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

[johnholmes]

hi

I hope to be able to use this thread to have a look at what the models appear to be showing from about T+96 out to maybe T+168, sometimes less, hopefully it can pick up where the thread from Paul B ends(http://www.netweather.tv/forum/index.php?s...p;#entry1152014)

I'll have a look on a wider scale at upper air features, compare the 3 main models, drop in on the NOAA discussions when they involve our area, and make my own comments about how I see things. I'll no doubt make lots of mistakes in any predictions I give but never mind its not a bad thing and all of us learn something new every day. I hope those who feel able will contribute to the thread. Those who may not feel able to, do please read it, ask questions on the thread or pm me, I'm sure if I cannot answer you someone else will be able to.

Looking a little further than Thursday/Friday

(typed am on Thursday)

The Atlantic is certainly in charge in the foreseeable future. Detail is uncertain and subject to change from one run to another let alone day to day.

I'll give my take on it for what its worth.

chart1

Over the weekend the upper flow sees the jet powering across the Atlantic, see the 200mb chart from 00z today. What is still not certain is where the jet position will be in another 72-96 hours. Will it split, one north, one south, if so which will be the strongest? Will it simply carry on eastwards? GFS seems to think so if you look at the Extra version below.

chart2

Looking at the jet pattern on Extra through the week and the jet later runs from north of Newfoundland, see below for T+72The jet is shown as a fairly strong flow across the Atlantic, fairly flat(or westerly) and keeping over or just south of most of the country. The possibility around T+72-96 for the low shown on the two Fax charts to deepen markedly is, I feel, a distinct possibility.

This was shown fairly well by the Met O Fax for T+96 and T+120(as of now), or so I thought, see below

chart 3

chart 4

However their latest idea see below at T+108 shows a rather different idea.

chart 5

I'm not convinced this is right and still favour their first idea (T+120), as the jet seems likely to show as we see on extra below. This assumes that the jet does power straight across the Atlantic and does not split into two. True it shows no sign of a major 'streak' within the main jet flow but it is possible for this to occur.

Even this, in my view, does not allow the low to deepen as much as I think it could. More like, the Met O T+120, possibly a bit deeper.

Obviously this difference has major implications for the latter part of the weekend and early next week.

Will it do what I suggest, what the Met O first suggested, or what they now suggest.

Having said that GFS keeps various small lows and runs then quickly east (roughly), before making more of one on Tuesday.

We can only wait and see.

So even at time scales of T+48 to T+120 there are various possible outcomes. The one thing that is certain is that it's the Atlantic in charge, and with the airmass being mostly Pm for much of the country, away from southern England, although even this is open to doubt, as the paragraph above suggests.

I'll put up any other changes and the actual chart for 12z Monday for comparison as we go through the time sequence.

Looking further ahead

This is the NOAA idea of how the 500mb flow will be in several days' time, and shows where the major lows and troughs are over N America and out into Europe.

It suggests a largish ridge over eastern Canada and a trough over/west of the UK.

No 6

The GFS Extra chart for about the middle of this period, say 10/01/08 shows this

No 7

This more or less fits with the idea of an upper trough to the west of the UK, although the upper ridge has moved away from N America by then.

Even this, in my view, does not allow the low to deepen as much as I think it could. More like, the Met O T+120, possibly a bit deeper.

Obviously this difference has major implications for the latter part of the weekend and early next week.

Will it do what I suggest, what the Met O first suggested, or what they now suggest.

It seems logical but one never knows this far ahead, so stay tuned as they say to see how the synoptics develop.

Edited March 18, 2008 by johnholmes

[PB22]

Thanks John, an excellent analysis, and even if I say so myself, I think it follows on well from the model summary.

[johnholmes]

adding to my initial post with some comments and charts currently out.

Just a few comments on the Sunday into Monday period

This is the Fax for Saturday 12z

chart no 8

It looks fine to me; the extra msl/jet shows this at the same time

chart no 9

It has the beginnings of a low about where the Met O Fax has it.

24 hours later=Sunday 12z it shows this shape in other words GFS simply moves the jet east, edging a touch further north, and decreases the central speed.

It runs the small low in roughly the same direction as the jet is moving and it shows no deepening. That seems reasonable as its outside the main jet flow and its left entrance or right exit areas (this is where surface lows tend to deepen). If it is under the jet then it will deepen and tend to turn to the left of its track.

chart no 10

If so how then Met O Fax shows this for the same time (as of 1650 Thursday)?

chart no 11

Even odder to me is this, 12 hours later

chart no 12

Hope at least some of you are following!

Either GFS is wrong in its jet prediction or the Met Office is wrong in its low position.

Quite where they get the 12z Sunday one from I'm not sure, I'm even more unsure of where the 00z Monday appears from, given what I've just posted above.

If we look at their own 00z model for Monday

chart no 13

I wonder which set of charts they are following?

The one above 'seems' to support their version.

If you read any of the text forecasts for the UK (issued around 1530 Thursday) they all talk of gale/severe gales for the southern half of the country but not for the north.

ie:-sw England

Outlook for Sunday to Tuesday:

Very unsettled with showers or longer spells of rain, some heavy. Windy at times with a risk of gales, perhaps severe in exposed parts. Temperatures near normal for early January.

Updated: 1541 on Fri 4 Jan 2008

and for sw Scotland

Outlook for Sunday to Tuesday:

Bright or sunny intervals and occasional showers, these heavy at times and falling as snow on high ground. Winds becoming strong at times.

Updated: 1439 on Fri 4 Jan 2008

I'm sure all will become clear over the next 24 hours or so but its very far from clear at the moment.

Its absolutely crucial where the jet is when the small low starts to appear and obviously just where that is.

Much as I am spitting into the wind so to speak I do wonder if the low is not going to deepen quite a bit and head much further south than the Met O currently show on their Fax charts.

Comments, beyond 1 liners with your views very welcome.

Edited January 4, 2008 by johnholmes

[Matty M]

I thought this chart might interest you JH

It is infact a sensational chart.

Lets hope we can build on it

[Cookie]

I very much look forward to reading, i think I picked up the main jesit of it , thanks for the effort much appriciated

[The Enforcer]

Bit of a jump in the UKMO fax chart projections for Monday (12z). Suddenly, it's looking much milder over the UK, judging by the DAM line positions. The only real change is a system has been thrown several hundred miles further north. In all other respects the synoptic pattern is the same. Arguably, to the west, the DAM lines are more favourable for cold. This seems to have come out of the blue and doesn't really tally with the other charts:

From:

To:

Edited January 4, 2008 by The Enforcer

[Cookie]

I think you'r all Determined to give me a sore head

[johnholmes]

Bit of a jump in the UKMO fax chart projections for Monday (12z). Suddenly, it's looking much milder over the UK, judging by the DAM line positions. The only real change is a system has been thrown several hundred miles further north. In all other respects the synoptic pattern is the same. Arguably, to the west, the DAM lines are more favourable for cold. This seems to have come out of the blue and doesn't really tally with the other charts:

From:

To:

much more realistic chart in my view, I'll post what I made this afternoon when I've loaded the charts for the outlook for next week.

might be quicker if I did this first!

all along I've maintained that the low would cross about the middle of the UK as I've shown for 00z, how much it deepens is a major factor on where it will cross and that is uncertain at this stage.

Met O latest now getting nearer my version, and I'm sure it will be modified even further by Sunday

Edited January 4, 2008 by johnholmes

[johnholmes]

Taking a look rather further head than the next 72-96 hours,

for that see here

http://www.netweather.tv/index.cgi?action=...e=view;blog=248

by Paul B with a good unbiased look at the models out to T+96.

This one is for the middle to end of next week.

First to pick up on the chart shown above, 10th January and from ECMWF which is also mentioned by Nick on the model thread for T+240 with the 850mb.

Just to show what ECMWF has at T+240, see below

chart no 14

Rather a nice looking chart for the cold lovers IF it happens.

So what are the probabilities of this happening when we start to day from this?

chart no 15

And in the so called reliable time frame, T+96 this

chart no 16

To be able to make some objective assessment of this we need to look at some other charts

The one below is the 200mb (about 40,000ft) chart for the northern hemisphere.

chart no 17

It shows the jet which I've been watching and got a log of over the past 4-5 days, now powering out across the Atlantic. Perhaps the GFS version might be easier to take in.

chart no 18

It appears to running straight into the block and doing a fair job of putting the skids under it shall we say.

I often witter on about everything is linked and you cannot just take one part of the atmosphere and ignore another part, so we must take account of what that hemisphere chart is showing. Its not the only part though, what is happening beneath it, say around 500mb (18,000ft)?

What may happen to them both in the forecast period we are looking at, out to T+240 and perhaps beyond a little?

I drop in most days to the USA NOAA 'techie' type discussion as it gives a good idea of how confident their forecasters are with the evolution of the models, and they do regularly give their outlook for 6-10 days ahead.

An example below from today

TOWARD THE END OF THE PERIOD THERE IS MODEST CONVERGENCE AMONG 00

UTC GFS/GEFS MEAN/ECMWF/NAEFS AND 12Z ECMWF ENSMEAN REGARDING A

MEAN TROF EVOLVING OVER THE PLAINS/SRN ROCKIES REGION.

TELECONNECTIONS RELATIVE TO THE TWO BEST DEFINED ANOMALY CENTERS

BY D+8...A POSITIVE NEAR THE CANADIAN MARITIMES AND A NEGATIVE

OVER ALASKA...GENERALLY SUPPORT SUCH A TROF OVER/NEAR THE CENTRAL

CONUS. THE STRONG DAY 7/FRI SYSTEM IN THE 00 UTC ECMWF MAY BE

OVERDONE

and one of their charts showing maximum temperature anomalies

chart no 19

One of the charts they use is the one below showing their suggestions of how the 500mb patterns may look some 6-12 days down the line.

chart no 20

In simple terms it suggests that a major ridge is likely over the eastern shores/western Atlantic with a marked trough over western areas. Downstream (our area) they show a major trough for the far east of the Atlantic and Western Europe with a subsequent ridge to the east.

Some of you may already be following the drift! For those not used to this type of analysis, worry not, I'll try to explain it. Major troughs and ridges are what govern the weather. They in turn CAN be subject to outside influences, such as QBO, NAO, and such like (for their meanings please read the NW Guides). Leaving that aside these major wave patterns in the upper atmosphere usually have particular weather characteristics. In major troughs there are often surface depressions and on the western fringe of the troughs much colder air is apparent in the far north. In the RIGHT conditions this, often intensely, cold air can flood south and can then be very difficult to move due to its density (cold air is denser than warm air). Sometimes in these cold areas large anticyclones or highs will develop (we saw one this week), and they are then not easy to displace with low pressure systems.

So to sum up, the chart shown by Matt M in my view fits in rather well with the 500mb anomaly chart given by NOAA, which would suggest that IF, big IF, all the parts come together then we MAY be about to see(from a week Saturday/Sunday) a change from Atlantic changeability to a block developing. If this happens then we would get a cold spell. Whether it is an easterly or a northerly is not certain but probably a northerly initially.

Something to watch over the coming week as we shelter from gales, rain, showers, and for some with good elevation, snow.

Anyway I hope that makes interesting reading, please do add your own comments (with the usual proviso, no one liners and no bickering about who is right) NONE of us are!

Also do ask questions either on here or via pm.

Edited January 4, 2008 by johnholmes

[Craigers]

explained really well, even for an unexperianced/knowlageable person like me!, really different this january!!!!

[Snow Queen one]

Thankyou John for such an easy to understand informative post. This has given me slight hope that might have a chance of seeing some snow settling before the end of winter.

[Cookie]

very intresting read, not what I hope for mind but still very infomative

[snowy owl]

Lovely easy to understand post, now know what to look for in the coming week. many thanks.

[johnholmes]

An update Saturday morning on the immediate future, or out to T+48 Monday 07/01/08

The latest sat picc and Fax chart show where the small wave/centre is.

And the Extra msl-jet stream shows us where the surface centre is under the jet flow

It appears its on the warm side, just, of the jet pattern.

The T+24 and 48 msl-jet stream charts also show where the jet and low/wave moves

Just the T+48 here

so we can see that the latest runs do not suggest any real deepening,(against my idea yesterday) thus the low runs with the jet flow and with very little deepening, but as a distinct centre with GFS.

The Met O version this morning is this for T+24

And for T+48 this

They appear to have made of a centre they have drawn to the nw of the centre GFS shows and then run that north east to about 59N 15W, with an occluded frontal system into the trough extending into the south west of the UK.

So even now, less than 48 hours away, two of the centres have a rather different outcome. We cannot look at the ECMWF as its not down to that time scale

So we watch and wait again.

[Stoxs]

Hi John

First many thanks for your clear and easy to read sumaries must be alot of work to produce these.

Going onto the forcast for the next week + , i like the optomisim of a couple of the forcasters on here for colder conditions but IMO i got a feeling it is going to be close but no cigar. I think the charts now could well look very simliar in another week i.e HP to our east ,jet no real change as it is now and dominante lp to our north . I could be totally wrong and we will see HP north of us for the next 2 weeks .

Just wondered what your thoughts are on what i feel could happen?

many thanks again

stoxs

[johnholmes]

hi Stoxs

From one point of view if we have such a difference and changes between the Met O and GFS only 48 hours ahead then what the models may show out into FI is probably hardly worth logging on for!

However, I still think its too early to be sure just what is going to happen 10 days down the line. As ever it depends on IF all the necessary bits of the jigsaw fall into place at the right time. If not then probably nothing more than a fleeting cold behind a large low.

At the moment I remain slightly optimistic.

I may change my views up or down as the days pass!

[jy]

People in wales reporting temps of 4 degrees and falling also mix of sleet and hail can this be possible and if so how has it come about please info only.

[Wosser]

Just had some hail here

[snowking]

Just to sort of add to this

My knowledge is obviously far far less than yours, but i tend to use just the basic output of NAO, PNA and AO. Of course as youve said, you cant really ignore certain parts of the atmosphere and just focus on others, so i couple this with things such as QBO output where i see necessary

It was using these three main factors that i was able to see this mini cold spell which has recently passed, which i commented upon on another forum. I tend to use the PSD outputs, which unfortunately only give the NAO and PNA, meaning that for the AO expectations i have to use the GFS output, which is generally far less accurate.

However, the PSD output does make for interesting reading

I have found it best to use the 7 and 10 day outlooks for accuracy

Whilst the NAO has in fact today become less certain in the sense that yesterday it seemed to suggest a liklehood of a -ve phase, the PNA looks to be eading farly strongly +ve.....of course normally coupling a strongly +ve PNA with the -ve NAO, provided that the PV and ultimately, AO doesnt spoil the party, it suggests a much higher liklehod of either a northerly or easterly flow across W Europe.

So, to the unfortunately GFS produced AO output

The 7 to 10 day outlook loosk fairly promising, although the 10 day outlook starts to suggest it heading positive again, with an admitedly very large spread across the ensembles

It looks like its going to be around friday time to me until we can ultimately see whether or not anything will materialise, which i have suggested elsewhere, may well be sometime around or just afte the 20th jan if it is to pull off

Kris

Edited January 5, 2008 by snowking

[BLAST FROM THE PAST]

JH

Thanks for that, a really excellent read and lesson. More of the same please!!

BFTP

[johnholmes]

I'll have a look shortly at the charts posted by Snowking although I'm far from well read and some of the data being shown, tks BFTP.

I'm going to take a look this morning at events in the next 24 hours, the continuing difference between the UK Met O and GFS as to how events may turn out, using mostly 00z data.

The next 24 hours with GFS and UK Met

They are still showing a slightly different evolution to the system that will bring rain with some hill snow overnight and into Monday.

This is the latest UK Met O Fax chart showing the position of the low(s) at 06z Sunday

with their view of the situation at 00z tonight (Monday)

Something of a half way house between their two versions over the past 48-72 hours.

GFS shows this (using Extra for more detail at the same time and off the 00z run

It continues to show two centres, one much like the Met O and one further south east.

If this is correct then areas just south of the second centre will get a windier spell., as shown above

In terms of ppn then areas further south than the single centre scenario would also get more.

In terms of snow risk then it probably increases the risk slightly for N Ireland and northern England, although its really areas with elevation anyway, apart from a short spell of leading edge sleet/wet snow which will soon change to rain.

Snow is likely to be mostly confined to ground above 500ft with possibly a few centimetres and over 1,000ft from N Wales northwards perhaps 3-5cm. Wintry type showers possibly for the higher elevations behind the main frontal zone during Monday.

The Met O Fax for 00z Tuesday shows just what a messy type of synoptic chart we may have. Quite cold air on the southern flank of the string of lows along 60N with further lows running west to east on two more frontal zones further south.

A broad brush treatment of unsettled would cover it, windy at times, and temperatures around the seasonal normal!

Later today we should be able to rack the low(s) as they move towards the UK and see which centre has the more accurate fix on the situation.

Edited January 6, 2008 by johnholmes

[johnholmes]

Just had some hail here

can we put entries into the correct thread please and I did ask for NO 1 liners.

sorry if I seem picky !

re the post by Snowking above on the longer term.

Your knowledge of this stuff is way above mine Kris, so don't belittle yourself. I'm an old fashioned meteorologist so I probably am more knowledgeable than most on here about basic synoptic meteorology but what you quote and others on this forum, GP to mention just one, is well ahead of me.

Its interesting that your take is not that different from mine. I've used my synoptic experience along with using that to try and convert NOAA forecasters comments, largely about N America to convert it into our area. The basic meteorology of upper air does seem to fit in with the ideas you express kris. Mind you this is hardly surprising since I often go on about everything is linked. So the factors you quote are linked to the more basic meteorology I've used.

I'll try and do another post this evening on how things seem to be shaping over the past 48 hours for the period in question.

tks again for your input, please keep posting it in.

Edited January 6, 2008 by johnholmes

[Cookie]

Thanks for the update mate another great read. I cant bealive how messy that last chart looked that you posted up.

[johnholmes]

taking a look at 12z data principally to see how the next 24 hours may develop

below is the sat picc visual from Dundee which shows the low very well(NW not very good on this run for some reason)

and the surface chart from UK Met

with the position of the jet/msl at 06z using the NW Extra GFS charts

to my eyes still the low should be somewhere over northern England/southern Scotland as it tracks east or a touch north of east rather than the more north east track UK Met still show, although this latest one is a bit further south than their previous one was

below is a very rough diagram of a couple of hours later rig reports along with the 12z upper air from Valentia in sw Ireland.

My predicted track may turn out wrong but it looks realistic to me at the moment. If its wrong I'll be on and apologise!

this is the GFS fuller version of winds at jet level and the msl chart

Edited January 6, 2008 by johnholmes

[johnholmes]

Time for another look into the mid term weather future.

My thanks to Snowking and also to GP on the model thread (post No 200 on page 12 today).

Both seem to suggest that winter is certainly not over so can basic meteorology support this. Its hard to find much support by simply looking at the 2 main models around T+240

http://www.netweather.tv/index.cgi?action=...5e9d5f72f71c2c0

By the time you read this it may have the 12z versions up so who knows what they will show. Anyway the 06z versions showed little to suggest any major change from what is currently on offer. Namely the Atlantic in one form or another. For 4 or 5 days GFS shows pressure relatively high in the far north across most of the chart, even tries to build a ridge in the Svalbard region, but all this has gone by T+240 and GFS has no sign of it returning out into its ultimate T+384(on its 12z run today).

The discussions on NOAA all suggest that the major long wave pattern is moving along in the normal west to east set up. The ridge over the west and troughing in the east taking the place of the reverse several days ago. This is just a small excerpt from this morning's discussion

VALID 12Z THU JAN 10 2008 - 12Z SUN JAN 13 2008

THE LARGE SCALE MEAN PATTERN DURING THE WED-SUN PERIOD SHOULD

CONSIST OF A MODERATELY AMPLIFIED MEAN TROF EXTENDING FROM ERN

CANADA INTO THE CNTRL-ERN CONUS AND A GRADUALLY AMPLIFYING MEAN

RIDGE NEAR THE WEST COAST INTO WRN CANADA. BY THE LATTER HALF OF

THE FCST PERIOD THE PRIMARY ISSUE IS HOW MUCH AMPLIFICATION OCCURS

OVER THE WRN CONUS/NRN MEXICO WITH RECENT ECMWF RUNS TENDING TO BE

MORE AGGRESSIVE THAN OTHER GUIDANCE.

The 200mb flow for 12z today is here and illustrates the points made in the NOAA discussion.

chart 1

A 500mb predict chart for 11-15 January shows small changes from the previous one I posted. Mean heights show a negative value in the east Atlantic into western Europe area but without any real sign of it shifting east. Nor of the opposite, of any sign of the high anomalies to our west and north giving any indication of edging into our area. So basically at 500mb, and also higher up, as well as the surface, we are looking at much the same as we are currently experiencing.

Having said all this it was without a lot of warning that the last high pressure appeared and moved closer to the UK. I believe it was KW on the model thread who made the observation that in La Nina winters, any highs are more likely to be Russia/Scandinavia rather than Greenland based. We have already had 2 from the former areas and the posts from GP and SK suggest we may get another. I have to say I am now less hopeful in the time scale I'm dealing in, much less so, but I have very little experience in trying to find how such situations can develop.

One thing I thought of looking at are the ensemble pressure charts by GFS.

Taking a sample of, say, Iceland, London, Berne, Helsinki and Moscow to see if they showed up anything that might help support the idea of colder weather in this time scale. They are the 06z issue

London

and reasonable agreement out to about 13/01 of a succession of low pressure systems, thereafter, wide scatter but a trend to higher pressure.

chart 2

Iceland

chart 3

This has pretty low pressure throughout although quite wide scatter from about 11/01

Now to Helsinki

chart 4

Relatively high pressure throughout but with very wide scatter by about 09/01

Moscow

chart 5

This started high and showed a general fall, albeit with some scatter to around 11/01, it then had perhaps the widest scatter of all of them so far with GEFS control, mean and GFS operational showing not much closeness after 16/01. >1050 to about 990mb at the end!

Finally to Berne

chart 6

Pretty close agreement up to 13/01, suggesting(to me) rather unsettled conditions into central western Europe in that period; then a slow recovery of pressure by the end with the 3 'main checks' only about 10mb apart. They also showed a slight drop in 850mb temperatures (I have to admit more than a passing interest here as my annual ski holiday will be close by!)

Now make of the above what you will, I'm not very optimistic I have to say. IF the ensembles have got anything near to what happens then there is NO sign of any pressure rise to the north west of the UK. What MAY happen further east is uncertain. Pressure does look to rise but, apart from that slight fall of 850's at Berne, we have no means of knowing what type of higher pressure or where it will be located.

I'll do another one mid week to see how things have developed and please do keep your posts coming in. PLEASE stop dropping one liners in here – thank you. However I'm happy to answer 1 liner questions or longer ones if I can either on here or via pm.

For a good idea in a more realistic time frame then don't forget this thread with Paul B, essential reading!

http://www.netweather.tv/forum/index.php?s...p;#entry1156821

Edited January 6, 2008 by johnholmes