JH and a look into the period from T+144, usually

[johnholmes]

best you ask Kevin Mr D for that kind of data, I'm sure if you pm him he will be able to give you an answer. It must be some time ago but how long since I honestly have no idea. sorry.

anyone else got an idea of Mr D if you read this please?

thanks

tks Paul for that input, I think you are right there is a chance but its got to have all the building blocks in place for it to work, and it does seem to be that this autumn/winter its to the north east we have to look. Interesting comment about that from KW on a couple of occasions on the model thread so if you read this Kold I'd be interested to read a more detailed comment on why you think that is. El Nina La Nina is not my speciality at all?

Edited January 9, 2008 by johnholmes

[chionomaniac]

a quick question John. (or anyone who wishes to answer) when was the last time a sustained Scandi High was prevalent over the UK. Seems that the westerly flow has dominated the winters for what feels like a lifetime

I don't know if these were the last, but they were certainly noteworthy!

Feb 1991

and before that Jan 1987

I love looking at those charts

[Nick F]

Yes, the area to our NE is showing the only positive signs atm for height rises to occur and perhaps bring a break in the Atlantic low pressure/strong westerly domination. A look at the 12z ECM and GFS t+168-240 mean 500mb heights shows +ve heights never too far away from Scandinavia over NW Russia

... so all it would take is a 'trigger' low going into Europe on a more Serly track, perhaps a deepening low moving SE across Sern Uk with a stalling of eastward/northeastward movement of subsequent Atlantic lows upstream to allow pressure/heights to build to the NE. There is a slight tentative hint of this t+180-240 on the 18z GFS, though the jet remains too far north and the cold pooling to the NW and N to prominent for a Scandi high to come off - rather any pressure rises to the NE are quickly pushed back eastwards.

[Roger J Smith]

The upper flow remains very strong from about 280 deg, reminds me of the set-up in Jan 1990, and with the strong energy peaks indicated from research on the 20th and 23rd, I would have to think there is a good chance of a major windstorm affecting southern parts of the UK in that time frame.

These energy peaks are probably better focused than some of the recent ones, which have seen 12-hour cycles of energy all competing for space in the flow. One or two have gained a lot of energy regardless, like Tuesday night's big blow in NI and Scotland.

Research also indicates some potential for blocking to develop late in the month, so the indicated storm for 23rd may be heading for North Sea and Germany, then redeveloping south, to allow this block to set up -- that's what the RJS model would be showing, if I had maps to put up, but before we get to that, a number of very mild systems likely 17th to 23rd with the northern blocking showing up around 24-25. Will it amount to much? The index values I am using do not show too much by way of sustained cold but they do fall to similar values to earlier this month. I would therefore favour a minor or perhaps moderate cold spell of 2-4 days showing up near the end of the month.

The big weather story of this winter may turn out to be one of the storms in the period 20-23, with very strong winds being the main theme.

[Nick F]

Roger, sounds like a cooler repeat of January last year then. Remember last Jan we had the most severe gale since 1990 affecting England on the 19th, with gusts up to 99 mph at The Needles. i agree, there's alot of energy over the Atlantic being created by the deep cold pooling flowing out from the higher latitudes and the SSTAs to the west (albeit not as accentuated as they were a few months ago) can only be adding to the energy that's bringing in these strong Atlantic lows.

Question is, is this current pattern solely an over-riding signal of La Nina ... and what will it take to stop this self perpetuating Atlantic domination other than a weakening of La Nina, GP usually has these answers.

[johnholmes]

oops had almost finished posting quite a long addition to Nicks post when I lost the connection, 3rd time tonight, not sure if its my ISP, my wireless router or what, anyway past my bedtime so I'll try and do it in the morning.

good to be getting feed back from various people and I notice Roger is now on although not yet read his post.

tks all.

interesting post that Roger, will delve further in the morning

Edited January 9, 2008 by johnholmes

[MAF]

thanks John and chiono

[johnholmes]

the charts Nick shows are, I think, a similar set up to the 500mb progs I have been using.

Missed the post last night due to pc problems so picking up from this morning after seeing the 00z runs.

Much doom and gloom re no sign of any blocking on the model thread, is it justified?

yes and no in my view. Still no solid indications of this happening but then at the time scales it MIGHT happen this has not been the case in either of the two previous blocks; the one in December(yes not quite in the right place but=2 weeks of cold if snowless weather, and the recent one which never got time to settle before the jet pushed more Atlantic weather at it.

I've always said that everything has to be in place at just the right time for an event, ie Scandinavian high to develop. I'd still be interested from KW if he reads this as to why the Greenland high is not ever seen in these La Nina years(if I have that right?).

As to the jet, the key, well it does appear to start buckling which can be a positive sign. Much of the time it still wants to send the main thrust away to the north, as it did in mid December, thus the high, if/when it develops, as in December is created too far south. On the past 3 runs there have been tentative signs of some kind of surface development in mid Atlantic with a ridge from the south almost linking with a ridge to the north, from about T+120 right out into the run to the end(T+384). Yes it changes its position and ends up with it trying to Link the Siberian high across Scandinavia, that is until the jet returns to the far north cutting that link off.

Just how reliable it is at that range is doubtful but I am still of the opinion that we may yet see some kind of block develop.

Reading the latest comments in the model section regarding Stratospheric winds seems not encouraging but then is that part of the forecasting any more reliable at that time frame than lower down in the atmosphere, the Troposphere?

Will do a check on the ensembles later as I get time.

Edited January 10, 2008 by johnholmes

[Coast]

John I have to say this is one of the best current features on NW - well thought out, researched and presented. Thank you for your very valid contribution.

[johnholmes]

many thanks for that, I just hope it will be an area with constructive comments posted in whether it shows cold or warm. A learning area for me that is for sure.

[Greyowl]

John I have to say this is one of the best current features on NW - well thought out, researched and presented. Thank you for your very valid contribution.

Got to agree with Coast. It's one of the best threads on NW at the moment. Many thanks to all who contribute to it.

[*Stormforce~beka*]

This is a great thread where I can dig out Johns post for the latest info when I dont have time. Like now ... I have to leave for work in 15 minutes. So a quick check here is perfect rather than spending hours trawling through the model thread. Thank you.

[johnholmes]

Glad some of you are finding it a useful thread.

Update at 1900z Thursday 10 January 2008

GFS over the past 24 hours has shown little inclination to develop high pressure in any area that might lead to a cold outbreak in the UK. That is ignoring the present mobile cold giving parts of the higher ground in Scotland and Northern Ireland, in particular, their snowiest spell for some time.

The jet, often well south, is never in the right place at the right time, thus any attempt to link across the north of the Euro GFS charts is bound to fail.

There seems little prospect next week of upstream events occurring to cause much change to this.

In the longer term then events that will unfold over North America may provide some conditions for high development. As the upper pattern over there shifts into a situation as described here by NOAA this morning

THE OTHER PRIMARY FCST ISSUE WILL BE THE DETAILS OF TROF

AMPLIFICATION EXPECTED OVER THE WRN-CNTRL CONUS BY TUE-THU...

WHICH OCCURS IN RESPONSE TO A STRENGTHENING ERN PAC RIDGE.

Shown on this T+168 hours chart

This in turn gives this at the same time over the North Atlantic/Europe

So two major troughs over the Atlantic and just one over the States

Trying to link the two together to see how the hemisphere is depicted to look at the same time

The jet continues to send most of its strength south. Whilst some comment that this is good, its not necessarily so (as the song says!) in that IF it decreased then it is POSSIBLE that the high to its south might attempt to link to rising pressure to its north. This is in fact what it showed a couple of days ago.

Obviously there will be differences as the models are, on a hemispherical scale, (I think!), correct me if I'm wrong, at a different scale.

The hemi one has a surface low just east of the UK whilst the Atlantic scale has it north west. Nevertheless they all show that the current set up does seem likely to be maintained out to about that time scale. Beyond that then the N American developments MAY start to impact downstream in our area.

Far too early to tell at the moment.

Remember though that the two cold spells so far both materialised at less than T+168.

just to add to the above.

The ensemble collection I used in an earlier post shows what appears to be a relatively good confirmation, in spite of the large spread in some cases, of high pressure in a belt from Moscow through central Europe down into the Iberian peninsula. This seems to be borne out by the 850mb temps for Derbyshire over the same period.

Edited January 10, 2008 by johnholmes

[WhiteFox]

Good stuff John. Keep up the good work! I hope you don't think it rude of me to add some bits from across the water....

The story over here continues to be one of a pattern change into next week. An amplified Pacific Jet ridges over Western NA and forms a trough over the Midwest. The devil is in the exact detail in terms of where systems form etc. and just how amplified the jet will become, but the forecasts are fairly consistent.

This is the 12z +144 chart:

and the 18z +138 chart:

Both look remarkably similar for such a long way out. Experience tells me that they tend to be pretty accurate at such ranges over here; once the Pacific jet amplifies then the rest falls into place. I'm pretty sure that the same cannot be said of the Atlantic!

[johnholmes]

thanks for the input, I hope more will do like you.

Our key is what happens over your part of the world, just as your key is the Pacific region.

If only it were that easy in an island with nothing west for umpteen thousand miles but ocean!

Not that its so easy in N America, the devil is certainly in the detail for you.

just been looking at the N America thread and the ensembles for Chicago and New York.

Can you imagine on this site IF we were predicting -10C and persisting for over a week! Even for 3 days, especially if it happened as it almost certainly will for New York.

Take a look at the GFS charts for N America, surface, 850mb, and then take a tour around the NOAA site for their public service forecasts, snow, frost, freezing rain. More like a novel to us over here!

Edited January 11, 2008 by johnholmes

[Cookie]

thanks for you'r contiued and very informative posts im really enjoying them.

[WhiteFox]

Our key is what happens over your part of the world, just as your key is the Pacific region.

Picked up on this snippet from a Met (who was in the warmer camp until today) on Eastern US boards:

The cold signs for last 10-11 days of January have been building for several days now. Model consensus is finally starting to come together. Still no sign of -NAO on the models thru day 16, but if the strong vortex forms in t Hudson Bay/eatern Canada, you would think a -NAO would come with time. If it doesn this cold pattern is 10-14 days and then out in early February, if the -NAO comes, colder pattern coudl be the main feature rest of the winter.

Only one Met's opinion, but maybe some hope...

[johnholmes]

Update on Friday evening 11th January 2008

Let's start with GFS now and the end T+384

T+00=12z Friday

And now T+384

The pattern change is certainly there, probably not just what most on this site may have wanted.

At T+240 GFS shows this

The pattern change already well under way as predicted and due to events upwind over North America which the models showed several days ago.

The ECMWF version at the same time is

Very similar as far as the main trough is concerned but a more ridgy showing by it from the eastern Atlantic high. Which is right will be interesting. On most runs, at some point, GFS has attempted to develop a tenuous link between the high over the Atlantic and the small pressure rises way north. Each time, as T+240 shows the jet stops it.

So we have a pattern change but whether it will eventually show a northern link or simply subside back south before events over America restart everything again is unclear. Model output for N America suggests that the cold spell in the north east of USA+eastern Canada will last for at least a week. This may impact further downwind than the models are currently showing although that event is obviously in the models.

The USA 500mb predict shows trough conditions to the north and ridge conditions to the south of the UK (anomaly lines are the pecked lines)

I am still of the opinion that a change will be there in the same time period as mentioned previously +/- 2-3 days but just how it will pan out is wide open in my view.

Once more we shall have to wait and see.

This will be the last main update as I'm off to try and find some skiing in the Jungfrau region for 2 weeks. Please do keep the thread up to date with inputs and I may drop in now and then if possible.

charts following

Edited January 11, 2008 by johnholmes

[bluearmy]

and, according to the prognostic prose, a return of ecm input for these anomoly charts John - just in time for the pattern change although next human input chart is Monday.

[Nick F]

Thanks John, yes definate pattern change occuring for the medium term over the Atlantic. Looking at the ECM H500s, this starts with a large trough amplification over Ern US/Can around t+72:

... this trough translates east across the Atlantic - so by t+168 it extends from Greenland south towards the 30'N line:

We then reach the uncertain t+168-240 (8-10 day) period - and the 12z ECM and GFS mean H500 comparisons show the mid-Atlantic trough eventually 'cuts-off' - with the possibility of a mid-latitude high building around the top close to the UK, ECM builds it further north than GFS which tends to keep the Nern arm of the jet flow stronger and flatter.

Lots of possibilities likely to open up with this pattern change around 8 days time, but whether it will be towards a colder outcome is up in the air atm and depends on whether the nern arm of the jet strengthens and takes back over again or we see a split flow with perhaps height rises building NE.

Picked up on this snippet from a Met (who was in the warmer camp until today) on Eastern US boards:

The cold signs for last 10-11 days of January have been building for several days now. Model consensus is finally starting to come together. Still no sign of -NAO on the models thru day 16, but if the strong vortex forms in t Hudson Bay/eatern Canada, you would think a -NAO would come with time. If it doesn this cold pattern is 10-14 days and then out in early February, if the -NAO comes, colder pattern coudl be the main feature rest of the winter.

Only one Met's opinion, but maybe some hope...

Looks like mainly a west based -ve NAO signal though - with high pressure still dominant over western Europe, rather than low pressure as would be the case in an east based -NAO. A west based -NAO tends to favour mild conditions for western and northern Europe, whereas an east based -NAO tends to favour cold for Nern Europe.

[WhiteFox]

Looks like mainly a west based -ve NAO signal though - with high pressure still dominant over western Europe, rather than low pressure as would be the case in an east based -NAO. A west based -NAO tends to favour mild conditions for western and northern Europe, whereas an east based -NAO tends to favour cold for Nern Europe.

You're right, and it's one that definitely favours us rather than Europe. Something to stall any coastal systems and keep the cold air flowing!

[PB22]

Following on from tonight's model summary: http://www.netweather.tv/forum/index.php?showtopic=44782

We can see its looking very unsettled for the week ahead, but there is a lot of difference between the models over the exact details, even as soon as T+96 hours out, just four days:

GFS:

UKMO:

ECM:

Now, the general theme is the same, but its these small differences that will end up making the difference and affecting what eventually happens further down the line....the butterfly effect as such. These is demonstrated to a degree by the eventual outcomes in the GFS and ECM runs tonight. GFS eventually brings a ridge of high pressure across the UK, with suggestions of pressure and height rises to our north and northwest, as this T+192 chart shows:

By T+240 the Atlantic has returned though.

ECM on the other hand shows pressure rising to our south, with a strong high over the Bay of Biscay by T+192:

By T+240 there is hardly change, and a mild west/southwesterly flow covers the UK, although it may be colder at the surface.

What can we draw from that then? Not a lot to be honest. There is definitely a tendancy towards high pressure affecting the UK in around a weeks time, but where this high may be situated is another matter altogether.

Looking at the various GFS ensemble charts doesn't tell us much more really. In fact it adds to the mixed output as they show that the GFS operational run to be something of an outlier, both in terms of pressure and 850hPa temperatures:

For London:

Pressure:

One of the lower pressure values in the second part of the run. Most other ensemble members went for London to be influenced by higher pressure after next weekend.

850hPa temperatures:

Generally not far from the ensemble mean, but a mild outlier for next weekend which is potentially the crucial turning point for a possible pattern change.

So where could any potential high be situated if it were to develop? Well looking through the European ensembles, we can see a clear suggestion of pressure being high to our east and northeast after next weekend:

And it turns a lot colder in Moscow:

With suggestions of colder weather spreading further west, i.e. towards Germany:

So definite possibilities of an easterly developing as we go into the second half of the month. Sure enough, a glimpse at the panel maps show a few runs going for an easterly by T+240.

Finally, looking at the ECM ensembles, it shows the ECM operational became one of the mildest runs by T+240:

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

To conclude then...there are further signs of a change by or after next weekend, with high pressure probably becoming the more dominant feature. However, we can't really say much more than that at this stage due to the differences between the models in the earlier time frame, and that both the ECM and GFS are something of an outlier at some stage in varying forms.

If I was a betting man, I would go for high pressure to be sat close to the UK by T+240 and most of Britain will be drier and colder, the drier part being welcome news for most people I'm sure!

Edited January 13, 2008 by Paul B

[phil nw.]

Thanks Paul.A good summing up.It really is down to how that High from the west develops later this week as to whether we get a chance of a colder shot.

[J10]

Looking at the GFS Ensembles at T+240, there is a clear pattern for high pressure to be close to the UK, however slight changes in its positioning will have major effects in the weather type, from cold East to SE feed, Settled conditions if the high is on top of us or a classic SW bringing mild conditions, definitely a case of waiting and seeing.

[Cookie]

thanks paul for a very good and well thought out post,