Glacier Point

Op GFS has just shifted in a massive 600m in its 500 hPa geopotential height over Kara Sea at day 7 between 06z and 12z runs. It also now has the North Atlantic a seething pool of meridional flow where once there was a unified deep upper low.... Atlantic hurricanes in January, this is just bonkers.

GFS has too much bias towards the MJO in phases 8 and 1 which invariably transposes too much negative pressure on angular momentum. Re Strat - not sure we'll get a proper warming, more another perturbed vortex albeit a pretty significant one.

CPC analogues rolled forward days 10-12 confirm the idea that we are heading towards an Atlantic ridge / Scandinavian trough solution in the last week Jan into early part of Feb... which might be useful as the models seem to be losing all coherence as we approach the business end of the winter. Relative angular momentum has peaked in the last few days and, as tendency in relative angular momentum (the rate of acceleration or deceleration) cannot be maintained forever, some negative tendency is expected in the next 10 days. Total and relative angular momentum will however remain high as a large surplus of westerly inertia remains in the atmospheric system, demonstrative of a fully coupled atmospheric - ocean circulation. That places the GWO in a quasi stationary phase 6-7 orbit for the next 10 days. Composites are a bit messy but broadly align to Scandinavia trough a deep low in the Western Atlantic. This is complicated as we are approaching a monthly change, and February's composites hold some value. But generally Atlantic attack from the south-west and re-asserted Scandinavian trough as the theme. The GFS and EC monthly and EPS MJO signals suggest the MJO to become coherent in the Indian Ocean and towards the Maritime Continent during weeks 2-3. It should be remembered that there will remain a low frequency signal for convective anomalies in the Central and Eastern Pacific as well, so the MJO projection onto the system will be altered and angular momentum will remain high. MJO composites alone of limited value and it should be stressed again that the MJO signal needs to be transposed onto the GWO. The main point to draw from this signal is that angular momentum will begin to rise again during week 3 (early Feb). This gives a stable GWO phase 7-6-5-6 type look to the pattern for the next 2-4 week period, with phase 6 being a strong attractor within the base state. Composite is very consistent and now familiar as we turn towards the back end of Jan into Feb...Scandinavian trough, anomalous ridge centred just south of Greenland. Those looking for early spring warmth in the first part of Feb may be disappointed. As wind vectors, I would be thinking NW, N and NE, allowing for a bit of westerly flow days 7-10.

Andrej - are you able to plot previous GEFS means on top of your zonal winds graph so we can keep a check on how the individual GEFS runs are progressing this ? Thanks

I would go along with Cohen's view on a temporary bounce in the AO as a precursor to the early stages of warming being programmed now widely across NWP. Think of at as a Tsunami. The seas get withdrawn prior to the wave breaking onshore as the tropopause is depressed over the Arctic and lifted around the edge of the polar region. That bounce may actually be from -6SD to -2SD, enough though to send the GFS into a tailspin. Today's EPS and GEM ensembles dropping strong hints of mid latitude highs being in position from day 10 onwards, and lowering of pressure over the Arctic. How long will they stay there though, that's the key question ?

@Noballslikesnowballs tropical forcing centred in the central part of the Equatorial Pacific. Check the period forecast off that analogue.....

Not sure the GFS is handling this North American trough, or indeed the blocking over the Arctic too well at all. 06z and 18z runs seem to be particularly volatile on this with large inter run variation.

Wholly agree with this assessment. With a +AO regime, this becomes horribly warm as per November and December. With a -AO, suddenly things begin to look a lot different. What was your foe now becomes your friend. Very good agreement between EC EPS, GEM Ensembles and GEFS around day 10 for increased rate of sub-tropical flow into the Atlantic. Further upstream amplifications already likely, which will all work to cold pattern's advantage. Definite signal for persistence of the cold. Whilst a west based -NAO is a risk at times (guidance suggests more long term trend eastwards - or centrally based to be more accurate), this does open the door for moisture to come into the SW approaches. The upstream amplification coming will help to correct any trend for too much west based NAO stuff I think. Meantime, total angular momentum off the scale.

comparable in terms of pattern, not necessarily temps as we seem to have more sub tropical flow this time round which is helping to perpetuate the northerly flow more into a European trough.

So I think I've spotted my torpedo off the starboard side in the North Pacific. Next week we see a strong jet streak crossing the Pacific. This begins to decelerate and amplify as it interacts with the trough in the eastern Pacific, aided by a further amplification in the Asian jet tied into a trough in the western Pacific cerca 13th. The sub-tropical ridge is pumped into New Mexico and California around 20th. That instantly forces an eddy to break off in the polar flow as much of the flow is driven into the southern arm off Florida. Net result, mid Atlantic ridge is pumped north and north-east towards Iceland. -Nao triggered. Period 17th January through to 7th February 1983 is your template. last 3 gfs runs have toyed with this Pacific side evolution and dropping hints for the North Atlantic around 20th onwards.

Precisely T. The obsession with shortwaves is delusional IMO, as is the reliance and buying into ops for anything beyond day 5 in this current set up. The modelling is getting to grips with the speed of the upper trough moving across North America in the medium range. The fact that this delivers more of a mid Atlantic ridge is no surprise here. I like the GFS op which echoes nicely the ensemble guidance we're getting, and which reflects the longer term thinking on the GWO. It delivers a cold pattern, which will remain cold for some time after, it obliterates the Euro ridge. It also exercises the sub-tropical jet over Mexico. It is here that those critical fluxes in momentum will manifest themselves subsequently in terms of the North Atlantic profile. The fact that the GFS is playing around with this idea (and the ridge close to Greenland) in the extended range should be noted. GEM Ensemble and EC EPS means look very good over the Arctic in the extended. Timing wise, I'm actually advancing my thinking on NAO flip to around the 23rd-26th January period.

Unless of course if the trough slides out through the Atlantic south-east being the catalyst for our proper -NAO flip......could well be our torpedo surfacing before it strikes its target.

Very appealing GEM Ensemble and GEFS tonight, illuminating a strong coherence to the mean over Greenland just sniffing Iceland in the extended range (especially the GEM). I would rate the GEM of most value here, as I think it has a particularly good handle on the Arctic basin.

and interestingly Tony, those fragments of the Kara ridge breaking away south and east are dropping useful troughs in the Western Pacific, helping to keep the amplified flow going in the longer term.

torpedo off and running, should acquire its target within 3 weeks.

Torpedo away ! These westerly winds, induced by the MJO will be fluxed poleward over time (takes around 21 days). On everything we've seen this winter, poleward fluxing has occurred. As soon as those westerlies strike the sub-tropical Atlantic belt, the NAO will flip negative. The AO being negative should also allow for the MJO to remain highly active, so we may see a further pulses of westerly winds being fluxed poleward after passage of the MJO through the Indian Ocean late January.

@blizzard81 I think maybe you interpretation of that would be different to mine.. Northerly flow period occurring during 15th-20th January, candidate pattern shift to classical -NAO around 25th/26th January. If the cards fell right, that could be cold throughout and would certainly denote potential for the second half of the month to be colder than the first, more likely the latter third.

So, following up on previous posting.... This is one of the situations that you just hope everything stays exactly as it is now, allowing for small scale adjustments (from a cold seeking NW European perspective rather than a parochial snow chaser's perspective). It will be one of the changes brought about by seasonal changes in wavelengths. The atmospheric coupling to El Nino continues with the forecast 'off the scale' peak in overall angular momentum and tendency in relative angular momentum now within the next 2-3 days. The pressure pattern over Asia looks ripe for further net increase in westerly tendency days 7 and again at day ten, so we may look for an averaged spike around the 10th January, although for the purposes of dating a possible flip in the NAO from poleward fluxing eddies, around the 25th looks to be the target. Look for troughing ahead and downstream of the mountain ranges for periods of transient amplification prior to this target date. These dates may be relevant to short term fluctuations in the jet flow allowing for more northerly component to the flow over NW Europe around / just after mid month. With the atmosphere loaded in the high angular momentum base state, composites for January GWO phases 6 and 7 showing excellent agreement days 1-15, factoring in some maturing and decline in the tendency of angular momentum as the MJO signal moves into the Indian Ocean (although how long for?). Phase 6: Phase 7: Possibly a little on the progressive side for days 11-15, but around the expected timing of a transient northerly. Regardless of the MJO entering the Indian Ocean, angular momentum looks to remain high with a strong convective component centred in the central Equatorial Pacific (mature El Nino signal). Ignore the GEFS related products for angular momentum as these will be bogus as the model (or rather the interpolated version of it seen here) doesn't reflect low frequency forcing very well. That takes us to the end of the month, ie. closing in on February. How does a continuation of the mature El Nino pattern look to be for February ? The point being that the closer we get to February, the greater the trend for any west based -NAO to correct more eastwards. Also, using the MJO for guidance during the second half of January will be of low value, with the GWO (which measures extratropical-tropical interactions) much more relevant. CFS weeklies and 06Z GEFS mean of interest there... I have nagging doubts about the stickability of ridges in that locale given the pattern of the last 8 months, although you could make a solid argument here for eventual evolution of a Scandinavian ridge from that. Bottom line looks to be continued reasoning using the Global Synoptic Dynamical Framework for height rises to the north, north-west of the UK and possibly NE in time towards the end of the month, or if you like it, the closer those composites get to reflecting the atmospheric parameters associated with February. Cold likely to be from the north from this pattern, and could well be something of a north-south divide, but that detail will only be resolved closer to the time. Steady as she goes..

Closest is 1982/83 but I think we are marginally ahead timing wise...

Actually Knock, the EPS and GEFS means are not that dissimilar at t360 over the Asian sector. The evolution slightly different with the EC dropping more of the ridge south-east during week 2 whereas GEFS retains stronger heights in the Arctic portion. The models differ substantively in the degree of amplification across the Eastern Pacific and North Atlantic.

Hugely interesting 2-4 week period upcoming. The MJO cruising through the Pacific has triggered a pattern change to a notable -AO and more neutral NAO, although in reality the NAO is more positive still due to a residual trough signal in the North-east Atlantic. Fundamentally the game has changed as angular momentum has been moved upwards and the consolidation of the MJO in the next week is going to take it to the heady heights of +3SD. For an angular momentum junkie like me, these are rarified times and emphasises the lofty company we're keeping - only 1997/8 and 1982/3 witnessed such high levels of global westerly wind balance. GEFS product below is off the scale ! This poses a really good opportunity to get stuck into the likely upcoming broad scale hemispheric patterns. The surge in westerly winds over the tropics is forecast to peak around the 6th January. That makes sense with MJO where it is now and likely to be in the next week, allied to sub-seasonal low frequency forcing related to El Nino. It will take around 21 days for these anomalous westerly winds to be fluxed poleward. Note the previous trend for fluxing of positive (westerly) and negative (easterly) wind anomalies over time. That sets up a date around the 27th January where we would normally expect the NAO to fully respond to this forcing and flip properly negative. The EC EPS is rather more keen than the GEFS /GFS in dislodging a part of the blocking high over the Kara Sea (favouring more of an Alaskan ridge). This subtle development opens the door for pressure to fall in the Western Pacific as the high drifts south and east. This also appears to coincide with a Kelvin Wave (yes, I'm using that term correctly) passing through the region. Net result should be for a further addition of westerly winds and spike in tendency in relative angular momentum around the 9th / 10th January. This should induce further hemispheric amplification as the Asian jet is extended and retracted. Allowing 10 days from this point, suggest a northerly type evolution (but still emphasis on cyclonic) is likely between 15th and 20th January. Outside chance of heights rising to our NE from this, but would favour the northerly route. Thereafter It gets really interesting. With an element of tropical forcing returning to the Indian Ocean (and possibly returning to the Western Pacific thereafter), the global angular momentum budget will have reached a high water mark and the only place for tendency in relative angular momentum to go is down, but still within a high overall angular momentum base state. That coincides with the expected lagged impact of the momentum fluxes from the tropical wave in the next week. The GWO framework is extremely useful here as it gives an indication of probabilities of each relative phase when taking account of high angular momentum. Given high angular momentum above +2SD, the only relevant phases here are phases 5, 6 and 7. The initial surge in angular momentum will drive the GWO into high amplitude strongly favouring phases 5 and 6 during the next 2 weeks. Composites favour a Greenland high but that should be adjusted a little to reflect existing and near time conditions, with the emphasis on phase 6 suggesting a continuation of the cyclonic pattern across NW Europe, including Scandinavia. Not overly cold, particularly with the residual+NAO imprint to the pattern, but between 15th and 20th, expect a cooling down. From the 20th we should see a shift in the emphasis of the GWO more towards phase 7 (and not phase 8 as this would require much more significant removal of westerlies which is unlikely given the high benchmark we are operating at). Phase 7 composite for January suggests a west based -NAO, although I've included the composite for February as this will be towards month's end. Stress again, don't be too literal with the interpretation with these composites and the probability of the AO and NAO being more negative at this time should be factored into the composite. This suggests a definite trend to colder conditions towards month's end with the likely key parts for us in NW Europe being a more defined European trough and anomalous ridges centred across the North-east Atlantic. The trough signal across the SE and E USA does imply blocking more towards Greenland. mjo forecast.bmp

I make that four out of the last six GFS op runs in the extended period, 12th-14th January, which have exhibited significant distress signals for the vortex - of the sort that signals something terminal: stretching across a displaced axis and rapid transfers of energy through the lobes.

And to add further to that, the previous update to the EC32 didn't have much of a mean -AO signal at all for week 2 and 3.

And with a general slowing of the polar westerlies tied into a negative AO, reasonable to assume that the ridge to the near W/SW will unlikely stick around in that position for long. EC week 3 to 4 transition begins to angle the ridge a bit further north and west.

and EC EPS extended effectively going for a Canadian Warming, with good support from the deterministic at day 10. Wave 1 activity is going to be pretty relentless now for the next 2 weeks minimum, which should continue the displacement. This signals a particularly toxic period for our upper vortex.