snowking

I'm pretty sure that is known as a Murr run.... Another volatile day of runs and this is why a good number of seasoned members on here are still urging caution (given the risk of a west based negative NAO I imagine nick has the Snowline hiring lots of xmas temps). However another stunning 12z ECM EPS suite, and beyond the shorter term uncertainty anybody not spotting the longer term potential in today's output needs to refer to Tamara's excellent (as always!) posts from earlier today - N Usa mountain torque looks set to make the stratosphere thread pretty lively in the coming weeks. SK

ECM Ens mean now hinting at potential split at 50mb in a couple of weeks time: SK

Those two charts are a very good indicator of the relationship between a negative EPO ridge and the resultant Atlantic ridge within the longwave pattern. Notice the stronger heights/larger ridge towards Alaska on the GFS v the ECM, and notice the resultant stronger Greenland high. The correlation is not always 100%, but in many instances over the years we have seen the two closely matched, especially in a low angular momentum scenario such as that we are entering. There is also of course the potential for a mountain torquing event across North America off the back of those charts which should aid developments up above us Positive steps in the overall longwave pattern, the shorter wave nuances continue this morning. Still lots to be cautious about! SK

I have to keep my cautious hat on for now because we have seen too many times over the last few years, especially from the ECMWF, an overestimation of heights around the Greenland locale and resultant (or concurrent) trouble with phasing of lows crossing the Atlantic... However, I would also caution that looking at such fine detail, including where the -10c 850 line is or isn't on each individual run, as well as the aforementioned phasing issues etc on day 6+ charts is very unlikely to ever lead to anything accurate in terms of projections. I will finish on this note though - that is a stunning EPS mean. I have seen it swing either way from there still, but at face value as a mean (and indeed from the clusters Nick so kindly provided) it's pretty encouraging. SK

Great new addition to the WeatherWeb website, GFS Ens mean 10mb temperatures: http://www.weatherweb.net/wxwebchartsgfsensnh10temppanel.php SK

Does it really? Or is a more accurate statement that this is a single operational run from a suite of 51 members, 50 of which we are yet to see from the 12z run, that it only runs out to 10 days (preceding the mooted period of change) and shows a lot of promise towards the end of the run on a hemispheric scale regardless, in line with the expected potential? SK

Absolutely the standout feature for me from the last few runs: GFS: We should of course be a little cautious and remember over the past few years the over-tendency to evacuate low heights from Greenland in the extended timeframe, however with ensemble support in the most recent suites all eyes should be peeled on this for now. SK

From our friends over at WSI: Co-incides with the renewed warming shown on the GFS too: SK

Just FYI with regards to the CFS MJO forecast. I did take a look at this yesterday but chose to disregard it as it is rather a long way out of sync with current NWP, which suggests the emergence of a new wave in around 10 days time - that CFS forecast is not predicting the new wave to emerge until the first few days of Jan (current OLR forecasts have it in towards phase 6 by this stage) That would bring tropospheric changes forward a little compared to your suggested timescale and the timescale suggested by that CFS forecast SK

Looking slightly further ahead beyond the current is it milder/colder than average debate (FWIW - ECM 12z would have us somewhere around average overall with a succession of short milder/colder periods vs. standard climatology), we have been seeing increasing example of this in recent runs: Can anyone spot the similarities? The main trend is to push the majority of the vortex energy towards the Eastern Hemisphere. What is the significance here? Well it could be that there is a disconnect between the Troposphere and Stratosphere right now, but it may also be a reaction to successive runs showing this: A very clear signal for an attempted Wave 1 attack, trying to push the vortex away from its home over the pole and over toward the E. Hemisphere. The most significant thing here is that it gives credence to the idea of upstream amplification across the US/Canada. We have seen plenty of discussion of this towards the xmas period and beyond over the last couple of days and the stratosphere is certainly supportive of this idea. To this extent, just taking a look through the ECM EPS stamps over the CONUS, an encouraging number of them support the idea of ridging just off the Eastern Seaboard, and a cut off low potentially amplifying the ridge, around the xmas period. Nothing too prolonged showing cold wise but enough to keep everybody interested for now and do not assume that anything beyond day 10 is set in stone with a lot of different solutions on offer upstream. The sort of pattern that could be priming itself is one which could offer up some eye candy at a much shorter range than one might expect and you can certainly start to see where the Met Office may be seeing some interest in supporting GloSea5 scenarios beyond the 15 day period, especially with the re-establishment of a stronger Aleutian low. It looks as though we are about to see a renewed MJO signal coming in to play through the second half of this month too: If this is to overwrite the global circulation once again then let hope we can drive it towards Phase 7 to set us up for some fun in January. Certainly this experimental OLR forecast sends us towards phases 6/7 in to Early/Mid January: SK

Some rather underwhelming output overnight it has to be said with just some fleeting NWly outbreaks - pretty good for Northern and Western upland areas but a little frustrating for those a little further South I am sure. However as Matt alluded to earlier with some promising activity continuing to showi up way above our heads, and this pretty well matching expected timing from a number of winter forecasts, I remain pretty optimistic in the face of the rather Scrooge like charts SK

The current forecast warming at the end of GFS FI exhibiting some similarities with that of 2012/13 as far as the 10mb temperature element goes: Current Forecast: Actual warming: If we look at the forecast for the period running up to the 2012/13 warming, here was a typical example of the charts which first started taking our attention: Of course we do not always see these warmings work their way all the way from FI to T+0, and indeed even during those weeks we saw plenty of waxing/waning of the forecast warming, so I am hoping this can act as a little bit of a warning to anyone hellbent on taking the rollercoaster ride of emotions (could read: tantrums) from the MOD over in to this thread - we will see significant inter-run variation of these forecast warmings, especially in terms of temperature profile. So prepare to see that and please try to avoid the knee-jerk reactions which would otherwise interrupt what is a thoroughly fascinating thread. Everyone got that? Great, I can stop being such a grumpy so and so now Also to say Andrej - the 3D cross-sections of the vortex are nothing short of stunning, and I hope we get to see more of these as the more interesting stratospheric setups start to appear. All in all the pieces are slowly falling in to place at the very edge of the reliable timeframe. Let's hope to see a few ensemble means backing this trend as the week goes on. SK

Beyond the obvious concerns for next week, this tweet from Matt Hugo is certainly worth a look: https://twitter.com/matthugo81/status/540075794903859200 That's some pretty serious clustering for +360. Obviously as we do not have access to these clusters every day it's difficult to know if this is a new development or a trend, but encouraging to see. It looks increasingly likely that the next response will have to be tropospherically led and this may be the first sign. Also, big thanks to Matt to providing a glimpse at some otherwise unseen data SK

No, it's cool dry air from the West: In all honesty the outlook this morning is two things 1 - Changeable 2 - Extremely uncertain (looks like our friend Shannon is here to stay for a while longer yet, which is not surprising given the present setup) SK

One positive from me today. Take a look at the following sequences: http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ecpv.php?alert=1&level=1000&forecast=all&lng=eng http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ecpv.php?alert=1&level=850&forecast=all&lng=eng Note the tendency for much of the vortex 'energy' to transfer towards the Siberian sector. We should of course bear in mind that this is only taking place at two of the higher isentropic levels and right towards the end of the run, but this is certainly a trend we would like to see downwelling as we head through December. SK

Hi David, I certainly take your point, but I think it is important to remember what we are looking here are not strictly tropospheric precursors, but stratospheric precursors (which later lead to tropospheric effects), and it is these which many are becoming more excited about. I don't have the links to Cohen's work to hand but I am sure if you wanted to read more in to these then somebody will be kind enough to provide a link I think the most important point to take is that nobody interested in the stratospheric season this year is expecting much to happen of wintry note tropospherically until later in December or even in to January, but what we are specifically looking for here are tropospheric patterns which lead to stratospheric wavebreaking. These happen to be the Scandinavian(ish) high and Aleutian low in tandem. I see you mention 2009, if we take a look at the November composite for 2009: Notice once again we do not necessarily end up with the features in the exact same area but they are there nonetheless - the Scandi high/Aleutian low combination. So, if all we are interested in is those two features, why would I draw attention to some of the other features of my original composite, such as the troughing to the West of the UK and the amplified pattern in the USA. Well the very purpose of creating a composite in forecasting is that you believe that the background features used to derive the composite years should ensure a close match as you progress through the current season to the historic composite. The standout feature was the tropospheric Scandi High/Aleutian Low combination, which we know from Cohen's work is a derivative of a high Snow Advance Index, and this pointed towards the likelihood of some serious stratospheric vortex disruption through the season. But the years were not chosen because of this tropospheric signature, they were chosen because they matched this years setup in terms of ENSO, QBO and OPI. As stated in my previous post, you are unlikely to get a pixel for pixel match between composites, but the overall longwave pattern is what we are interested in and so to see that, as we have progressed through November, that we see the same basic longwave setup as the composite years predicted heightens my confidence in the likelihood of a colder than average winter overall, whilst we of course maintain the Scandi high/Aleutian low signature. Of course as ever this is simply a forecast and nothing in meteorology is guaranteed, but to come back to the point that every year which has finished with a sub -1 OPI has also featured a below average CET (and the consistent theme through that is a below average January in every year), and then adding this factoring in to the fairly accurate composite forecast for November, confidence is raised. In unison with this the disturbed nature of the vortex continues to encourage too. It may also be worth re-iterating that we should have the expectation of the vortex strengthening a little through December tropospherically, and this is in line with expectations. SK

Always worth viewing the charts with some geopotential heights attached: Very promising in terms of keeping the vortex weak overall - still not the killer blow, but with the vortex in such a state of disarray you feel it is only a matter of time before we see such a scenario... Of course it's also worth bearing in mind this is a single operational run at quite some way out, but it does tend to tie in with the limited shots of the ECM mean at this range from WSI SK

Still liking the look of this: Poleward flux will certainly help break in to the surf zone if the warmings right at the top do indeed downwell. Speaking of which: At 16c, it's likely to be warmer up there than it will be at the surface here next week. The only concern at the present moment is the forecast location of the split vortices, but when we bear in mind the very early stage of the season we are at right now there is plenty of time for these to be shifted around pretty extensively within the very inhospitable vortex environment at present in the stratosphere. I would imagine the mood across these forums will be very different indeed in around a months time. SK

Hi David, and sorry for taking so long to get back to you on this. Let me start by addressing your second and third points. When matching composites across the space of 30 days such as this (and especially when you then factor in adding multiple years together with the historical composites) you are very very unlikely to ever get an exact match. I think it is also worth bearing in mind that these are 500mb composites. We are not looking for an exact match pixel for pixel, what we are interested in is the overall longwave pattern insinuated. In this instance I have picked out those key longwave features, the Aleutian low, the Scrussian high, the amplified pattern up across the US, and indeed the troughing to the West of the UK. These may not match pixel for pixel across the two composites but you can certainly see the longwave pattern matches very well. As mentioned in my previous post these features all align well to Cohen's expected climatology following a high SAI, and to address a further point, the fact that the positive anomaly around Scandinavia is further west than the baseline composite is not a bad thing, it's actually a very positive thing stratospherically. As for previous November composites from milder years lets take a look at two of the more nightmare years as far as collides are concerned - 2013 and 1988, with this years November to date composite alongside: I'm sure I don't need to point out the differences here, but notice the much flatter pattern overall, with the loss (and indeed reversal) of our positive Scrussian anomaly, and vice versa around the Aleutians too. I hope this helps and if there are any further queries do not hesitate to ask SK

That is a terrific bit of research and hopefully dispells the idea that just because some cold air happens to flood out of the Eastern seaboard we all of a sudden will see a roaring jet stream. This idea may be the fault of the media - there were a lot of explanations last year about how the thermal gradient created across the Atlantic lead to the strengthened jet stream. Whilst very much true, this does not automatically mean that the same will happen every time a little cold air exits the US, and there were other factors which colluded to increase the jet strength. Good work once again and next time I see the ridiculous notion that cold air thousands of miles to our west precludes cold here for the rest of the winter I will be pointing the poster in the direction of this.

That's certainly what caught my eye this morning S4L - early days of course but it would certainly be nice to see that become a trend over time Otherwise much as we were really, continued attacks on the upper vortex, lead primarily by some very strong Wave 1 activity, though signs after waning of some further Wave 2 action towards the end of the run again helping to keep the vortex humble. SK

I thought it may be worth dropping in a reminder of why so many of us are very optimistic for the forthcoming winter (i think it's also important to highlight that it is still Autumn - for most that leaves us still 14 days from winter, for traditionalists that could be 35 or so days). So the November analogue which I produced was formed from years with the following profile: < -1.5 OPI eQBO El Nino As has been said several times before, the key features to pick up are the signal for the Scandi (Or Sceuro, or Scrussianâ„¢) high, and Aleutian low. These two features in particular fit with Cohen's predicted climatology following a high Snow Advance Index, and help to drive wave activity in to the stratosphere and consequently help to weaken the Polar Vortex significantly. In addition to this we can also pick up on troughing just to the West of the UK, and the amplified pattern across the pond. So how do we fare with each of those features at this the half way point of the month? Well all the key features are there, the amplified North American pattern, the troughing just to the West of the UK, and crucially the Scandi high/Aleutian low combination. This all follows the ideas laid out by Cohen to a tee, and when many of us saw analogues with such climatology projected, and now having seen these ideas progress and manifest themselves, it does bring a certain level of optimism. So despite all the doom and gloom at times over on the model thread, to be expected given how early some started on what I would term "silly season", there is much to be optimistic about in the longer term, with many peoples thoughts aligning around the late December/January period right now. Whilst we talk about the model thread I have seen one or two comments about how the 'Vortex is ramping up' - tropospherically speaking we will see a bit of an increase in vortex strength in the coming weeks, but not only is this to be expected prior to anticipated events during December, it's also important to apply thoughts of the vortex strength in relative terms against the backdrop of last winter. It is also important to think about the Polar Vortex in a three dimensional sense. I think people can get a little carried away with seeing Blue's and Purples on the charts north of 60N and automatically assuming the Vortex is starting to ramp up. But the vortex does not just exist at the 500mb level - it stretches all the way up in to the Stratosphere. A strong vortex is one which exhibits strong Westerlyness all the way up in to this layer of our atmosphere too, and for as long as we see activity such as this high above us: A happy vortex it shall not make. I think finally, I will leave everyone with this thought - every January following an OPI of < -1.5 has finished with a CET below the 71-00 average. SK

We do get sudden heavy snowfalls in the UK too. A couple of examples occurred in back to back winters here in Essex, first of all in late Jan/Feb 2003: http://news.bbc.co.uk/1/hi/england/2712045.stm http://news.bbc.co.uk/1/hi/uk/2708283.stm And a year later: http://news.bbc.co.uk/1/hi/uk/3440449.stm I remember both vividly, but particularly 2004 where an inch of snow fell in around 10 minutes, and around 4-6 inches fell overall in just a couple of hours. You could see it coming down the road from the North like a cloud, with some associated snowfall too. However of course it does not stack up to anything like what is experienced over in the Great Lakes, where perfect geography plays its part. SK

Beat me to it but yes remarkably strong anomaly for such a long way away. Unfortunately the 850's remain slightly above average by then, but no telling what the situation at the surface may be. The best note by that stage is the continuation of WAA towards the Greenland locale as a result of the longwave pattern. SK

Indeed, very visible on the 0z ECM EPS mean too even out to day 15: Also using the very handy tool you guided towards yesterday, you can see the swing in the EPS over the last 24 hours towards this: 12z Yesterday 0z Today The suites at this range are far from infallible, but offers the best NWP insight available to us mere mortals. SK