Glacier Point

Nope. Other likely forcing factors are at play. Exceptional agreement between EPS, GEFS and balance of GFS ops right now on the placement and magnitude of warming. No SSW forecast as yet, and mindful of the composites for IO forcing, we could maintain status quo for some time. Any official warming not likely until early Feb, when just as it happens the MJO may well be in favourable phases 7 and 8.

Correct

There is a suspicion here, advertised by the 06z GFS op, that the extended range modelling will be subject to the (false) tropical forcing signal, but which will not tend to get this beyond the day 8-10 range as the extratropical / tropical interactions become apparent to NWP. Phase 5 of the MJO is where the modelling will want to go, but this idea of ridging to out south is false IMHO.

Gfs becoming more and more apparent with the southern arm of the jet over the US day 8 onwards...

This isn't new, but reanalysis of 10hPa temps after passage of strong Indian Ocean MJO events underlines the potential relationship between tropical forcing and the stratosphere. I reckon we peaked tropical signal in phase 2 around the 8th or 9th Jan. For years with strong MJO signal centred in phase 2, 10 hPa temps: Rolled forward, by day 15, displacement starting to occur: By day 39/40, we get peak warming signal: The surprising thing is the duration of the warming signal (days 20-40+) but this is more likely a result of the large number of dates used smoothing out the warming signal. Now, current during the same peak in MJO phase 2: Much more perturbed with wave 2 already in evidence from previous forcing. Different location of warming being forecast, much more aligned through 260 - 180 W rather than Asia to the Atlantic. Suggestion: warming and substantive weakening of the vortex likely to occur given the scale of the MJO wave passage, timings probably more advance given the state of the vortex at onset. Whether a trigger for a SSW or MMW are sufficient will be worth monitoring but not guaranteed.

Don’t have it to hand but it was mjo RMM for each phase ec vs gfs vs cfs

Worth noting that the likely evolution of the coupled tropical wave in the next 10 days across the maritime continent is where the EC shows its weakest skill score. So this models' performance might just dip a little compared to the gfs. The 00z eps smacked of no coherent view for mid to latter part of week 2, albeit not much cluster variability.

Looking at the extended days 11-15 EPS mean I would be supportive of the pattern and forecast temperatures for the UK (2C below 30 year average). The GEFS is broadly similar capturing the key elements, North Pacific ridge, ridge across the eastern CONUS and ridging over the Arctic: Tropical convective potential is forecast to shift into the Maritime Continent and far Western Pacific during week 2. That remains a very coherent signal, this time suggesting a rise in angular momentum. Against that, we have the GFS (and EC to a lesser degree) persisting a low angular momentum base state. This suggests a GWO showing forward (westerly) tendency but juxtaposed onto a low AAM base state. Phase 3 a strong candidate for week 2. Composite: The signal over NW Europe is rather muted. However, with the North pacific ridge and East CONUS ridge, I would be happy to go along with the modelled trough over Europe, temperatures below average given a stronger Arctic ridge. The key questions going forward will be how much overall angular momentum notches upwards given a favourable convective regime, taking us closer towards a phase 4 outcome: So for the extended range, the focus shifting to Greenland as a potential source of cold before a possible shift in the focus back towards Scandinavia.

So we have a big Indian Ocean MJO event, and the dashboard suddenly starts to light up. That near -4SD gwo value would be a good proxy for the depth of the mjo's atmospheric impact. Both future hemispheric amplification and the stratosphere showing signs of strong wave 2 activity are direct consequences.

00z eps was very easy on the (coldies) eye in the extended. 12z going down the same route, particularly Arctic ridging and lack of any upstream pv. Kiev and Moscow 850s might also be starting to light up.

Time perhaps to dig these out... I think a lot of the tropospheric response is related to how predisposed the polar field is to blocking signal from above. 2010 - very rapid response. 2006 - more classical Baldwin and Dunkerton Not a done deal though, although hemispheric pattern beginning to look very much like the precursor to wave 2 weakening of the vortex.

Keep an eye on that flattish anomalous ridge in the central Pacific. GEFS and GFS both moving it eastwards through day 9 - sure sign of evolution in the MJO. The ideal for subsequent amplification is for this ridge to weaken and a second ridge to develop in the North Pacific towards the Aleutians. Many reasons to be positive for cold going into the final third of the month.

Today Very coherent MJO Phase 2 signature in the Indian Ocean Composite and next few days 500hPa mean anomaly Week 1 very coherent MJO Phase 3 Allied to the GWO composite for phase 2 (low angular momentum) Sound support for the mean trough to edge over / closer to the UK. Week 2 continues to progress as a Phase 4/5 MJO evolution. Composites: But, the nuances of the GWO may well kick in if we get angular momentum on the rise,. Composites for phases 4 and 8 are relevant and very different to the MJO (as are the composites filtered for weak / east based La Ninas). Additionally, the MJO composites may also contain El Nino years which would bias the outcome. So two different takes on where week 2 and 3 might be heading. I would hedge to the weak La Nina being a crucial thing here, in which case your GWO composites are the ones to follow in the very extended period, January 20th onwards - but crucial here to monitor for signs of not just the MJO being the only show in town.

I know WSI provide a GEFS based AAM / GWO product, and also provide EC based Hovmollers for zonal wind analysis and forecast, although I've not seen a GWO ECM product. It would be doable if you had the right data to work off. EC will show the same negative anomaly across 20N-30N as GEFS.

That's a cache issue with WDT. Updated.. Note the -ve AAM anomaly 20N-30N which the GEFS is renewing days 5-12.

Mid Atlantic ridge development would be derived ultimately from extension and retraction of the Asian Jet, heralding phase 3-4 transition. I wouldn't be entertaining that idea until after day 10.

Yesterday I was sceptical. Even more so now. GFS drop in angular momentum is now inching forward day by day sufficient to be taken notice of. That ensures us in a GWO Phase 2 type scenario, cyclonic but still with the ridge tantilisingly to the north-east. The lack of any real depth of cold the crucial thing here. After day 10, the lowering AAM trend should abate and steadily reverse. With the eastward progression of the tropical wave, westerly inertia should pick up signalling a movement in the GWO towards phases 3 and 4. Phase 4 being the phase in which a proper easterly could take root - but stress, that is some way off yet.

Eps is excellent support for the op and has further cooled through days 7-11. Plotted the last two ops are bang on the mean for down scaled T2 (not raw model). You couldn't want anything more for model consistency. One thing that looks highly suspect from both extended range eps and gefs means is a notable lack of any discernible wave pattern across the NH. That never happens, so something will fill the void...

Allowing for a 10 day cycle in MT, we're probably at low point on a micro oscillation there Alistair - would tend to be supported by current GFS analysis and tropical forcing centred in the Indian Ocean. It's not until 9th January pattern looks vaguely +AAM over East Asia into the Pacific, and even then backend of week 2 into week 3 is when the tropical forcing signature becomes wholly supportive of a phase 4 transition. So if you buy into that GFS forecast dip (large -ve zonal wind anomaly forecast around 15-20N - annoyingly just out of range of Hovmoller plots to understand where this is occurring), a phase 2-3-2-1-2 type evolution looks in play for the next 10-14 day period.

Indeed Nick. The initial push from the NE looks reasonably secure and a dip in T2 this weekend into early next week. Thereafter it gets very reliant on the 200mb flow across North Africa (especially towards Egypt) to allow westward advection of the cold 850s. So not just undercutting the UK but also all the way through the Med. That's in the day 6-8 timeframe. GFS and GEFS really not there yet on this, holding the flow back across Algeria and ridging in the crucial time frame to prevent any notable sustained dip in T2s. On the plus side, EC, UKMO and GEM ops all do this. However, long way to go to hold this consensus together. From a non-NWP perspective, struggling to see how this could be sustained enough to deliver the necessary throw back of cold air. Difficult to know exactly where we stand in terms of angular momentum, probably around phase 2 GWO heading towards phase 3. GFS related forecasts continue to advertise a dip in angular momentum through days 6-12. Plausibly a phase 1 evolution could support a transient Euro trough to bring the cold back, but the likely evolution thereafter to phase 2 would swing the Atlantic trough back in towards the UK (not a bad result if you're looking for frontal snow). It's not until the GWO reaches phase 4 that enough amplification will be generated to sustain height rises over Scandinavia. That's still probably some time off, likely backend week 2 into week 3. Of course, GFS could be absolute buncum on the angular momentum and completely overdoing the forecast dip, which would keep us more tightly to a phase 2-3 type trough into mid latitude ridge evolution. So an awful lot of questions there still to be answered and still some time before we get to reasonable certainty on them.

Yes Alistair, angular momentum held up better than expected given the onslaught from forcing centred in the Indian Ocean. That stated, verification for late December and early Jan will be extremely good on Phase 2 composite for Europe. I suspect we are seeing an initial push towards phase 3-4 in the coming week but not fully drawing support from tropical forcing until back end of week 2 / early week 3. I think the bottom line is to expect more of this dance throughout the month. Going to be interesting monitoring how much the atmosphere responds given eastward progression of the upper level trop wave across the Maritime Continent into the West Pacific. Phase 4 composite for GWO sifted for La Nina years..

and there is a third question there Nick, whether the synoptic will return in the back end of week 2 into week 3 ? The GFS bias for low aam is posing a particular conundrum here. On the face of it, week 2 (GFS) velocity potential forecast shows a likely +ve tendency in angular momentum developing into week 3: For comparison, here's the composite for January with a +1SD tendency in angular momentum (phase 3>4 transition in the GWO). Phase 4 GWO would be a signal for amplification to develop in the longwave pattern and height rises to north and north-east. However, GFS suggesting a -1.5 SD drop in angular momentum keeping the GWO in a phase 2 (strongly La Nina) state during early part week 2, which would incline the mean trough position to our west. Without doubt the GFS has a -AAM bias. However, it's not until the end of week 2 that the tropical forcing becomes more coherently favourable for amplification (ECM noted a little more progressive in this respect). The broad scale monthly analogue signal maintains a signal for troughing over western Europe and ridge to the NE. Putting these together, I would favour the return of the trough to western Europe next week (more akin to GFS here), but for the mean ridge to be maintained to the NE with the likelihood of a second, possibly third bite of the cherry after mid month. Weather wise that translates to a breakdown of the cold next week, chances of it returning during weeks 3 and 4 - so a something of a stalemate taking hold next week.

Today's (GFS) tropical outlook underscores why we are heading for a substantive drop in angular momentum. The only bit of forcing being 60W, lots of easterly wind addition across the Tropical Pacific and northward momentum transport. To rub this in, GFS also predicting a -ve zonal winds developing in the upper stratosphere over the Equator, which will add easterly inertia to overall angular momentum budgets. Net result is that were are heading for GWO phase 2 New Year onwards. As a basic template, low to the west, ridge to the east but not far enough west or north to bring about an easterly flow and not conducive for cold outbreaks to our east.

So, tropical forcing has gone really quiet of late, and the pattern throughout November has ended (for how long?). -ve velocity potential anomalies across 150E abruptly ending and the MJO heading through phases 1-2. That's a sure signal for dropping angular momentum, and a GWO Phase 2 evolution for the New Year period. Composite for this and GEFS days 12-15 look exceptionally good matches (unfortunately for those of a cold disposition): So a mild, wet and windy start to the year looks a reasonably good call, and the longer range GEFS can be supported with confidence. I'm not totally sold on this being it for the forseeable. The late October - November tropical state was too sustained for it to be a passing phase and I suspect we may pick this up again. The MJO rising through the West Pacific would be a crucial thing here in allowing more of the trough to slide under that ridge to the east and a bit more amplification in the Atlantic. The lack of any cold air to our east noted however.

GEFS mslp anomalies for days 1-5, 6-10 and 11-15 over Siberia: Add that to already observed: Strong +ve anomaly over Siberia. Comparable with December 2005, but interestingly the Aleutian Low not so classical this time round. January 2006 featured a major mid winter warming.. The Aleutian Low conduit working to effect on wave 1 there. This time round, maybe not so much Wave 1 likely to impact the vortex into January, but perhaps more Wave 2 a possible driver for a strat warming event (QBO was stronger in 2005/6).