Glacier Point

January 16, 2020

1 hour ago, jules216 said:

@Glacier Point can the MJO trail the extratropical pattern rather then lead it? One would think that if its going to phase 6 now with lag of 10 days it would be reasonable to assume MJO is leading the way with Scandi through and mid atlantic/western EU ridge. Also would it be reasonable to assume teh Scandi trough will be here for a while looking at strat vortex displacement and EL Nino Jan/Feb climo? thanks in advance for answers

The GWO provides a useful measure here of both extratropical and tropical responses. I suspect with increase of upper westerlies, GWO will orbit in low amplitude within the El Nino attractors for the remainder of the month, next cycle of the MJO through the Indian Ocean likely to coincide with a big spike in AAM tendency (circa 18 days from now).

January 16, 2020

25 minutes ago, mountain shadow said:

Looking at the RMM plots though, there is little sign that the tropical signal will persist into phase 8 though. It looks like dying off in phase 7, therefore i don't think we have any chance of these analogues coming off.

RMM plots are something of a blunt tool - and will not capture neither lagged influence of poleward westerly momentum transports nor low frequency influences. The suggestion is that the MJO may appear to be weaken during late January, but other measures may be far more instructive.

January 16, 2020

38 minutes ago, jules216 said:

The height anomalies are perfectly aligned to MJO Phase 6 January composites. Now can they match phase 7 after?

Velocity potential component suggests more of a Phase 8 type projection to the MJO, which would also fit GWO cycling to falling AAM tendency.

Phase 8 for January:

That's a very weak signal there.

Phase 8 for January with El Nino filter (which is relevant):

That's not far removed from current week 2 modelling, and Euro ridge type solution there:

Kind of underlines my antipathy towards January for anything meaningful.

However, if the tropical signal persists into February, then look...

Phase 8:

Phase 8 with ENSO filter:

January 13, 2020

@Jules216 2006/07 cited as being a carbon copy of this winter.

Yes, in lots of respects. Similar MEI / ENSO structure. Similar QBO evolution. Similar warm phase early / mid winter characterised by monster +AO during December / January with coupling between trop and strat PV. And now, similar MJO evolution.

Fair to say 2006/07 has been on the radar for some considerable time. Hopefully we'll see a 2007 style reversal in the AO for February. Be interesting to see if the lower solar conditions this time round deliver anything more tangible for colder outbreaks further west than in 2007.

January 13, 2020

Blog – Centaurea Weather

CENTAUREAWEATHER.COM

If you have any questions on this, probably best take them to winter discussion thread to avoid going off topic. Thanks

January 13, 2020

2 hours ago, North-Easterly Blast said:

Certainly now as we are able to say that the first half of winter 2019-20 has been much milder than average and brought next to nothing in terms of cold for most of the country, does anyone have an idea of what could have gone wrong to limit cold potential for the UK in this winter so far? I would at least have thought that low solar activity would have been more favourable for cold than it has been since 2012-13, and I would have thought that a near neutral ENSO would not have had a big impact on reducing the chances of cold weather for the UK? Also a close to neutral QBO so far this winter (less westerly than winter 2018-19) I thought would have been more helpful than last winter. The only negative thought I have on the background signals is that through the latter part of December and the first half of January the MJO has not been in favourable phases for cold in the UK (it has been mostly in phases 0 then 4-5 through this last month up to including this coming week), which may have reduced the UK's cold chances.

Unless it turns out that the +IOD has been overly dominant (we are extremely hampered by low sample size in determining this - and possibly a hint that low solar has been over-cooked as driver), it's been more a case of nothing overly supportive of cold pattern. The best indicator out there has been the MEI. That's been bumping around borderline El Nino for the last few months:

ESRL : PSD : MEI.v2

WWW.ESRL.NOAA.GOV

US Department of Commerce, NOAA, Earth System Research Laboratory, Physical Sciences Departmant

Weak El Nino / warm ENSO neutral climatology is against cold patterns for Northern Europe during the early part of the winter, more conducive later on depending on other factors.

January 13, 2020

On 10/01/2020 at 12:28, jules216 said:

now would be a good time to hear some of @Glacier Point views on where we are heading in the second half of the winter weather or not he thinks we might get benefits down the line from MJO wave if it hits phase 7 with decent amplitude

New blog entry up which will hopefully paint a broader picture.

This winter has always for me been about February having most wintry potential.

The evolution in the MJO and wider low frequency signal for the remainder of January looks like favouring central Pacific tropical forcing, so expectation would be for the current MJO wave to behave as per GEFS, high amplitude phase 7 weakening and more sustained low frequency signal to take over in phases 6, 7 and 8.

That ties in with enhanced wintry potential for very back end of January but more likely February.

I'm getting a very 2007 vibe right now, so worth seeing how facets of current modelling might evolve as we head towards end of the month and into early part of February.

First, MJO signal:

Notice how 2007 wave developed in late January in the Western Pacific and persisted as an artefact signal for the rest of February in phases 6-7. Overall velocity potential for month more phases 7-8:

And now forecast:

Charts end of January 2007:

Note the Alaskan / Chukchi Sea ridge development there. This looks solid in the modelling right now, and is expected to be a recurring theme over the next few weeks:

Also looking solid is the positioning of the stratospheric vortex shifted towards Siberia and away from Greenland / Canadian Sector. The two together suggest a high potential for transient ridge development in the North Atlantic to interact with this ridge and force blocking structures in the polar region sufficient to diver the jet south. Very much the evolution in February 2007.

850 hPa profiles are going to be hampered by lack of in situ cold air over Scandinavia and Eastern Europe, although this should change with time under this pattern.

Still likely that marginality will be the key buzzword, but at least and more realistically, potential for something to watch going forward, and one big back end winter easterly to chase.

January 3, 2020

12z EPS depicts a very elongated vortex all the way up to 50hPa towards the end of the run. A starting point if you’re looking for an upward split.

January 2, 2020

The way end of week 2 EPS and GFS look, wave 2 bottom up splits could be in play.

December 19, 2019

Blocking signatures starting to show up in high latitudes consistent with precursor pattern as per above.

Next Wave 1 attack expected early in the New Year and EPS beginning to pick this up with warming over Siberia projected and our now familiar displaced vortex centre. Would expect this continue to build and a SSW very possible during second half of January.

December 18, 2019

GFS op advertising the direction of travel for the New Year given current thinking..

December 18, 2019

1 minute ago, Catacol said:

Possibly...and one of the conundrums of this winter so far. Magnitude of Pacific signal has been veiled and progress of the convection signal seems to have varied enormously in modelling.

And yes - “eventually”

One of the outcomes manifested by the unusual occurrence of a record strength +IOD event outside of a strong El Nino.

December 18, 2019

Just now, Catacol said:

A flattening was always the likely longer solution, but It is still good to see a number of colder drivers progressing as they are. Jet angle, if is remains at that angle, will eventually create better options once climatological peak of Atlantic strength has passed and next round of forcing creates ever more potent wave breaking in second half of winter.

I still find myself thinking though that models have misread the Pacific this month and more forcing is present than they are spying. EAMT will help with Pacific wave break and downstream amplification. Flattening of the pattern may take longer than expected.?

My thoughts would be as highlighted. Think of loading a dice. Currently 35-65 against. The more we progress down the road of +IOD / +ENSO climatology / weakening of the wQBO, the greater the loading in favour of colder outcomes.

+EAMT might be overdone on 5 day averages, an angular momentum uptick / GSDM may be more low amplitude that first thought.

December 18, 2019

42 minutes ago, Catacol said:

Will it get there properly and embed, or will it flatten in the days after? Still a decent amplitude Pacific signal on NYD so amplification signal still present at that point.

I reckon it will flatten out soon into New Year.

There is a narrow window for a wave 2 induced pattern (high pressure centred close to UK) arising from a recent enhanced trade / reduced westerly across the central Equatorial Pacific and spike in tendency in angular momentum. Worth noting the direct correlation with this in the polar stratospheric pattern.

However, that won't last long. GFS suggesting a westerly wind burst across the central regions of the Equatorial Pacific in the next week.

That will increase angular momentum and trend more to a wave 1 pattern (both tropospheric and stratospheric) with associated lowering of surface pressures in the North Atlantic and dropping of Arctic air mass into the mid West States of the US. That should fire up the jet across the North Atlantic displacing any mid latitude ridge across North-west Europe. Strong presumption for jet angled NW-SE into Europe with moderate level +ve heights to our north within this regime.

GEFS 06z ensemble mean makes perfect sense to me within that broad context.

What does strike me from current modelling is the propensity for scrambling of the mid layer flows across the North Atlantic, probably the low solar conditions beginning to take effect. Therefore, heights likely to be greater to our north than analogue guidance would suggest - but still overall signal is for troughing across NW Europe beyond next week's ridge.

December 16, 2019

16 minutes ago, Catacol said:

JMA monthly is interesting for weeks 3 and 4. Trough maintained over SE Europe and high anomaly to the north. 850s to the NE below average. Hmmm. Slightly surprised to see this but matches GP’s take on January. Something simmering?

One thing is for sure - nothing in the least simple about the prognosis at the moment. Compelling...

and add cfs week 3 to that ..

However, before champagne corks start popping, interpretation of this z500 pattern requires strong health warming in translating to T850 and T2:

1) no source of deep cold across Europe and temperatures likely to be well above average prior to this;

2) trough access likely to favour milder Atlantic air mass across much of western Europe, including the UK.

Bottom line - looks good, and something to draw interest but from my perspective, nothing to see here suggesting cold nirvana in the next few weeks.

December 16, 2019

This looks about broadly right to me, and sets a template for January....

Jet broadly aligned NW-SE digging through a trough across central parts of Europe. Wouldn't get too excited on the back of this for cold for some period of time however, and the trough alignment will become a real issue for much of the next month or so.

December 12, 2019

12 minutes ago, jules216 said:

@Glacier Point isn't there a slight weakening forecast of IOD by looking at VP forecast? The profile to me looks similar to late November which combined with cyclonic wave break in Atlantic caused a short term flip in NAO.

Still seeing convective centres 60W, 170E, 60E, which is symptomatic of the base state since the late part of the summer. The latter centre does look like weakening, but how much faith do you place in that persistent low frequency stuff fully disappearing ? Plus, atmosphere will be imprinted to a degree with this signal.

December 12, 2019

Recent uptick in easterly zonal winds across the Equator was pathetically weak and transient. No way there's going to be any settled spell of the back of that, so current drift in op GFS and ensemble guidance suggesting a more unsettled theme look on the mark to me.

That tropical wind profile suggests a return to low frequency Indian Ocean Dipole forcing. Expect troughing centred over the UK and near continent to be the key feature, in tandem with a -AO regime with moderate +ve height tendencies to the north - but not enough to properly displace Arctic airmasses.

December 9, 2019

8 minutes ago, jules216 said:

GWO phase 8 between Christams and New Year? UK based high pressure?

Looks like it. Exact positioning - to east or west of UK up for grabs.

December 9, 2019

Definite signs of a change back end of week 2 into week 3.

Enhanced easterlies / weakened westerlies showing up around the Dateline. This will drop angular momentum budgets and manifest in more of a wave 2 pattern across the hemisphere.

Last few GFS ops have depicted a shift to more anticyclonic conditions for NW Europe, as have GEFS means.

Also worth noting stratospheric winds have dropped across the Equatorial Region in last day or two. Signs of transition to East phase during January I suspect.

December 6, 2019

Displacement K=1 type was most favoured by the analogue set, and would also be consistent with a mimicked +ENSO event.

Upcoming 2-3 week period might deviate away from that enough to generate wave 2 pressure on the vortex.

February would most favour a wave 2 split, probably Alaska to Siberian sectors.

December 6, 2019

22 hours ago, Don said:

I wonder if GP’s thoughts have changed regarding February?

As per the blog entry..

Solving the winter conundrum – Centaurea Weather

CENTAUREAWEATHER.COM

It’s that time of year again when the energy sector, hedge funds and weather enthusiasts are deluged with long range weather forecasts, the key question – what will the winter hold ? I’ve been given...

December thus far playing out as per the expected cyclonic, troughy theme for NW Europe. Can't state enough that this winter is about an absence of any strong drivers. What we're left with is effectively a vacuum, which we know nature abhors so very low confidence when assessing any winter forecast this year.

What is undoubtedly evident over the tropics is a strong + Indian Ocean Dipole event. Quite what that equates to for NW Europe is very challenging to assess, although basically it would probably mimic an El Nino event. Not seen enough +ve heights over the Arctic region to have full confidence in this driver although the coming NW flow and jet driving south would be consistent with this.

What about the solar minima I hear some of you yell out ? Not convinced this alone is as big a driver as it might be. That stated, the state of the stratospheric polar vortex does seem to be reflecting an inactive sun phase. The problem here is that the QBO interface isn't quite affirmative as it needs to be for an out and out cold winter signal.

Put all of that together and I'd hold with my preliminary thoughts on January, whilst having some potential, is unlikely to deliver. To me it has Troughy written all over it, and analogues were notable in their inference that the trough axis would be unfavourable for cold advection to Western Europe.

For February the analogue guidance was more encouraging for the trough axis to pull colder air back west, and this would also be consistent with climatology for +IOD / +ENSO events where February is most favoured for cold outbreaks across NW Europe.

Could be wrong on all of that of course (nature abhors a vacuum and all that), but right now, I wouldn't change those winter thoughts from when they were first authored in October.

Golden trinity for a cold European Winter: Weak to moderate La Nina (with the atmosphere demonstrably coherent with this); low solar (preferably year after minima); east QBO. How many of these are current ? Arguably a la 2009/10, a weak to moderate El Nino would also work but that lack of at least two of these from this year's set up highlights the problem. Possible that the IOD / warm ENSO neutral may just qualify for tropical favourability, and the QBO likely to switch during January also tilts the balance more towards favourable during the latter third of the winter.

December 6, 2019

1 hour ago, Man With Beard said:

Watch out for potential height rises to the east just before Christmas (not necessarily in a location that will aid UK cold):

Within the context of what I suspect will be a trough dominated early and mid phase to the winter, the extended week 2 - 3 period might offer something of a noteworthy deviation.

Easterly wind anomalies starting to show up in the eastern Equatorial Pacific and associated cooling up the subsurface.

Same thing happened in August and September (although this time round no where near as strong). That was a precursor to a Nina like phase of weather characterised by falling angular momentum.

So a negative tendency to relative angular momentum = retraction of Asian Jet and removal of westerlies from the system. Global Wind Oscillation phases 8 and 1 favoured.

Global Wind Oscillation phases 8 and 1 are remarkably similar to each other.

Current extended range modelling in the last 24 hrs has developed this trend:

Not a perfect match on the analogue model, and positioning of the North Pacific ridge 20 degrees further east (therefore shift analogue ridge close to UK to the east).

What that does highlight is a potentially drier phase with pressure rising to the east / north-east for a period weeks 2 - 3. Wave 2 activity might also uptick on the polar vortex distorting its shape somewhat.

Given the last time models went for a North Pacific ridge it was massively overdone, I'd be sceptical of the duration, and mean anomalous trough would be the expectation for Europe as we head into January. Still, something at least to watch in the next 10 days to see how this develops.

December 5, 2019

38 minutes ago, feb1991blizzard said:

I wonder if it could be the start of GP's 'how much Arctic air can we tease out in the second half of Dec'.

On current evidence not enough. Wavebreaks timed for around 10th and 21st are the point of interest.

Issues here are that the displacement of the SPV favours Arctic outbreaks across North America first, which is likely to fire up the northern arm of the jet until we get sufficient blocking structures in place to the north. We also have a base state that is devoid of strong leading (other than mute signal from Indian Ocean Dipole) and lacking any real impetus for change other than intraseasonal peturbations as westerly inertia is added and removed from the sub-tropical flows.

On balance, whilst it's not what snow lovers want, happy with the start to winter being cyclonic in nature across much of Europe and rather average temps if nothing else it helps to temper expectations which may become even more of an issue as we head into (an even more cyclonic) January.

November 27, 2019

Looks to me as if the early winter skirmishes are confirming two things:

stratospheric polar vortex weaker than normal;
stratospheric polar vortex displaced towards the Siberian Sector.

That should temper enthusiasm for proper early season cold across Europe as it doesn't favour sufficient blocking strength to displace cold air masses south and westwards to the degree necessary.

Tropospherically, our low frequency base state, which is nicely evident across OLR anomaly fields in the Tropics....

... is about to undergo destructive interference in the next two weeks as a more coherent convective wave develops and pushes further east. This is a good signal for the PV to rev up a bit and westerly influence extend across the North Atlantic.

When this relaxes, the low frequency state should take hold again on the hemispheric pattern. Deep upper low in the North / North-east Pacific a facet of this which should to further reinforcement of the weaker and displaced (Wave 1) SPV.

Weak level blocking expected to re-establish to our north and north-east within a broadly north-west flow regime for second half of December. It will be interesting to see how much angular momentum rebounds in the next 2 weeks after being driven to lowish values of late, as this will be key to how much amplification in the upper level flow across the Pacific and Atlantic can be generated to tease out Arctic air masses within that regime.

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