OldMetMan

I've been sitting back for a few days wondering if the models would do anything with the developing massive northerly blast developing E of Greenland but alas no. Although the overall 500mb has some noticeable troughing and significant vortices here and upstream, they are all too mobile at the moment, and with no mid-Atlantic ridge and associated HP there is nowhere for that Arctic blast to go but SW and feed yet more LPs. However, a couple of glimmers of hope as I see it now, there are minor upper highs forming just north of Scandinavia as well as off the Pacific NW which to my mind may indicate the mobility of the 500mb flow is slowing down a bit, to hopefully begin the process of forming a more static wave train. The models still are changing quite markedly even in the reliable time frame, well at least in terms of detail of LPs and where/when they will develop, so short cold blasts are entirely possible over the coming days. In fact, the GEM is slowing things right down in the long term with some pretty cold air being brought to us in association with the major and complex LP it is predicting by then. It is worth remembering that occasionally when cold air is being persistently held back from our shores by LP after LP running in from south of Greenland, a slow-down can occur over the US E coast with a more deeper LP forming, allowing the last in the LP train running across us to let,the cold air suddenly plunge S. I have seen this happen a few times. Meanwhile, remarkable mildness is with us for now. I don't buy the usual GFS stuff with endless LPs in the longer term because that is what it always seems to do, but keep an eye on that incredibly cold stream E of Greenland - it may yet turn out to not have been in vain from our point of view! Merry Christmas folks if I don't get a chance to say before then and many thanks to all of you for adding so many "likes" to my posts, that means a lot to me. OMM

Yes indeed TEITS, more logical. More so would be for the more northerly placed LP to get absorbed into the developing wave running E, but a much more W-E jet orientation. It seems the GFS at least is now taking more account of the strength of the cold air blocking - well for the moment anyway! By the look of the remainder of the run, the GFS has again gone bonkers so I will have no hesitation in ignoring it!

Very interesting that the Atlantic LP by T144 on the GFS has not made nearly as much northward progress into the cold air as previous runs. Jet configuration looks a bit different too, not so much of a northerly component.

Hi Frosty, It is certainly the case that I have described a number of different possible cold scenarios in recent days because we have quite an unusual synoptic pattern at present with which, as I said, the models seem to be struggling. Yesterday, I did suggest that this warm/cold struggle could go on for a while and that would seem to be the case. Historically, some notable cold spells, indeed cold winters, have been preceded by unusual mildness - 1981/1982 springs to mind or 1978/79 - but I remain convinced that the pattern of a low latitude jet and blocking european high are, to my mind, clear signals for cold, if not immediately, then in the not-to-distant future. It will be fascinating to watch the pattern shifts as time goes on.

I am continuing to be bemused by the bewildering variations in model output! Also, with each day it seems the reliable forecast time frame is shrinking! The plain fact is, we have a cold air block just to our NE so inevitably approaching fronts are going to occlude and trough E or SE. This is one aspect which all the models seem to be having trouble with. Furthermore, the jet is still below 50N and the northern stream is virtually non-existent, quite unusual. With this configuration, it's common in my experience for approaching LPs to not gain much latitude and to spiral off NW in the Atlantic and elongate as I said above by troughing. Also, each subsequent LP tends to do this ever further south as the cold block holds its ground. One other factor that is, in my opinion not be properly addressed by the models is that the depth of cold air gradually creeping westwards is increasing with 498dm thicknesses starting to appear over Russia.This does not suggest it's will be going anywhere in a hurry! I am most unimpressed by the model runs so far today because the synoptic development forecast from where we currently are simply does not look realistic, even in the fairly near term for reasons given above. So I'll see what later runs come up with. But it still makes for fascinating model watching!

Major shift in the surface pattern between 12Z and 18Z with the GFS, and that is before T180. That in itself suggests a high degree of uncertainty. Plus a NE moving LP as depicted earlier in this run is not something you would expect to deepen and rush E as shown. As I have said before, not a logical development!

As i see it, the models are struggling a bit at the moment. It is interesting to note that from what appeared to be a fairly straightforward case of the Atlantic systems seeing off any possibility of a cold air incursion, what is apparent now is that it may not be the case. Yesterday, I noticed one of the GEM runs had frontal activity stalling and a new HP building the E. Today, I saw the 00Z GFS bringing us some bizarre cold conditions and the UKMet seems also to be backing off somewhat with a more slow-moving frontal approach. I have also noticed a couple of things that are bugging me and which appear to have some bearing on whether the cold air will - eventually - make it. 1. There is still cold air advection heading W across Europe, courtesy of the large Russian HP. 2. Although it is not very strong, there still exists a 500mb high over Greenland. Now I know for a few days the GFS in particular has been amplifying the upper flow pushing some very mild air up over us ahead of deepening Atlantic systems but the runs are changing in a subtle way, with more trough disruption happening along each frontal boundary that crosses the UK. This has also been the case with some of the other models. I have been describing a number of scenarios whereby we could get a return to cold conditions, mostly because I have witnessed the kind of synoptic configuration we have now a number of times before and, although the battle between mild and cold had been quite prolonged at times, in nearly every case, the cold air has won out. Here's the 500mb chart for today: Apart from the Greenland high, the Russian upper high is still there and the jet is still low-latitude. With Atlantic systems predicted to turn NE pushing warm air ahead of them, this will, I think, help to maintain the Greenland high, plus it will also keep a meridional flow in place over much of the Atlantic and W Europe. In other words, it does not look the kind of arrangement which would allow a full scale over-run by the Atlantic. What I suggest is happening basically is that this warm/cold struggle will continue for a while yet. High pressure will be maintained over Greenland and over much of W Europe and eventually, either from the N or NE, a significant incursion of cold air will happen. I base this to a large degree on what I have seen happen historically. In particular, we need to keep an eye out for cold air starting to head S to the N of Scandinavia, such as suggested by the end of the last GFS run. All this could take a while as I said, but it will be fascinating to see how the models will handle it.

Yes, I agree about the GFS. What I find so odd about its continuity and logic is how it goes off at a tangent for no obvious reason. It's showing an entirely reasonable development up until around T180 - amplifying upper trough to the W, a slower moving LP drifting N over Canada and then suddenly whoosh, it destroys all the meridionality is about 48 hours! Assuming it is getting nearer the mark up until T180, that's a very familiar scenario - IF the amplified flow persists - for a HP build from the E or NE as the upper ridge builds NE. It's a big IF though but encouraging nevertheless.

Today's output continues to be irritating with its dithering! There are still basically 2 scenarios across the models in the medium to long term; one is the cold air E and N of us puts a brake on the Atlantic systems and two, the Atlantic systems just keep on coming. No one model seems to favour either particular outcome. Once again, let's look at what evidence we have at the moment as to which way it will go. The 500mb flow is quite revealing: First thing to note is that, whilst LP has pushed in for the moment, we still have an upper high over Russia that's been there quite a while now but, interestingly, we have a new 500mb high over Greenland that's been developing these past 2 -3 days. This should, at least for now, keep any LPs further south than they might otherwise go. I also think that this is one point in favour of us getting an easterly. There is still a lot of energy heading SE in the E Pacific into the US and, whilst the situation there is fairly mobile, I would suggest at some point, as I mentioned yesterday, a more slow moving vortex will develop, possibly over the E of the US. The LP shown by most of the models emerging from the US around T120 could well be the key to this development by deepening and slowing down, again as I talked about yesterday. Given that we already have a 500mb over Greenland at the moment, this deepening LP could assist in maintaining this. However, the models have other ideas and simply keep moving systems along across the Atlantic towards us and I do not believe that the essentially blocked pattern over the N Atlantic and Greenland is conducive to this, hence I believe we will see LP sliding away off the block, This is a pattern that is probably one of the most difficult for the models to get to grips with but I think there should be a bit more certainty within a day or two - maybe!!

Hmm, 18Z GFS looks reasonable up until about T180, then it goes kind of demented. The Nova Scotia LP is more slow moving in this run but at around T180, it would be logical to see a triple-point get caught in the jet and rush E. Instead, the GFS moves the whole works bodily E - not logical at all! Note too the appearance of a new HP nearer to Scandinavia, which the GFS, as you would expect, quickly dispatches. However, the small signs continue. Should make for some fascinating model watching the coming days.

That's a lot of thumbs! Thank you I appreciate it. Can't wait to see the 18Z GFS!

Thanks PP, I appreciate it. Nice WV satellite, never seen a hemispheric one before, thanks for the link! Yes, the US has been Pacific dominated for quite a while so maybe a change really is imminent.

I do think there is some justification other than wishful thinking as regards whether coldness is on the way, even though the model output of late has shown more than the usual false trails. I think we all agree on the low-latitude jet being one such indicator and I have suggested a few others. This entire year has been one of extremes - not that this in itself is indicative of a cold winter - but as someone who has witnessed some notable past winter cold spells, I remained convinced that we will get one this winter. Call it basically a "weather hunch"!

I have had a chance to review all the latest model output and it raises some interesting possibilities. First, a quote from the HPC Discussion: "ONCE DOWNSTREAM OF THE CONTINENTAL DIVIDE...MUCH OF THE FRONTAL WAVE ACTIVITY CENTERS ON A DRY...NORTHWEST FLOW PASSAGES ACROSS THE CENTRAL PLAINS. CONFLUENCE DOWNSTREAM INVOF THE OZARKS AND EASTWARD INTO THE CAROLINAS IS ANOTHER FEATURE OF THIS PATTERN AS A SUCCESSION OF PROGRESSIVE SHORTWAVES GRADUALLY CARVING OUT A DEEP TROUGH IN THE EAST." It was the highlighted bit that caught my eye. I have seen so many times in the past a tendency for deep and slow-moving LPs to form off the E Coast of Canada following a train of short-wave features which have headed out into the Atlantic, and this seems to be what this discussion is saying. If so, then it has major implications as far as we are concerned. The 12Z GFS shows that as the deep LP moving in on us slows down and begins to fill, a second low will follow and take up position to our west. So far, so good, seems reasonable as the WV satellite is already showing signs of this LP forming. Then, the GFS develops a secondary system forming to the SW of that, and here's where it gets interesting, as I posted earlier, as the secondary, as it gets to our W, is shown eventually as sliding SE introducing (albeit briefly) NE winds, before, in typical GFS style, mobility resumes. Here's the T183 image. What's so interesting is that yet another LP shown deepening near Nova Scotia seems to be developing as I mentioned above - into a large slow-moving one. Given what the HPC says above, it would seem to suggest that, rather than heading out into the Atlantic, the low slows down whilst further downstream, a mid-Atlantic upper ridge could form and thus we would come under European influence. Yesterday, I agreed with others bemoaning the Russian HP being stuck where it is, but if the above scenario were to develop, this HP might yet play an important role in bringing in cold air from the Continent, It might be worth mentioning here that there are some interesting similarities between the 500mb around mid-November 2010, and now. First, 15th November, 2010: Here's todays: What happened 2 years ago was a slow down in the flow over the US and an upper ridge building in mid- to central Atlantic which allowed a very amplified upper trough to develop over us to pull in all that cold Arctic air. I noticed another interesting feature on the 12Z ECM, which shows an intense HP near Hudson Bay in Canada, with its associated upper high, an indication of blocking. I think there are real indicators now of an impending slow down of mobility out of the US and hence downstream over the UK. As ever, these are still too far out to put much faith in this happening, but the signs are there. It is also worth mentioning finally that the pattern has been blocked to our E for some days now - these patterns do have a tendency to repeat.

Some early thoughts. I'm just watching the 12Z GFS roll out, and the story is keeping more or less to what it has told for a couple of days but with one important difference - at least so far - namely by T180 we seem to be getting a slider LP going SE into Europe, whilst off Newfoundland a big LP that looks strong enough to distort the flow and remain where it is. This would have important consequences on our side of the Atlantic clearly, by allowing pressure to build back westwards from the Continent. I expect (I haven't looked yet) that the GFS will just maintain mobility but we'll see. This could be a significant development. I'll have a proper look at everything later.

I agree, they are conspicuous by their absence. Got to be a reason - something to do with lack of certain types of upper air blocking.

True, it didn't actually provide much weather other than the cold, but it shows it can extend to our shores even from that position - sometimes!

Yet at the beginning of February this year, it delivered the goods, from more or less the same location. You never know!

Once again, the models are providing a bewildering variety of solutions, even in the short to medium term to some extent. I guess there is a certain amount of consistency between the different models up until around T144 with a LP dominated pattern but even here, the GFS in particular is changing run to run. I am finding it hard to believe that by T144 we will have yet another LP sat on us with its associated upper low. Looking back through the 500mb charts so far this month, one feature that caught my attention was the flow over the US and Canada has shown a tendency, especially over the past few days, for the broad upper trough to slowly amplify further and further S with systems moving SE from the Pacific NW. Further upstream over the Pacific there has also been more noticeable amplification. As a result of what's happening, it seems possible for this amplification to spread downstream. Already this has resulted in the southern jet over the US sinking well S before pushing out into the Atlantic, again on a low latitude. Further N, over N Canada all the way to Scandinavia, the jet is quite weak and fragmented. So, I would expect the main jet energy to remain well S for the foreseeable future. The GFS shows a new LP forming as the one approaching now starts to fill and it seems very unsure what to do with it. With the deep vortex over N America one would expect a certain amount of ridging developing ahead of it as I mentioned before and another amplifying trough ahead of that in the W Atlantic. In other words, we could see the flow amplifying across the Atlantic to Europe. With so much variation in the models beyond T144, I think we need to concentrate on changes in the runs only up until that point (even more than we usually do), especially around the T120 to T144 period because what happens with that 2nd LP will show, I think, whether there is going to be a significant change in the upper flow. If this amplification pattern develops, and blocking starts to develop, then I still believe this would give a real chance for pressure to build across to the N of us, as the remains of the LP near us sinks away to the SE. Meanwhile, the large Russian HP does now look too far away to directly affect us, but its mere presence at this point in the winter signifies to me that it may well redevelop and quite soon. Only if and when it does, we could see its influence. The critical thing as I see it at this stage is to watch for any amplifying trends upstream. I see the 18Z is coming out so it will be interesting to see what new variation it comes up with this time!

I agree this LP will be swilling around for a few days and, while I freely admit to being an eternal optimist and am willing to stretch credulity sometimes with the things I say, this has been such a highly unusual year as have the patterns this autumn and winter so far. In my view, this is why there have been such massive swings in model output recently as they are having a hard time really getting a handle on the developments. Get your sledge dusted off for January!

Yes I think so, while the HP persists, the air is growing colder anyway as we move towards January (temps below -30C kind of thing) but the thickness charts bear this out. I know an awful lot of things need to happen for this to take off but I remain convinced that we are entering that "kind" of winter with some significant blocking at some point. Goodness knows we have had enough LP dominated weather this year! Time the hP got a look in.

The run to run model variations continue to intrigue today. Two things again are, I think, of special interest in the longer term; the low latitude of the Atlantic jet and the big, fat HP over N Russia. I have also noticed small shifts in the location and complexity of the big Atlantic LP - like I said yesterday, I think the actuality of it may be somewhat more complex than the models can detect at this stage, with still, I think the possibility of a triple-point LP developing by the time the frontal zone gets across the N of the country.. I am just watching the 18Z GFS roll out and I am thinking what I thought earlier with the 12Z that there are continuing indications of rising heights out of N Russia westwards across to Greenland. Also, the 18Z is developing a new LP off the coast of Newfoundland by T120 and I think this could indicate the start of a more pronounced distortion of the 500mb flow, namely a more amplified pattern from the US eastwards. If the Russian HP is to have any effect on our weather in the days to come, I think we need to see that kind of development - a deep slow moving LP off the Canadian E coast or somewhat further E, that would become the dominant upper low feature over the Atlantic, so that our own LP will disrupt and allow pressure to build W and SW towards us, It is interesting to note that the GFS, by T144 has HP extending all the way from N Canada to N Russia - that's got to mean something. From this point in the run, I don't think it wise to give much credence to the developments, in fact even less than usual as recent days have shown some wild variations. Having said that, the JMA model's latest run is showing the kind of development I am talking about: I think what scuppered the chances of colder air arriving by now was the strength of the Atlantic jet and the models suffered much confusion over this. But one thing that has persisted from run to run over a few days is that big Russian HP and while that is still lurking, I sense there is a high probability of a more stable blocking pattern setting up and consequent arrival of cold air. All this, of course, is highly dependent on what happens on the other side of the Atlantic in terms of jet strength and direction but, at this point, the upper flow orientation has a distinct look, one I have seen before ahead of cold spells in the past. All in all, I think the outlook is very promising for cold fans so be patient if you can and don't set too much store by the model to model and run to run variations. I think we may see some memorable weather in the coming weeks.

I felt I had to comment on the 120H FAX chart: Not only is the jet running VERY far S, but the Russian HP is still as strong as ever. This looks more like it to me - the big LP will swill around for a while but ultimately HP will I am sure take over. It looks as if any emerging jet from the US, from that point on, will be much more likely to track on a low-latitude course. Very promising.

Well, after so much dithering amongst the models for so many days, they now seem determined to bring the Atlantic LPs our way. Even at this quite close range, more or less within the reliable time-frame, I am still finding it hard to accept this solution after so many different variations in recent days. As I see it, the main problem seems to have been determining the development of the US jets, which now have combined and, together with quite a vigorous short-wave feature running across Newfoundland at the moment, and a tight baroclinic zone, are producing the rapidly deepening LP which they predict will push aside the cold air over the UK Previously, the models have been showing a more separated jet arrangement, with a weaker northern stream, and with the southern one bringing a less active LP on a more southerly track. Hence all the different evolutions we've seen especially from the GFS. However, on this side of the pond we still currently have an intense HP over N Russia, plus quite a respectable one over Greenland, together with quite a persistent upper trough over W Europe. I think what I am finding troublesome about this developing LP is that, if it deepens as much as predicted, which is entirely reasonable, this will leave us with, not only a large 500mb low over much of the US, but now one covering most of the central Atlantic, so I don't think it impossible if heights were to rise over the N Atlantic and Greenland. So we could end up with a very broad trough from the US to the central Atlantic, with the jet heading even further S, plus a sizeable upper HP to our N - a good receipe for a significant cold air incursion. For now, what I think we could see is maybe a triple-point LP pushing ahead of this deep LP, together with HP being maintained to our N, so that eventually cold air will come S at us, as the Atlantic LP fills. This may take a while - it's a shame the Russian HP is that far E else it may have happened sooner - but for now, I still believe the end of the week will not be as straightforward as it appears at the moment. So, don't lose heart, cold fans, I am convinced it's coming (well it is here now I suppose) but we may see a "proper" NE or E flow in the next few weeks.

Thank you PM, much appreciated.