Glacier Point

Aside of the op gfs froth, I make that the last 9 gefs means to end up at a negative AO, themed on an extension of the Alaskan ridge poleward towards the Kara Sea ridge. The ridge over Alaska looks reasonably assured given model consistency and assumed Western Hemisphere tropical forcing. The Kara / Siberian ridge isn't as assured, but has definitely gained some traction in terms of longevity and strength. It also fits the idea that the for the first time this winter we get an injection of warm air into an area of unsually warm seas / surface temps. so musing a little, cyclonic signal for NW Europe, good fit for upstream ridge and some reasonably grounds for thinking the ridge to our NE is a player, that places us on tenterhooks. The 18z gfs whilst probably a bit progressive, may be revealing the route map to cold. Block to the NE deflecting the flow increasingly south and east, advancing westwards over time towards Greenland forcing the AO more strongly negative. Lots of uncertainty, not least because for me this is a touch premature (better confidence if tip his were second half of January). Key here is the block to the NE. Any weakness in that, and a more south westerly flow would be able to exploit. Worth also noting that there is some scope for retrogression and for Western Europe to remain under a sw flow in this current regime. Going to be an interesting week or so model watching I feel.

Which equates to stable, high, +AAM signal, global wind oscillation phase 6 untainted by Indian Ocean convective anomaly. Quite good model agreement for a cyclonic phase to develop, and residual height anomalies centred over the Kara and Barents Seas will tend to force a more negative tilt to the jet. Still no imminent sign of anything unseasonably cold, yet, but this shift in global forcing to a more classical Nino will make life interesting from mid Jan, not least the stratosphere where we will see some more tangible developments from 11th onwards where a big wave 1 and 2 hit is being lined up. cfs hovmollers consistently persisting the tropical forcing just east of the dateline suggesting that this +AO / west qbo regime is beginning to relinquish its grip

So the CFS and EC weeklies are in reasonable agreement. Week 2 very solid agreement (and EC EPS and GEFS) on Sceuro ridge. CFS persists this into week 3, EC not so keen. Either way, a good period of Wave 2 upcoming (and typically GFS showing this (rushed) manifested in some operational outputs). Week 3 to 4 transition with a more westerly / NW'ly component with EC more bullish on the upper trough extending into Scandinavia. Essentially both being driven by the same tropical forcing pattern, so understandable that they're so alike at this range. Both EC and CFS showing week 4 indication of cross polar +ve height anomalies developing Siberia to Alaska. Not ideal for deep cold getting to Europe fast, but stratospheric developments may be unfolding and influencing the pattern by then. Broadly my week 3 and 4 attention to any developing ridges over Canada and sub-tropical flow over the southern US, and of course, stratosphere from 11th January onwards.

Both EC and CFS week 3 - 4 outlooks suggest the core of tropical forcing shifting towards the central and eastern Pacific (equivalent MJO phases 7-8-1). That's Western Hemisphere. EC is less coherent, although would expect the (El Nino) low frequency signal to produce a slightly more coherent signal (aka CFS) nearer the time. That's very similar to September and October this year although the seasonal wavelengths will be different this time round. This doesn't look to me to damage angular momentum too much, so expected high angular momentum base state expected to persist well into January. That's a nod towards modelled pattern for weeks 3 and 4 with NW flow developing with scope for periodic northerly flow given the development of storm tracks across the Mississippi Valley towards NE Canada. Source: http://monitor.cicsnc.org/mjo/current/v2/ Before that though, plenty more warmth to get through and solid agreement from EC EPS and GEFS for strong anomalous sceuro heights in the day 8-15 period. Strat will be interesting to keep tabs on period 10th January onwards.

Nothing at H500 that might suggest so, but that's right on the edge of potential time lines.

Nice trend on EC week 3 to 4, taking mean trough to the north and eastwards. Not unexpected although still with a +AO/+nao signature but more of a more west or NW flow. Scope for northerlies given some amplification which the model won't pick up at that range. Let the trend be your friend.

Nick, I posted a little while back about the pattern over the next day or so over the Pacific and North America as being ripe for amplification through mountain torques. That I suspect has a role to play, as does the lagged impact of spikes in angular momentum tendency 21 days ago. The beautiful choreography of the atmosphere as other elements of tropical forcing come together ! But you're right, there has been a trend for tropical forcing to become more coherent.

Quite. If it smells like a dog, barks like a dog and growls like a dog, it is a dog. The MJO, Kelvin Wave and other forms of intraseasonal tropical modes share measured parameters. The most useful is upper level velocity potential. The only thing that differentiates Kelvin Waves from the MJO is the speed, with Kelvin Waves showing much faster propagation. Taking Mike Ventrice's plot: He states Kelvin wave projection for next week. Beyond that, the week 2 forecast shows a classical signature of +ve velocity potential around 120E and negative velocity potential around the Dateline. That would imply a strong convective anomaly around the Dateline consistent with tropical forcing centred in what would equate to MJO phases 7 and 8. The CFS forecast shows more MJO component, and low level forcing becoming sustained just east of 180 degrees. Note the similarity to September and October in terms of where positive and negative velocity potential anomalies lie. That strongly suggests that the atmospheric forcing is becoming solely Central and East Pacific with positive velocity potential through the Maritime Continent. Whether this is the MJO, Kelvin Wave or other tropical mode is somewhat irrelevant. It is the reinforcing of an El Nino atmospheric pattern and lack of destructive interference from Indian Ocean convection that is key. The really crucial point here is that tropical forcing is getting into a position where angular momentum will be raised and in doing so, the hemispheric circulation will become more amplified. We continue to see this with excellent and eye taking intra and inter model run consistency. What that tells me is the Arctic Oscillation is beginning to loosen its grip, and tropical convective activity, in all its forms, is responding. Composites for high angular momentum velocity potential for January are consistent with an MJO phase 7 and 8 type solution. Note the relative positioning of positive and negative velocity potential. Now, phases 7 and 8 > Arguably, early / middle of January looking phase 7ish. But, this will be transposed across a pattern that is thus far robustly +AO, so there will be inevitably be a degree of adjustment that we need to make (turning around the super tanker).

Day 11-15 on both GEFS and EC EPS showing a very strong signal for Sceuro ridge, in a perfect position for wave 2 forcing. This has excellent agreement with MJO phase 4 composites, and indeed the concept of anomalous mid latitude or Branstrator ridges tied into MJO/GWO phase 4 - 5 evolutions. But to stress, it isn't necessarily about the MJO per se but what that means in terms of the hemispheric pattern becoming more amplified via increasing tendency and overall angular momentum. The start of the process to take the +AO down.

We can see this convective activity now: NWP now seems to be dropping big hints of a high amplitude phase 4 MJO wave in the next 5-10 days, moving into the Western Pacific. Westerly winds will be introduced on the back of this and tendency in angular momentum will spike upwards. The key issue is where we go from there ? Weakening MJO signal, +AO re-establishes itself - or - Sceuro ridge takes root and begins to inflate further north and north-west serving it up to the tropospheric AO, in turn reducing the polar westerlies and promoting momentum transport southward of 30N, further feeding westerly wind additions and further weakening of the +AO ?

We appear to have a major model divergence here John. UKMO (MOGREPS) very different to the GEFS / GFS: EC somewhere in between: But interestingly more developed than a few days ago and keener on a phase 6-7 propagation: The key here is not the relative magnitude but the phase space, and perhaps the final destination of the MJO signal (although the strength of the signal evolving through phase 4-5 is of importance in determining degree of amplification). The EC demonstrates reasonable skill when MJO waves are in progress (although all show issues with tropical wave formation over the Maritime Continent). What we are seeing with this morning's EC EPS and now GFS 06z op confirms the idea that the atmosphere is about to get substantively more amplified as westerly wind tendency is introduced and fluxed poleward associated with a phase 4 evolution. In the short to medium term, that may mean we get even warmer as the Atlantic trough signal interacts with the amplification, but ultimately this is about both the tropospheric AO and stratospheric vortex.

Unbelievably strong sceuro ridge on this morning's EC EPS from Boxing Day onwards (gaining strength at end of run). If that is anywhere near the mark, wave 2 would be serious player and very troublesome for the vortex 10th Jan onwards.....tick tock

Worth noting that during November the ENSO signal got trumped by an unusual Indian Ocean convective signal, so it's not the dominant player that it could be. Today's forecast and updates for the MJO awaited with a lot of interest, as current trend seems to be for coherence and eastward propagation, at least for upper level velocity potential and convective components. Both EC and CFS forecasts currently showing phase 6 progression for week 2. That in itself not particularly useful for shifting the wavelengths, but more significance in terms of raising levels of angular momentum and how that choreographs with the AO and degrees of amplification in the Northern Hemisphere.

For the first time this winter we may have something to focus on. But stress that the net impacts in the immediate term may not be felt over NW Europe. Forecast pattern 16th - 17th looks ripe for addition of westerly inertia both across Asia and North America. That's probably before more westerly additions as the mjo drives into the western Pacific around the 24th. Net impact will be increasing amplification of the flow as the Asian jet is extended, retracted and then extended again. That puts the period 27th December onwards as of interest hemispherically. Could just be the trigger for the AO to become more neutral / negative.

I wonder, do we have a slow burner ? A slow burner that perhaps leads to a more assured route to a warming event in January ? The pattern as of yesterday and for the next 7 days is within the envelope for generating Wave 1 activity in the upper stratosphere with a deep upper trough centred across the central North Pacific. The atmosphere is also reflecting a strong El Nino passage with relative angular momentum topping +2SD. Both this morning's EC EPS and GEFS mean at 10 hPa show remarkable consistency on a big North Pacific ridge and slightly displaced upper vortex. We have also operational GFS showing warming at 1hPa, peaking around the 22nd-23rd December. That is much more in line with what we would expect given the tropospheric forcing right now and lagged impacts 12-21 days. It also underlines the operational GFS' propensity for rushing stratospheric responses. A couple of things to consider where we might go from here. The atmosphere is starting to take on a well defined rhythm tied into tropical forcing. A recent flare up of tropical convection in the Indian Ocean has generated a lagged El Nino response. We expect to see a slight waning of El Nino next week as the North Pacific ridge is pushed northwards and the atmosphere becomes more La Nina like for a time. As a result, the lagged stratospheric response will be for a backing off of the Wave 1. We can see this waxing and waning in tendency in relative angular momentum with pulses of westerly (red) and easterly (blue) tendency being fluxed poleward over time. Thereafter, MJO forecasts are interesting in developing another eastward wave through the Indian Ocean and into the Maritime Continent. That should give the atmosphere another kick and develop a bigger upward trend in angular momentum and further wave 1 and possibly wave 2 forcing during the final third of December and into January. EC monthly forecast very consistent with this, and should be reflected in the stratosphere during the first week of January. In other words, enjoy the current wave 1 period, but don't be surprised if it doesn't result in a warming event just yet. More focus I would suggest on the forecasts over Christmas week.

EC week 2 forecast relents wave 1 forcing a little during week 2, but really ramps it up again during weeks 3 and 4 with a very coherent N.Pacific pattern for displacement to continue.....

Hi Ed. I'm sorry I don't have access to any WAF type forecast plots. I'm not surprised in the least about the vortex this far. There are reasons outside of ENSO and the QBO which have flagged this for some time (although at this stage I'm unable to detail them). Thus far, we do have a text book Cohen model response - October snow cover, November Siberian High, December Aleutian Low. Just need that to be sustained (and latest EC week 4 plot was good for that) and it's over to the strat response.

.. and this little bomb is interesting... Deep low pressure system tracking through the North Pacific trough, allied to around 10 days worth of low level wave forcing in the region. Very amplified Pacific sector as well, strong +dt/daam overlaying this, and +MT over N. America within 5 days.

A credible window for some amplification opening up in the 10 day timeframe, although the positioning of any subsequent blocking structure looks to be too far west to significantly influence Europe, and there are doubts as to whether this would be enough of a hit to dislodge the +AO regime, for now at least. Tendency in relative angular momentum showing a sharp injection of westerlies 40N due mainly to frictional torques and earth atmospheric momentum but also a hint of mountain torque. This is likely to be at the high end of recorded spikes in relative angular momentum for December. Net result is a poleward fluxing of westerly inertia or amplification. We see this in day 10 EPS and GEFS solutions, EPS in particular showing a deep trough carving right across North America and downstream ridge extending through the Canadian Maritime into the Arctic. The majority of solutions show a gradual relaxation in the trough as upstream amplification fades (as it can only do). Ideally, for a blocking structure to form, the amplification should deflect most of the flow to the south. This is possible still, despite what the models currently advertise. However, this block would be forming well west of Greenland and would retrogress if a true blocking structure. Therefore, Greenland and canonical -NAO looks unlikely, and the European profile still remains above / well above average. There is a risk of this amplification transferring through the Atlantic, but it may take another phase of amplification to fully dislodge the polar profile. However, in the longer term, the raising of angular momentum counts towards making the next period of amplification much more favourable for a switch in the NAO although once again, the risks will be a west based NAO.

Extended range modelling has wave 1 forcing written all over it for mid December onwards, and if gfs is anywhere near the mark, wave 2 also in the mix. Should be fun watching the normally over-progressive gfs op in the next few days / weeks? And, we have a likely tropospheric injection of angular momentum in the next 2 weeks leading to greater amplification. Interesting.

Agree here Nick. Stressing that at this juncture it does not likely translate to any potential cold patterns for the UK and Western Europe, perversely it may drop the trough to our west. However, the indirect inference is that the atmosphere is responding to drivers delivering a 2 wave pattern and not being blown away by an inferred +QBO / +AO pattern. FWIW day 7-8 pattern may be a bit more amplified than suggested by the ensemble means with a deep upper low passing through the Western Pacific and generally favourable conditions for amplification of the Asian and Pacific Jet(s) [plural]. That will only serve to feed the anomalous ridge over Siberia and the persistent surface warmth over the Kara Sea.

Impressive Siberian Highs showing up on both EC and GEFS extended range modelling right now, which has traceable origins to anomalous snow cover growth during October. This has no direct relevance to the UK or European patterns for now, however, in terms of promoting a first order Wave 1 response in the stratosphere through North Pacific lows, some logical thought process here might suggest battle about to be joined with the cold upper vortex end of November into early December. The caveat is that wave 2 needs to be a player too, as without it the vortex will descend on Greenland (although what we've seen so far and El Nino forcing would trend otherwise).

The strengthening of upper level winds to extreme levels as a precursor to warming events was something I came across a few years back. Certainly will be worth keeping an eye on. With the current pattern of little value to wave breaking, some further cooling likely, although the nagging forcing around the east Indian Ocean definitely worth an interest to see if we get some tropical convection in the Western Pacific in the week 2-3 timeframe. Compare forecast for week 2 and most pronounced tendencies in relative angular momentum and you'll understand why that might be of interest, perhaps more tropospherically... Southern hemisphere - no sign of the break down of the polar vortex, and we are now nearing summer, so this is extremely late. Strongly positive west QBOs feature this, so a vote for this being a player on our vortex for now.

Looks more impressive as an anomaly at this stage. Only picked up by the GFS op at this stage on an inconsistent basis. EC EPS continues with a warm theme across much of the NH, and tentatively suggests some warmth over the Canadian sector and cooling over Eurasia. Northern hemisphere profile around 26th October also looks good for Wave 1 & 2 activity to be a player again, particularly with a big MJO wave in play over the Indian Ocean although that might have more relevance for early / mid November.

Well it would certainly make life interesting Ed. A strong wave push through the maritime would generate a stark pressure gradient across the Asian massif and inject a surge of westerlies across the Pacific. That would normally amplify the tropospheric wave pattern, and probably set about feedback loops in the stratosphere. Intuitively that would suggest wave breaking through Alaska and counter to the El Niño expectation. But that is highly speculative at this stage, as the main issue will be the destructive forcing from ENSO w/r/t the MJO around phases 3 and 4 through 5 and 6, which so far this summer and autumn has been spectacularly effective.