OldMetMan

Great picture! Yes, I could see some VERY low DPs earlier over N France. How frequently are these plots produced only it would be fascinating to watch it progress.

You're right there! Rain here is heavier, BUT I think there are a few snowflakes in it. Hard to tell, we've had our street lighting replaced recently to these dazzling white ones. The old amber ones were much better for spotting snow. I'm convinced now that my electronic thermometer is reading too high, perhaps as much as a degree. Pressure is falling steadily too.

I am finding this remarkable. I can't recall ever seeing snow developing in this way - and that's saying something!

Yes! I must say though that I cannot remember a situation quite like this in 45 years of weather watching - hence my scepticism! Temp still edging up here - 3.4 - and the wind is picking up. But the rain is easing.

Sorry Uncle Barty, I haven't been back to look at earlier posts.

Thank you lancs_northants, not sure about the knowledge but I appreciate the compliment! I have followed the weather since 1967 so I guess I do have a lot of experience!

Quite agree, hence my original questioning of the Met O warning. Dec 2010 was exceptional and winds were largely offshore, the airmass had very low thickness values, 516dm which is pretty remarkable for December or any time in the winter for that matter. But I take your point. I used to live on the IOW and have seen some strange things during snow events, such as snow, followed by ice pellets (frozen raindrops) and then back to snow again, with short spells of rain mixed in. It's all most interesting to follow that's for sure!

Yes, that's very interesting. Let's see how it progresses!

Yes, I've posted below what I consider to be the reasons for the Met O's confidence in there being snow everywhere, I thought it unusual. I hope for all us "coasties" that they turn out to have been justified with their confidence. But I'm long enough in the tooth to remember many past snow non-events so I am always somewhat sceptical!

Hi GTLTW, this is what I found puzzling about the MetO weather warnings, they are normally at pains to exclude the coastal strip if there is any uncertainty about if it'll be rain or snow, so I was trying to fathom the reason for their confidence! As I mentioned, they seem to be putting their faith in colder air being drawn in from France on the strengthening SE flow, OR it could be that as the frontal zone approaches with a triple-point LP forming, then winds across our area will turn ENE, maybe even NE thus bringing us a land track, rather than a sea fetch. But to answer your question, I shall be very surprised if immediate coasts from the IOW westward get anything but rain. But it is so finely balanced. A few miles inland it could be a different story. I notice on the latest surface obs from the N French coast, although the temps are above freezing, the dewpoints are sub-zero, so as the gradient increases, there may be less chance for the air to pick up heat from the Channel. I shall be watching temps closely throughout the evening to see how things change. But I am not getting too excited until I actually see the snow!!

I agree Chief, I'm actually quite surprised at the confidence of the Met in including all coastal regions in their weather warnings for tomorrow. It's been raining here in Southampton on and off for a couple of hours, temp 3.1 (that could be half a degree too high) with 86% humidity so dewpoint around 1deg. Admittedly, temps are pretty low over N France and the Low Countries and our point of view here on the coast, with SE-E winds picking up, it MAY pull in some of that colder, drier air. There's too much cloud for any nocturnal cooling so I guess the reasoning by the MetO is that cold continental air. Past experience has taught me that fronts moving into our area from the W or WSW rarely bring snow to the coastal strip UNLESS the air is exceptionally cold, which it isn't. I saw it snow once here in December 1981 when the temp was around 4deg but it has been VERY cold beforehand. I think it will be interesting to see what happens later when the wind picks up but I'm not holding my breath here as there have been too many snow non-events before.

Quite agree S4. One other factor to consider is the actual strength of the front itself so it's possible the precipitation could fizzle out quite a lot the further E it gets. I'm in the same boat geographically as yourself so I am not pinning too much hope on Friday's system but yes, there sure looks like more of the same in the coming days.

Some very interesting days ahead! However, a forecaster's nightmare for sure, as they agonise over the eastward extent of snow for Friday, and indeed beyond. I said the other day that I thought the overall circulation pattern looked anomalous and there are features at 500mb that do, I think, favour a rather longer spell of cold that looked likely earlier in the week. The most interesting feature I think is the building ridge heading up the Norwegian Sea, helping to solidify the surface HP, together with the amplifying upper trough extending further S into the Mediterranean. It has taken a while for the models to come into reasonable agreement that approaching fronts will occlude out or for triple-point LPs will form and slip away SE as that formation gradually developed. The real dilemma lies in deciding how far E this process will happen, which quite unusually is causing the Met Office to be ambivalent only 48 hours out from the event. At 500mb, because of the above configuration, there is much more of a NW/SE component to the flow over the whole UK rather than a W/E one, at least for the next few days, so looking at the latest 12Z FAX charts, I'd say the placement of the frontal boundary for Friday's system looks pretty reasonable. Beyond that, the uncertainty increases considerably. The strong jet out of the US/Canada is not showing much sign yet of propagating E as the GFS has been saying for some days and my feeling at this stage is that it will gradually do this but at a more southerly latitude. There have been strong hints in the GFS for more decisive pressure rises building further W to the N of us in the mid- to long-term, although today's 12Z has once again reverted to zonality as it so often does. The 500mb flow gives me the impression that heights will build significantly further W across Iceland and Greenland bringing about these pressure rises. So, I think we face some very interesting conditions, perhaps a more vigorous LP early next week may warm things up slowly for a day or so but then rising pressure will bring back colder air once again as next week goes on. We have ideal conditions for some significant snow Friday - several very cold days preceding it so the ground pretty well frozen - that together with a slowing frontal system could well dump a fair amount of snow. Not to sure how coastal areas such as where I am will fare. I would have preferred a more SW approach than a W one as a wind off the sea could turn it all to rain. Nevertheless, I am becoming convinced that we are going to see model output stretching the cold spell out longer as time goes by. It's all going to be really interesting to watch!

Simple answer is no-one know for sure! The model output itself is confusing and contradictory. Yes, a few more days of cold seems likely, but the difficulty lies in whether the cold block will hold firm under the onslaught of Atlantic systems or whether it will simply collapse bringing in milder Atlantic air. By mid-week we might have a clearer idea - might - but these kind of situations are often very difficult to forecast. OMM

Much depends on where the frontal boundary lies. Anywhere N of such an occluding frontal zone could see snow but S of it with a fetch from the S or SW off the sea would be somewhat milder, so only rain would be likely. Similar to what happened today with the E/W split between rain and snow but a N/S split this time. OMM

Fascinating model watching today as each grapples with the fate of the cold block. Rather a sharp temperature contrast today across the occluding front as it slips south, and this process seems to be the pattern several of the models favour in the days to come as approaching fronts slide away SE. The GFS and GEM are showing a partial block collapse at least - but I am amazed at what looks like a pretty weak upper high still shown to be there even by the end of the week. The 500mb flow and the associated jet is very revealing: The jet in particular, by its current orientation, suggests that most of the energy will head NE, not E. Indeed, as I suggested yesterday, we could end up with a distinct split stream to our W with fronts occluding out and slipping into France. I am surprised by the UKMet showing a deep LP out in mid-Atlantic with marked troughing over the S of the UK, suggesting a slow-moving occluding front somewhere over England - classic prolonged snow territory this is, well, for some at least. I am surprised because I thought this model would follow the GFS and destroy the block. The other extreme is shown by the ECM with fronts being kept well back. The small 500mb high has been gradually shifting E to the N of Scandinavia and if the jet energy does indeed push NE it could well maintain this high or cause a reformation further W, while at the same time, small short waves feed into the Mediterranean upper low, thus keeping the block intact. At this stage, I would favour the UKMet as being a happy medium so the extent and location of snow would most likely be north of the Midlands. This is a very interesting type of synoptic development to watch unfold, indeed it has been one that has featured in the notorious 1947 winter but with the S of the UK bearing the brunt of the snow. Fact remains, the upper flow is very distorted and meridional right now. It is tempting to say that maybe heights will rise and link up right from Scandinavia right across the Pole to the Bering Sea and the NE Pacific ridge!! The Canadian vortex is gradually sinking S after all. Some model predictions are showing rising pressure over Greenland, so we just need a stronger HP to our N, plus that all important feed of new cold air coming into Europe. It's a lot to ask for I know but something looks quite anomalous in the flow right now - something conducive to cold.

Just out of interest, these are the kind of max temps currently across Europe, not excessively cold until you get to Poland although Germany has cooled down a bit in the last few days. I think this highlights the difficulty in the next few days of determining where, or indeed even if, the snow will fall. Successive model runs have increased thickness values over the UK. Overnight Monday/Tuesday would be my best guess for any significant snow, but in these situations it can sometimes happen that a trough, even a small LP can move W in association with the lowest thickness values.

Looking at later runs, I can't add that much more to what I said this afternoon, apart from the fact that the longer term model solutions are even more varied. One thing of interest is the fact that the GFS are still keeping the Scandinavian block in place, in fact are even intensifying the surface HP right out to T180, presumably in answer to the intense Atlantic LP it is predicting by that time. Thereafter, it goes a bit mad with raging Atlantic storms blasting all cold European air way back to Russia. Overall, the 500mb pattern is looking a lot more amplified than it has for a while, and I am more inclined to think that the powerful forecast jet will dive ESE or SE, as the earlier GFS run suggested or perhaps even a split stream with more energy heading NE as well. In that event, I think blocking would be more likely to be maintained, maybe the upper high reforming further W near Iceland. It's interesting too that the latest FAX charts are showing quite a respectable HP to the NE and developing LP coming from the US and Canada looking more like it will head NE. Lots to keep an eye on in the coming days!

If the Met Office Cold Alert is anything to go by, then we're in for an interesting week ahead. As per usual in these situations, the models continue to disagree and change significantly from run to run. The LP just starting to head SE across us presents a very difficult forecasting problem, and I have been following with interest the model predictions. In particular, one thing strikes me, namely that the LP is embedded in thickness values of 528dm or below which, in theory at least, should allow for the possibility of snow almost anywhere. In practice, the further E or N you are, then snow would seem more possible, but with the UKMet showing the occluding front wrapping around the centre as the low heads out from the SE of England, then when the NE flow sets in, THEN I think the snow risk increases significantly across much of the Midlands and SE. Looking further afield, the still rather weakish block we have is being kept intact for a least a few more days by most of the models. I noticed the GFS in particular is wavering about whether the strong jet forecast to emerge from the US later in the week will head SE or whether it will turn more NE. I think much depends on how entrenched the cold pool over us and W Europe becomes. Yesterday's GFS gave an interesting scenario of a new deep Atlantic LP associated with this jet developing a triple-point which runs SE along the Channel or N France. Again, much depends on the depth of cold here but such a development is, historically at least, a real potential for some widespread snow. I am not very confident in the persistence or intensity of cold this time around simply because the block looks pretty fragile, but, as I mentioned in my last post, if there is a fresh influx of very cold air heading down across Scandinavia in the medium term, which was actually shown by the GFS yesterday, then I would feel more confident. I hope later model runs might help clarify things. Meanwhile, there will be much to watch in the next 48 hours!

First real taste of winter is on our doorstep so, setting aside the media hysteria talking about prolonged Arctic conditions for a moment, what are the realistic prospects for the coming days? The 500mb flow has some interesting features: The first significant feature as far as cold prospects are concerned is the closed upper high over the Norwegian Sea, which has developed over the last couple of days. Not very strong admittedly but it will help to maintain HP to our NE, also not that strong, but sufficient to filter in colder continental air. Further W, a large and complex upper low, with centres off Nova Scotia, and the main centre over Hudson Bay, with a short wave to our west slipping SE. Further W still, quite a strong upper ridge of the US W coast is an unusual placement compared to what's been happening there for some time past. The jet situation is also curious with much of the central and N Atlantic having weakish streams, with a modest flow around the top of the upper ridge, with the strongest jet coming out of SE Canada and heading SE Together, these 2 configurations would seem to support the general model consensus up till around T120 or so, fairly shallow short-waves running SE across the UK, pressure rising to the N (at least for a time) following these maintaining a gentle E flow over much of the country. Beyond that, the GFS begins the LP train once again, the ECM and GEM build pressure from the SW - again. From a purely historical perspective, that sort of development is not one that looks very likely. The current blocking pattern is our area is not a very strong one, and the air coming W at us is not that cold, thicknesses only just below 528dm. Yes, there IS a snow risk here, probably most likely over the E and SE, in the short to mid-term but for the longer term, unless we see a fresh influx of colder air into Europe, or a stronger HP building to the NE and to the N, there is not much to suggest a prolonged spell of cold - well not yet. As I said, HP building from SW again in the longer term just does not look realistic, especially as we have just had such a synoptic pattern. The 12Z GEM at T144 presents an interesting scenario with a resumption of LPs heading our way BUT being steered on quite a southerly latitude and running SE into Europe, the cold air would still be present over us so again, that would carry a more significant snow risk. If the weakish jet over the Atlantic persists the cold air could hang on into next week and beyond. I am wondering if the Pacific upper high might induce a more static wave pattern downstream. But meanwhile, I think there will be much model ambivalence as to how this cold will resolve. I think what needs watching is how persistent the upper high to our N is, and whether the 500mb wave pattern becomes more slow moving. Once again, I am reminded of how fleeting HP over the UK has been for so long. Meantime, enjoy the next few days - at least some of you will see some snow!!

Some remarkable long-trends in recent days, mostly with the GFS. I have been waiting for the 18Z to see what new variation would occur. It seems to me that the development around T120 is proving hard for the models to get a handle on, particularly the large, slow-moving LP E of the US. Earlier GFS runs in the last few days have shown this swirling around and not moving much, On this basis, warmer air and an upper ridge kept being shown building N, setting the scene for a blocking pattern with very cold air sweeping SW across us. Not so now, however, as today's GFS runs are bringing LPs back in from the NW - no sign of any significant blocking. At present, there seems little to support any real cold - yet - apart from the short burst of NE winds over the next few days, mostly a cyclonic flow with a weak HP to our NE. We do still have a weak upper ridge across us. However, in spite of the above, there are some signs that the pattern is changing, notably the Atlantic jet is becoming quite disorganised and it's hard to see where the main jet energy will be - that suggests an opportunity for HP to build across the N Atlantic. The ECM and GEM are still showing cold in the longer term, but overall I don't think any of the models look anywhere near realistic from the mid-term onwards. Tomorrow's runs may revert to the cold theme once again. The key feature to watch is that large W Atlantic LP, and the big upper vortex associated with it and to see if there is any sign of heights building to the N and NW of this.

I've been watching some remarkable GFS long-term charts in runs over the last few days in terms of icy blasts. But as ever, it reverts to westerlies again in some of the most recent runs. However, that said, there are some very interesting possible scenarios based on where we are right now. Firstly, there is a reasonable consensus across the models until about T120 for the current surface and upper ridge to decline - BUT with a vigorous LP forecast to develop off Newfoundland in the next few days. it looks entirely reasonable for the upper ridge to reform to our west this time and for surface pressures to rise in association with this. This is where the models come up with a complicated variety of solutions beyond T120, some showing HP building to our north, and a rather vague, slack LP field over W Europe including the UK. They DO seem to agree on the LP of the Canadian E coast slowing down and for the situation to take on a much more blocked configuration. Looking at how it is now, the large upper vortex over NE Canada has retrogressed slightly in recent days so it looks highly plausible for a significant upper ridge to form central Atlantic, perhaps even a closed upper high forming S of Greenland. Most of the jet energy at the moment is heading SE out of the S US towards Spain. But there is an interesting jet heading S out of Scandinavia towards the Mediterranean which would, I think, favour LP development along it, which would subsequently draw in some very cold air into Europe. If the upper HP develops to our N or NW then we could indeed see some really cold air heading our way in the longer term. The signs are certainly there - once again. There will doubtless be a great deal of dithering about from the models in the coming days though!

Happy new Year folks and hope Christmas was good for you all. 2013 is starting in benign mode, for quite some days ahead by the look of it and, as I said late last year, we are so overdue for some extended, quieter HP dominated weather. The models seem quite consistent in the short to mid-term but go a bit mad thereafter but just some early thoughts on possible evolutions to the pattern from where we are now. My first thought is that the axis of the upper ridge developing over us is that it is well placed to retrogress over time - there are some hints of this in the model output - but, at the same time, the ridge itself does not seem to be gaining much amplitude and thus, as the models suggest, will be subject to erosion from Atlantic systems. On a broader scale, the upstream pattern is quite interesting with broad upper lows from mid N America to just E of the UK, also covering much of the Pacific, with a smaller ridge over the US W coast. Overall, this suggests to me a more static wave pattern in the longer term but again, on the other hand, there is still a LOT of jet energy heading out from the E US. The GFS in recent runs has shown a complicated variety of longer term solutions, mostly on the cold side, but none of the models I have seen to date seem to have any sort of consistency in how the HP near us will change in the longer term. I mooted this a while back regarding the current evolution in that a stronger upper ridge building across and to our N could place the surface HP to our N also but it didn't happen this time. However, I still think the possibility exists in the longer term, which has been shown on the GFS at times, thus pulling in colder continental air.. But at least until mid-term I think, we seem likely to suffer a rather slack SW flow with weak fronts wobbling E at times with pressure staying quite high. However, we need to look for any upstream amplification with the main upper vortex settling over the W to central Atlantic, thus aiding a stronger upper ridge near us. I think the GFS longer term outlook will be particularly interesting to see if it maintains the cold theme. Personally, I still believe from mid January we could well see winter arriving in earnest.

I would say there are a few signals in today's runs that suggest that we have the potential building for some January cold. There seems to be a consensus developing in the mid-term amongst the models for a strong HP to build from the SW over us but those kind of situations can hold a lot of cold potential. This 12Z ECM chart shows what I mean: This type of configuration has many times historically developed into an easterly or NE'ly as the upper ridge pushes NE and a cold trough digs in beneath it, SW towards us. This is not what the ECM is showing in this run, but it can and does happen. A few other hints - apart from the US blizzards currently ongoing, there are signs that the polar front may finally be taking a more northerly track across North America rather than crossing centrally and continually sending LPs in our direction. The HPC's 7 day forecast charts show just this. This would be advantageous to the ECM situation shown above as LPs taking a more northerly path would help maintain the upper ridge. Presently, the jet has quite a contorted appearance having been not that strong and fairly flat, at least on our side of the Atlantic, which is a bit odd considering the lively weather we've been getting: I think we need to see this N American northward jet movement happening before drawing too many conclusions. In any event, as I have often said in recent times, the presence of strong HP near the UK has been conspicuous by its absence for so long now - at least anything that persists more than a few days - and the mobility has been excessive.It always balances out eventually. It will be most interesting to see how the models handle this HP build as we get nearer the time. Doubtless there will be many mixed messages, especially from the GFS, but, even at this stage, it is worth considering the possibility of the "right" kind of blocking. I said a while back that there would be a battle - yes it's a full retreat by the cold at the moment - but I have a strong suspicion that will all change in January!

Merry Christmas folks, I hope it all went well. The models are not feeling festive and it's hard to find crumbs of comfort for the cold seekers. However, there are some subtle changes taking place over N America that could signify a shift in the pattern. At 500mb, there is some re-arrangement of the upper pattern with the persistent upper LP pulling back further into the Pacific from off the NW US coast, more of an upper trough digging down over the SE US and an upper high cell gradually moving E across N Canada. I am wondering if it will continue eastwards towards Greenland which could have some bearing on us. The persistent upper vortex off the E coast of Canada is once again spawning a new vigorous short wave whilst downstream over the UK the upper low that has been nearby for a while has lifted out so it does seem that the model prediction of a major LP pushing warm air over us in a few days will likely happen. Interestingly, the models lift out the corresponding upper vortex quite quickly in favour of a continuing zonal flow. I am interested in this shifting upper high though as it hints towards blocking near Greenland or a little further east, This raises the possibility of an extended upper trough stretching westwards across the central Atlantic and, as I mentioned before, maybe a LP pulling in the cold air to the N as the trough heads S. There are some small hints of this on some of the models, such as the GEM and JMA. Yes, bit of a long shot for sure but I still do not think much of the long-term pattern favoured by the GFS and these small changes I mentioned could turn out to have some significance in the long term. See how the next runs turn out.