OldMetMan
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Posts posted by OldMetMan
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I think it worth mentioning for everyone glued to the model output that, as things develop this week, it would be a useful addition to include watching the satellite imagery.
On this occasion, with the forecast low developing way south, the GOES-East images, accessible from the National Hurricane Centre web site, provide a variety of detailed pictures and animations.
http://www.nhc.noaa....satellite.shtml
If we are to get this storm, then there will be tell-tale satellite features that might indicate it's possible intensity, for example, the baroclinic leaf feature of lows that are likely to deepen rapidly, that is, an anticyclonically curved arc of cloud that appears north of a rapidly developing centre.
It is also useful to see where the main baroclinic zones are; judging from the UKMet forecasts, we seem to be seeing a merging of 2 zones in the forecast up until Friday, with a somewhat complex frontal structure. There appears to be 2 jets already involved looking at the latest satellite, one coming across Canada, the other heading NE from Florida. This is another arrangement that favours rapid low development. No doubt the models are picking up on this already.
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I love the way it doesn't go below 950mb! i wonder how low that is!
The density of isobars makes it difficult to see, but it looks like 920 something millibars!
I think it must have blown a few fuses on this run!
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Here is a sequence of forecast charts from the NOGAPS model which shows an interesting take on the predicted Friday storm.
NOGAPS depicts it as a much faster moving system and takes it eastwards rather than NE. Note the extreme gradients on the southern side, plus the addition of a secondary low to the west of the main centre that effectively prolongs the period of maximum pressure gradient.
If this scenario plays out, then the south of the UK would be worst hit.
I know that NOGAPS tends to be dismissed here as not much of a model, yet I have seen it perform pretty well sometimes in the 5+ days timeframe. I just hope on this occasion it lives up to its unreliable reputation, for all our sakes!
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I'm in general agreement with you, OMM, but with one qualifying point. The core of the jet is forecast to be coming from an almost due westerly point across the Midlands on Thursday/ Friday rather than its usual steering trajectory from SW to NE.
The low approaching for Tuesday has been shifted gradually north/ north west on the models and the jet is firmly recurving northwestward close to north west Scotland.
If the fearsome looking jet core on Thursday/Friday maintains its current track would not the tendency be for the centre of the low to be steered on a more due westerly course, rather than the more usual north westerly?
Hi Terminal Moraine, thanks.
You could well be right, I am basing what I say on what Ihave seen happen in the past. Lows of such intensity as forecast distort the upper flow considerably, and it is a well known phenomenon that rapidly deepening lows always turn to the left as they deepen.
What is clearly critical to the storm's path is exactly when and where the rapid deepening occurs. If that happens well before the storm approaches our shores, then it may well turn NW and perhaps only the N and W of the country will be worst affected (looking at the newly issued Met O warnings, this seems to be their thinking at the moment).
On the other hand, if the main deepening happens later, as the storm is coming into Ireland say, then yes, a more westerly track is entirely possible. This is more or less what happened on Thursday last, the track of the low being to the N of Scotland with the isobars squeezed along its southern flank.
In my experience, there are 2 main types of situations where a core of extreme winds can form around a low; one in a warm sector where the pressure gradient is squeezed ahead of the associated cold front (as happened in October 2000 for example) the other as happened on Thursday with the main action happening after the frontal zone has passed through. (the Burns Day storm I mentioned is also a good example). Such extreme gradients tend to be on the southern (SW or SE) flank of a low.
As far as the models go in handling this storm, there has been a remarkable similarity between individual runs of each model, plus a consistency between the different models themselves. Personally, in this situation, I would be more inclined to trust the UKMetO output which during today and tomorrow will begin to show what the GFS/ECM are now showing.
In any event, I would suggest that from about Tuesday/Wednesday onward, all the models should have a pretty good handle on the ultimate track and intensity of this storm. Until then, an awful lot could change.
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Given that the models are still sticking to the Friday storm, perhaps it's worth considering this forecast in an historical context, compared to other major storms in the past.
In my experience, lows coming from the forecast direction that are deepening rapidly have always curved to the left, so from this point on I would expect the projected path to take a more NW route and take the strongest winds further north.
Of course, the one major exception to this was the October 1987 storm, but that was a rapidly developing secondary low, not like the Friday one.
On the other hand, there is the famous Burns Day storm in 1990, but on that occasion the low came in from the west and the south of the country got hit worst. I also recall a major storm in January 1976, when I was weather observing for the Met Office, and I clocked the highest gust at the station I was at, of 82Kts. That again was a low coming in from the west.
Everything depends on where the major deepening occurs for this predicted low. At this point, I'd say the models are looking feasible. But we have to keep firmly in mind that this is an extreme event being forecast - and a LOT can change in the meantime.
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Here's NOGAPS 18Z take on this forecast storm. I find it remarkable that the models are in pretty good agreement so far out.
The jet forecast for the end of next week is also impressive - >200KTS if I am reading the colour code right.
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I hope you dont mind me asking this question. I am a lurker that posts now and again but with the informative help of JH and others i wated to ask this question. At what point could if as models are forecasting at the moment could this system on Friday be classified as a hurricane? the mb are dropping and dropping and would surely mean a sustained wind speed close to that would they not?
Hi Jimmy, hurricanes and mid-latitude depressions are completely different beasts. Hurricanes are tropical in origin, form over sea with high heat content and their structure is convective, i.e. large areas of thunderstorms plus their evolution is different from the lows that we experience. Low pressure systems that we get form along frontal zones where cold and warm air meet.
The only comparison you can make is clearly in terms of wind speed. Hurricanes are usually classified as such when the mean wind speed reaches or exceeds 65 knots. For that to happen in this country as a result of an Atlantic low is pretty rare - last Thursday saw it happen for a time in some areas of Scotland. If the model development shown verifies then we could see hurricane force winds over parts of the UK - all dependent on the exact track of the low - but this does not make the low a hurricane.
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Before we get to the main event Thursday, Tuesdays weather is notable enough in itself. Always like to think of this as energy disapating and since it is December this might have an impact on the type of weather we get later in the winter.
This is a very good point - we saw the effect of a weakened jet last winter after the autumnal LPs fizzled out . I have noted in the past that particularly active phases of winter depressions crossing the UK have sometimes resulted in blocking of the cold variety. Often the transition can be sudden.
I shall be interested to see how soon the UKMet start issuing advance warnings for Friday. To their credit, they were spot on with last Thursday's warnings. Today's 120H chart from them will be worth noting.
Even the NOGAPS model is picking up on Friday and it's not generally very good at picking up trends that far away. Obviously, the exact path of the storm will be critical when it comes to determining the areas most likely to experience the worst of the winds. It is interesting to note that this forecast low is developing at quite a southerly latitude over the W Atlantic and would therefore carry very warm air with it. That in itself adds to the probability of it being particularly intense.
Think I will get my camcorder at the ready - might see some rare weather this week!
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The last 2 GFS depict an interesting, and somewhat unusual pattern of development. Now that the Atlantic LPs seem to be pushing through unimpeded, even if pressure is still relatively high over the south, the development shown by those models would seem quite possible, at least in the short- to mid-term, with LP taking progressively more southerly tracks, extending the upper trough to the NE and E further and further S into Europe, and consequently bringing down thickness values over the UK.
The 06Z GFS end of run shows strong HP taking up position mid-Atlantic, a scenario I suggested might happen some days ago, and if the upper trough to the E does amplify as shown by the GFS, then that seems a distinct possibility. Thereafter, a more amplified upper pattern might allow LP to provide the UK with some northerly bursts - of course, that's a long way off.
Just something to remember, in a situation of LP tracking progressively more to the S, the cold air usually wins. This has often happened in the past. What is in doubt is whether this involves a setting up of a more static upper wave pattern, which, given the mobility and energy shown over the Atlantic right now, doesn't seem very likely to me - yet - so any cold would be short lived.
Having said that, last November switched very quickly from a mobile to static pattern in a very short time prior to the intense cold starting. I'm not suggesting a repeat of that I hasten to add, but, as I have said before, if such a situation is to evolve, watch for very cold air accumulation, and associated HP, to the N or NE. I shall watch subsequent GFS runs with interest to see if the development it shows is maintained.
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With the European block still hanging on for now, it looks as if this will finally break down soon according to all the models.
Others have mentioned the tropical disturbance(s) getting swept up by the Atlantic upper trough and jet next week. This would be a very rare event if it happens, I don't recall this ever happening so late in the season. I think it should be carefully watched as it has the potential to produce a very vigorous LP. It would also serve to re-inforce the warm ridging to the E and SE of the UK - for a time at least.
Beyond that, I still suggest that we may see the block retrogress from Europe with the main HP in mid-Atlantic and the models have been hinting at this. In my experience, it has happened many times in the past; a SW flow changing to NW with the associated risk of a northerly blast as LP travels SE from Iceland to the Norwegian Sea and Scandinavia.. That would be interesting indeed!
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Interesting trend in the GFS over a couple of runs in the long term, suggesting a mid-Atlantic HP block, with LP running over the top and then SE. I suggested a couple of days ago the possibility of the present block retrogressing, as i have often seen happen in the past.
The ECM seems all over the place to me over recent runs, don't see any realistic continuity to its output, based on where we are right now.
I think the GFS and to some extent, the UKMO are showing a reasonable scenario of Atlantic systems pushing the HP SE in the short to mid-term, with some possible intense LP running NE close to the UK. As I said before, at least it means some weather for a change instead of this persistent murk!
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Interesting change with the 12Z GFS, flattening the upper long wave pattern, with a strong zonal flow late in the run, fast moving LP and possible storminess.
What caught my eye was the significant cold pool over Greenland at the end of the run. I think it worth mentioning for those looking for coldness, if the blocking pattern breaks down as depicted by the GFS, the tendency for blocking to recur is quite common in my experience, and when it does, it has tended to re-establish itself west of its previous position. In other words, the axis of the upper ridge has been just E of the UK for a while, so if it reforms in mid-Atlantic, look out for Arctic bursts. I think many are looking to the E and NE, but some notable cold spells can occur from northerlies even early in the winter - check out early December 1967 as a good example.
I think one thing seems pretty sure from all the models - a strong jet is heading our way so we will at least get some weather!
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Hello OMM,can i just say how much i enjoy reading your posts you somehow reasure me the glass is half full,keep them coming,cheers.
Thank you Wolvesfan, my thinking of late is along the lines of the UK being subjected to continued blocking patterns, a trend that has been strongly in evidence in the last couple of months and which I have seen persist many times in past autumns and then on into the following winters. Of course, the $64000 question is where geographically future blocks will settle!
If such a switch as I suggested is likely, it will still be some days yet before the models start really picking up on it. Nevertheless, my instincts tell me it's at least a possibility.
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Not much change from yesterday as far as the models go, although subtle changes are evident.
I've taken a look back over the last weeks to see how we got here, and the European blocking HP has been in its current position for the best part of a month, rebuilding and moving slightly at times. Therefore, I think it's reasonable to accept what the GFS is depicting still, with the HP sinking away but pressure remaining high over much of Europe only with HP centred a bit further south than at present. All this depends on the development of the strong Atlantic jet next week. The UK Met should pick up on this later today if it's likely to happen as the GFS says.
Although too far away to be taken too seriously, I notice a hint at the very end of the GFS 00z run that suggests a sudden switch of upper flow - LP digging further and further S in mid-Atlantic, suggesting a corresponding upper ridge over the Iceland area, with associated HP building to our north. I have seen this happen in the past and, as I mentioned yesterday, changes from mild to cold are sometimes very sudden. Worth watching this trend I think.
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Good post, nice to get some historical context on this HP. The evolution shown between the 7th http://www.wetterzen...00118810107.gif
and the 12th is very clear.
http://www.wetterzen...00118810112.gif
Will make a mental note to look out for this slow moving LP mid-atlantic, ironically something that the maligned GFS is good at trending albeit in a dartboard fashion on occasion.
Thank you Lorenzo, of course a few days after the charts you posted there, saw one of the worst blizzards ever across the south of the UK. The cold air had had many days to consolidate over the UK so it's hardly surprising it snowed so much once the Atlantic systems tried to push in.
When slow-moving LP does develop like that it tends to favour the downstream upper ridge positioning itself over Iceland or thereabouts, with a corresponding upper low digging SE from N Europe. Such patterns can be very persistent..
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Hi, thanks for such a detailed response.
By blocking becoming a feature, are you referring to the Euro High becoming a more dominant feature throughout this winter than perhaps the last few, or are we talking Greenland High, etc?
Hi Backtrack I have sort of answered that point in my reply to Dewei, the HP over W Europe giving us mild SW winds does happen a great deal.
It is worth poinitng out, however, that notable cold spells, for those looking for them, have historically quite often been preceded by very mild conditions. It is also the case that the transition from mild to cold has sometimes been very sudden. I mentioned the pooling of cold air to the NW and NE as I have seen this happen some days in advance of a cold spell in the past. But as I said, very early days yet. All the cold winters I have lived through began around late December!
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Not what I'd like to hear but I recognise the voice of experience here!
Thank you Dewei, as I mentioned above, I look at current and forecast patterns and see if they look reasonable based on what I have seen happen before. To my mind, the GFS seems most reasonable; it is far more common to get the situation is shows in the longer term, i.e. HP fairly close over Europe, than to see HP developing to the NW, from where the situation is now. Goodness knows we saw the mainly anticyclonic SW enough times in the mild winters of the last 2 decades!
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What makes you think that the GFS will be right? By all means everyone is entitled to an opinion, but although I am a coldie, I would certainly back the ECM. I just don't favour the Euro High staying with us for much longer, and although it isn't impossible, I think that the most favourable scenario would be energy transferred into the jet due to a weakening PV helping to push the HP away.
Although the ECM may be being a little progressive with what it's showing, I certainly think this is the model to watch.
Hi there, I base what I say largely on how I have seen similar situations develop in the past, which I know is by no means a foolproof way to determine how a current synoptic situation will develop! I did also suggest that I see blocking as being a feature in the coming weeks, although quite where it will occur remains to be seen.
The ECM has been quite ambivalent this week although I agree with you that it often seems to pick up the longer term trends better than the GFS.
I think a lot of folk here are hoping for a repeat of this time last year which it hardly needs saying is pretty much a once in a generation scenario, I have certainly never seen anything like it in over 40 years of watching the weather. However, I do recall winters where blocking was prominent in the late autumn/early winter which have produced some notable cold spells later in the winter (the winter 1968/69 springs to mind). It's very early days yet. The main thing i shall be watching for is significant pooling of cold air either over Greenland or N Scandinavia, plus signs that major, slow-moving LP is developing mid-Atlantic.
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I've been watching the models dithering this week, trying to determine how the current blocked situation will develop. It's interesting to note the ECM keeps trying to retrogress the HP. For those looking for significant cold, there don't appear to be any strong indicators, although the pattern suggested by the ECM, if it persisted, with HP to the N or NW would certainly drag in some cold air from the NE.
If you look at the current blocking pattern from an historical point of view, I cannot recall a situation where such a persistent HP as we have had over Europe all this time takes it upon itself to start retrogressing. Usually, any prolonged block of the kind where a NE flows develops over the UK often seems to occur when HP develops over or near the UK and then bullds to the NW (take a look at the classic January of 1881 to see this process working at its best!).
All things considered, I would suggest that the GFS could possibly be right in the longer term, with the SW /W flow gradually displacing the Europe HP further S. However, I also suggest that the fact we have had this much blocking so far this autumn tends to favour its recurrence.
We'll see!
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Interesting to see the GFS sticking to its blocking pattern in today's 2 runs so far. I'm inclined to agree with others here that the ECM might be nearer the mark with a more indeterminate block, or with westerlies resuming. But I do feel that a more meridional flow seems likely in the coming weeks so I think it unlikely there will be prolonged unsettled conditions.
Quite apart from anything else, it's been a long time since we've had any major, persistent HP anywhere close by so it's about due. I think the longer range UKMO later today will be the one to watch in terms of how and where the blocking pattern will develop.
Incidentally, the slow-moving cold front over us in the next couple of days could cause some significant rainfall problems - depends where it gets stuck.
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I've been sitting back a bit from commenting on the recent models as we are in a very commonplace type of flow but something caught my attention on the 120H UKMet last night. I think what happens a few days from now will determine the course of synoptic development for some time.
Large upper trough and associated LP looks likely to disrupt in a few days and there is some considerable uncertainty over what happens after that. The UKMet chart I mentioned is showing HP building N of Scandinavia, looking as if it would replace the persistent HP over much of Europe. We have already had this upper low disruption once this month, after which the westerlies simply resumed. The question is, will it do the same again this time? The GFS seems to think so but not the UKMet.
It is tempting to think that the remarkably early snowstorm over the eastern US is a flavour of things to come for the UK. Certainly, for this to happen we would need an upper trough over the E US with a mid-Atlantic ridge allowing a deepening upper trough to develop over W Europe, something that could develop from chart the UKMet showed at 120H..
It will be interesting to see if the UKMet continues with the HP buildup idea over the next few days or indeed if the GFS/ECM pick up on it. Anyway, for the time being at least, unseasonably mild air for the whole UK; don't be surprised if temperature maxima set new records!
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As to what our experience shows us then with almost 40 years as a professional I am going to have to disagree with your view on upper air features. During my time with UK Met no indiviudal nor team ever found any linkage of preceding months as a means of predicting what would happen a month or several months later. I think that is still the case apart from my comment above about shorter term links and those which GP uses.
John, I am sure during your long professional career you came to rely on "instinct" and "hunches" when it came to determining your forecasts on occasions, rather than simply using model output alone. I agree, from a scientific point of view, such links as you describe do not seem possible (having said that, the global warming models appear to have cracked it with their projections 50 years ahead, but let's not go there!).
Anyone who studies a particular subject for a long time develops a "nose" for it, which can defy the logical approach in that it can sometimes go straight to the answer, without the person knowing how they got there! I do that sometimes fixing computers, a field I have worked in for 24 years.
All this is rather straying from the subject of this thread I know but I still think it is relevant. I think the forecasts issued by the National Hurricane Centre in Miami illustrate the point very well. You often see subjective interpretations of the forecast model outputs where the experience of the forecaster is a key factor, given the fickle nature of tropical disturbances!
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Another caveat is that even if this pattern does repeat as the season goes on, it doesn't mean we will have a snowy winter, as a lot depends on precisely where the Scandinavian high sets up. It's true that a fat high over Scandinavia has, in the past, often been one of the key building blocks towards an extended spell of cold snowy weather, as the high ridges west to our north sending very cold Russian air across from the east, but there have also been plenty of other times when the high sat well out to the NE and gave us a generally south-easterly regime with "inversion cold" and dry cloudy weather.
Yes indeed, I can remember many such winter situations with HP blocking to the E and NE and only surfaced-cooled air coming at us as you describe.
Although I use the model output to get a sense of longer-term trends, I also get an intuitive impression of what is coming by other means, for example, this year the autumn tree colours are turning several weeks earlier than usual, at least where I am.
Also, I have saved synoptic charts for the year and replay these as slide-shows, as I find this very useful in seeing longer term shifts in the flow patterns that have led to where we are now. If one then reviews current model output alongside these past patterns, it is possible to determine whether or not any given output looks realistic. The models at the moment have shown reasonable agreement in the medium term, and from what has happened over recent weeks, the deep low and upper trough disruption next week looks entirely possible. What I find interesting is how the models will pick up development from that point on; more Atlantic systems or a blocking pattern? As I said, I favour the blocking but we shall see!
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The high developing over Scandinavia has nothing whatever to do with what may happen 1 month let alone 3 months down the line.
I agree that there is absolutely no way of knowing for sure, but in my experience there has often been a strong tendency for upper air flow patterns to repeat themselves, so blocking HP over Scandinavia MAY be something that recurs during the winter. Given that we have had an extended period of zonal flow ever since the fine spring weather broke down, I think it entirely possible for us to experience a greater tendency for blocked situations from this point on. Quite where any such blocks occur is obviously crucial in terms of how that translates into actual weather.
As someone who has studied synoptic patterns for over 40 years, I have noted that it is often the case that clues to up-coming notable extremes in heat/cold in any season show up in advance. What I say is mostly based upon this experience; I sometimes get a sense of what direction synoptic development is taking from what I have seen happen in the past. I view the model output from this perspective. Therefore, what I say sometimes may not sound as if it has much scientific basis to back it up!
However, I will stick my neck out and suggest that in the longer term we may see increasingly blocked flow, which MAY - and I emphasise the "may" - involve HP to the NE. I think I will have a better sense of the likehood of this happening once we get to November. Meanwhile, the medium term looks most interesting with a strong jet heading our way, so some real autumnal storminess looks likely to me.
Model Output Discussion - 12th December Onward
in Forecast Model Discussion
Posted
Subtle changes in the models this morning, the predicted storm for the end of the week now looking to be more complex, with warm frontal wave(s) running ahead of the main LP. This idea was suggested yesterday by the NOGAPS. This suggests to me that the LP will take a more W-E track, moving faster and deepening all the while as it crosses the country. It also suggests the area of strongest winds will be over the S of the country, within the warm sector.
With the added complexity of the LP though, there could well be strong gradients S of the centre or centres after the fronts have passed through. Judging by the forecast jet, these systems will be going really fast.
I notice the MetO are hedging their bets by including the whole country in theor latest warnings, so clearly there is consdierable uncertainty at this stage.