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OldMetMan
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Posts posted by OldMetMan
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Many thanks for that link, I was just amazed at the cloud pattern, clearly there must have been much damage with those wind gusts.
Imagine the chaos in London and the SE if that has been further NW in its track!
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It is tempting at this stage to claim the forecast from yesterday was all wrong, but this is still a developing situation.
The frontal boundary right now has a N-S orientation but upper winds are still SSW so everything is currently shifted further E. But the satellite presentation shows the boundary is forming a wave to the S and storms are still developing just to the E of it.
What I find particularly interesting is the huge storm cell that moved up the Channel overnight. It's appearance on satellite gives every impression of it being a meso-cyclone; the cirrus outflow is like a mini-hurricane, so it is so powerful it has created this. I don't recall seeing such a storm in a long time.
Rain seems to be gathering to the S, so anything might happen as the day goes on.
The model longer term outlook brings us firmly into Atlantic air, at least for a time, but the prospect remains for another plume situation developing in a few days.
Fascinating weather!
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Quite a dangerous looking outlook in the short term developing and I expect the forecasters are understandably nervous!
The models have been playing around a little with the development of this weekend's thundery LP and I think it will be a close call. Synoptically, LP developing as depicted is entirely possible; a slow-moving cold front separating the very hot air over France from Atlantic air; a slowly amplifying upper trough to our W, with the main LP to our W sinking slowly SE. Quite a noticeable jet on the forward side of the trough (satellite images have been showing this quite well), all the ingredients for a slow-moving, deepening LP to track NNE or NE across the S, SE and E of the UK.
Given the upper pattern, I would expect such a LP's track to turn more to the N as it develops. Meanwhile, the heat over France will doubtless set off storms (as it did today) and the net effect is for a potential for very large amounts of rain. The latest forecast centre fix on the Met O FAX looks quite plausible. The severe weather warning talks of a "signal" indicating the frontal boundary will lie through central S England, not sure what that means but it sounds ominous. East of the frontal zone, there could well be embedded thunderstorms sucked into the circulation.
In these situations, clearly the best guide is in satellite imagery, over the next 12-18 hours, to see how the frontal boundary is behaving.
In the longer term, there looks like there will still be an upper vortex to our W, with further opportunities for hot continental air to be drawn into any frontal developments. There seems to be some ambiguity as to how this will finally resolve, but historically, such LP situations in August are followed by pressure rises. On the other hand, the Atlantic hurricane season is kicking off so that might change.
All in all, some very interesting weather to look forward to!
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Some interesting prospects as depicted by the models today after a lively 24 hours' weather (not a drop of rain where I live though!)
One interesting trend I have noticed, with the GFS certainly, is that future LPs are being shown arriving over us from a much more southerly point. Also, although this varies from run to run, the systems (mostly) seem somewhat weaker. We do not appear to be approaching anything like an early taste of autumn yet, with LP anchored to the W, at least in the short- to mid-term. Looking at the jet orientation, strength and location we could continue with respectable heights to the E and NE for some time so this is essentially still a blocked pattern, even if everything has shifted eastwards a bit.
The high thickness values remain just to our E so there appears to be much further scope for thundery activity with any further lows likely to get the benefit of these high values being drawn into them and, according to the latest GFS, a more sustained southerly associated with a deeper and more slow moving LP, with a renewal of the hot conditions and building pressure to the E, with maybe a slow moving cold front and associated thundery activity to the W.
Other models provide variations in the mid- to long-term taking the LP to our W further N, allowing a more direct W flow. At present, the GFS looks to be the most realistic and the long-term development of a new HP from the SW looks entirely possible.
So although the pattern is rather unsettled, it'll still be pleasantly warm in the main with the possibility of something hotter in the mid-term, and some drier interludes - quite an interesting mix - and the prospects for some really significant rainfall amounts
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Thank you very much Steve, that's much appreciated.What a great and balanced post by OldMetMan.
The kind of post that 95% of people reading this thread want to see.OMM
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Further to my earlier post, these basically depict the alternate development I mentioned, with no breakthrough jet and slowly rising pressure, rebuilding from the north. It will be interesting to see which will prevail.
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Interesting although subtle changes in model output so far today.
There seems to be a reasonable consensus now of falling pressure over the UK as we head into next week with LP moving into our area accompanied by hot, humid air and thunderstorms, at least for a time. Currently, the air over France is becoming increasingly unstable, with storms breaking out as far N as Brittany, so the SW of the country could be at risk of storms already. What seems quite likely to happen, I think, is the development of a more organised trough, even a frontal zone, heading N across the country with much thundery activity embedded in it. The cloud pattern over France at present suggests this is already starting to happen, albeit slowly.
The trickiest and most intriguing part of the output is what the development is likely to be later next week. As I have mentioned before, the N American jet is the thing to watch:
Today, it looks somewhat livelier than hitherto. The latest GFS 12Z run shows a much more vigorous jet heading E and then SE with developing LP along it, which will feed into the thundery low over the UK. Yes, it has been saying something similar for some time, as it likes to do, but there are now hints that the other models are developing along similar lines. The latest 500mb has some clues.
An active shortwave near the Great Lakes is intensifying the upper vortex over the E of Canada. Downstream, we now have a more noticeable upper high right over us whereas previously it has been quite flat. If the jet proves to be as strong as the GFS suggests, then it would seem more likely for it to propagate E and then SE as the GFS depicts. Along with this, we would have an upper trough extending eastwards at our latitude, with the upper high weakening and heading NE. This injection of energy across the Atlantic would, I think, break down the block, at least for a while.
But I must stress, there is a big question mark over this happening as far as I am concerned. It's quite possible that the whole development could just run out of steam and we could remain in a slack pressure field with gently rising pressure towards the end of next week.
In any event, there remains still the possibility of some record temperatures in the early part of next week and some interesting thundery activity. Perhaps by the end of the weekend, we will have a clearer idea.
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Some early thoughts on today's model output so far and where we actually are at the moment.
One thing that caught my eye this morning is on the Jetstream analysis.
The southern stream, running into Spain and the Med seems to be strengthening and this appears to be backed up by the cloud motion at that latitude. As I see it, this gives more impetus to falling pressure to the S and SE. That, together with a disrupting Atlantic trough feeding in from the NW, seems likely to increase this development
It's common for such blocked patterns as we have, summer or winter, to break down from the S or SW, as I mentioned the other day. If you want to see a good example of this in summer look at what happened at the end of August 1976. However, there still seems to be no clear cut evidence yet of a major change of pattern. Yes, there does seem to be a likelihood of falling pressure and hot humid air drifting our way next week with the changes mentioned above, yet, at this stage, I think it more likely that HP will reassert itself within a few days of the thundery breakdown, as LP to our S and SE fills again.
Nevertheless, it's still worth keeping an eye on the N American jet strength and orientation. I still believe that we will end up with a slow moving 500mb vortex to our W or SW, it's just a matter of when. With no Atlantic tropical disturbances around right now to enhance the upper flow, as I keep saying, it could take a long time.
I think later output today may give us a better picture.
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It might be worth pointing out again that, in blocked situations, especially winter blocks, the GFS has a tendency to want to keep turning the pattern zonal. Therefore, I agree that long-term GFS output is to be treated with even more suspicion than normal!GFS has been pushing and pushing this 'breakdown' back for days now though. Thought last Sunday was game over for the heat about Wednesday and Thursday last week? Only turned out to be the hottest day that far in this persistent heatwave. Think we would have had this breakdown by today if GFS FI was correct too? Yet we are potentially about to see temperatures soaring to 33-34c into next week. Look more to the stuff happening in the more reliable and accurate timeframe, then what you point out might be a bit more logical and correct.
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Some subtle changes in the model output today.
The current HP is transferring NE a little, enough to allow an easterly flow across the S of the country. But the more definite incursion of zonal flow, especially the GFS, has backed off noticeably. Instead, we seem to be looking at a slack pressure field in the mid- to long-term, with a gradual falling of surface pressures and thus increasing risk of thundery outbreaks.
One thing worthy of note is that with a light SE drift, we could see even higher temperatures than currently, and with increasing humidity and slack air flow, this is a receipe for some notable heat storms and locally very intense rainfall.
In the longer term, there is still no real sign of major changes, the upper flow remains weak and although at the 500mb level, looks more like cyclonic activity will sink a little further south in the Atlantic, with the jet accompanying it, there is little at this stage to suggest a replacement of these blocked conditions, merely a temporary breakdown. There are some similarities as I see it to previous prolonged settled summers, such as 1959 and 1976.
I suspect eventually - and I think it will take some considerable time - an upper vortex will form in mid Atlantic and a spell of unsettled weather will follow.
I wouldn't be at all surprised to see new records in temperature and/or intense rainfall in the next couple of weeks.
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John Holmes. He is older than the hills !
lovely to have fans on this forum!
Stanmore=oh yes that was when we used to watch the ladies play basketball, but then the mierable sods ordered us to stop!
Darn, wished I'd known about that when I was there!
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Hello OMM,
I was at The Met Office training College in Shinfield park not far down the road from Bracknell in 1971.I did make a visit to HQ Bracnell during the forecasting course to see the new super computers in operation. Were you there then ? I think the DG was Dr Mason and he showed us round. Could never understand what he was on about though !
C
Hi Carinthian, yes I was there until 1972 when I got posted to Bedfordshire. In those days, we had to go to Stanmore in NW London for training I was there for a month in 1970. Yes, I remember Dr. Mason, think I saw him - once! My favourite pastime was perusing the Library at Bracknell - wonderful place. Ah happy days!
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im only basing my analysis on what i see from the models, the GFS model in particular. It has just updated and once again shows a significant change from the 23rd onwards! I realise this is FI, but to suggest the Azores high is the form horse or to boldly predict the heat is here to stay is reckless. I want this heatwave to stay a few more weeks, but that now appears wishful thinking.
As I understand it, the GFS has a tendency to want to revert to zonal weather when things are blocked, well certainly in winter months so I guess it might have that same tendency now.
I mentioned it above, but in my opinion keeping an eye on the strength of the jet is a good guide to the way things are shaping. Long spells of hot weather in summer - and I have seen quite a few - are characterised by a slack Atlantic flow, with little energy there to shift any block. Granted, the upper flow has cyclonic activity in high latitudes at present, unlike previous dismal summers, which I think tends to favour more of what we have now. So, never underestimate the persistence of "heat" blocks.
Either way, I find it interesting to see how the models develop from this point.
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Were you there in the Bert Foord era, OMM? Cos he's the guy that made me obsessive about the weather in the first place...He did a series on BBC, if I'm not mistaken? Late 1960s?
Hi Pete, yes I was, I started working at Bracknell in 1969. In fact, I once went up in a lift there with Bert who was on his way to the canteen! Not sure I remember the series you mention although I was an avid weather fan so I must have seen it!
I wish we'd had the Internet and weather forums in those days. As it was, we held mini forums each day when the CFO brought down FAX type charts to display in the main entrance. It used to get every bit as heated then as it does here sometimes!
OMM
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Hi OldMetMan. Nice to see you posting in here during the summer months. Thanks for your detailed analysis, always welcomed.
Many thanks Jason! It's been a while since we've had a lengthy spell of "real" summer weather and to see upper and surface patterns as I remember them from my younger days! It seems hard to imagine what happened this time last year!
OMM
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Interesting to watch model developments at the moment and how there is a growing consensus of a shift of position for the HP later this week.
The 500mb flow is curious. Although the heights are well up, the pattern is somewhat flat:
The action remains to the north but with surface pressures not that high over the UK, coupled with such high surface temperatures, then as we have seen today, a formation of a "heat low" might continue to allow some strong convection here and there, with local pockets of instability in the overall high pressure field.
That apart, the consensus I mentioned involves steady troughing over the mid-Atlantic allowing heights to rise to the N and NE of the UK and thus transferring the centre of HP further NE, bringing in somewhat cooler NE winds. If anything, this kind of development will re-intensify the HP and prolong the current settled spell. This seems a very plausible outlook given where we are now.
What I have noticed in the last couple of days is a strengthening of the N American jet as well as the N Atlantic. Apart from the GFS long-term, there is still not much to suggest any Atlantic incursion for some time yet, but the strengthening of the jet needs to be watched.
Summer "heat" blocks such as this can take a LOT of shifting as many of us know, as do corresponding winter cold blocks. The models seem quite vague in the mid- to long-term as to where to take the HP. If it does indeed anchor itself to the NE, then I think we need to look to the S and SW, as well as to the near Continent as, certainly from an historical perspective, thundery conditions often develop from this situation. If that happened, and SE winds develop, we could see temperatures going even higher.
With no Atlantic tropical activity at present, there seems little likelihood of anything there affecting the upper flow in our area. So, all in all, more of the same with the possibility of isolated thundery downpours in the short term until pressure rebuilds. That apart, the possibility of any rain in the foreseeable future looks very remote, so drought warnings would seem to be imminent in some places.
Enjoy the sunshine!
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as an ex met man judging by your avatar OMM I would assume you understand how the senior man, now at Exeter, rather than Bracknell in your and my time, assesses all model outputs, sometimes showing a preference for Met output sometimes for ECMWF?
Just as an addendum to my previous reply, I have seen a similar phenomenon of model output variability in Atlantic tropical forecasts. A good example occurred this week with Tropical Storm Chantal. It started life as a vigorous tropical wave which had all the satellite features you'd expect to see with a potential hurricane. Yet by the time it entered the Caribbean, it degenerated into an open wave, when all the previous day's output suggested steady development. Today, they are talking of it possibly reforming again.
I realise the atmospheric conditions to be considered are somewhat different for tropical storm development, plus it involves determining how the environment around a storm will change over a much longer time scale, but the development of upper level factors, such as wind shear and the presence of upper lows are often very hard to determine, because they are often quite weak in nature and the models cannot so easily get a handle on what they are likely to do. I have seen many a forecast come unstuck because of this.
To their credit though, the storm forecasters in the past have had some spectacular successes and much of this is down to the experience and knowledge of the forecasters involved and how they interpret the model output. I wouldn't care for their job given the heavy responsibility it can carry at times!
OMM
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as an ex met man judging by your avatar OMM I would assume you understand how the senior man, now at Exeter, rather than Bracknell in your and my time, assesses all model outputs, sometimes showing a preference for Met output sometimes for ECMWF?
Hi John, yes I understand the process of how the FAX charts are produced, it's just that on this particular occasion, I could not see which particular model output or outputs were showing a definite development of LP as shown on that T120 chart. Obviously, I do not have access to all the data a forecaster would but it still looked incongruous.
I still maintain that forecast model output when the flow is weaker at this time of year is less reliable, especially when most of the 500mb flow action is happening at a higher latitude. I'm not saying the output is always wrong, which it isn't, just that significant changes in weather type, such as that FAX chart indicated, are not so easy to foresee, as evidenced by the fact that the LP development was ditched on the next run. Just my impression anyway.
OMM
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You are most welcome...So, do you think the models are lagging behind a bit?
Not so much lagging behind, I think, more like the 500mb lows are quite a long way to our north and quite weak - more like you'd expect to see this time of year compared to recent summers - so I think the models have a harder time determining when and where these upper lows might develop and thus significantly alter the wave pattern and thus the surface features. That's what puzzled me a bit about the Met FAX chart as it seemed to have picked up on a strengthening of the flow which I could not see reflected in other model output.
What we could see if the heat continues is a monsoon effect if the continent gets really hot. That used to be a common occurrence in years gone by, not so much these days, when LP develops there and spreads its influence to the UK or it induces Atlantic LP to develop and push across the country, in a similar way to the Indian monsoon although nothing like as drastic thankfully!
See how the model output, especially the GFS and UKMet change in the next day or 2 that should give us a clue as to the long term of this current hot spell.
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Good to have you back, OMM...We have sorely missed your input.
Thank you Pete, that's most kind of you. Before you know it, we'll be speculating about winter, then I should be around a lot more!
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Sorry to hear about your health OMM, a very warm welcome back. And glad your on the mend.
Many thanks PM, very much appreciated! Got to remember my age now and slow down a bit!
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Hi folks, haven't been around for quite a while. Had a few health issues (slight stroke in May) but I'm getting back to normal slowly.
I thought I would add a few thoughts to the current settled spell, not least because it contrasts so much with this time last year. The model output is, not surprisingly, a bit vague from day to day. The Met FAX from yesterday was a bit of a surprise with some significant LP developing to our west at T120, but this seems out of step with other model output.
Overall, the upper air pattern looks pretty sluggish at our latitude; rather a weak jet from N America and across the Atlantic. Quite a solid looking 500mb high over us with not much to shift it, the Met O FAX T120 notwithstanding! Given that, it seems quite plausible for surface HP to remain over or near the UK for the time being, with perhaps weak cold fronts, or minor troughs moving SE at times. Not much seems likely to develop low-pressure wise over the near continent in the near future - I guess much depends on how much heat builds up there.
I often think that the Atlantic hurricane season can significantly affect our weather from about this point in summer onwards, but so far it's been a bit slack in that area too, with most of the energy in the E Pacific.
There have been the odd hint from the GFS of a more noticeable disruption to the upper pattern with troughing coming from the NW towards us but no clear signs yet in the short term that it will really happen.
As it see it, this kind of pattern often appears in August and changes only slowly. So, I'm looking for any signs of some energy getting injected into the Atlantic flow, most likely from any tropical disturbances. Meanwhile, for those of you who enjoy the heat, looks like there will be plenty on offer in the coming days!
See what the Met O come up with later re the LP..
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Hi folks,
Some interesting similarities right now with the cold spell last month although the current evolution is somewhat different.
Although we are now getting Arctic air flooding S over us, it's not what I would call a "proper" northerly, I would prefer to call it an "eventual" northerly, happening as LP gradually transfers NW/SE pulling in the cold flow behind it. As such, they tend not to last long in my experience as the upper flow over the N and central Atlantic is too flat. For examples of "proper" northerlies try December 1967 or February 1969.
However, the models seem to have been trying for a few days to set up with an easterly, especially the ECM, which in its latest run as a significant HP over Scandinavia.
At 500mb, there are some similarities to what happened in January. The Canadian vortex has moved further E, pushing out into the Atlantic, and an upper ridge seems to be trying to form ahead of it, not very successfully as yet but there are signs that it could. Overall, the hemispheric flow is fairly flat but that can quickly change as we know.
As far as the other models are concerned, there has been a lot of uncertainty as to how the Atlantic systems will behave after this northerly moves away, with some suggesting disrupting short-waves running SE. It seems quite possible with the European upper low amplifying as the current cold air spreads SE.
Normally, with this kind of evolution I would tend to dismiss it for the purposes of significant cold over the UK but after what happened last month, with a fairly weak 500mb blocking pattern, I don't think it would be wise to do so!
I shall be watching to see if we get increasing heights near Iceland, maybe even an upper high cell, if none such happens then we seem to be heading for a rather indeterminate spell of chilly weather. However, if the block returns, we could be in for more significant snow.
Tricky one this but worth following!
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LOL,not one comment on the 18z gfs tonight.
Well, at T300 a stunning looking northerly blast with a strong mid-Atlantic ridge extending to Greenland. Not sure how it dreamed that one up!
The kind of post that 95% of people reading this thread want to see.
South West/Central Southern England Regional Weather Discussion 27/10/13 1730z ------->
in Regional
Posted
Hi folks, been away from the forums for a while, but I couldn't let this developing storm pass without chiming in!
First, well done to the models for picking up on this LP so far in advance. The media is clearly in quite a frenzy over this one. One thing I've learned over many years is that such a hugely anticipated weather event rarely pans out as predicted. Having said that, let's look at where we are now.
A closed low has formed in the last couple of hours in the SW approaches and looking at the steering flow, the predicted path looks pretty likely - across the Midlands. Whilst I would agree that the gradient on the S and SE flank looks likely to be pretty tight, given the speed this system is moving, as evidenced by the IR satellite images, I am wondering if this low will actually have time to deepen as much as anticipated. Thus, maybe there won't be so much of a tight gradient, especially on the W edge, the "backlash", well at least until it gets to the E coast. The GFS model suggests as much on the 12Z run.
Nevertheless, these beasties can be very tricky so I will not underestimate the threat! One thing resulting from the speed of the system is that at least the winds, however strong they become, will move away pretty fast.
I shall be following the hourly analyses with interest until I get too tired!
Stay safe everyone!
OMM