snowking

Last one from me tonight. 18z NMM shifts things a little further S and E across the region: As has been said many times this evening, surprises are not out of the question! SK

They are indeed - between now and 1-2am they are expected to rise by about 1-1.5c, before falling away again after that. So that's certainly something to keep an eye on. If you find your DP rising less than that by 2am then perhaps there's still a chance of something interesting through the night. In all honesty though I am planning on getting a good nights sleep instead! SK

Dew point check: A little lower than projected in the North of the region, around where expected in the South: This could still neutralise in the coming hours though and the Euro4 projection not far away (I would guess at least given low resolution): SK

No you are spot on, it is certainly a trough sliding in from the West...the complication comes from the fact that at the same time that front in the channel starts heading back inland a little too. Plenty of scope for change even at this very late stage as a result, just at the moment it seems unlikely to me. SK

It feels slightly like i've been a bit too negative this evening so far, so to confuse everybody totally, let's offer something a little more positive. *N.B - Despite the nature of the image below I at NO STAGE condone setting up any sort of BBC graphics watch, these should be used simply as guidance and not as exact placement projection* Everybody got the above? Good. So the most recent BBC forecasts I have seen still show a fairly similar scenario to the 6z Euro4, which at least offered a little more hope for the higher ground of East Anglia as discussed earlier today. Here are the last graphics I saw: Why am I bothering to post these? Well as far as I know the BBC graphics are now driven by the modified Euro4 fields from the Met Office. Now it may just be that these particular graphics were a little out of date when Nick showcased them on the evening news, but if these were indeed driven by the updated 12z suite then clearly the Met Office have made some fairly significant (relatively speaking given the timeframe) alterations to the raw Euro4 output (whilst there is no absolute confirmation as far as the precipitation across us is concerned I do know that the Met Office rather heavily modified the 12z raw Euro4 fields shown on that frontal system across the far North, bringing it more in to line with the NMM output). It is a rather large straw clutch, but may just offer a glimmer of hope to a few of you, presumably any such modification would be either MOGREPS or UKV driven (last UKV run would have been at 3pm so the timing would fit). All speculation but nevertheless it would appear to me that the Met Office are not especially satisfied with the 12z raw Euro4 offering...that of course isn't to say it is definitely wrong. SK

Unfortunately that's based on data from this morning.Not sure what data WSI use to initialise that model but I suspect possibly 0z ECM. We can hope! SK EDIT: Looking at time stamps actually it may be 6z NMM (essentially a WRF-GFS)

Fairly big correction SW by the ECMWF vs 24 hours ago:

Sorry if I'm a bit slow to this, but I notice that Meteociel have now added the GEFS ensemble mean 10mb temperature (Sylvain - PLEASE add heights ) Very strong mean signal toward the end of the run for this: All pressure on the vortex is good pressure, though lets hope this isn't correlated to the position of any geopotential wave pushing - it would be just our luck to get a Wave 1 displacement from the USA over to the Siberian sector, and then 5 days later get a Wave 1 push from 180 degrees opposite and push the vortex right back over the pole! SK

Comparison from the last 4 GEFS: Notice the initial spike from yesterdays 18z around the 22nd with all that uncertainty regarding the slider potential (op and control included!) before slowly the mean flattens out through the day. Does this mean this is the final solution? By no means. But it does go to show how even at relatively short timeframes NWP really struggles with these situations where West meets East. For those newer members this was an almost 'known' bias of the old GFS deterministic run, and it appears that the shiny new GFS det. seems to continue this trend (the GFS ensemble suite also tends to struggle to model these situations, as is apparent from the above). Still a lot of marginality about it and a lot more twists and turns to come, but it's hopefully a perfect example of why nobody should be making any assumptions about any precipitation discrimination during the coming week. SK

Unfortunately the Euro4 is pretty poor for the whole region - barely any precipitation to show and dew points...well: We will need to hope for some nice surprises if we want to see anything wintry. I would say modelling has been wrong in these situations many times before, however the Euro4 did handle the situation this morning rather well at this timeframe. With regards the some of the previous posts re: warnings. At this stage there is nothing hazardous to warn about. SK

Latest NMM once again shows a mixture of rain/sleet/snow, and shows that there is unlikely to be much precipitation on the system by the time it reaches here: The good news is the bringing forward of the precipitation - with nocturnal cooling just helping to edge a few locations on to the correct side of marginal potentially. Dew points though looking really not very supportive - anything that falls is likely to be rather wet in nature and without some intensity accumulation seems unlikely: We await the Euro4, but hope for some surprises! SK

NOTHING is nailed on, whether it be for tonight or indeed in to next week...and that works both ways (i.e. no guarantee of rain or snow) Steve is pointing out the possibility via the modelling - as others have done through the day - but it's one of those situations (as ever!) where conditions are so marginal it will be a case of keeping an eye on all lamp posts through the early hours. Now just need to get on the phone to the council to persuade them to keep the lights on tonight... SK

Looking at the potential overnight in to Sunday - it does look rather limited. In terms specifically of this region, the best chance looks likely to be across any higher ground of Essex/Herts. This is shown up for tomorrow morning on the latest run of the Euro4 - which incidentally, as per the below, handled today's occlusion pretty well: The complication with the overnight potential comes from the slight mixing out of the colder air towards the surface layer as we see interaction with the disturbance running across the English Channel. This is best demonstrated by the 850-1000mb thickness profiles, compare the current situation: And then in to the overnight period: We can see that during this mornings activity we saw marginal profiles of around 1290-1300 to the North of London, hence more sleet/snow seen here, where as to the South of London we saw profiles of 1300 +, and so elevation would have been required for anything especially wintry. You can then see by midnight tonight the profiles show values well over 1300 (this looks due to a slight onshore flow at 850mb). However we seem to see a pulse of energy run through the system towards tomorrow morning, which brings precipitation a little further North in to East Anglia: This falls back in to profiles which would be more supportive of sleet/snow to the North of London once again: The only marginality question mark will be around dew points: Obviously not a high enough resolution output there to check for sure but we are looking at dewpoints around the 0-1c, though with intensity this should bring those values down a little potentially. There is only likely to be a rather narrow strip of the Northern edge of the precipitation (possibly only around 30 miles or so) that falls as snow, you can actually see this on the high-res GFS: If we break that down to hourly precipitation using the NMM, you can see that the precipitation by tomorrow morning will be rather patchy: So any accumulation may be a little optimistic. So if we bring all of that together, we can see why we have the Euro4 projection as follows: And as a conclusion I would suspect that if the precipitation does indeed make it to the North of London (which does seem likely if current modelling is correct) then the only areas I can really see getting anything more than sleet is the small area of elevation through Herts and Essex, which you can see to a certain extent here: http://upload.wikimedia.org/wikipedia/en/9/90/East_Anglia_%28circa_650%29.svg As the precipitation clears away, chased in by the colder air again from the North-West, we may see a short back-edge period of sleet/snow further South in the region, but beyond this, if face value modelling is correct, nothing too much to excite just yet. SK

Well I am sat in a car dealership just of the A120 at Stortford for the next hour whilst they do a software update on my car, I have taken up prime position right by the large window with a cup of coffee to hand and it has just this very moment started snowing - albeit rather lightly for now of course. Looking at some of the pictures over on Twitter just west of here I hope that will change to something a little more significant shortly. What better way could there be to spend a Saturday eh? SK

RE: stratPosted a couple of days ago about this so I'm glad that consistency has remained (I too have not had a chance to monitor inter-run consistency on this) However my fear with this, tropospherically, is how much energy around the Greenland locale gets left behind - obviously far too far away at this juncture to put any sort of accuracy on that given recent model trends to underestimate energy in that area (apparent even from events over the last few days) before correcting closer to T+0. But with a really rather disjointed vortex it really isnt taking much to budge it across to the Siberian sector - the wave 1 that appears responsible is not hugely impressive in scope but still manages to do the trick according to current forecasting. So a potential return to something a little more mobile whilst this transition takes place seems fairly likely at this stage. Im sure some members will be sick of people saying this this winter, but what we see the other side of this is the best potential for some sort of blocking based to our North-West for some time. Of course question marks remain on the transition tropospherically given the building Siberian high, and ongoing uncertainty (due to rather poor mid-term modelling) surrounding the progression of the MJO and any over-riding effects this could have. SK

More of a shortwave disturbance than a full blown low but a similar sort of idea - it does develop a closed circulation as it tracks beyond the meridian SK

Looking more broadly at the output beyond the aforementioned ECMWF track, Euro4 has it just scraping the South coast tomorrow: GEM has it further North but as rain: GFS actually doesn't have it at all on the 12z. And finally UKMO is something of a middle ground: When there is this much uncertainty at just T+30, it shows why anything beyond should not yet be viewed as set in stone

Hi Daniel, The snow around +72 is actually caused by the low tracking across the channel - the one tracking down the East coast dissipates (should read: disrupts) as it moves South. There is snowfall forecast tomorrow night from the ECMWF forecast so that is something to keep an eye on, you can make that out here too: Next event then Sunday evening: SK

That is Total Snow actually up until day 10, but it has all fallen by day 6/7 before becoming drier as the high collapses across us. Even for Stansted (a little North of the main zone) the projection from the meteograms are ~4 inches (10:1 ratio considered of course). But anyway, just a single deterministic run that we should not pay too much attention to just yet - even the weekend snow potential is still very much uncertain. I just posted to illustrate the point that the potential for some significant falls is always there is these type of scenarios. SK

That one is from WeatherBell SK

It should be noted that despite the complaints about the ECMWF 12z det., from a very selfish point of view for this thread, it was a very snowy run indeed for Kent, Sussex, Surrey, London, Essex and Southern and Eastern parts of Herts - as a one off I will post you a snapshot: The scale on the right is in inches, though it should be noted that carries a 10:1 ratio (probably a little optimistic) - but thats falls from 3 separate events. It shows that whilst everyone worries about what comes after +120, theres plenty of potential before we get anywhere near that, and after last winter I'm sure many would take this. SK

As ever sensible advice from Mr. Sussex. I mentioned briefly last night my niggling concern at the modelling of any remaining vortex energy around the Greenland locale (despite the overall movement of the upper vortex to the Siberian sector), and caution is advised because this is just one set of runs amongst a very varied suite of ensemble runs through today, but unfortunately in recent years (for some reason) if something is going to scupper any longer term cold potential it ends up being this. But before we get to any of that, plenty of snowfall opportunities to look forward to over the next 5 days, so not all is lost by any means - especially as we continue to see such a vast array of solutions. It should also be noted that despite the angry look to the vortex at +240, that big -EPO ridge, along with plenty of MLB around elsewhere still, means that cold potential is never far away. SK

I can't post the images alone up because I'm on my phone but this might help:https://twitter.com/wsi_euroenergy/status/555754301394796544 Fairly evenly split clusters but I like the look of the strongest cluster days 11-15 SK

I've always rated the GME... SK

That's certainly my take on it and I imagine by the time we get out to +360 it's just noise from the likely variable clusters by that stage (Nick L may be able to offer some clarity there) Whilst nothing is nailed shorter term in terms of the details, we know the overall theme is cold. As you say the suspicion would be a colder than average for much of the remainder of January, especially when you look at the stratospheric signal for a Wave 1 displacement at a useful angle from the US: Visible all the way down: It's not an especially strong event but as Ed and Tony (and of course our resident dazzling chart producer Andrej) have been saying, the vortex is very much on it's last legs following Ed's now infamous 1/2 SSW (I would look at patenting Diet SSW), and doesn't need much prodding from either direction to influence its location. The concern I have is the tropospheric modelling further down the line of remaining energy around the Greenland area, which has been notoriously badly modelled in recent years, but there's plenty of water to travel under the bridge before we need to concern ourselves with that. And as Tony has just said to me - the Alaskan ridge on the ECM control tonight would make very light work of any ideas the vortex has of leaving a little exit present around the Greenland locale. All in all plenty to be excited about in the shorter term, whilst the potential in the longer term takes the attention of those more seasoned members with memories of all the worrying and concern of run-to-run nuances for shorter term snow prospects - it's all too much to handle. SK