In Depth Model Discussion, Analysis and Summaries

[snowking]

Its still very difficult to know where we are headed really

Operational wise, we are actually looking pretty good this morning, agreement of an easterly of sorts into the weekend (after the LP encroachment on saturday) apart from the ECMWF:

So, as you can see, a fair amount of support!

The next thing then is day 10, and at the moment, some decent support amongst the operationals to rebuild pressure just to the north or west of the UK, and induce another potential easterly (note JMA is 192 and from 12z, and CMA is also 12z):

However, when we translate that to our ensemble means:

Of course, though, we do have the potential for dilution within our ensemble means, so if we take a look at our anomalies:

It perhaps becomes apparent, then, that ensemble means, at the present time, don't do us many favours. Initially looks like a weak easterly, into the foreseeable, a potential pressure rise to our north and a second easterly. Can't see anything too spectacular just yet in the medium term. Of course the cautionary note is that NWP continues to be thrown into disarray into the period beyond 120+, and ive never known such wild switching of the GFS ensemble suite (ECMWF isn't infallible either in terms of H5).

SK

Edited January 7, 2013 by snowking

[Gibby]

Good morning. Apologies for no report last night. I felt a little under the weather (forgive the pun). However, Here is the report on the 00zs from GFS, UKMO, GEM and ECM for today Tuesday January 8th 2012.

All models continue to show some rather colder air moving in after the recent mild weather. Some rain is to be expected today and again on Thursday and probably Saturday too as troughs move in from the West. In between drier spells with some sunshine is shown as ridges of High pressure crosses from the West in an airflow which gradually becomes chillier as time passes.

GFS then shows the weekend being unsettled and rather cold as Low pressure drifts East to the South with rain here with the chance of some sleet or wet snow on the hills for a time. It then clears away East to be followed by further Low pressure drifting SE over NE areas with further chilly weather with rain at times in a chilly NW wind. In FI today Low pressure slides SE from the Atlantic as pressure builds strongly to the North. Winds back towards the SE with the Low becoming dominant to the South and SW with spells of rain and strong East or NE winds turning any rain rapidly to snow with widespread disruption likely in the South and East should the FI charts verify right out to the extremities of FI.

The GFS Ensembles show a rather colder spell than what we have been accustomed of late. The Operational above was one of the colder options on offer with some rather milder options on offer too. Overall the most likely trend from this morning's output is for temperatures to be rather below normal with some snowfall possible, especially but not necessarily exclusively on the hills in the North.

The Jet Stream shows the current flow soon to ridge High to the North of the UK while a new Southern arm though weak takes the flow over France for a few days before in a week or so before the flow ridges strongly over the Atlantic and dives South over the UK in a week to 10 days time.

UKMO for midnight on Monday shows High pressure off SW Ireland with dry and rather cold and frosty conditions everywhere with some pleasant if cold sunny spells likely on the day that follows.

GEM shows the South still under influence of a Low pressure well to the South on Monday with a cold East wind but by then it is likely to be dry. Over the following days the weather stays mostly dry as a ridge collapses slowly SE over Britain with dry, bright days mixed with cold and frosty nights look likely.

ECM shows a cold ridge lying NE across the UK with cold and bright conditions with frosty nights looking likely before the trend to milder SW winds and some rain look likely late in its run with temperatures returning to normal.

In Summary this morning the models are staggering their way to something rather colder. The path to it though is slow and hesitant, mostly due to high heights down to the SW failing to link to High pressure at more Northern latitudes, while allowing Low pressure to sink SE over the UK or just to the East feeding none too warm but never very cold NW winds for many at times. The GFS operational just shows what could happen if the pattern backs West with a cold and snowy end to its run. With many twists and turns to be expected in the output over the coming days it's going to be a long and bumpy road still if it's widespread cold and snow that your looking for.

[johnholmes]

copy of post in the model thread reviewing the 500 mb anomaly charts this year

Changes in the 500mb anomaly charts-teu 8 jan 12.pdf

[trisnow]

copy of post in the model thread reviewing the 500 mb anomaly charts this year

Changes in the 500mb anomaly charts-teu 8 jan 12.pdf

Thanks John. Great for me as someone unable to understand it all.

[bluearmy]

copy of post in the model thread reviewing the 500 mb anomaly charts this year

Changes in the 500mb anomaly charts-teu 8 jan 12.pdf

i guess it depends what faith you place in operational output days 6/10 john. i know you like these charts as a final check but i think they provide poor guidance at that range based on operational output. i do accept that if they are in line with the ens guidance ref noaa cpc/naefs then that does provide solid support.

[johnholmes]

Each to their own method ba but I have seen enough anomaly charts to feel confidence when they, let alone anything else, show consistency. They are not showing it so I don't have the confidence in them until they become consistent again. I don't believe to the same extent as you do either the comments about 6-10 operational being the case nor ens guidance ref cpc/naefs is any more reliable.

Like I said at first, each to their own. I'm happy to use anomaly charts in the way I have for several years. 65-70% accuracy in the upper air 6-15 days with now and then good guidance out to 20 is as good as anything we see for free on the web in my view.

It also needs stressing that everything we can lay our hands on is needed for each of us to analyse and decide which to use and which to discard to provide some kind of reliable outlook at 6-20 day time frames.

Edited January 8, 2013 by johnholmes

[Zenarcher]

Evening everyone about 48 hours ago we had uncertainty between the models and most felt downbeat about them then yesterday we saw a better GFS and UKMO and some of the lesser known models show something good as well, today these models continue to show good charts but the ECM lately was having none of it but this evening it has changed a lot and now we have agreement between the big three.

Next 3 day forecast - Wednesday we see the North of the UK mainly cloudy but dry and the South seeing sunny spells. Thursday Scotland and Northern England will have clear sunshine but Ireland, the rest of England and Wales will be cloudy with rain around which will be heavy at times. Friday showers around Ireland and Southern parts of England but elsewhere cloudy with a chance of sunny spells. Gales over Northern Scotland on Wednesday and gales for South Western Ireland and England on Thursday. Friday a strong but cold breeze from the South East across the UK. Temperatures over the next three days will be colder than what they have been lately and night frosts are likely.

96 Hours Saturday - We have decent model agreement here we have the ECM, UKMO and GFS showing something very similar here the main three and it's so rare to get them all to agree they do get support from the JMA and the Indian model.

So what the models show here is cold temperatures and snow likely as well,

This is from the GFS,

It shows snowfall across Southern and Eastern parts of the UK,

Very cold minimum temperatures as well.

The models this evening do give this support but at 96 hours it's important not to get carried away.

120 Hours Sunday - As expected disagreement starts here but one important thing sticks out between most of the models is they all seem to be keen on bringing in heights up to Greenland. The ECM which is a good run tonight does get good support from another 4 models so that's 5 out of 8 at this point showing a positive agreement. But even those that don't agree are still good in their own right.

As the GFS shows snow still likely with the set up the models agree on,

And once again very low temps,

144 Hours Monday - 6 of the 8 models show heights continuing to rise up to Greenland of course exact details between the models vary at this point but they do show a similar picture which is a positive sign.

As the GFS shows again snowfall across the UK,

Temps still staying very low,

ECM Changes - The big change from this evening's ECM just shows how quickly things can change and how agreement between the models is a important thing remember the ECM yesterday went against most models in the early timeframes and today it has moved over to what most are saying and it does have support much better support than yesterday,

15th of January chart yesterday,

15th of January chart today

Overall - The models were actually good yesterday it's just the ECM that put a downer on things and this morning it showed a flat pattern again but continued to go against most of the other models but this evening it finally agrees. Model agreement is better than what it has been lately the models were struggling to understand the situation a day or two ago but now that they have a better understanding and better agreement in the short timeframe they are starting to show better charts further out. So a positive change in the models tonight but I will say it's very important that people don't get carried away with what they are showing do not get your hopes up yet.

Edited January 8, 2013 by weathermaster

[Alex]

Not much has been said about the other variables so lets take a step back and have a look at some other drivers of our atmosphere,

1) MJO - http://www.cpc.ncep....k/MJO/mjo.shtml

We are moving fast into phase 6, this suggests blocking to our west/northwest with a trough to the east.

http://raleighwx.ame...Phase6500mb.gif

2) angular momentum is rising - at this stage this would support blocking

http://www.esrl.noaa...m.sig.90day.gif

Alot has been said about the stratospheric warming recently, but the current highly variable models isn't helped by the fast moving MJO and rapidly rising angular momentum.

My conclusion is that we are likely to see quite possibly the most prolonged cold spell this winter, however the stability of these variable will help determine the strength of the blocking in place. Keep an eye out!

[Gibby]

Good morning. Here is the latest report of the 00z output from GFS, UKMO, GEM and ECM for today Wednesday January 9th 2013.

All models show a cooling trend over the remainder of the week and weekend. Most areas will see a bright day with some sunny spells after frost and fog clears from the North. The front from yesterdays rain is just to the South of the UK keeping things rather cloudier here. On Thursday a front approaches the SW with some rain while other areas see drier and brighter conditions though there could be some showers in the East. Friday sees a dry and bright day away from the East Coast while on Saturday a Low pressure is shown to move SE over the Western side of Britain and on down into France later in the weekend. Rain will move across West and SW Britain with some sleet or snow over the hills possible before an Easterly wind sets in for Sunday with some wintry showers of sleet or snow in the East. It will become cold everywhere by then.

GFS then shows a ridge moving across the UK from the West replacing the Northerly flow with an Anticyclonic flow, especially over the South with frost and fog by night. North-Western regions become milder under a SW flow with some rain at times. Through FI this morning High pressure is shown close to Southern Britain with a lot of fine weather here with frosty nights while many areas see more cloud at times with occasional rain running across from the West with colder and brighter spells in between. Temperatures through this period will be just below normal although rather milder in the NW for a while.

The GFS Ensembles show a rather cold spell to come with the operational on the mild side of the pack in the second half of it's run. There are many very chilly runs with the Control Run taking us into the freezer with time although it takes us back into the very mild category later next week.

The Jet Stream shows a Northern arm ridging high up to the North of the UK while a Southern arm is shown moving East to the South of Britain for a time before returning North to the UK later.

UKMO for midnight on Tuesday shows Low pressure over NE England with a chilly NW flow over the UK with rain at times, falling as snow in places over more Northern and Eastern areas.

GEM shows a much colder scenario at that time with Low pressure further South over Northern France with some snowfall for many under a cold Easterly wind, a pattern maintained for some time as new Low pressure keeps winds in the East with further snow later in the week. Winds back Northerly by the end of the run with a cold Northerly flow and snow showers down all Eastern coastal counties while the West sees dry and frosty conditions.

ECM shows a very similar sequence to GEM with Low pressure to the South keeping a snow risk for many Southern areas at times before winds back towards the North with even coder weather likely for many by the end of the run with heavy snow showers to many Northern and Eastern areas.

In Summary this morning we have a typical complex set of runs which are struggling to handle synoptics that could bring a significant cold and potentially snowy spell over the UK. GEM and ECM both show a very wintry back half to their run while GFS has done a reversal in its operational keeping high heights close to the South while UKMO after a cold and wintry weekend shows at least a temporary incursion of milder air towards Southern and Western areas. Further swings are likely over the coming days and though the temptation of excitement over mouth-watering charts for snow lovers remain I would caution to keep feet well and truly on the ground as things may still not turn out as some models currently show, mild or cold.

[phil nw.]

There`s usually one model or run that tries to throw us wrt the pattern.Previously it was the ECM and today it`s the 06z GFS operational that looks out of kilter with all other output.

I use the same guidance as always by looking at the trending in the mean outputs day to day alongside Height anomalies.

Here`s some images to show nothing has changed for the medium term,certainly up to 10 days.

The latest means from both runs at 850hPa for a week today.

Just to compare the 006Z gfs Op.

and the latest mean Height anomls for day 10

still a solid -AO and an increasingly-NAO with falling hts over Europe.

To underline how even the 00z GFS Op was unsupported by it`s own Ensls here are the Index graphs

enough blocking to send the jet south with the UK looking cold.

In the short range as well we have good agreement for the cold air spreading west.

We can see from the latest fax and GFS image it`s on it`s way west over the weekend.

as low pressure starts to undercut the building heights to our north.

In summary still some uncertainty with the placement of the surface features ie the exact track of those little lows coming south east but with enough of a mean block modelled to our north the overall pattern still looks cold for next week and beyond.

[johnholmes]

To follow on from the very objective post above from phil, just a brief and generalised simple update from me

Just a very quick post from me. Reading the model thread really is funny. So many folk going up and down like a jack in the box as each run, not even a full run, each frame comes out. You really should look at yourselves.

Meantime what is the overall pattern into/over the weekend and beyond?

Cold sums it up, rain or snow for some during Friday into Saturday and snow showers down the eastern side on Sunday.

Detail-silly question as always. Precipitation is never sure even 24 hours out-yet again I have to say add on 7 more additional variables for do you get snow or not. That is reality.

Beyond that and the overall view to me is staying cold for most. The anomaly charts are LARGELY, note the word, in favour of a block persisting, most probably NW of the UK. All but GFS support this idea, NOAA, consistently now for 8 or 9 days, ECMWF for about 6-7; GFS is the odd one out with it being both less consistent and less in favour of blocking than the others. NAEFS, since it started to follow the blocking idea, about 3-4 days ago is generally along the same lines as NOAA.

Obviously there has to be reservations in the 6-15 day time frame let alone further out. As I’ve posted before on my confidence levels they vary from about 65% to 90%, at the moment I would say 75% or so for cold to dominate in the 6-15 day time span, and in the 1-5 day also with this at about 90%.

Edited January 9, 2013 by johnholmes

[stodge]

Afternoon all

Apologies if this isn't the right thread for this, but I'm musing on the GFS and the discussions thereof. Correct me if I'm wrong but there are at least 22 versions of the output available on Meteociel (Op, Control and twenty perturbations). Now, these all start from the same point so they would be identical at T0 and there wouldn't be much variation at say T+48.

It seems that variations increase (as mathematical theory and probability would suggest) from T+72 onward and by T+144 the 22 versions are starting to vary quite considerably. This is where we begin to talk about "groupings" of cold and mild runs on the Ensembles produced later in the day.

By T+240 it seems that the 22 versions are going to diverge even further and while there many be some common features, that commonality will erode further so that by T+384 there are a series of wildly different outcomes on display. Those who think that all 22 versions will all go the same way at even T+240 are not merely barking but well on the way to upminster (a little London Tube humour). In every ensemble set therefore, there will be a minority of versions which differ from the majority let alone the Operational or Control runs.

What I don't know is whether this is a complete lottery (in the sense that any one or none of the 22 might verify at that range) or whether there are "form" horses. At T+24 I would expect the vast majority (if not all) the outcomes to verify, at T+72 I would expect a majority to verify but has anyone studied whether at T+240 any version is any more likely to verify than any of the others. Is the Operational considered the most likely followed by the Control or is it even less ordered than that?

If you have an Operational run which shows one scenario at T+144 and more than half of the other versions show an opposite scenario, I would be tempted to argue that the opposing scenario is more likely to be correct but if the Operational has more data or more "form" if you like, then we can weight the probability of its verification accordingly. I've "heard" that "more data" is programmed for Op and Control runs but I have no idea whether that is a) true or B) it enhances the verification statistics of those runs.

I appreciate that you could argue that tonight's Op will verify at T+6 and probably even at T+24 but those who follow every frame of the Op run as it rolls out are not only deceiving themselves as to comparative analysis but also to ensemble analysis. Looking at the ensembles as a bloc would seem to be the coherent way to analyse the output and ignoring the average (will have outliers) and look primarily at the largest cluster of scenarios as, by definition, the most likely to verify.

I suspect somehow it doesn't work like that but I'm a historian not a mathematician or physicist.

[Gibby]

Good evening. Here is tonight's report of the 12z output from GFS, UKMO and ECM for today Wednesday January 9th 2013.

All models are agreed on the general plan of the trend to much colder conditions over the coming days. A band of cloud and rain will move slowly into SW areas tomorrow following a cold, frosty and in places foggy night. the rain peters out on Friday as the front dies a death over the UK on Friday leaving a cold and dull day with drizzle here and there. On Saturday a new front together with Low pressure moves SE over the SW and sets up a strengthening Easterly flow with an area of rain moving North. The undercutting cold air lis likely to breate a wintry mix of rain, sleet and then snow for many Southern areas on Saturday night. On Sunday a cold and raw East wind will be blowing with some wintry showers of sleet and snow likely near Eastern coastal counties through the day with residual sleet and snow leaving other Southern areas on Sunday morning.

GFS then shows a ridge of High pressure collapsing SE over the UK giving some cold and frosty weather before milder Atlantic SW winds develop over the UK with some rain at times later in the week. After several days of Westerly Atlantic type weather before High pressure reforms close to SE Britain drawing a colder feed of air back ino the Uk from the SE late in the run.

The GFS Ensembles shows the operational on the mild side of the pack but not without some support. there are though many colder options shown and on balance it looks as if the operational has minimal support with the average 850's for the run staying below the long term mean throughout, after the next few days. Some precipitation is shown from time to time , no doubt some of which would be snowfall. The most precipitation though is shown from the Northern Ensembles in association with the milder members.

The Jet Stream shows the flow running East to the South of the UK with a Northern arm riding high well North of the UK. Later in the weekend the flow becomes disorganized and differs between the models with the general concensus for it to remain South of the UK.

UKMO for midday on Tuesday shows Low pressure stretching from Northern Norway right down into the North Sea with a cold Northerly flow establishing over the UK with areas of snow or snow showers moving down over the UK in very cold conditions.

ECM for the same time point shows Low pressure close to SE Britain with a very cold NE flow over the UK with some disruptive snowfall likely in the South and East. Over the following few days things are shown to become if anything rather worse with a strong to gale Easterly wind and potential for blizzards to hit the SW on wednesday and more generally over the South on Thursday. A quieter but bitter cold day is shown on Friday before next Saturday shows further wintry weather close to the SW and over many Northern areas in continuing bitter cold.

In Summary the cold spell is well and truly on the way. After a gradual cooling of conditions over the coming days the weather turns decidedly wintry as we move through the second half of the weekend and (as much of the output shows) much of next week too. Details will change from what I have described above as various scenarios develop through the period but it does look as though there will be a lot of interest for those looking for cold and wintry conditions. The only one caveat to mention is that the American model (GFS) is less supportive of the wintriness shown by the other models and will have to back down in favour of the others or vice versa. It all makes for fascinating model watching as the power of Mother Nature battles it out over the coming week to 10 days.

[Gibby]

Good morning. Here is the morning report on the 00z output from the big four, namely GFS, UKMO, GEM and ECM for today Thursday January 10th 2013.

All models show a colder and wintry spell spreading into the UK over the coming days. Today shows a chilly and cloudy day though with some bright intervals in places.as a slack area of Hugh pressure weakens further as a trough moves into the SW later bringing some rain. This trough weakens in situ tomorrow with a dry and cloudy day likely tomorrow before Saturday sees a more meaningful area of Low pressure move in close to the SW. With pressure building to the North a cold Easterly flow undercuts the rain area moving in from the West and SW with rain turning to snow later on Saturday and into Sunday when wintry showers move into Eastern areas too. Early next week then shows a strong divergence between the models.

GFS shows a ridge of High pressure drifting SE over the UK and on down into France. After a couple of days of cold and frosty weather milder SW winds move into the UK bringing rain and strong winds across the UK from the West towards the end of the week. In FI today the GFS operational shows a potentially wet and stormy period as deep Low pressures steam across the Atlantic and over the UK with frequent bouts of rain and showers falling as snow on Northern hills at times.

The GFS Ensembles show a short cold spell before a return to more average conditions as the Atlantic brings a return to wind and rain at times. This doesn't proclude the risk of some snowfall over Northern hills in the rather chilly conditions following the rain bands. The operational is a slightly warmer meber of the pack while the Control run shows a very deep cold spell late in its run.

The Jet Stream is a little disorganized at present with the main arm well South of the UK for some time to come. Later a strengthened arm moves East across the Alantic to the UK in a week or so.

UKMO for midnight on Wednesday shows High pressure to the North of Scotland with a ridge South over the UK. the weather would be very cold and frosty with some snow showers in the SE slowly dying out.

GEM shows High pressure North of the UK too at that time with a very cold NE flow over the South with further sleet or snow showers in places. Later in its run the cold weather persists with winds keeping an Arctic element to them with sleet or snow at times in very cold and frosty conditions.

ECM shows something a little different this morning with the cold Easterly flow more restricted to the North while Low pressure moving further North over the UK than previous output re-introduces milder air into the South with rain heare while the North sees more snowfall. However, the pattern remains essentially a very cold and unsettled one over the UK towards the end of its run with spells of sleet and snow for all at times.

In Summary the stand off between GFS and the rest persists this morning. Never in the history of my model watching which in some shape or form has been over 20 years have I witnessed such a stark contrast between one model and another meaning totally different weather conditions to be experienced at the surface. The Euro models maintain a basically cold and wintry outlook though widespread snowfall looks less likely from the UKMO output away from the East after the weekend.. ECM does also show a hint of milder air making inroads into Southern Britain early next week just for a while. But it's GFS that still shows nothing particularly wintry at all going for wet and stormy weather as it's likely outcome in association with deep Low pressure rushing east from the Atlantic. It's Ensembles also suggest a very brief cold blip followed by a return to normality spare the Control run. I wouldn't want to be a professional forecaster today as they must begin to feel pressured on making a call on where the weather is likely to go as we move into next week.

[johnholmes]

For those new to model interpretation, simply read the two summaries above by Gibby. It shows quite clearly how over a 12 hour period the emphasis can change.

last evening

In Summary the cold spell is well and truly on the way. After a gradual cooling of conditions over the coming days the weather turns decidedly wintry as we move through the second half of the weekend and (as much of the output shows) much of next week too.

this morning

In Summary the stand off between GFS and the rest persists this morning. Never in the history of my model watching which in some shape or form has been over 20 years have I witnessed such a stark contrast between one model and another meaning totally different weather conditions to be experienced at the surface.

[johnholmes]

a look at what the upper air charts have shown over the last 3 days and other data that may also affect what the weather may actually be like in 7-15 days time?

500mb charts-a summary past 3 days on thur 10 jan12.pdf

[Methuselah]

Thanks again John. What's a 'strunf'?

[johnholmes]

here it is

http://forum.netweat...-forecast-snow/

remember there are lots of other guides on models and a host of other things in there

Thanks again John. What's a 'strunf'?

a what-I'll investigate-sounds like the idiot typing it type error!

obvious mate what;s up with you, still being not English I suppose!!

the word should be strung

my quick notes sometimes in intelligible english obviously sometimes not

Edited January 10, 2013 by johnholmes

[Methuselah]

here it is

http://forum.netweat...-forecast-snow/

remember there are lots of other guides on models and a host of other things in there

a what-I'll investigate-sounds like the idiot typing it type error!

Cheers, John!

[johnholmes]

from the model thread for Ian B and Ian F hopefully

Totally disagree - with respect to Stewart and the METO - both were wrong in December and the METO did a quick volte face.

I'm surprised the METO are talking about snow early next week, I thought the 6-15 dayer would stress the uncertainty. The GFS must be a huge elephant in the room at Exeter right now.

I have to admire you Ian-I think!

How about in the quieter thread you give a detailed explanation of why you think this.

It would also be interesting if Ian F could spare time to drop in the senior man's comments as to why they feel so confident this morning?

I will drop that in that thread as well-pages will soon cover this post

[Gibby]

Good evening. Here is my evening report on the 12z outputs from GFS, UKMO and ECM for tonight Thursday January 10th 2013.

All models show a trough crossing slowly NE over SW Britain and an old front closed to the East Coast. The net result will be a mostly cloudy 24 hours with some heavier rain in the SW at first and some drizzle near the East Coast. It will feel rather cold. through tomorrow a slack airflow over the UK will mean light winds. low pressure will then approach the SW on Saturday with the Easterly flow on its Northern flank moving across Southern Britain on Saturday. A band of rain will move NE over these areas before receding away South on Saturday night giving spells of rain at first turning more to sleet and snow later giving a covering in places, especially on higher ground. By Sunday a cold Easterly flow remains over the UK with snow showers near the East coast and dry weather in the West once any remaining snow left from Saturday clears away. It will become very cold everywhere.

GFS then takes us into next week with a further trough slipping SE over Britain on Monday with a band of rain, sleet and snow for many for a time. By midweek a slightly milder SW flow develops over the NW as Low pressure deepens and slips SE over the UK. Rain would develop widely but the air would be cold enough at times to give some snowfall, chiefly over the hills and in the North. through FI tonight the weather remains very disturbed and potentially stormy and rather chilly with showers or longer spells of rain, sleet or snow, with the snow risk maintained for the higher ground and more generally in the North at times.

The GFS Ensembles show a very cold few days from late in the weekend with the moderation of the cold as we go through the week with Low pressure delivering rain or sleet at times in generally cyclonic conditions. There is generally less spread between the members with some unity on the spread around the -3 to -4c isotherm.

The Jet Stream shows the flow currently split into two arms, one well North of the UK and a weaker arm to the South. With time the flow increases its complexity before a strong arm exits the States towards, then South of the UK in a week or so time.

UKMO for midday on Wednesday shows a cold ridge of High pressure from a centre well to the NE of Britain lying over Southern Britain. Low pressure is sinking SE through the Atlantic towards the SW by Thursday. A cold and frosty spell at this time point before rain and snow move into the West in the following 24 hours.

ECM at the same time shows a much more pronounced wintry synoptic setup with Low pressure sliding ESE towards the South of the UK throughout its extended part of the run with periods of snow for many with some temporary incursions of milder air working its way into the far South at times. Frost ice and travel disruption problems would be inevitable should this run verify.

In Summary the weather still looks decidedly wintry tonight with GFS, though not exciting showing a little more leeway towards cold scenarios than was shown on earlier output. I always think the UKMO charts show very simplistic looking synopses on their outputs and that is true on the 12z 144hr chart tonight. At first sight it appears poor but with the Low in the Atlantic moving SE snow would feature for Southern and Western areas in the day that follows. ECM speaks for itself and ensures a prolonged and sustained wintry spell next week with major disruption for some at times. Some milder air does flirt with the far South at times though it looks unlikely to spread further North than Southern coastal counties in the forecast period, though of course when talking at specifics at this range things can and will change. Nevertheless, the UK could be on the cusp of something as wintry as that we experienced in December 2010 should some of tonight's output verify.

[nick sussex]

I decided to repost this in here as it will probably get lost in the model discussion:

For those following this thread today you would have seen me putting up some SREF charts in an attempt to look at the upstream pattern.

This model is the USA mesoscale model upto T87hrs and works similarly to the UKMO NAE, in the SREF they take 21 ensembles plus the NAM operational run time lagged by 3hrs and the mean value is whats shown on the SREF charts.

Quite happy to see that this model does get used by NOAA in their diagnostic discussion today, they actually used the 09hrs SREF mean together with some of the other models for part of their forecast.

This suggested on its 09hrs run that the GFS had called the pattern incorrectly, as we saw on the 12hrs the GFS deepened that ne Canada low and left more shortwave energy behind, this did indeed at least lead to more favourable phasing with that trough in the west Atlantic.

Perhaps it might be another model we can use for the upstream pattern in these knife edge situations, I certainly will keep a check on it over the coming weeks to see how good it is compared to the normal global models.

[summer blizzard]

I decided to repost this in here as it will probably get lost in the model discussion:

For those following this thread today you would have seen me putting up some SREF charts in an attempt to look at the upstream pattern.

This model is the USA mesoscale model upto T87hrs and works similarly to the UKMO NAE, in the SREF they take 21 ensembles plus the NAM operational run time lagged by 3hrs and the mean value is whats shown on the SREF charts.

Quite happy to see that this model does get used by NOAA in their diagnostic discussion today, they actually used the 09hrs SREF mean together with some of the other models for part of their forecast.

This suggested on its 09hrs run that the GFS had called the pattern incorrectly, as we saw on the 12hrs the GFS deepened that ne Canada low and left more shortwave energy behind, this did indeed at least lead to more favourable phasing with that trough in the west Atlantic.

Perhaps it might be another model we can use for the upstream pattern in these knife edge situations, I certainly will keep a check on it over the coming weeks to see how good it is compared to the normal global models.

Do you have NAM discussion? Has it gone with the ECWMF?

[johnholmes]

Good evening. Here is my evening report on the 12z outputs from GFS, UKMO and ECM for tonight Thursday January 10th 2013.

All models show a trough crossing slowly NE over SW Britain and an old front closed to the East Coast. The net result will be a mostly cloudy 24 hours with some heavier rain in the SW at first and some drizzle near the East Coast. It will feel rather cold. through tomorrow a slack airflow over the UK will mean light winds. low pressure will then approach the SW on Saturday with the Easterly flow on its Northern flank moving across Southern Britain on Saturday. A band of rain will move NE over these areas before receding away South on Saturday night giving spells of rain at first turning more to sleet and snow later giving a covering in places, especially on higher ground. By Sunday a cold Easterly flow remains over the UK with snow showers near the East coast and dry weather in the West once any remaining snow left from Saturday clears away. It will become very cold everywhere.

GFS then takes us into next week with a further trough slipping SE over Britain on Monday with a band of rain, sleet and snow for many for a time. By midweek a slightly milder SW flow develops over the NW as Low pressure deepens and slips SE over the UK. Rain would develop widely but the air would be cold enough at times to give some snowfall, chiefly over the hills and in the North. through FI tonight the weather remains very disturbed and potentially stormy and rather chilly with showers or longer spells of rain, sleet or snow, with the snow risk maintained for the higher ground and more generally in the North at times.

The GFS Ensembles show a very cold few days from late in the weekend with the moderation of the cold as we go through the week with Low pressure delivering rain or sleet at times in generally cyclonic conditions. There is generally less spread between the members with some unity on the spread around the -3 to -4c isotherm.

The Jet Stream shows the flow currently split into two arms, one well North of the UK and a weaker arm to the South. With time the flow increases its complexity before a strong arm exits the States towards, then South of the UK in a week or so time.

UKMO for midday on Wednesday shows a cold ridge of High pressure from a centre well to the NE of Britain lying over Southern Britain. Low pressure is sinking SE through the Atlantic towards the SW by Thursday. A cold and frosty spell at this time point before rain and snow move into the West in the following 24 hours.

ECM at the same time shows a much more pronounced wintry synoptic setup with Low pressure sliding ESE towards the South of the UK throughout its extended part of the run with periods of snow for many with some temporary incursions of milder air working its way into the far South at times. Frost ice and travel disruption problems would be inevitable should this run verify.

In Summary the weather still looks decidedly wintry tonight with GFS, though not exciting showing a little more leeway towards cold scenarios than was shown on earlier output. I always think the UKMO charts show very simplistic looking synopses on their outputs and that is true on the 12z 144hr chart tonight. At first sight it appears poor but with the Low in the Atlantic moving SE snow would feature for Southern and Western areas in the day that follows. ECM speaks for itself and ensures a prolonged and sustained wintry spell next week with major disruption for some at times. Some milder air does flirt with the far South at times though it looks unlikely to spread further North than Southern coastal counties in the forecast period, though of course when talking at specifics at this range things can and will change. Nevertheless, the UK could be on the cusp of something as wintry as that we experienced in December 2010 should some of tonight's output verify.

note how the summary from Gibby is somewhat different this evening from the morning issue-another indication of the variability in the models.

[Gibby]

Good morning. Here is the report on the 00z output of the big four models from GFS, UKMO, GEM and ECM for today Friday January 11th 2013.

All models show a colder period developing over the weekend as Low pressure moves in towards the SW with an undercutting cold Easterly flow developing over the British Isles. After a benign type of day today rain reaches the SW later tonight and spreads slowly East over Southern England turning the rain to snow as it engages the cold air late tomorrow and overnight. The front recedes away South on Sunday leaving a cold East or NE flow with sleet or snow showers near the East Coast for a while, dying out later as a ridge collapses SE ahead of a new area of rain, sleet and snow on Monday as it moves SE over Monday. This then remains in situ on Tuesday as a change to clearer weather on a Northerly flow arrives in the West with continuing sleet and snow for the East.

GFS then shows a continuation of cold and wintry weather through much of next week with snow in places, more especially in the North while much of the precipitation will turn to rain at times in the South as milder air infiltrates from the West at times. Through FI this morning the cold and unsettled weather situation remains in place with deep Low pressure areas crashing into the UK and on each Northern and Eastern side of these sleet and snow will be widespread and heavy and disruptive in places. Over Southernmost areas some snow is also expected though down here this may turn to rain on occasion as milder air comes tantalisingly close, especially late in the run.

The GFS Ensembles show the operational as a slightly milder run than the member pack in the South as the milder air entrapped under the depressions pass through with many members showing rather colder positions. There is plenty of unsettled weather shown and with coldish uppers around some of this will fall as snow almost anywhere in the UK.

The Jet Stream shows a flow high over the Arctic at the moment and a weaker flow to the South of the UK. Over the coming week or so a strengthening flow over the Atlantic moves South over or to the West of Britain, turning East over Southern Europe in a week or so.

GEM this morning also shows cold and unsettled weather next week with sleet or snow at times as successive Low pressure slips SE over and to the SE of Britain at times. It too shows milder air flirting with the SW briefly with some milder, rainy periods here before cold weather return to all later. High pressure gradually becomes dominant over the UK late in the run with some very cold nights with severe frost likely then as the precipitation risk subsides.

UKMO for next week shows cold and unsettled weather continuing in as small disturbances (in it's case) running SE with rain, sleet or snow at times for all in a very cold week away from far Western and SW areas where milder air infiltrates at times.

ECM finally shows the first half of next week with the cold and unsettled flow with as described above but later in their run High pressure slips down from the NW, eventually cutting off the cold weather as returning polar maritime air topples round the High and down over the UK bringing milder and rather cloudy weather late in the weekend with a thaw.

In Summary there is still a cold spell on the way. I detect a lessening of the snow risk early this weekend as the rain looks like causing more of an ice risk rather than settled snow for many in the South. Through next week further opportunities for snow remain for many as SE moving depressions engage cold air over the UK. The pattern in the far South and West will be more marginal at times as milder air is close by to our shores. Later in the output GFS maintains the pattern as above while both GEM and ECM show a UK High pressure moving in from the NW which ECM slips South later to bring less cold weather and a thaw late next weekend in from the NW.