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

[PB22]

Thanks John, top quality reading as always.

[johnholmes]

thanks Paul, its very interesting I think, maybe not to others, as it still shows no real evidence of 'winter' appearing.

However that 200mb circ polar chart again shows the very slight westward drift of the main axis of the ridge. Its much further north than yesterday but its axis is a touch west along with a cut off low way south.

The NOAA 500mb anomaly chart shows something similar in that its now got +anomalies in a separate cell north of Greenland. Negative anomalies are now being show on their 6-10 day 500mb progs(14-19 Feb) for much of the Atlantic and most of Canada+Alaska and westwards.

I have nil experience of any of this in terms of forecasting but it will be interesting to see what the two main models response is over the next 3-7 days.

Edited February 9, 2008 by johnholmes

[johnholmes]

no update this evening, the post this morning sums up the situation.

As to the 500mb and 200mb then I will keep an eye on them both, but the next human 500mb anomoly chart will be on Monday, or so I'm led to believe.

[johnholmes]

just so I have a copy of the latest NOAA anomaly chart at 500mb I'll drop it in here

its not totally uninteresting in that it shows the most +ev anomaly to our ne and the lowest, one of them to the wsw, although well out in the Atlantic still.

These two areas may, along with what happens over the east Pacific and continental N America, may hold the key to events in about 10 days time.

Edited February 9, 2008 by johnholmes

[johnholmes]

Update Sunday evening 10 February 2008; for day 7 out to day 14

The original post checking on T+240 and 192 for Monday, tomorrow, is about done. My comments a couple of days ago in that neither of the two main models gave first class guidance. Both had the surface high to the west of the Greenwich meridian, giving the idea perhaps of a cold plunge about to occur. As we now know this will not occur, apart from a cooler/colder cloudier feed of air off a colder continent during this week.

So attention now turns to the next check, days 7 out to 14 the week following, Monday 18 Feb-Tuesday 26 February 2008

USA and Europe charts T+00

same for T+168 hours

As you can see the net effect over our part of the world is, not much change in the overall 500mb pattern, over and west of the UK. Events during the T+00 to T+168 have caused the deepish push of cold air in the far east. There are signs over N America of some buckling of the 500mb flow which will not doubt impinge on our area over several days. This may take the form of a more buckled flow over the Atlantic, but as to how long, or indeed if this may happen, I really have no idea. NOAA are not convinced either as to what is going to happen upwind of them, ie over the eastern Pacific. All the models they use are rather less than coincident even for such a large land mass.

Further ahead than 7 days(T+168)

The 200mb flow shows no sign now of retrogression, simply extending the 200mb ridge further nne leaving the cut off upper low off the N African coast. The main flow MAY go into the southern arm, for a time, but its by no means certain.

Looking at the last 500mb predict from NOAA the pattern seems to suggest that there will be no major change. By that I mean pressure will remain relatively high roughly east-west just south of the UK in the term under discussion, that is day 7 out to about 12-14. This assumes that the main jet flow will by this time be in the northern arm,(the southern arm having sunk so far south its really the Sub Tropical Jet), and although with some buckling it seems set to be relatively flat most of the time. This will put much of the UK just north of it, so mainly in the PM(Polar Maritime) air with temporary influxes, especially for southern areas of milder TM(Tropical Maritime)air as the relatively minor ripples in the jet flow run across the Atlantic.

Edited February 10, 2008 by johnholmes

[bluearmy]

low confidence in the 500mb output from NOAA on friday John - worth noticing the difference again between the automated output from yesterday and the forecaster modified on friday - quite a difference which i think might negate yesterdays output

Edited February 10, 2008 by bluearmy

[johnholmes]

yes be interesting to see what it shows on the Monday one, I had mentioned that before, I don't honestly feel it will make much difference to my summation though.

[johnholmes]

little to add to any summary tonight.

The period 7-15 days, at least the part I'm keeping an eye on, out to T+360 now, shows nothing of any major interest or marked change.

Changes in the upper flow over N America seem to be feeding into the Atlantic, as one would expect, with a more pronounced buckle in the flow; likely to give a brief north to north west colder flow for perhaps 24 hours IF it happens beyond T+240.

Beyond that then nothing seems to be likely to give any major changes.

The T+240-300 I'll monitor but it does depend on what happens way upstream over N America several days before.

Edited February 11, 2008 by johnholmes

[Frosty.]

Such a thorougly depressing winter, nothing on the models to generate interest. A cloudier and chilly second half of the week is expected, perhaps with a little drizzle, oh joy.

[johnholmes]

Looking at T+168 and beyond this evening

The surface low exiting N America at T+168 along with another one involved with a following short wave upper trough seem likely to be the mechanism, together, for Pm air being dominant in the latter half of this current run. The short wave upper features are pushed along by events over west to east N America, in turn from events over the Pacific. By T+168 there is a marked trough extension over the east which in turn will swing across the Atlantic. Whether that is the set up as shown by GFS for the period T+264 out to T+384 remains to be seen but it may just be that. A pattern change as NOAA are suggesting for N America by T+168 and here/the UK area by/from about T+240-260.

Its an interesting situation and one to keep an eye on from now on.

Not yet got the NOAA 500mb anomaly predict but that may give a clue for our area.

The one from yesterday certainly supported the idea of a largish PVA area settling over the north eastern part of the USA by T+168. This would certainly impact on the UK area in about the time scale GFS seems to be suggesting.

The first low will push the Polar Front largely south of most areas from about T+240 onwards but its not until almost the end of the run(T+360 onwards) that the trough extension appears to develop.

Just remember though this is a learning area for me, so if anyone 'sees' things differently please post so.

prior to T+168

as to before that and following on from the clear prediction from Paul B at this link

http://www.netweather.tv/forum/index.php?s...p;#entry1190426

(this was last evenings link)

then the upper air over and west of the Atlantic suggests that the models have it about right with the high in charge as it drifts south east out to about T+168 when the Atlantic begins to have more effect although even then high pressure is never that far away out to about T+216 but to our south and south west rather than south east.

for a view on what happens above the Tropopause then this link is always worth a read.

http://www.netweather.tv/forum/index.php?showtopic=45358

the final para by GP is very similar to my view taking just synoptic meteorology into account, so perhaps we have something here. The +ve anomoly mentioned by GP seems to be likely to occur judging from upper air patterns.

Edited February 12, 2008 by johnholmes

[KTtom]

Like GP, John an interesting read. Funny how you need a spell of settled predictable model outputs to get you to relax, and bother to read the more technical posts and actually learn something as opposed to the usual mayhem on the model thread

Cheers

[Steve Edgefield]

Thanks John - an interesting read - not sure I always understand the technicalities of the charts and terminology but am slowly learning. What would be helpful if it's ok to say is for you to put a brief summary at the end of your account for the non-techies amongst us - to give a view in laymen terms of possible upcoming patterns and weather impacts.

Would also be good to get GP's take on how things are shaping up compared to his last post which I read - key seemed to be how the AO is progged over the next week or so..

[johnholmes]

hi Steve

which part of my post did you find hard to understand and I'll try and put it in more everyday language if I can?

as to GP then you best ask him to do that, I would welcome his input into this thread.

[johnholmes]

Update for Wednesday 13 February at 2240

The 12z run today seems to have taken a ‘walk about’ in terms of the last 2 or 3 days and how they fitted in with events over the eastern Pacific and across North America. True they do put the UK, or much of it, into Pm air rather than Tm air for much of the time after T+192 but not with any real sign of a polar outbreak. Odd really as the links/teleconnections if you like are all still there. NOAA even point to the close agreement at T+192 of the 500mb ridge in the far west of the Atlantic. Maybe its just a bit of a blip, we shall have to wait and see. Patience is the name of the game quite often in trying to tie up so many loose ends in forecasting even beyond about T+120.

The latest NOAA assessment for the period 19-23 February or about T+192 to T+240 shows some changes from the previous one. The major trough/ridge set up is much the same over North America with an elongated +ve anomaly around 50N 40W, similar, as one would expect on the GFS through that period.

ECMWF is not that different for much of that period although at T+240 it splits that high into two one in the west and one in the east of that area, not unreasonable looking at the information available. This has the effect of pushing the 500mb trough further south with high pressure building to its west. This is what is needed for the north or north westerly to develop over the area of the UK. By T+240 GFS goes for a similar solution, so most of the building blocks seem to be in place one would think. However a short wave feature then exits the USA on a developing jet which carries on deepening and thus tends to turn more north east. Later the jet pushes east and amplifies near the UK but yet another short wave feature is carried from way south on another developing jet. All very complex and it remains to be seen at what is now about T+216-240 for verification as to what actually happens.

In summation this evening one could say the predicted cold spell is ‘on hold’ for the moment!

[Steve Edgefield]

hi Steve

which part of my post did you find hard to understand and I'll try and put it in more everyday language if I can?

as to GP then you best ask him to do that, I would welcome his input into this thread.

hi John,

I really enjoy reading your thoughts - the minor point that I was trying to make is that it is sometimes hard to translate them into a forecast.

Please keep them going..thanks..Steve

[johnholmes]

cheers Steve

I sometimes purposely leave out making any comment regarding doing a forecast. Not because I don't feel able but simply to allow people to make their own mind up based on the evidence I put down.

[johnholmes]

Quick update only for Thursday evening 14 February 2008

The 12z today continues from that of yesterday with no sign post T+168 of anything other than a very temporary north west flow behind a continued succession of surface low pressure features, running through the major long wave circulation, from off the eastern seaboard to north of Norway.

There is, perhaps the first sign, of the pattern change over the North Atlantic right at the period end (T+384), but its much too early yet to know if its ‘real’ or just another temporary blip by GFS. For much of the time it’s a mix of Tm and Pm air over the country once we lose the current hig pressure set up.

We start to lose the major high of the past week or so from about T+216 as the Atlantic begins to take some effect. Not that high pressure is very far away, either to our south east or the south west as the surface lows track just a little further south with time. This can be seen as a direct result of the strongest upper flow tending to migrate further south. In turn caused by the movement of the upper ridge over the north west of N America and its replacement by an upper trough, thus moving the whole wave train east.

So after the forecast with Paul here for T+96

http://www.netweather.tv/forum/index.php?s...ry1190426(this

then high pressure remains in charge with lightish winds, patchy low cloud at times off the North Sea but also some days with clearish skies=notable night frost with a few fog patches and fairly long sunny periods giving temperatures up to or just above normal at times.

this out to about T+144 then a rather less settled look for the more northern parts of the Uk with some rain at times and strong winds now and then.

from about T+240(on present timings) generally rather more unsettled for much of the country with rain or showers at times as low centres tend to take a less northerly track across the Atlantic. Some very temporary colder incursions behind one or more of these systems, with high pressure never all that far away in a band south of the country west to east.

by about T+336 the weather systems look rather more active but still no sign of any deep cold air for the country. Just a glimpse at T+384 that upstream events, along with the comments from GP (see here http://www.netweather.tv/forum/index.php?showtopic=45358) that the start of March MAY see a pattern change.

Edited February 14, 2008 by johnholmes

[johnholmes]

Update Friday evening 15 February

First a comment on the period I first looked at on 13 February for Monday 18 February.

This looked at the time as if it MIGHT be the lead in to a more Pm type of airmass for most of the UK for most of the time from then onwards out to what was then T+384 with indications of a more definite pattern change showing through.

What about it then?

Well the then T+168 is now the T+72 and is shown below, and we all know now where the deep cold air is going to be! So that part was not good guidance.

What about the T+384, at that time, what is now Wednesday 20/02/08 or the T+120 today, below is the chart for Wednesday 20/02/08

No sign on that of the imminent change anywhere on that chart.

so much for that cold outbreak, yet another one that GFS promised with and did not deliver, or am I being too harsh?

To look at further ahead

So now to look further ahead to a possible change

out to the current T+384=end of month into early March

You may remember in a post by GP and a later T+384 for 01/03/08 there SEEMED to be the first agreement with the two methods of trying to predict a pattern change that something might be there! Yesterday it was not, today it is. Mind you it was there, to an extent yesterday, but not as evident as it is today! I'll explain.

Play the period T+240 through to T+384 our well loved 'it never really happens' set of charts.

Look at the most northern fringe of those charts and see what happens slowly but steadily.

T=300 for the first look for those not picking up my idea of a building block.

I've marked in a wavy red line the pressure of > 1020mb at T+240, compare it to that at T+300?

By T+384 its even higher along most of the northern edge. Is this the arctic high moving south? The low in the west having deepened quite a lot is out of the predicted main 300mb flow so should not move very quickly east or even north east, possibly drift north. This would allow, if it happens, high pressure to continue to build over/east of Iceland and further north.

Is there any back up for this projection?

The latest charts from 2 sources are for 12z today for T+240 and are the GFS and ECMWF

GFS ECMWF

They are not that far different, different yes, a more pronounced extension in the 500mb on the GFS over the Atlantic with the far west low in a rather different position as a result. Where they do have a similarity is the far north with both showing the first signs of the rise of pressure. So there is a little agreement that the POSSIBLE pattern change MAY be real.

Its too early to say with any certainty but it is worth watching that area along with any other information which comes to hand over the next 3-5 days(T+72-120 hours). By T+120 this would bring the time scale down to T+240 when we would also have routine outputs from ECMWF to compare with. Also by that time the NOAA 500mb anomaly charts will be covering that period.

Like I say its far too early to have even a slight degree of certainty about it. But like the other POSSIBLE events I'll keep watching it and reporting.

technical 'itch so please ignore the one at the bottom of the post.

Edited February 15, 2008 by johnholmes

[chionomaniac]

John do you think the long range modelling of both the GFS and ECM are taking into consideration the knock on effects of stratosphere warming filtering down when programming tentative pressure rises to the north? I realise that his is big time FI, but trends have to start somewhere don't they? I have read elsewhere on here today that strong La Nina signals may override any warming events but I guess we will have to wait and see.

c

[johnholmes]

no idea C if I'm totally honest, I have no in depth knowledge whatever about links between La/Le Nina and above Tropopause connections which is why I regularly read the posts from GP. He may have an idea about it.

Its an area I would love to have fully explained in simple terms to me. Maybe we could have a meet up at a seminar by someone with a good knowledge of these topics.? Anyone seen any advertised?

[chionomaniac]

no idea C if I'm totally honest, I have no in depth knowledge whatever about links between La/Le Nina and above Tropopause connections which is why I regularly read the posts from GP. He may have an idea about it.

Its an area I would love to have fully explained in simple terms to me. Maybe we could have a meet up at a seminar by someone with a good knowledge of these topics.? Anyone seen any advertised?

Thanks John. I too find it a very complex subject and this is with just scratching the surface. GP and Brickfielder have been a great help in unscrabbling this.

c

[johnholmes]

update Saturday evening 16 February

Just a few brief comments as I've been out most of the evening.

Comparing the 12z today GFS with that from yesterday.

There is less sign of pressure rises to the north, especially the far north west of the chart over the time scale T+216 out to T+384. It does give a temporary colder flow from north of the UK around T+312 and then has a mix of Pm and Tm air over the country.

Looking at the T+144 charts the UK and GFS are closest with low pressure being shown ese of Newfoundland whilst ECMWF has not got this. By T+216 GFS and ECMWF(=deeper and further west) are similar with deepish low pressure to the west of Scotland but have the centres in rather different areas and differing pressures. This has evolved by T+240 into rather different patterns with essentially ECMWF showing a south west flow and GFS having a more north of west flow.

Little sign tonight of the marked pattern change which was hinted at in the last two 12z runs.

Edited February 16, 2008 by johnholmes

[johnholmes]

Update on Sunday 17 February

For the latter end of February into March, looking at any pointers in the GFS output in that time range.

A quick look at the GFS output and there is nothing definite to suggest that a major change is under way. Yes there is a change being shown but its at the back end of the run and there is no other evidence to either back it up or disprove it. So all we can do is monitor it. Perhaps a post from GP either in here or the model thread might give some indication of what effects are expected to take place above the Tropopause that might impact below it in the time scale shown above. I certainly have no idea. I am unsure as well of just how realistic the changes GFS suggests in the ‘top lhs’ of the latter charts, say from T+288 onwards. It shows a surface high and coming ahead of it a depression which seems to be pushed ESE with the 300mb chart showing a strengthening NW jet coming out of Canada by T+360. This MIGHT cause the surface low to slow down and help develop rising pressure over/north or north west of Greenland along with the ridge coming out of Canada.

IF it did then it SHOULD help to push colder air further south into the UK behind the trough shown south of Iceland and the parent low over Scandinavia, but its pure speculation on my part at the moment.

There is some suggestion on the last NOAA 500mb anomaly chart of pressure showing rises to the north west of Greenland/north east Canada area with –ve values over/east of Iceland. A very long shot at the moment.

[Glacier Point]

A couple of observations John:

1) The NH circulatory looks very messy with no overall obvious driver and the spectre of height rises over the Arctic resultant of the series of stratospheric warmings allied to a strengthening Asian Jet. In short, the models are likely to struggle to pick on a consistent basis the extended range pattern. I'm a big advocate of using model output as guidance, but equally, have your own view as to where we might be going. The models have come up with a variety of long range solutions in the last few days which might suggest the NOAA interpretations and our own views carry a higher weighting.

2) MJO #3 has passed into phase 7. Tropical convection, which might fuel this wave passage, has slackened off a little of late although a recent increase between Indonesia and Philippines is to be noted. Note the strong -ve OLR anomalies in the area - which is going to comlplicate matters because this may teleconnect to a comparable MJO phase 4/5 response (pressure increasing in the mid latitude Atlantic).

http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

http://www.cdc.noaa.gov/map/images/olr/olr.anom.gif

3) At the same time, zonal wind anomalies are falling as a result of more easterly wind anomalies being added, particularly to the Northern Hemisphere consistent with a mature La Nina and mountain torque event over East Asia (likely to signal further Stratospheric warmings 12-15 days time):

http://www.cdc.noaa.gov/map/images/aam/glaam.gif

http://www.cdc.noaa.gov/map/images/reanaly...ltaum.90day.gif

4) We are seeing the 3rd warming episode within the stratosphere. This most recent is ongoing and has lead to a striking rise in temperature and associated drop in zonal wind anomalies extending suddenly down to the 200 hPa layer. This is almost certainly going to lead to a lagged raising of the tropopause late Feb into (more likely) 1st week March although this situation is confused somewhat by any potential impact of the 2nd warming event which was largely restricted to the 10 hPa layer. Of note w/r/t this 3rd event is the continued forecast influence at 30hPa and lower down - shown here zonal wind and temp / pressure anomalies extending down to 100 hPa with a likely ridge response over northern Canada / Alaska:

http://www.cpc.ncep.noaa.gov/products/stra...JFM_NH_2008.gif

http://strat-www.met.fu-berlin.de/cgi-bin/...p;forecast=f192

http://strat-www.met.fu-berlin.de/cgi-bin/...=f192&var=u

5) GFS AO ensembles have, for the last few days, shown a big rise then suuden fall. Today's ensemble mean shows a drop from +4 to -1 SD. That's a 5 SD point reduction which means more cold air being bled from the high latitudes and greater likelihood of cut off lows in the Atlantic and Pacific as the thermal gradient at mid latitudes is reduced.

http://www.cpc.ncep.noaa.gov/products/prec...ex/ao.sprd2.gif

This may be a little progressive, but this drop is entirely consistent with stratospheric warmings.

So putting this together, I think we are still progressing along the lines as set out in the February thoughts thread. The presence of an Alaskan ridge is consistent across operational GFS and ECM modelling, which may lead to a split vortex and height rises over Greenland as the AO tanks -ve into March.

Weather-wise, perhaps more of a signal for high pressure to persist into the next 2-3 weeks with only partial Atlantic breakdowns. Winter may not have done with us just yet, for all its disappointments, into the 1st week March with emphasis on a northerly or NE'ly type wind during this time.

Edited February 17, 2008 by Glacier Point

[johnholmes]

many thanks GP, a lot in there to read and digest over and above your excellent summary; much of this is pretty new to me so your help is much appreciated.