Glacier Point

Reasonably good agreement out to day 8/9 between 12z GEFS and 00z EECM mean heights. Thereafter, 06z and 12z GEFS mean becomes increasingly vague and is characterised by some fairly rapid developments over the Arctic field with a number of ensembles amplifying both the Alaskan and Atlantic ridges. Would fit the bill in terms of a first rapid response downwelling wave to stratospheric warming and sharp reversal in mean zonal wind vectors centred on day 5/6.

Going to come at the extended range (10th Jan onwards) from a slightly different tack. Over the last week, tropical forcing (convective activity) has really cranked up in the Indian Ocean. OLR plots depict a moderate to large -ve anomaly in this region. Tropical activity can be seen as adding westerly inertia to the planetary system. This is registering as a suprisingly +ve tendency anomaly in relative angular momentum over the Equator. Over time these wind bursts can, if the extratropical circulation is conducive, work their way poleward and contribute to a net increase in total angular momentum. The most likely initial response from the GWO is a phase 4 projection, which indicates an anomalous mid latitude ridge centred somewhere in the north Atlantic and UK. This is similar to the MJO projections for phase 6 which shift the balance of probability towards the mid Atlantic for height rises around 10th January. MJO forecasts (ECM) pretty well aligned on this phase 6 projection by 13th Jan. I key consideration thereafter will be whether the MJO can migrate eastwards towards phases 7-8 (currently a strong pulse of east winds ahead of the MJO which it will need to negotiate) and the response of the middle and high latitudes, which a stratospheric warming would favour. It's worth noting that the oceanic heat content in the Equatorial Pacific east of the International Dateline is well above average which might help pep up convective activity ahead of and enhance the MJO in phase 8 in particular. The plot below shows this on the right panel whilst a wall of easterlies lying ahead of the resurgent MJO is shown left panel. With increasing angular momentum, this favours a GWO phase 8 response, This tends to edge us closer towards an MJO / GWO phase 8 solution for the most likely atmospheric response to the stratospheric warming. I'm going Greenland height rises after mid month. Whether that is too far west or just perfect for a direct hit from the Arctic for the UK and NW Europe we'll have to see but the idea of this being a long-lived warming event which will fundamentally shift the hemispheric pattern (and feedback loops) is one I'd been keen on pushing - so sooner or later would be the message.

Indeed Kris. The residual vortex is basically ripping the upper level westerly circulation apart indicative of a reversal of the mean flow across much of the polar field. The trop PV on the 18z op becomes very constricted and shiftward south and west as the upper level changes occur before emptying rapidly. Fun times ahead.

A couple of thoughts as we stand on the brink of a major mid winter warming.. The last few GFS runs have pointed towards a large junk of the residual split vortex centred initially over Hudson Bay with a general trend to retrogress this as the entire upper and middle stratosphere demonstrates a negative (westward) gyre. 12z t300 a good depiction of this. That suggests a large poleward flux of ozone through the North Atlantic around the eastward flank of the cut off vortex from the mid and low latitudes as colder air is pulled into the tropical stratosphere. The last few runs indicating warming around Greenland are consistent with ozone flux. The question arises how quick if any will the propagation be of -ve zonal wind anomalies ? I suspect the answer to this may be quicker than a conventional event given the state of the atmosphere ahead of the warming lower down in the mid and lower stratosphere and troposphere and the trospheric longwave pattern projected days 11-15. If we look at zonal winds there is a persistence of -ve zonal wind anomalies. That means less wind shear for any wave working its way down. The programmed GEFS mean height anomaly pattern for days 11-15 depicts a developing -ve EPO pattern with a ridge over the NE Pacific extending into Alaska and troughing into the mid West USA and Canada with +ve heights over the mid Atlantic. That largely coincides with the 10hPa GPH forecast for around day 13, meaning that the trosphere doesn't have to move much towards the upper level flow. An instant tropospheric reaction to the warming is possible, but perhaps we should be focussing more around days 10-14 following the warming (5th Jan) for the first real impact ?

@gustywind We've 'enjoyed' a lot of tropical convection in the Indian Ocean (MJO phases 1-2) in the last 2 weeks and this follows on the back of the sharp uptick in solar activity at the end of November beginning December which may have lifted the tropopause over the tropics and a lagged response in terms of taller thunderstorm cloud developed. That, allied to a sharp drop in angular momentum (tied into the tropical response) explains nicely what we are currently seeing. Fortunately, the longer term GEFS, UKM projections suggest the centre of tropical convection to be shifting eastwards and away from the Indian Ocean.

GEFS at least starting to sniff the UKMO lead on the eastward progression of the MJO. At the extended day 11-15 range, a developing +ve height anomaly in the mid Atlantic (still fairly flat though) consistent with phase 6. Once we get to this point, the Rossby Wave activity will help shift out the low heights to the north associated with a phase 7-8 projection after mid month. This has been a theme for a few runs now so some confidence in it, as well as support from UKMO ensemble system and operational. Noteworthy that an anomaly strengthening the further out you go in the runs.

To paraphrase Steve Cram's commentary... Beautiful! As indicated, a seismic scale split in the upper circulation, the cooling of the tropics takes the eye and completes the circle nicely. Given the amount of low heights we've seen over the Aleutians just recently (not to mention the recent spike in global mountain torque), further warmings are on the cards.

... No Nick - net yet.. it is a mountain torque amplification.

Would add on to that analysis that we've seen a strong + global mountain torque in addition to strongly positive frictional torques which have added significant relative increase of westerly tendency to the atmosphere. Tendency in relative angular momentum is very positve. http://www.esrl.noaa...ltaum.90day.gif http://www.esrl.noaa...ltauf.90day.gif http://www.esrl.noaa...d.sig.90day.gif That's a solid signal for amplification in the 10 day timeframe and anomalous mid latitude ridges. Worth keeping an eye on modelling of this high as it may well stick around long enough to work off the initial wave response in the atmosphere from the upper warming and adopt a higher latitude feature. In any event, that tells us that the atmosphere is attempting to add westerlies and repeat late October into November. There will likely be a second pulse of westerlies coming in 10 days which will also amplify the flow and the cumulative impact should draw the GWO into phase 5-6-7-8 orbit, maybe the third pulse in mid to late Jan the signal for higher amplitude GWO phases 5-6-7-8.

With the modelling congretated on a persistent zonal theme for the forseable, and people extraploating out from that into March, seems like a good idea to take a look at the positioning of the global synoptics. Total angular momentum has plumetted of late and is now running well below average thanks to sustained scrubbing of westerlies over the tropics and Asia. The strong flat northern arm of the jet and low heights being offered by model guidance is very consistent with this type of synoptic. However, I suspect we are in a very similar place to where we were in late October and early November so the next 10-14 days should provide some interesting viewing of the models as they are likely to overdo one signal and the hit the reverse gear as they realise something's going on. Analysis of the low points of angular momentum confirms the addage, what goes down must come up. A forward projection puts our low point in angular momentum in the next week. That suggests that there is unlikely to be any quick turnaround in the outlook before New Year. However, with frictional torques basically saying to the atmosphere 'I'm not with you', and the emprical reasoning of a low point being reached and natural rise theresafter, I would suggest that we are heading for another large uptick in angular momentum early in the New Year. The recent rise in temperatures in the western Pacific should aid this process in lending oceanic support to the atmospheric rally. With increasing tendency in relative angular momentum we should see a spike in the GWO towards phase 4 which teleconnects to anomalous mid latitide (Scandinavian in this case) ridges, possibly more westward in extent towards Iceland around 10th January. That's a handy date as it corresponds with the possible first rapid response to the upcoming warming of the stratosphere which in itself should alter the global synoptic and stress the U-fields allowing for increasing westerly winds and a further rise in total angular momentum further down the line. Basically, there are times when a vortex looks like a vortex and is a vortex which is sustained. There are times when a vortex isn't a vortex but looks like one. This is one whose chirade will soon be exposed. In contrast to many a recent year, we go into the Christmas period with cold hanging on but ominous signs developing into New Year. This year quite the opposite I think.

Recretos - superb post there. So maybe we can give this some credability. Last few GFS runs have really ramped up 1 hPa values at the end of the run. 12z for reference: Translated to the Berlin site, that would be close to going off the scale. 10 hPa warming is showing up around 7th/8th. Most effective downwellers showed a characteristic warming at the top layer of the stratosphere.

and contradicts the guidance from the principal tool normally used in the preparation of this outlook.

An objective assessment of what the AO has done to us thus far. T2 anomalies.. That's a very good manifestation of what would be expected given the modality of this index. The NAO looks like moderating in the next 7-10 days, which teleconnects to the zonal projection across all NWP. Just how mild or cold will depend on usptream amplification off the Californian coast / Texas and then mid Atlantic. The broad axis of a deep trough just to our east, but with depressions running into the back of the trough periodically introducing milder phases. The fewer the depressions, the deeper the trough to our east and the further south the pM airmass gets. Further ahead, the linear correlation between NAO and AO rises in January compared to December so we would expect the AO to assume great influence on the North Atlantic domain. That's before you factor in a shifting Pacific pattern, PNA on the turn, increasing angular momentum signal and, stratospheric warming.

ohh, how close ? Good to see tropical stratosphere temperatures forecast to fall which I think would be a pre-requisite for warming at the Pole. Warming also now very pronounced at 5hPa and 1hPa: I think the date around 7th / 8th January continues to be the most likely date of a warming event. Note the continued similarity with the 62/63 warming event in terms of GPH profile.

The upstream uncertainty of the storm track across the US makes the operational GFS a very limited tool at the moment. CPC have cited horrible performance of the ops of late. Ensemble means are a bit fluid, and some health warning on these, but for what it's worth, day 8 GEFS H5 mean anomaly puts the UK more in with the Scandinavia trough (note the absence of the strong +ve heights to our south there). Not abundantly cold, but the control demonstrates an option in with that troughing.

Wouldn't worry about that. Basically the net impact will be for an ultra-excited response between tropospheric coupling and the strat warming in its initial phase. These will blur the lines between phases 7 and 8. The basic gist would be for height rises in the North Atlantic / Greenland locale to start.

Warming event on 7th/8th January (based on position of ridge over Canada on 27th/28th December) ? That's a fair few GFS runs to go through yet before it comes into model view and even more ECM ones. Reinforces the idea that stratospheric timescales are extremely slow ! Still, should give us something interesting to look at over Christmas.

Actor at the theatre entrance ?

however, not entirely for this thread... we are not soley relying on the stratosphere going into mid January. Nino region 4 is about to show a not insignifcant jump in temperatures in response to Kelvin Wave and another westerly wind burst (the most easterly since 2009) is beginning which should add fuel to the tropospheric signal converging on a net increase in angular momentum / MJO phase 7/8 type pattern for mid January onwards which should really gun for a -NAO/-AO pattern. Moreso than any other month, the strength of the AO should force the NAO negative which in most cases should deliver the goods.

... was definately along the lines of a Canadian / Alaskan ridge and displaced vortex towards Russia. The key think for me looking at Lorenzo's plots is that troposhperic pressure falls in the North Pacific. If that occurs, I think we stand a well above average chance of latching onto a piece of the vortex. This is what I like about our current projected pattern. It screams El Nino type pattern across the NH rather than the 2002 La Nina type variant.

and the GFS and ECM runs at day 10 are almost identical which gives confidence that at that point, the modelling is fairly robust. The issue is around days 12-15 - how fast and what overall shape the vortex takes in its final days ? GEFS days 6 through 10 look like further adding to the tropospheric preconditioning for a vortex destruction with ridges over E. Europe and troughing over the Aleutians. Mountain torque activity should be high at this stage, so more killer blows if we need it around mid month.

Actually Phil, that's a pretty strong -NAO. GEFS days 6-10 has a very well defined blocking structure over NE Canada and Greenland. Looking very likely now that December will come in as a -NAO / -AO month.

1962 warming event at 10 hPa and 30 hPa at ten day intervals, heights and temperature anomalies....starting to show a similar type evolution. 01/12/62 - 10/12/62 10/12/62 - 20/12/62 20/12/62 - 30/12/62 ... note the elongated vortex in the final frame at 30 hPa, stretched across the Pole.

Indeed, violent movement in the pv starting around the 28th December, manifesting primarily at 30 hPa but shifting upwards a few days later on. We also continue to see warming of the very outer stratosphere. At around day 8 we are seeing a moderate strength warming in the middle and upper stratsphere with the core warming over Canada which lasts until around day 12-13.

..which is interesting because if the polar core temperatures are cold and relatively robust, the Canadian warmth rotates eastwards towards Greenland and supports heigh rises in time in this sector.