet ? Cheers 

Still on the 29th

http://brunnur.vedur.is/kort/ec-ens/2018/11/

[feb1991blizzard]

They'll update at around half 10.

[aitchbomb]

56 minutes ago, johnholmes said:

I'll do an update with the 500 mb anomaly charts later today, not all gloom and doom for you coldies though!

Deary me, been waiting a long while for you to say something more positive John!

[Singularity]

Catacol very much on the right lines with his recent posts I believe. Resonating to with a good deal of recent GP input too and it looks like tight isobar is also seeing similar potential (as far as can be reliably interpreted).

It pays to remember that that models really struggle to resolve the tropical-extratropical-stratosphere sequence of interactions sufficiently well for them to be of much use beyond 5 days or so when those interactions are in an excited state (high amplitude events).

Stratosphere looking the most interesting for this time of year since 2009 if I'm recalling correctly. Scope for a mid-Dec taster and the main course by January? Hmm... cautious it may be, but I'm becoming optimistic too!