Glacier Point

Which tallies with an eastward forecast shift in (negative anomaly) upper level velocity potential: Week 2 MJO forecast definitely showing some coherence in the Indian Ocean and GFS simulated products picking this up: This MJO wave is not without some considerable interest. If it manages to stay coherent over the next few weeks, and propagate eastwards, angular momentum will ramp up again, and give more assistance to surface warming in the central Equatorial Pacific. Lots of interest also to see whether October's MEI value breaks the magic +3SD only achieved by 1982 and 1997.

A couple of observations w/r/t the next few weeks in the stratosphere. Both GEFS and EC EPS depict a deep upper low forming over the NE Pacific around 8th October persisting for several days, followed by sequential +ve 500hPa height anomalies over the North Atlantic and then Scandinavia in the extended range. With a 14-21 day lag applied, planetary wave activity over the Pacific low should allow for some moderate Wave 1 activity displacing the upper vortex towards Siberia and Wave 2 activity following end of the month into November. All in all, reasons to think that the stratospheric vortex will be on the weak and slightly displaced end of the spectrum come November. The extended 00z EC EPS has continued to depict a warm 10 hPa layer over the tropics. This is an unusual pattern, not really seen since 2002 for the same period. 1997 was also similar in pattern for date, although warm anomalies slightly further north for these two years - although it highlights the differences this year compared to previous. Both these advertise an El Nino type pattern deeply engrained in the atmosphere. Check the correlation between 10 hPa temps and angular momentum> All in all, a very different start to the stratospheric season beckons.

Not a great fan of using the PDO to interpolate AAM from as its long duration tends to smooth out any meaningful relationships. Just looking at the Pacific windflow anomalies for those years, I suspect that the lack of tropical - extratropical interactions during 1972 was the most likely candidate in driving the low AAM regime. Worth reiterating that this year tropical activity is relatively high (currently standing at 197% accumulated cyclone energy compared to normal for this point) and there appears to be much more tropical - extratropical interaction going on. http://models.weatherbell.com/tropical.php

The reasons why these three key strong El Nino years, 1972/73, 1982/83 and 1997/98 differed so much in their atmospheric responses is very interesting. Purely on ocean surface / subsurface data, all three were comparable. http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml Also comparable in terms of MEI: http://www.esrl.noaa.gov/psd/data/correlation/mei.data Also broadly comparable in terms of tropical activity as measured by accumulated cyclone energy, with 1997 running strongest (as would fit the theory of an atmospheric - oceanic coupling), 1972 was next, and 1982 probably most closest to current set up (although tropical activity is likely to be high this summer / autumn period for the hemisphere as a whole). Key differences in angular momentum - how the atmosphere was responding and particularly so during the summer / autumn period. http://www.esrl.noaa.gov/psd/data/correlation/glaam.data.scaled 1972/73 was almost Nina like in its GLAAM values, whilst the other two years were more characteristic of an El Nino base state. We probably sit somewhere between 1982 and 1997 right now. Definitely tilted towards the high angular momentum base state. Also differences if you look at the June - August upper level velocity potential across the tropics. Current: Note the different scaling there. Arguably 2015 running well ahead of 1997 in terms of upper level circulation features and most El Ninoish if we take 1997 as the benchmark. I can't work out what was going on in 1972/73 to drive such a low angular momentum regime relative to El Nino forcing (the negative QBO was a factor). Conclusion: some big differences in the extratropical response to El Nino, and so far we look much more like 1997/1982 rather than 1972, but I would keep an eye on how the extratropical atmosphere is responding. Right now, current modelling looks most like a hybrid of 1997 and 1982 for September.

If I could interject here.... The upper level divergence signal in the Indian Ocean (MJO related) is slowly edging across the Indian Ocean towards the Tropical Maritimes. That is a region where the GEFS frequently struggles and shows negative bias, so given the importance of this tropical driver, I would not be in a rush to back the GEFS means here - this is not the model to show us out of next weeks rather large trough dominating north and north-west Europe. With the tropical signal migrating through the Indian Ocean, we should see a fall in pressure to the east of the Himalayas and pretty rapid spike in tendency in relative angular momentum and the Global Wind Oscillation move towards phase 4. That's a decent signal for Rossby wave influence for rising pressure over NW Europe within a 10-15 day timeframe. EC EPS 00z going for a pretty impressive turnaround in pressure end next week into the following week, with the longwave trough replaced by a moderate strength +ve height anomaly centred to our east. So much more settled and becoming warmer again in the extended outlook period.

I've been a member of Netweather since 2005. In that time I've seen the idea of the sea temperatures over the Pacific having an influence on global weather patterns go from very doubtful to routinely accepted and monitored on a daily basis. The idea that the polar stratosphere exerts a huge influence on the hemispheric pattern in winter go from almost unspoken to now accepted long range guidance. Regulars will know that I champion a non numerical weather model approach to long range weather forecasting - that in order to accept a model forecast you must first understand and form an opinion of how the global pattern is being driven. This has had its failures, but it's had its successes too. These successes have not gone un-noticed and I've been fortunate enough to have been offered a role with a large multinational providing consultative long range weather forecasts. A tremendous challenge but one I'm very keen on. This requires complete dedication and precludes any public forecasting role. Therefore, this posting will be my last on Netweather. I would like to take this opportunity in thanking Paul for his support over the last few years and the platform that he's given me. I would also like to thank all those others who've attempted to understand my postings over the years, and those who we've shared ideas with, no matter how bonkers they seemed at the time. No doubt others will pick up and run with the approach that I've been keen to promote as the way forward. You may see me lurking from time to time, but from me for now, I bid you adieu. Best regards Stewart

Don't forget Fred we have four days and opportunity to make up any losses with 10 race cards, and 13.30 starts so that should allow for temperatures to get above 0 by around 11 to enable covers to be removed. Wednesday into Thursday looks interesting with both ECM and GFS picking up the potential for a shortwave to slide SE. It's not going to be a warm Festival, infact I think we'll be calling it the 'Frigid Festival'. Long johns already packed !! The key consideration being state of the ground and with Clerk of the Course not watering (and probably prevented from watering from Saturday onwards due to frost covers being in place), should enter the Festival with a mix of good, good to soft in places. On a more serious note, lots of alcohol and temperatures this low are going to lead to some serious risks to health.

I suspect the mechanism at play here is a modification of the Walker Circulation allowing for increased (decreased) wind shear allowing for taller and more extensive thunderstorm clouds (increased divergent flow) to develop. Here are the analogues for 30 hPa zonal winds with a high degree of similarity for this year and rolled forward to June-July-August And the OLR anomalies that go with them depicting a very clear suggestion of increased TC east of the Dateline and Africa and decreased convection in the east Pacific / Central Americas. at this stage, probably better than 2010-2012.

Interestingly our current 30 hPa zonal profile (again very similar to 1969) suggests a continuation of the anomalously cold upper stratosphere well into the spring and summer with a cold banding of below average stratospheric temperatures across the tropics, which should allow for enhanced convection in the central equatorial Pacific this summer - MJO phase 8. The really eyecatching piece of analysis is for a strongly positive Antartic Oscillation at times this Austral Winter (therefore average stratospheric conditions over the Equator, therefore better chnaces of maintaining colder stratosphere over the Arctic therefore less blocking this summer).

I would make the most of next weeks relatively benign conditions, our west based NAO looks like heading towards a more east based solution in the longer term associated with developing heights over Alaska and the Arctic. Spring likely to feel a long way off for the middle part of March when I and 59,999 other people will be enjoying the Cotswold fresh air. Today's GEFS consolidating yesterday's CPC idea of loosening the block over Canada in favour of Alaska, which builds heights to our north and north-east.

High water mark approach to model interpretation in evidence once again...(Steve not you !) The ECM op evolution is very reasonable in my book, in bringing in an increased cyclonic signal towards the UK from the SW and falling pressure over Europe with height rises across the North Atlantic extending right across to Hudson Bay. Cold with a ppn signal with on ongoing risk of snowfall. UKMO evolution this morning therefore considered unlikely.

Indeed, GEFS mean height anomalies broadly reflective of ECM EPS and UKMO 12z output, as well as state of global teleconnectors. Day 6-10 H5 anomaly Day 11-15 H5 anomaly That's a very plausible and smooth transition going on there from Scandinavia to southern Greenland and likely back again. We would be looking at the back door for cold pools coming westwards and to the south-west for possible channel low type scenarios. The T850s aren't anything special at the moment according to the GEFS but that might change. Either way, still looking like a below average February.

This part important variation from what would appear to be a concensus from extended range modelling. The state of overall angular momentum favouring a phase 4-8 type evolution in the Global Wind Oscillation (see model summary and technical thread for the height anomalies associated with these two phases). That suggests a lowering of pressure over Europe and in the Atlantic. So perhaps a reasonable expectation that within 8-14 days we'll see an attempt for lows to swing up from the SW, but equally a strong signal for +ve height anomalies over Scandinavia extending across towards Iceland and southern Greenland (Iceland to Scandinavia I think most favoured). Not a signal for above average or even average temperatures and increasing risk of ppn signal the further sw and in time we go.

Yes, the GWO takes a bit more work, but the rewards are potentially a whole lot greater ! We can use MJO forecasts to help us understand what the tropical component might be 'adding' to the GWO. At the moment the general trend is for the MJO to head into phase 4 (avoiding the +NAO phases 2/3), which couples us nicely with the GWO signal, extratropical and tropical signals as one. With the heat content in the middle part of the Equatorial Pacific really quite high, conditions are ripe for increased cloud cover and tropical forcing on both the western and central tropical Pacific. This would be consistent with net addition of westerlies, and, in conjunction with previous westerly wind propagation, we should see the whole dynamical synoptic model driven towards the high AAM base state (MJO phases 4-5-6-7- 8 ), where mountain and frictional torques are generally positive. That gives us a reasonable signal for the next 2 weeks to be oscillating between phases 4 and 8 given that overall angular momentum has fallen but generally levelling off.

Thanks for doing that Recretos. The inference here is that we should see an evolution in hemispheric synoptics as shown here left to right (the two lines are all amplitudes and high amplitudes) starting in the 6-10 timeframe. The starting point is our anomalous ridge over Scandinavia tied into a phase 4 projection of the GWO, assuming a phase 4-5-7-8 type orbit. GEFS H5 mean anomalies for days 6-10 and 11-15 appear to be in agreement, taking us through a swift evolution from phase 4 through 8: Once this project gets up and running, would be looking for volunteers to undertake anomaly correlation scores for the hemispheric pattern and composites, so speak up if you think you can help !

I would take a punt on a GWO phase 4-5-7-8 type pattern. Recretos, now would be a very good time to put up those composites....

Indeed Chris, v. similar to UKMO global model. Blocking structure over Scandinavia still looks very much in evidence over the next week making life very interesting ! Torques are on the rise once more adding westerly inertia to the system which should slow the flow in the mid and higher latitudes. With the PV emptying from the Canadian sector, a lot of [cold] options coming onto the table in the next 6-15 days.

An interesting morning's model runs. The trend from both 00z and 06z GEFS, and perhaps more nuanced signal from ECM EPS days 6-10 continues with low pressure signal across UK and much of Europe with resident +ve heights over Scandinavia. GEFS in particular keen to pull the centre of the ridge away from the Azores in a NW direction allowing continued risk of low pressure systems dropping NW-SE across the UK into the upper trough, persisting a cyclonic and below average temp. signal. Beyond that, the GEFS continues to simultaneously withdraw the PV away from Canada and develops mid Atlantic ridge signal, with this becoming the dominant force in upper circulation in our quadrant as the ridge over Scandinavia weakens in response. Given the persistence of the +ve anomaly between Greenland and Svalbard, that makes for an interesting pattern to see out the latter half of the month.

Today's 00z GEFS has toned that mid Atlantic ridge anomaly down (still very evident), which maybe reflects the divergence in modelling (of the longwave pattern) at the moment. Interesting that yesterday GEFS was alone with its AO forecast. Could be significant that GGEM has joined the party so to speak,

12z GEFS H5 anomaly at day 10: I have rarely seen a height anomaly of that magnitude modelled at that range. This must be a persuasive indication from the GEFS of upstream amplification, and synoptically the presence of low heights over southern US suggests sub-tropical flow is strengthening. The heat content in the central / western Equatorial Pacific is reaching anomalously warm values (enhanced potential for convective forcing) and westerly wind development is notable, all signs that we going to see a weakening of the Azores ridge in the 8-10 day timeframe allowing it to shift its position into the North Atlantic. That is likely to mean that any easterly component will be killed off in 8-10 day timeframe as the axis shifts to a more north of west vector. CPC's update tonight (maybe more so tomorrow) will be illuminating.

Meantime for the products that demonstrate the highest level of skill past day 8, the theme remains very consistent despite the inter-run variability of the operationals. If anything, the drum is beginning to beat louder. Day 10 GEFS H5 mean anomaly: The ridge in the Atlantic is developing day by day as the circulation becomes increasingly amplified. The troughing over Europe well ensconsed (and colder than normal temperatures) whilst +ve heights persist over Scandinavia. At some point, the mid Atantic ridge will assume dominance and direct the flow from the NW / N rather than the east. Then two options on the table I think.. another pulse of energy from the residiual pv which would focus the ridge on Scandinavia, or a heights rising further NW. Either way, looking below average, and the longer this goes on, the more we sleepwalk into a below average winter.

Jason, if they were so chaoitic, the mean anomaly would be incoherent. Those representations are showing a relatively strong signal given the potential peturbations. The other notable thing is the timing. One would expect the further out you go the more incoherent the signal but the reverse is true here.

Some quite bizarre model interpretations going on here. GEFS mean height anomalies and T850s painting what would be a reasonable picture for the day 6-15 range (in addition to days 1-5 which are cold). Trough signal over Europe is persistent and gets sharpened in the 11-15 day range as the ridge signal in the Atlantic gets organised. Temperatures below average throughout.

GEFS mean becoming really quite bullish here. Developing anomalous ridge in the North Atlantic (teleconnected to strongly amplified ridge over Alaska) and increasing tendency for +ve heights across the north eastern quadrant. Model seems to be dropping big hints of another injection of westerly inertia into the Pacific sector with consequent downstream ampification. (remember the GWO options - rinse and repeat phases 5-6-7-8 or head down into phase 1?). We remain under the influence of a cold trough throughout. Out to day 10 and temps below average acoss Europe. GEFS has Switzerland as the core 'low' at 9C below average, but values 2-4C below for the UK. T2 analysis (and cyclonic signal) suggesting little diurnal range - read convective and frontal potential + below average temperatures (do the maths). If the GEFS mean is anything to go by, there will be another easterly attempt within the 15-20 day timeframe (that's in addition to the one now being modelled) and wouldn't be suprised at all if the models suddenly latched onto a piece of pv dropping round the back of the ridge over Svalbard in the 8-12 day timeframes.

No, not wrong. Maybe a touch progressive, but both GEFS and ECM ensemble means are synoptically supporting the ECM op evolution to varying degrees and critically, they appear to be suggesting renwed upstream amplification. The potential continued impacts from downwelling will only be evident when we get the slightly time delayed zonal sections through.