snowking

Well before this turns any more into a mild vs cold battle royal (snow shovels vs beach towels) perhaps we should take a look at the evidence in front of us. Det. Runs @ T + 240 cmanh-0-240.png gemnh-0-234.png (Sorry - it would only let me post a certain number of images!) So fairly useful agreement between deterministic runs of some kind of mean Northerly flow by day 10. We can also see this from our ensemble suites: You will also notice some support stratospherically for the trough to drop close to the UK from the ECMWF: And from the GFS: Note though the subtle differences over the Atlantic with far more tendency towards ridging on the GFS. What is important to note though from a stratospheric viewpoint is the tendency for the vortex to move across the pole from the Siberian sector towards Canada. Unfortunately at the moment this path also takes in the Greenland locale, and this tends to scupper chances for any extended periods of Greenland blocking. We go from this at day 3: To the day 10 chart shown previously. With a pretty significant portion of the vortex shown to be close to Greenland, as indicated by the vorticity charts too: Now of course there has been some discussion of a disconnect between the troposphere and stratosphere in recent weeks, perhaps a little justifiably, and so if we continued to see the same disconnect between stratospheric and tropospheric modelling we could potentially look at things a little more optimistically, however after a quick consultation with the extended ensemble means: NAEFS From this: ECMWF From this: To this: Whilst the transition occurs a little later we still see the transfer of the main energy of the vortex from Siberia to Canada, and once again part of the journey takes it across Greenland. So in terms of what we can look at factually for now yes there is some good deterministic support for a cold spell once again next weekend, with all the usual potential for wintry showers/snowfall/snowmageddon headlines in the media/tantrums on here and somebody in Inverness ends up with 2cms more snow than somebody in Plymouth, but in terms of expecting something more extensive to develop? Sorry I am a big fan of cold weather in winter (along with warm weather in summer, just call me Frosty jr.) but even looking through optimistic eyes at present I cannot see anything too extended in terms of cold occurring if we are to take the models at face value. Now of course there is the argument for second-guessing the models. This is a tricky debate because on the one hand I fully agree with such a sentiment. But on the flip side of the coin you are then second-guessing a process which is designed to make an educated guess at the weather - essentially we are guessing a guess. It is clear from previous years that the GFS does indeed struggle with it's modelling of anything blocked or split across the Atlantic. However if we are to take a look at the biggest winter-time model frailty of recent years for me it has to be the tendency for all NWP to over-estimate the extent of any height rises around the Greenland area. We saw this last year (both tropospherically and stratospherically) despite the cold conditions when forecast models were continually suggesting that we would see something more substantial developing close to Greenland both early and late in the season (as it was we ended up with a rather decent steve murr sausage - available from all good stores) and we have seen this occur once again in recent weeks. So with all of this taken in to consideration then yes there is the potential for a cold snap towards the end of this week and this is, as BA has been saying, something which should not be of surprise to anyone who has been following the ensemble suites in the extended range in the past 5 days or so. However it has always been suggested that such a spell would once again prove to be a short spell rather than something more extensive and that still looks to be the case as we draw slowly closer to the period (still lots of time for ups and downs between now and then of course). The only hope would be that the likely high pressure area that would then return to the UK following the colder spell ends up a little further North-East as the vortex energy starts to drain away from Scandinavia/Siberia. I think the mild vs cold thing has always been a part of this forum and for me personally always adds to the drama, but it has mostly been not only in good jest but also usually with evidence to back it up. What there seems to have been in recent days is more of a case of accusations being thrown backwards and forwards with very little evidence to back up any arguments (this is of course not true of everyone here with some fantastic posts amongst the bickering). But for me it seems simple, if you have a point to make back it up with evidence. This is how I have been fortunate enough to learn the amount I know about meteorology over the last 15 years, by viewing forums (all the way back to the good old BBC slow-watch days) and reading through the excellent posts made by members that still exist on here even today, and long may such learning methods continue to be applied. I am sure there are some newbies lurking around here who would wish to have the same experience and until we can get back to providing such a posting format that is going to be difficult to achieve. Kind regards to all, SK

Absolutely, feel free to use it as needed John

Beat me to it! Interestingly if we take MJO Phase 4 (roughly projected phase for 10 days time) days from previous years with amplitude <1, in West QBO years and with ENSO Neutral conditions, we get this plot: Not really a million miles away from where we look set to be in reality with the notable height anomaly around the locale of the Aleutians. It has long been argued that MJO signals within the 'circle of doom' should be ignored, but I am finding more and more that if you isolate all other variables that could potentially affect global patterns in combination with both high and very low amplitude MJO phases the results really aren't too bad at all. Incidentally the closest match period for these conditions is early December 1980: SK

Yep latest SESC counts show after the highest activity we have seen for some time things have calmed down somewhat over the last couple of days: (Green is 10.7cm Flux, Blue is Sunspot Count) SK

We almost seem to have gone full circle on this one, with the initial idea of the high toppling in to the UK (but propped up by lower Iberian heights) seemingly the favourite this morning. As has already been pointed out this morning with the upstream pattern still variable overall still time for some changes, but if we remember back to last winter we saw some similar issues with the modelling of the vortices of the polar vortex and how much energy they would leave in various places. We have seen similar today, with the stratospheric ECMWF charts showing us the split upper vortex at day 8: We that split all the way up to the 20mb level too by day 9: The trouble is though that by day 10: The weaker of the two vortices moves just that little bit too close to Greenland (at least according to yesterdays 12z ECMWF that is). This is also shown well by the vorticity charts: This is a slightly different situation to last year though in as much as we were seeing such charts as this last year following an SSW. This year we are looking at such charts showing up whilst we still have a developing vortex as we head towards the winter season. Whilst it still stands to reason that the above charts show bags of potential in the medium range with a few subtle tweaks (the most notable one being the movement of the weaker vortex away from Greenland), we are not likely to get as many shots at this pulling off anything substantially colder at this time without further disruption to the vortex. Still we haven't even reached winter yet and to put a more positive slant on things the early signs of this disruption to the vortex, at a time when the composite years (accounting for wQBO, ENSO Neutral and something approaching solar maximum conditions in terms of the Labitzke et al. Solar Flux definition) suggested we would struggle to see such developments can only be seen as a good thing. Patience SK

Thanks Ian as always

Ian, any insight you can offer us about the 12z UKMO GM run out to 144 in terms of whats happening just to our North-West? Us poor non-Met Office/BBC types have lost access for now *cue worlds smallest violin* Cheers SK

I think it might have been on the Model Thread BA

We're obviously limited by the ECMWF's decision to take away the EPS postage stamps just as we move towards something interesting *stomps feet on the ground* But in terms of the temperatures heres a comparison between the ensemble maximum and minimum temperature projections between the GEFS and the ECMWF EPS: Key: ECMWF Max. Temp ECMWF Min. Temp GFS Ens Max. Temp GFS Ens Min. Temp Pretty good agreement in terms of the overall temperature trends at least. I'm also quite happy with this as an ensemble mean solution from the GEFS at T+300: High pressure to the North, low pressure to the South, and the tropospheric vortex really rather stretched. A few signs of some sort of disturbance up in to the stratosphere at the same timeframe, whilst not necessarily a full split, certainly two visible centres with some potential here: We even see something similar up to the 30mb level based upon the 6z GFS: Whilst this is of course just one run we did see something similar from the 0z too at the 100mb level at least. Meanwhile whilst we don't see anything too similar from yesterday's ECMWF 12z stratosphere forecasts, we do see the very obvious ridge to the North-West of the UK at the 100mb level, signalling the potential for high pressure to remain around this area out to day 10, along with a troughing structure to our East and South-East: Once again this is reflected right up to the 30mb level, though other than the ridging structure the vortex looks otherwise rather stable at this level: So the significant cool down and the likelihood of some wintry precipitation next week. Could we be looking at something tropospherically-led more extensive? The signs all appear to be there but I remember a similar situation involving a Siberian high from last year too. Totally different kettle of fish with GIN corridor heights, but still some need for caution beyond the start of next week at this stage. SK

Should probably read as any of the following: Jonathan Powell, scam-artist for Vantage Weather Services Jonathan Powell, taking a blind stab at the weather for Vantage Weather Services Jonathan Powell, checking the sea-weed for Vantage Weather Services Jonathan Powell, *insert profanity here* for Vantage Weather Services etc etc.

I think the thing to remember here GB is that nobody has realistically suggested such a scenario. There have been numerous warnings from various people throughout the last week about not getting too caught up in the excitement and having higher expectations of the upcoming cold snap than warranted. But as Summer Blizzard points out above any toppling high looks likely to set up an inversion over the UK - crisp, dry days, frosty nights (assuming we don't get too much cloud trapped underneath). You can't realistically ask for much more than that at this time of year other than in the most extreme of circumstances SK

I think at this stage so that Nick doesn't have to hand out the prozac too early it may be best, at least for a short while, to temper expectations just a little. First of all lets take a look at the positives. It should be of no surprise at this juncture to see the sort of ensemble mean setup depicted by the two major suites as below at day 10: An amplified pattern over the Atlantic, most likely leaving the UK under some sort of mean North to North-Westerly flow - risk of West based negative NAO aside as discussed by BA. The trouble is at 10 days away as we have seen winter after winter there is always the potential for some smaller scale spoilers to throw a spanner in the works. The most obvious thing to say at the time of writing is that anybody expecting more than a toppler scenario based upon current output will most likely be sorely disappointed. The primary reasons at the moment for not building expectation too highly are twofold. First of all if we take a look at the projected NAO/AO outlooks (bear in mind the ECMWF NAO projection is still 12z yesterday): Whilst we see an overall tendency towards lower values of both indexes, what is most crucial to note is that the higher resolution outputs are currently the most amplified solutions - hence seeing some of the operational runs that are currently being thrown at us. What this means is that the majority of the ensemble suite are throwing out slightly less amplified patterns overall - something closer to the classic mid atlantic ridge toppled as opposed to something closer to a Greenland-based high. Now of course it could be argued that on many occasions in the past its been a case of the higher resolution operationals/controls leading the signal ahead of the ensemble mean suites. Such an occurrence could be on the horizon here too, but at present that is mere speculation and something that we will simply have to monitor over the coming days. But I think that overall the chances of the first wintry blast of weather in around 10 days time for the UK are now looking pretty good based on current NWP. The second reason though that I would just warn against, at this juncture, anybody getting too excited over the prospect of a cold spell that would give widespread lowland snowfall is both the time of year and the current SST profile around and to the North of the UK: Bearing in mind the most likely N/NW flow, and the amount of warmer water such a flow will encounter to the North of the UK at present - I would suggest the likelihood of some modification of 850's the closer we get to the timeframe, which is pretty standard fare for a Northerly at this time of year in the UK. The other thing to be wary of is any sort of expectation, based purely on face value current output, of this to become a more extensive cold spell. We are all too aware of the discussions that have been taking place about the chicken vs the egg (stratosphere vs troposphere) and so I won't go too deeply in to that. But needless to say whether you're looking at the stratosphere or the troposphere, in order to achieve something more extensive in terms of cold spells you need some sort of major disturbance to the polar vortex, and unfortunately thats just something that isn't shown at present. Even if we manage to see some sort of uptick in mountain torquing in the Northern Hemisphere in around 10 days time, with much of the activity at present in the Southern Hemisphere: We still need a favourable flow of energy towards the location of the Polar Vortex, and at the moment E-P Flux is not moving polewards at all: And neither is it forecast to: And the final kick in the teeth for the hopes of anything longer lasting is that even though the GEFS suite maintains the negative NAO signal out to day 16, it is unfortunately a West-based signal, as was suggested by BA: So right now I would say we are looking pretty good for the first wintry blast of the season, and that's something I'm sure we'll all be looking forward too as the summer hibernators start to come out of their caves, and I am sure this place will become rather more lively over the coming 10 days or so, with plenty of triumphs and tantrums to look forward to. But to avoid the latter a little it would be wise at present to place expectations towards something more of the late 90's early 00's toppler variety. A re-loading pattern? Maybe so. Even in a pattern with a raging polar vortex mid-atlantic ridges can still deliver successions of cooler NWly flows to the UK, particularly when we are seeing the upstream amplification as strong as it is. But for now that remains speculative. SK

Might be best to provide some evidence of that Gaz. The russians certainly agree with that prognosis based purely on 2m temps: As does the latest run of the GLOSEA met office model: We then have the last 3 days of runs from the CFS which places us pretty much average to perhaps just slightly above: We then have the JAMSTEC model pointing to below average (and has done now for some months): And whilst I can't manage to load a temperature anomaly image for the northern hemisphere from the Chinese model, with this sort of H500 anomaly profile: One would envisage the UK being left on the polar side of the Jet Stream a number of times through the winter. To that extent too it should be pointed out that the T2m anomaly projections from the CFS seem rather out of kilter with the projected H500 anomaly over the Arctic, bearing in mind this image is averaged from 21 days of CFS runs: And when we isolate that further to look at January and February (again, averaged from over 21 days of CFS runs) in isolation: We see plenty of potential for something colder. So it's always best to provide some evidence to back up any such claims. From what I can see to be honest its a very mixed picture with plenty of warmer and colder solutions in there - i.e. overall it really leaves us none the wiser. Part and parcel of the reason I don't tend to pay too much attention to long range forecasting models when compiling thoughts on a seasonal basis SK

That upgrade is going to be a rather significant one too, funded in the aftermath of the total failure of the GFS to deal with Sandy. The horizontal grid is getting updated globally from 27km to 15km (to match the ECMWF) and the NOAA have also spent a fair bit of money hiring in new atmospheric scientists to alter the methodology of data collection and input to make it far more similar to the ECMWF too. They also project that overall data processing will trump that of the ECMWF too, with an estimated 2600 teraflops vs (they project) around ~2150 teraflops at the ECMWF. I have seen a number of job listings recently at the ECMWF which makes me suspect they might be about to up their own game in response too. We could be about to enter a really golden age for computer forecasting...I wonder what the UKMO plans are amongst all this with new funding having been secured... SK

Couldn't have put it better. Around 20% of the GEFS and ECM EPS members still develop something more rigorous, but amongst the other 80% which reflect the operational and control runs really rather well (albeit some subtle differences in timing), maximum wind speeds are modelled to be around 55knots (~63mph) along some West facing Irish sea coasts. Still worthy of a warning I'm sure, but present modelling does not lend too much credence to a scenario similar to that of Sunday Night/Monday. A few wet and windy bonfire's this weekend though. SK

I haven't seen any statistics online from the usual places, so I can't quantify it with numbers, but from experience of monitoring it I could possibly sum it up in one rude word... GFS, GEM and UKMO all so far, whilst varying slightly in the track, are giving the same general idea of any low pressure weakening significantly just to the West of the UK before making landfall - UKMO demonstrates this best: This has been a pretty consistent theme during today, with the exception of the 0z GEM and about 25% of the ECMWF and GEFS ensemble members. So at the moment the most likely scenario is a pretty standard autumnal low. Probably enough to create some warnings closer to the time, but I suspect, as has been commented on through today already, that it is the rainfall that may be more headline-worthy than the winds this time around. And for anyone who lives in the areas most affected yesterday, I'm sure they would be rather more relieved at that for now. Of course though to those in Western parts of the UK, the potential for some concern by the end of this week. SK

Lots of variation in the ensembles on the track of it, but having taken a look through, the potential very much there for another bout of gale, or perhaps even severe gale force winds this coming Sunday. 17 of the 20 GFS 6z Ensemble runs go with this idea, and around 35 of the 51 ECMWF EPS members do as well. At present the most favoured track (around 50%) takes the strongest winds through Northern Ireland, Scotland and Northern England - but there is still a LOT of variation, as one would expect from this range, of the exact track and depth. I think perhaps the most notable thing in 2013 has been how often our any extreme weather has occurred on a weekend...very thoughtful of the weather. SK

Something just posted by Matt Hugo over on Twitter that may be of interest - the ECMWF EPS and the EC32 are getting an update: More here: http://www.ecmwf.int/products/changes/ifs_cycle_40r1/ Best news I can see from that is from a stratospheric point of view...now if only they would let us see some of that data! SK

Unfortunately in the two weeks since the above was compiled (its only updated monthly) there has been a notable increase in both sunspot numbers and 10.7cm flux. I keep my own records for this now and this comes from the SESC daily counts - its calculated in a slightly different way to the ISES measurements, but it provides an overview of the general trend. As you can see, after a quiet September, so far October has seen a rather large increase in activity. It's nothing to panic about for now, as it tends to need extensive periods of change for it to have an affect over the course of a season, but it ties in nicely with the idea of a less impressive first half to the season from many quarters. Of course it can also be viewed in a different light - with flux creeping up to levels near 150, the Labitzke et al. work on QBO/Solar Activity then proves more promising in terms of any potential SSW SK

Forecast snow cover change out to 192 from the 0z GFS: Nothing spectacular but every little helps - especially with much of the increase (blue) being South of the magical 60N. SK

It certainly did okay for 2011/12: But not so good, in my opinion, for 2010/11: Perhaps the 2010/11 example is a good example to show why looking at mean sea level pressure across a whole season can be very deceptive indeed. If you were to look at the above composite from that period, one would assume it was a winter driven by mild SW'ly winds. Whilst January and February certainly were far from cold, we managed one of the most memorable spells of winter weather for many decades in December, and yet we still produce a composite such as that overall for the season. This is not to bash the GloSea model at all as some terrific advances have been made. But this is part and parcel of the reason that I very rarely take in to account seasonal forecast models themselves when making seasonal predictions. SK

I think the correct term people are searching for here is 'Surface Cold'. I.E. we have an inversion set up with colder air at the surface promoting overnight frost and perhaps freezing fog too, but temperatures at the 850mb level are not cold enough to support snow. SK

And quote of the day goes to good old Jonathan Powell, rubbished as chief forecaster of a previous forecast organisation and now the head of presumably his own company: Yeah, I can't stand those isolated winds. Keep at it Jonny SK

It is yet another interesting one to monitor. It's difficult to get your head around given much of the theory is published in Italian but I see they are currently writing it up for publication in English which will be useful.One thing just to say, from what I can make out from that forum thread it's a positive AO as opposed to +NAO that is being predicted there. Whilst that's still not good news necessarily, we can still see a negative NAO under positive AO conditions. It's rarer ill grant you but not an impossibilitySK

It's certainly not up there with 2009 or 2012, but what I would say is that I don't think we have seen a starting point as high as this certainly in the last 5 years or so, so it will be an interesting test of whether it has to be rate of change or whether the albedo effect alone is enough to create a strong Siberian high.I realise that a comparison of extent vs advance has already been looked at over a couple of Cohen's papers, but I do think we are in to unfamiliar territory here given the strong start to the season potentiallySK