In Depth Model Discussion, Analysis and Summaries

[phil nw.]

Nothing to be down about this morning if you are a cold lover.

The main trend by all of the models is colder air coming from the east with chances of some snow over the weekend in eastern areas in the form of showers and then from the north west spreading south on Monday from a shortwave development.

As the system goes through we see a renewal of the cold from the east

maintaining the wintry feel.

After this point as ever some differences are apparent between the models with the amount of blocking showing to our north west but i think at the moment it`s best to view developments iin 4-5 day blocks as the pattern is continually changing.

At the very least it looks to be quite cold now well into next week.

[Stoxs]

right i will try my questino here as it was just deleted from the model discussion thread .

going on from the massive variables at close range.

Do the models have or use past cinarios to help produce current model runs?

I.e will they take on board recent events then next time this sort of situation occurs they mightbe better placed to deal with it.

A top forcaster like john Holmes with many many many years experiance will be able to interprit the model information and put his own twist on it with his knowledge.

In 40 years time will my grandchildren be sat here having a panic attack when the threat of snow is forecast.

Please if this is in the wrong thread MOVE do not delete, Thank you.

hope someone can help, cheers

[phil nw.]

Hi Stoxs,

In laymans terms each model run is simply fed with up to date atmospheric/ocean/land observations and the computers crunch the numbers.

Here some links about the models that you may find useful in our learners area.

A good site for weather related questions here.

Hope that helps.

http://weatherfaqs.org.uk/

[Stoxs]

cheers phil

yes i know how the models are fed with current infomation ,

I am trying to establish how they deal with the infomation, so in 10 years time will these models witht the same info inputted produce the same results?

I guess fine tuning of the program running it is how it will improve.

otherwise as i said in 40 years time i can imagine the weather models to be 100 times than they are now.

say FI being 6months!!!! lol

the weather dosnt get any more difficult to predict it has done this for 2013 years atleast!

wil have a look at your links. if any has any input to this subject it would be gratefully recieved

[Gibby]

Good evening. Here is the report from my perspective on the 12z output from GFS, UKMO and ECM for tonight Friday January 11th 2013.

All models show a colder flow from the East gradually developing over the coming 24 hours. A low pressure gradually moves into the SW approaches tonight and on into Europe later tomorrow. An occlusion will move North into the South of the UK by morning with rain which may turn to snow on higher elevations tomorrow evening and night. On Sunday a cold NE flow gives way to slack winds as a weak ridge comes down from the North. This will be followed by a wave depression running SSE over the British Isles over Monday with some widespread snowfall for many Central and Eastern areas at least.

GFS then shows Low pressure sliding away into Europe by midweek with a bitter cold and wintry NE flow establishing briefly with snow clearing to snow showers over the period. Late in the week the weather moderates though with some hard overnight frosts persisting with the least cold conditions likely in the NW over the weekend. Through the start of FI the weather will remain on the cold side of average in the South and East close to High pressure just to the SE. The North and West would see less cold and rather cloudier if largely dry weather before a cold front crossing East over the UK later brings fresher and milder conditions for all with a little rain at times but some good drier spells too.

The GFS Ensembles show a rather cold picture for the next few weeks though the deepest cold weather will be reserved for the early days of next week. The weather looks unsettled at times with some wintry precipitation expected for many at times though with some milder interludes likely in the West especially.

The Jet Stream shows a disorganized pattern for the next three or four days before it looks like a strengthening flow comes across the Atlantic, ridging High over the Eastern Atlantic and down over the UK towards Southern Europe late next week.

UKMO for midday on Thursday shows High pressure near the Shetland Islands with a ridge South over the UK. A depression in the Atlantic looks like sliding SE towards the SW approaches pushing a band of rain, sleet and snow into SW areas later in the day and the following one.

ECM tonight shows High pressure slipping South over the UK later next week with the cold and frosty conditions associated with it releasing their grip as milder Atlantic winds return to the UK late next week and through the weekend with troughs bringing rain East in the flow. A return to rather cold conditions look like developing in the late stages of the run with rain at times and snow on the hills, especially in the North with the days to follow showing potential for a return to the freezer.

In Summary the pattern remains a cold one for at least the next 5-7 days. Snowfall is much harder to predict and is totally dependant on the track of the Low pressures tracking down from the NW. There will always be a trend for Mondays event to be a messy wintry mix over Western Britain while the East look guaranteed for a good snow event. Later in the week there are more opportunities shown from UKMO in particular but thereafter it looks like milder air will gradually develop over the UK though probably not as pronounced as GFS shows. ECM shows great potential for a return to deeper cold following Day 10.

[johnholmes]

Not just me re experienced forecaster-what we see from Ian F and the senior man's comments is this at the top of the tree, highly qulaified with a fair amount of experience, first class forecast staff support, masses of data, tight schedules to meet but his will be the closest on I would say 90% of occasions to anyone else. As I've said before so he should be but unfortunately quite a lot on the web fail to see just how good and how often they are good preferring to pick up the poor forecasts. Of course they get it wrong meteorology is a science but with more than a touch of art in presenting it.

The key for anyone is not to give knee jerk reactions, not to change without having considered all the options, use every bit of information not just things that seem to fit better. Be objective, even the senior man will have a weather preference on that I would bet but he has to ignore it and after assessing decide objectively and clinically what is the most likely outcome based on what he has in front of him.

a bit wordy but hope it helps and the post by phil is spot on-nothing goes in to the model, no gugance as to how it should react to recent events, just the data as it is at cut off time. Then it follows the rules of thermal dynamics using immensely complex mathematics to do the number crunching, the sites phil quotes are well worth reading and try Google for other info or the Met O web site for details on the different models they use. Presumably ECMWF and GFS offer the same background information?

Will your grandchildren be in a similar position in 40 years, almost I suspect, the accuracy will have improved and the distance from T+00 will have increased as well as improving but I honestly cannot see major improvements in what I call synoptic forecasting, how warm/cold wet, will it snow-probably accurate at perhpas T+48 but not much further.

Perhaps I should add to that seasonal forecasting may well show the largest improvements but don't expect muc detail, warmer/colder/wetter/drier accuracy should improve though.

end of sermon!

Edited January 11, 2013 by johnholmes

[Stoxs]

I appreciate there are many top forcasters like yourself john. You were singled out due to the massive experiance you have LOL

thank you for your infomation.

I can see technology catching up with nature to be honest maybe 40 years is to soon but unexpected weather events could well be a thing of the past!

Look how technolgy has improved in the last 40 years! Weather/ nature still the same?

current technolgy/ forecasts are amazing really with more and more regular accurate winter/summer forecasts occuring.

thank you all again

[Gibby]

Good morning. Here is the report on the 00z output from the major four models of GFS, UKMO, GEM and ECM for today Saturday January 12th 2013.

All models show a cold spell to come. There is a lot of difference between the models and their specifics from quite an early stage in the runs and by nature of the up and coming cold spell I will not deal with specific synoptics this morning as things will change by the next run but indicate trends shown by the models themselves as they move through the period. In the short term there is some agreement that a trough over Southern England currently is engaging cold air through today with rain, some of which is quite heavy lasts on and off through the day. Later in the day as the front sinks South the rain may turn to light snow before clearing away South tonight. Ice will form behind it as the South joins the rest of the UK in a cold night with some snow showers near the East Coast of NE England. This persists through the early past of tomorrow before a front slips South over Scotland later tomorrow, through Sunday night and Monday with a mix of rain, sleet and snow for many with brighter showery weather in the far West later on Monday with snow mostly restricted to the East.

GFS then shows its trend this morning with a UK battleground with snow a risk throughout with a more general period of cold weather under a cold ridge midweek with snow showers in the east and sharp night time frosts. Then spells of rain and snow occur frequently as Low pressure slides SE over or just to the South of the UK maintaining the cold and wintry theme.

The GFS Ensembles show a cold theme this morning with the average 850's for London remaining between -3C and -9C throughout. With Low pressure around too there is likely to be some snowfall mixed in with cold rain in many areas too North and South.

The Jet Stream shows a flow to the south of the UK for some time to come with a continuation of disruption in the flow as it strengthens to approach the UK, turning South to Southern Europe in a week or so.

UKMO for midnight on Friday shows a Southerly moving Jet and a High centred over Scandinavia with a ridge over the North of the UK in very cold air. Low pressure in the Atlantic is moving SE and would probably replace the snow showers in the East with more prolonged snowfall in the SW later.

GEM shows Low pressure to the NW disrupting and sliding SE with outbreaks of rain and snow with the risk of a strengthening cold setup at the end of its run as pressure builds over Scandinavia.

ECM shows a totally different setup ending the cold spell but sooner as the Jet charges NE around a sinking High over the UK next week with a return to mild SW winds everywhere with rain at times later next week and onwards.

In Summary the models are still struggling on how to handle the complex synoptic patterns over the UK from now on and through next week. With the lack of High pressure to the North we rely on the positioning of Low centres as to whether any one area receives snow or not and it may well be that some Western areas see very little snow from this cold spell. The East may well see plenty through next week but the specific detail of movement of depressions is entirely dependant on that even here. Longer term there is an enormous difference in the models with ECM seemingly out on its own pushing the Jet flow over a sinking UK high and returning milder and windier weather to all areas late next week. The other three show a Jet well South of the UK steering Low pressure SE across the UK with further wintriness for some at times in fairly cold conditions. Which one is right? Is ECM barking up the wrong tree given that its last few operationals have indicated a quicker route to milder weather than it's colleagues? These are the questions the forecasters have to work out over the coming week or so.

[bradymk]

just want to compare some long term developments. JMA and CFS anomalies up to week 4 show surprisingly relatively good agreement with the pattern. Not saying they are correct but they both go for the same pattern at the moment.

JMA here has +ve heights western greeland and the iceland area for this week. For days 9-15 it still shows the +VE over Greenland and Iceland with also a strong signal for low pressure over southern Europe with a strong North Easterly flow and low pressure running to the south of us. Week 3 and 4 shows the main heights moving slightly westwards with low pressure over europe still but further north with slightly milder weather for the southern half of the UK but northern parts of the UK still cold. Temperatures still below average but not as cold as week 1 and 2 but that is a long way out.

Now the CFS V2 has been consistent with this cold spell along with many other anomaly charts. This for week 1 shows +ve heights to our north, low heights to our south with an easterly flow. Week 2 shows strong +ve heights over Greenland and Iceland again with low heights to our east and south with a north easterly flow. Week 3 shows a similar pattern but with heights to our north moving westwards slighty into Eastern Canada with low heights still to our south and east although low heights further north into the southern half of the UK so staying cool but not as cold. Week 4 showing similar to week 3.

Now im not saying these are right but thats pretty good consistency from CFS and JMA anomaly charts for each week and both show a similar pattern with a easterly this week, north easterly next week before heights move more west based causing temperatures to rise but still below average.

Please dont go away thinking that +ve heights means a Greenland High because +ve anomalies for Greenland just means higher than normal and normal is pretty low for there during the winter. All they are is a deviation away from the mean. Also, I am not sure these are correct myself as I think the first week of February maybe colder than these suggest but i thought it was interesting how similar both long range models are at the moment. Both are cold into February with below/well below temps.

[If Wishes made Weather]

I am posting this in here on the basis that it is a complex couple of questions, and that they would rapidly get lost were I to post them in the 'cold' thread. Mods, feel free to move however. So if there are any more knowledgeable members who fancy a stab at answering:?

1 - we have seen a couple of FI and semi reliable charts this winter (inc. THAT ECM) that have shown conditions that would quite possibly bring blizzard conditions to southern lowland England. Typically low upper temps, easterly source, moderate to strong winds, heavy PPN from low heights or possible undercutting channel/northern France low tracking westerly. In all instances, these charts have collapsed in the semi-reliable time frame accompanied, as far I can tell, with the collapse of several members nervous systems. Thus, what charts should we be looking for in FI and the semi-reliable (circa 96-144 in times of low Shannon entropy) that will mature into the conditions I mentioned above at T0?

2- now that the SSW is in full gear (possibly overdrive), is there anything in the charts that indicate at the moment that we will start to see unusually cold winter weather rather than the sort of cold snap (which used to be standard winter weather for a week or so) which is now more or less programmed to last through the upcoming week, or is it the case in times of high Shannon entropy, that there is no correlation between what charts at say the 120hr plus mark show, and what actually happens?

Sorry that this sounds a bit like an old-fashioned A level paper. Discuss.

[Gibby]

Good evening. Here is the report on the 12z output from GFS, UKMO and ECM for tonight Saturday January 12th 2013.

All models show an Easterly flow over Southern Britain bringing cold and breezy conditions to the South currently with rain and snow in places clearing away South over the coming hours. Slacker winds are present further North where things stay dry for a while before a front slips SSE over the UK from the NW reaching NW Scotland soon and trundling down to Southern Britain by tomorrow night. Snow would occur for many with at least a covering for most and rather more for some particularly in Central regions. On Monday a further frontal system is shown to move SE over the UK with snow again for many before it looks likely to change to rain for Southern and Western areas through the day.

GFS then shows several days with a cold East flow over the South with the chance of snow showers near the East Coast while other areas stay dry and cold with sharp night time frosts and sunshine by day. Towards the end of the week further sliding Low pressure near to the SW brings the risk of substantial snowfall here while Northern and Eastern areas are more likely to stay drier if still cold. Through FI tonight conditions do slowly warm up though it never becomes mild. Low pressure is never far away from our shores and copious rainfall with some snow on hills would do nothing to help the still saturated ground of SW Britain.

The GFS Ensembles show a cold set tonight with the operational on the warm side of the pack while the majority show 850's some way below the long term mean at around -5C. With precipitation around through the run nationwide some will fall as snow for certain.

The Jet Stream shows the flow moving East to the South of the UK with another arm subsiding over NE Europe. later in the period a stronger arm moves out from the States but is blocked in mid Atlantic pushed well North to Greenland while a secondary arm moves Southeast from Biscay to the Med.

UKMO for midday on Friday shows High pressure over Scotland with a weak NE flow over SE Britain. The weather would be dry and very cold with widespread very sharp frosts by night, sunny, frosty days too with a few wintry showers possible in the SE.

ECM shows an area of High pressure centred over Southern Britain next Friday with very cold air entrapped in it's circulation and near the surface resulting in very harsh frosts but dry and bright conditions by day where any freezing fog patches clear. A weak front becomes trapped between two High's near the UK late next week with the life squeezed out of the trough along with any rain or snow with the end of the run looking like maintaining a cold anticyclonic pattern more or less over the UK with a continuation of the settled conditions as before nationwide.

In Summary tonight there are contrasting messages between the models yet again with GFS keeping very unsettled and chilly conditions over the UK latterly while ECM and UKMO become UK High pressure influenced later in the coming week after all models show the coming 4-5 days as very tricky for forecasters to get the predictions right as to where it will snow and where it will not. However, there are no mild charts on the output tonight and with the support of a chilly looking set of GFS Ensembles suggests to me that things are going to continue to feel more seasonal over the coming few weeks, snow or not.

[Gibby]

Good morning folks. Here is the report on the 0z output from the big forecasting models of GFS, UKMO, GEM and ECM for today Sunday January 13th 2013.

All models show that the coming week and weekend are going to be cold everywhere. In the short term an area of slack pressure covers the UK before an area of cloud and sleet and snow is spreading sown from the NW though the day reaching the SE tonight. All areas will probably see a little snow away from the far SW and near coasts exposed to a breeze off the sea. As this dies out a more active band of precipitation moves SE down the East Coast in association with a Low cell bringing further snow tomorrow for the North and East but more likely to be rain in the West and South before the cold weather in the East returns back West through Tuesday with some occasional snow. By Wednesday a cold airflow covers the UK. In a rather complex pattern snow showers could occur almost anywhere with frost at nigh widespread and sharp. Later in the week specifics will change but it looks like staying cold and frosty with a fair amount of dry weather though fronts close to the SW could bring some snow here at times in a cold and raw SE flow.

GFS then moves through Week 2 with Atlantic Low pressure ganging up to the West pushing troughs up against a fairly weak cold block to the NE of Britain bringing rain and strong winds into the UK once more falling as now at times, especially towards the NE and on higher ground at times elsewhere. In FI the operational shows Low pressure trundling across the UK and out to the East with a pressure rise over Greenland replacing the rather cold and wet conditions over the UK through this period with a bitter Northerly flow with widespread snowfall for a few days before slightly less cold air with further sleet or snow around moves back into the UK at the very end of the run as the Jet Stream stays well south of the UK.

The GFS Ensembles show quite a lot of spread between the members from next weekend with a lot of milder and colder options on the table skewing the average trace to near normal for late January. The operational was not far from the long term average for much of the run wavering milder and colder as the Lows pass through. The Control run was a cold outlier with the UK staying in the freezer through the second half of the run with all areas at risk of precipitation at times.

The Jet Stream shows a flow running to the South of the UK at present with this pattern continuing for several more days. Later in the coming week the flow strengthens out of the Atlantic and disrupts in mid Atlantic with some energy flooding North and the main energy sliding South once more South of the UK.

UKMO at 144 hours shows an Arctic High extending a ridge South over the UK with Low pressure over Scandinavia and the mid Atlantic. The Jet Stream lies well South of the UK with the nation lying under a very cold setup with widespread severe night time frosts and snow showers down Eastern coasts.

GEM at 144hrs shows a complex structure of High pressure to the North of the UK with fine and cold weather away from snow showers near Eastern coasts and the chance of a spell of snow in the extreme SW as a disrupting Low pressure slides to the South propping up the High which becomes centred over the UK at Day 10 in continuing cold and by then dry conditions.

ECM for Day 6 shows High pressure over Scandinavia with a cold SE flow over the UK. A few snow showers are possible near Eastern coasts at that time with the West cloudier with the risk of snow as a trough moves up against the cold air over Britain. Through the following days the High to the NE gives way and a slow transition to milder Atlantic based weather develops with time lifting temperatures following bands of rain and snow feeding East by the end of the run with winds turning South-Westerly.

In Summary all models have a very cold flavour to them this morning. Week 1 looks guaranteed to stay cold now with some snow about, especially in the East over the next 48 hours and from snow showers later. Elsewhere chances of snow are more limited with some rain or sleet likely tomorrow before here too things become cold with at leas the chance of snow particularly in the SW as small disturbances run SE towards the SW approaches. Frosts will be persistent and very sharp, especially under clearer skies later in the week. As usual in Week 2 things become far more complicated and are dependent on what happens to our cold block to the North or Northeast which are notoriously fickle to forecast at this time in Winter. However, as shown it looks like the Atlantic develops enough punch to bring us back into a most likely cold zonal type pattern with rain and wind at times which does not exclude the chances of further snow events as cold frontal sectors pass by, especially in the North.

[johnholmes]

Final 500 mb check after 12 months-during today I will try an post thoughts on how the upper air pattern may look in 6-15 days time.

No 31 500mb outlook 1-12 Jan 13.pdf

[Polar Maritime]

Final 500 mb check after 12 months-during today I will try an post thoughts on how the upper air pattern may look in 6-15 days time.

No 31 500mb outlook 1-12 Jan 13.pdf

Thanks for putting all the time in JH, and sharing with us all.

Edited January 13, 2013 by Polar Maritime

[TonyH]

My regionally biased look at the week ahead:

http://forum.netweather.tv/blog/309/entry-4544-latest-weekly-weather-guide-monday-14th-to-sunday-20th-january-2013-west-wales-and-the-midlands/

[johnholmes]

copied from the model thread

a look at the 500mb charts to see if they help peer into the future?

8-500mb anomalies on sun 13 jan for next 2 weeks.pdf

[Gibby]

Good evening. Here is the report on the 12z output from GFS, UKMO and ECM for Sunday January 13th 2013.

All models show a cold week to come. Early in the week troughs and a developing Low pressure slips SE over the UK and away to the SE midweek. This brings a mix of rain, sleet and snow for many with snow restricted but significant to the far East of the mainland. Elsewhere rain or sleet is far more likely with little disruption likely. In the second half of the week the pattern becomes more complex though still cold as the Atlantic moves up against the UK with the threat of heavy snow and/or milder weather knocking on the door by the weekend.

GFS shows a cold Easterly flow midweek quickly replaced by a cold SE flow to end as Low pressure approaches from the West. Some snow may well move into the West before dying out over the start of the weekend as the High to the NE rebuilds briefly. However, as the axis of the ridge sinks South the Jet rides over the top and the Atlantic cranks up a gear with the milder SSW flow taking shape quickly at the weekend. Thereafter, the pattern of Low to the North and High to the South with a strong West flow over the UK lasts for some time with some rain at times, especially in the North. There would be a few cooler intervals as cold fronts pass by but nothing remotely wintry at the surface felt for late January.

The GFS Ensembles are not so good for cold lovers tonight with a cold week being replaced by a trend towards more normal conditions later as the Atlantic takes control in week 2.

The Jet Stream shows the flow being directed under the northern High for the week to come before a strong turn North in the flow towards the North late in the week runs the risk of the flow riding over the top of the sinking or receding european High pressure at the weekend.

UKMO shows the midweek period dominated by High pressure to the NE with a ridge over England. The down side of this is that the stronger Easterly flow shown on the 00z is much lighter, hence less chance of penetrative snow showers inland from the East coast but on the plus side Low pressure slides SE close to SW Britain on Thursday with the risk of an area of snow in the SW causing problems here as more Northern areas stay cold, dry and frosty. By Friday a monster Low to the SW is a rare sight for UKMO with a strong to gale East or ESE flow blowing over the UK with an active front in the English Channel. With rain and sleet near the South Coast and Cornwall other areas of Southern Britain, Wales and the South Midlands would encounter potential blizzard conditions and major disruption should it verify.

ECM shows the midweek period as cold with an East flow and some snow showers in the East and SE for a time before the end of the week sees a complete difference to UKMO with a Scandi High holding solid with it's ridge over the UK maintaining frost and ice by night and little thaw of any lying snow in the East. Later in its run the High does give way slowly as the Atlantic pushes in to the UK with a band of snow followed by rain. However, with Europe remaining locked in cold, successive low pressure disrupts and continues to pull energy SE and although on this run it is too far East to mean anything other than rain for the UK away from the far East.

In Summary tonight there is a mixture of outcomes shown which make things no clearer on where we go forward from Thursday of this week. With blizzards (UKMO), cold and frosty weather, (ECM) and mild Westerly winds (GFS) are all on offer over the next few weeks. Much as I would like to see UKMO's evolution come to fruition I very much side with the ECM evolution with GFS far too progressive too quickly. Nevertheless, the GFS Ensembles are disappointing tonight and it looks like after a week or so more of cold we may have to confront the power of the Atlantic winning over early next week.

[Thundery wintry showers]

Potential for some moderate to heavy snow over much of the UK tomorrow, but temperatures will be pretty marginal due to a pool of warmer air with 850hPa temperatures around or above the -5C mark, especially the further south and west you are, so it is doubtful as to how much of it will settle on low ground. The GFS is suggesting that north-east England is most likely to be heaviest affected:

http://cdn.nwstatic..../uksnowrisk.png

We have seen a significant toning down of the subsequent easterly- many earlier runs would have seen a fair number of snow showers come in off the North Sea, particularly for SE Scotland, NE England, Lincolnshire and Norfolk, but it has now been slackened somewhat. The ECMWF and UKMO versions are a little less slack than the GFS and more in line with what the FAX charts show, and thus would bring snow showers further inland than the GFS precipitation charts are suggesting, but if the GFS version comes off then it will only be coastal fringes that will see any showery activity.

The easterly flow is likely to slacken off almost completely by Thursday with snow showers restricted to coastal fringes, but there is considerable potential for classic "frontal battleground" snowfalls as Atlantic weather systems struggle to make much headway against the Scandinavian blocking high and also bring some fairly potent polar maritime incursions in behind the fronts, causing cold air to meet slightly less cold air. A fast breakdown from the west is not implausible as we saw the models overdo Scandinavian blocking as recently as mid-December, but at the other end of the spectrum, nor is something similar to the 5th-7th February 1996 when some parts of the UK had a sizeable dumping.

[Gibby]

Good morning everyone. Here is the start of a new week and the first working week report on the 00z output from the big four, namely GFS, UKMO, GEM and ECM for today Monday January 14th 2013.

GFS shows a cold week to come with the current weak Low pressures trundling away SE to Europe over the next 48 hours taking their rain and snow with them The cold intensifies somewhat midweek as the High pressure over Scandinavia throws a ridge SW over Britain with very frosty nights and dry weather the form horse before the Atlantic pushes into the block at the weekend. Thereafter, after a period of snow turning to rain the weather becomes Atlantic based through FI as deep Low pressures to the North steer wet and windy weather across Britain in a rather chilly cold zonal pattern. Some snowfall would occur at times over the hills as cold fronts pass and showery interludes intervene.

The GFS Ensembles show a trend towards less cold conditions from the end of the week and with the increase in precipitation spikes the influence of the Atlantic is likely to win through with rain or showers likely next week, though still with a snow risk at times over the hills.

The Jet Stream shows the disrupted flow currently gradually giving way to a stronger feed across the Atlantic towards the British isles by the end of the week and the weekend as the High to the NE gives way.

UKMO today shows a depression moving SE over Eastern Britain over the coming 24 hours with a band of rain, sleet and snow currently moving SE over the UK gradually clearing away in a day or so with winds changing to a raw and cold Easterly for a time with some snow showers in the East. With a blocking High over Scandinavia Low pressures from the Atlantic take their energy SE, one on Thursday to the SW with a sleet or snow risk there before stronger versions move up against the cold air over the UK late in the week and weekend giving some heavy snowfall for Southern areas with a trend for this to revert to rainfall in the far SW and South Coast with time in strong winds by then.

GEM shows Low pressure too sliding SSE across the UK today and tonight with some rain or snow, chiefly across the East. High pressure then pushes a ridge SW from Scandinavia with a cold few days of dry and frosty weather away from the East Coast where some snow showers could occur. Late in the week and weekend it too shows sliding Low pressure into the SW of the UK with snow turning to rain with time as somewhat milder and wetter conditions win through from off the Atlantic next week.

ECM finally also shows Low pressure clearing away SSE over the next 24 hours as well as another wave to the SW taking attendant rain and snow with them. A few cold days under the Scandinavian ridge then ensues over the middle of the week before it too brings disrupting Low pressure SE again late in the week. With the cold air in place over Britain some snow would develop again towards the weekend, turning to rain as the cold air is diluted and pulled slowly away NE leaving a snow risk just for NE areas with time with some copious rain events likely for the South and west at times.

In Summary this week is going to be cold with a snow risk at times, chiefly in the East and later in the West and SW. Thereafter the cold weather looks like being slowly displaced by milder air moving in slowly behind successive frontal troughs giving snow back to rain scenarios with snow restricted to the higher ground of the North and NE as we move deeper into next week. Some heavy rain is likely though again, especially in the SW should some of the output of this morning verify. It should be noted that the models only bring a tentative return to milder air and changes on the output over the next few days back towards cold or more decisively mild options are likely to be shown.

[phil nw.]

I thought i would just have a look at some of the medium range outputs just to see where we might be heading past the weekend and i picked T192hrs-day 8 from the 00z ECM/NAEFs runs.

For any new members the NAEF`s is the North American Ensembles Forecasts which are the combined outputs from the Canadian(GEM) and the American(GFS) models-they also share this information with the Mexican MO i believe.

First the mean Ht anomalies and actual mean hts.at 500hPa level

and the actual mean hts

A pretty solid picture of the Atlantic low pressures heading south east as they comes against those heights to our north.The direction and development of the troughing is across Ireland across the south west of the UK and then Europe.

.We can see on the mean 850hPa temps we are on the edge of the cold block which will ebb and flow through this week and into next as that relatively weak Atlantic energy tries to come through but then looks to take the easier route to the south.

These outputs of course are watered down somewhat because they are average results but never the less show what a fascinating pattern we are in.

We can`t relax for one day with the Op runs as they seem to be constantly changing beyond days 4-5 and so the weather for the UK is a nightmare to forecast.

Often in a typical UK Zonal(mild)pattern we can have confidence much further out.

All we can deduce from these is that areas of the UK further north and east will be closer to the coldest air and will have the highest chance of snowfall as any frontal systems come in.

Some mixing out of the cold air will probably happen from time to time but this look at the wider picture tells me currently that we are unlikey to get into a mild setup as we start next week.

A glance at the latest London Ens continue to show low 2mtr temps with the 00z GFS run a mild run.

All in all a very interesting few days to come especially if the models continue to go the way of the 00z UKMO and ECM outlooks.

[johnholmes]

I thought i would just have a look at some of the medium range outputs just to see where we might be heading past the weekend and i picked T192hrs-day 8 from the 00z ECM/NAEFs runs.

For any new members the NAEF`s is the North American Ensembles Forecasts which are the combined outputs from the Canadian(GEM) and the American(GFS) models-they also share this information with the Mexican MO i believe.

First the mean Ht anomalies and actual mean hts.at 500hPa level

and the actual mean hts

A pretty solid picture of the Atlantic low pressures heading south east as they comes against those heights to our north.The direction and development of the troughing is across Ireland across the south west of the UK and then Europe.

.We can see on the mean 850hPa temps we are on the edge of the cold block which will ebb and flow through this week and into next as that relatively weak Atlantic energy tries to come through but then looks to take the easier route to the south.

These outputs of course are watered down somewhat because they are average results but never the less show what a fascinating pattern we are in.

We can`t relax for one day with the Op runs as they seem to be constantly changing beyond days 4-5 and so the weather for the UK is a nightmare to forecast.

Often in a typical UK Zonal(mild)pattern we can have confidence much further out.

All we can deduce from these is that areas of the UK further north and east will be closer to the coldest air and will have the highest chance of snowfall as any frontal systems come in.

Some mixing out of the cold air will probably happen from time to time but this look at the wider picture tells me currently that we are unlikey to get into a mild setup as we start next week.

A glance at the latest London Ens continue to show low 2mtr temps with the 00z GFS run a mild run.

All in all a very interesting few days to come especially if the models continue to go the way of the 00z UKMO and ECM outlooks.

yes an interesting position coming up. I looked at those this morning and, rightly or wrongly, when making my post above regarding what the upper air might look like in 6-15 days time, decided they were perhaps suggesting that the upper flow was a touch too far north of west. As you say taking both any upper lows and their surface features rather further south than I felt they will be when the time arrives.

I judged both NOAA and the ECMWF-GFS outputs to suggest that they might be a shade further north and chose to use those to illustrate my idea.

You may well be right, for sure it is a fascinating period of model watching whichever versions one chooses. I certainly cannot see 'mild' as per UK Met definition featuring much away from the far SW at times.

[Gibby]

Good evening. Here is the report of the 12z output from GFS, UKMO and ECM for tonight Monday January 13th 2013.

All models are beginning to come together in how they see things shaping up as we go through the rest of this week and the weekend. tonight will see snowfall near the East coast slip back West then South over East Anglia and the SE overnight giving a further covering in places. Further West some wintry showers will occur becoming restricted to Pembrokeshire and Cornwall by the end of the night with a sharp frost developing elsewhere. Tomorrow sees a light Northerly flow over Britain with snow showers near the East Coast and a few wintry showers elsewhere with good sunny spells and dry if cold conditions inland. By Wednesday cloud will encroach into the extreme West as a weak Low pressure slides SE close to the SW with a little sleet and snow possible. rather more snow showers could occur in the East and SE as winds veer more Easterly. The ridge from Scandinavia lasts through Thursday too with further snow showers towards the SE with most other areas dry, very cold with sunny daytime and clear, frosty nights. By Friday all models show an approach of the Atlantic with a sliding trough moving into the SW on Friday. A spell of possibly disruptive snow will move slowly NE over many Southern and Western areas while Northern and Eastern areas will stay dry and cold until late in the weekend. Dependent on the progress of the trough will determine if and where the snow changes back to rain as milder air will be very close by to the SW at the weekend.

GFS then moves us out of the weekend and into next week with Low pressure close to NW Ireland with the band of snow and rain edging further NE into many areas by the early week with milder air well into the South with some heavy rain showers. Through FI tonight further deep Low pressure areas cross the Atlantic to the UK with further rain and showers and with the cold air never really leaving the far North further snowfall is likely for Scotland and the NE of England at times. late in FI little change has occurred with the cold air limping away from the North too leaving all of Britain in a cold zonal pattern of periods of rain and heavy showers with snow on the hills and potential flooding problems renewed in places too.

The GFS Ensembles show a good agreement on a return of the Atlantic by the end of the weekend with rain and strong winds becoming commonplace with temperatures near to or just below normal for many. In the North there is tight agreement with limited spread between the members on conditions gently warming to nearer the long term mean with an equally unsettled look to it as the South.

The Jet Stream shows a SE moving flow over the UK at present. Over the latter end of the week and weekend a powerful Jet moves East over the Atlantic through areas of Europe South of the UK.

UKMO for midday on Sunday shows a deep Low West of Ireland with an active trough lying across the South of Ireland and Southern England. To the North of the trough will be disruptive snowfall with some drifting in the bitter ESE wind. To the South a spell of snow will turn to rain as milder air slowly encroaches NE from the SW as winds decrease and veer Southerly.

ECM shows a classic winter battleground scenario with warm and wet Atlantic air moving up against a cold block over the UK at the end of this week and the weekend. There will be cloud and snow moving into the SW by Friday moving slowly NE over the weekend and turning to rain for many Southern and Western areas later. Over the remainder of the run the pattern remains complex and blocked with the milder air being squeezed out slowly by a slow moving low pressure over the UK keeping the risk of snow going in the North and East at least but more showery weather with somewhat higher temperatures in the South. By the end of the run the cold air wins back bringing us back into very cold conditions with a snow risk this time most likely in the South and West as the next attack from the Atlantic sets up.

In Summary the pattern is excruciatingly complex as we move into the latter end of the week and weekend and beyond as a barrage of Atlantic Low pressure moves up against a cold wedge of air over the UK in association with High pressure over Scandinavia, All areas are at risk of snow over the next few weeks but with some milder and wet interludes towards the South and West at times. Exact details have a strong chance of being very different to that shown tonight and the eventual outcome could go one of three ways. It will either go as shown above or progress as per GFS FI or the mild air could win so far before being pulled back later. I'm afraid it's going to be a painful wait through the week as the events of the weekend unfold.

[virtualsphere]

This will be a slightly different type of post, so mods feel free to move if necessary. In the context of an evolving stratospheric pattern, some fascinating teleconnections and long range forecast work by members of the team, I thought it would be an interesting idea to see how well the models perform over an extended period by looking at a variety of charts for the same timeframe across different runs. With today (Monday 14th) being indicated some time ago as a possible date for the effects of the SSW to start to be felt in the troposphere*, I started saving charts a couple of weeks ago on a daily basis for 12:00pm today to see how well they would verify...

Firstly, just a word of warning to note that I'll be looking at the weather over the UK when looking at the charts. The rest of the northern hemisphere may well be a reasonable match but if the UK synoptics are different then I would guess the majority would consider the chart to be of little use. It isn't a scientific analysis - just a simple look at the charts - but I'm also posting them here to save them as an indication of how well the models may perform as a SSW evolves and also leading up to a possible snow event.

All charts are from the 12Z runs.

The first chart is today's GFS T+0, which hopefully represents the actual synoptics at 12:00 today:

Now the first model predictions, saved from Friday 4th - T+240.

ECM:

GFS:

At this stage there is actually remarkable agreement between ECM and GFS considering the timeframe, although as you can see with high pressure centred over the UK they are both wide of the mark - in fact, as you can see in the T+0 chart above, low pressure was actually centred in a similar place to the high shown in these T+240 charts.

On to Saturday 5th, and we're now at T+216:

ECM:

GFS:

First thing to note is the stark differences between these charts, which illustrate that the models are still trying to find a clear solution. Neither are very accurate and there is actually more of a difference between them than in the T+240 above.

Sunday 6th, T+192:

ECM:

GFS:

While ECM is again wide of the mark, GFS compares remarkably well to our T+0, especially at that range. The big question at this stage is, if GFS has found the pattern, will it continue to show the low in that position off the NE coast on Monday 7th?

Monday 7th, T+168:

ECM:

GFS:

Notice here how the models seem to have started to come closer in terms of the northern hemisphere. Both show the Azores high, and similar positions to the surface lows, although there are still differences in the Atlantic and the UK. On balance I'd probably go for the GFS as most accurate here, but it's not as good a match as the GFS T+192.

Tuesday 8th, T+144:

ECM:

GFS:

UKMO:

We now have UKMO charts. ECM has now started to catch on to the pattern and is probably more accurate in terms of the UK than GFS and UKMO at T+144.

Wednesday 9th, T+120:

ECM:

GFS:

Again a good match from ECM, with the low tracking down the UK from the NW. GFS has the Azores high positioning almost correct, but ends up with two cut off lows either end of the UK and a ridge in between, so not a correct pattern. Apologies - didn't save UKMO.

Thursday 10th, T+96:

ECM:

GFS:

UKMO:

ECM has backed away slightly from the correct solution, with the low too far north. GFS has moved towards the ECM and the correct solution with the ridge removed from the UK but also has the low too far north. ECM probably still the better of the two.

Friday 11th, T+72:

ECM:

GFS:

UKMO:

Now we're getting there. Better agreement here from ECM,GFS and UKMO on the elongated low tracking SE across the UK. ECM and UKMO probably slightly have the edge, with GFS having the low slightly too deep north of Scotland.

Saturday 12th, T+48:

ECM:

GFS:

UKMO:

Again GFS persists with a similar shape of low, but it's now not quite as deep.

Sunday 13th, T+24:

ECM:

GFS:

UKMO:

As you'd hope and expect, the pattern shown by all three models is a good match for the actual chart.

Summary: if you've ever wondered why the models never verify, just look at how many different solutions we see day in, day out for the same time, of which only one can be accurate. It's strange to see both ECM and GFS agree on a 'false' solution at T+240, and I wonder if anyone would have been fooled by this agreement at long range. The first relatively accurate chart is from GFS at T+192, and although ECM doesn't seem to catch on too well until T+144, it then seems to be more accurate right up until T+48.

Obviously this is just one example, and it would probably be a good idea to do the same in a standard zonal pattern to see how well they compare.

You can of course just go to http://www.emc.ncep....gmb/STATS_vsdb/ to see the official verification stats, although these don't tell you specifically how the models are performing over the UK.

* see http://forum.netweat...00#entry2448734 and http://forum.netweat...80#entry2457976

Incidentally, considering the snow in the east today, a good call from those who mentioned the 14th in the stratosphere thread a good few weeks ago...

[Gibby]

Good morning folks. Here is the report of the 00zs from GFS, UKMO, GEM and ECM for Tuesday January 15th 2013.

All models show a cold spell established over the UK for the next 4-5 days. For most there will be a lot of fine and frosty weather as a finger of High pressure ridges over the UK from High pressure out to the NE. A few wintry flurries could occur near the East and SE cast over the next few days. Later in the week pressure falls as Low pressure moves up against the cold block over the UK. The associated Low pressures under cut the Scandinavian High and eventually form Low pressure close to Southern England with a spell of sleet and snow, possibly disruptive late in the week and weekend, though it will turn to rain in Southern England later as milder air infiltrates NE from the SW.

GFS then shows cold conditions holding on in the North with further snowfall and strong East or SE winds. In the South skies will brighten somewhat with less cold weather and heavy rain showers early next week with possible thunder and hail near the coasts. Through FI a rinse and repeat pattern of a wintry North with further snowfall and somewhat less cold weather at times in the South persists with repeated spells of rain then thundery showers. It's not until the end of FI when the less cold weather spreads to all areas with the axis of Low pressure then further North with showers or longer spells of rain for all by then with just snow on Northern high ground in winds turning more West or SW everywhere.

The GFS Ensembles show a continuation of the cold weather in the South over the next three to four days before a moderation in the levels of cold occur from the weekend as unsettled weather moves in with precipitation at times. The members continue to be relative tight in the North with little spread. Uppers even out at around -3C to -5C in the South and close to -5C in the North. The operational is on the cold side of the pack in the North while in the South the operational isn't far from the average level for the run.

The Jet Stream shows a weak but Southward moving flow over the coming 48 hours or so before a strong surge of the Jet crosses the Atlantic South of the UK later this week as deep depressions on its Northern flank buffer up against the cold block to the NE.

UKMO for midnight on Monday shows Low pressure having moved gently NE into Southern England. After a cold and in places snowy weekend milder air will of filtered into Southern Britain with heavy and thundery rain showers here while Northern areas maintain the cold Easterly winds with further sleet or snow in places, especially over the hills.

GEM shows Low pressure too having moved a trough North over Britain with sleet and snow turning to rain before a complex Low structure moves into the UK and away slowly SE later. The weather would remain on the cold side for many with a lot of cold rain about but some wintry flurries around too at times, chiefly over the hills and towards the end of the period.

ECM shows a similar evolution to UKMO this morning, pulling Low pressure into Southern England next Monday with copious rain events following snowfall over the weekend as milder air gradually infiltrates North. As the Lows fill and move away ESE a renewed push from the Atlantic means a rinse and repeat pattern though with so much mixing of the air by then mostly rain will continue in the South while the North may continue to see periods of snow at times.

In Summary this morning despite a complex pattern there is quite a bit of agreement on the course of events in the coming week or two. This week looks like being essentially dry with just a few wintry flurries in the East. Frosts will be sharp and severe with some freezing fog possible. The next phase of the weather will be over the end of the week and weekend as milder air tries to displace the cold pool over the UK with a messy period of snow and sleet moving steadily NE over the UK. How much snow and for how long remains an open for debate question this morning as the models can sometimes overplay the speed at which cold air in Winter can be displaced but as shown this morning most areas of Southern England and Wales will be into less cold and showery conditions early next week while the North hangs on to colder easterly winds and the threat of further snowfall. In the longer term the weather remains complex and shows that the cold, though modified remains stubborn and could return back South on occasion though with a strong Atlantic it does look this morning that a gradual advantage to the milder air out to the SW will succeed. However, having said all this there is plenty of time for the models to change and for the milder conditions to be held back more than is currently shown which could have major implications down the line.

[johnholmes]

the link below shows how the ECMWF-GFS 500mb charts suggest the upper air may look in 10 days time. A fairly vigorous and overall westerly pattern at UK latitudes over the Atlantic. By the time it reaches the UK ECMWF turns the flow to come from north of west more than GFS does but both have quite low contour heights, around the 528 DM mark over the UK, as the flow then drives way into southern Europe with higher values and some sign of ridging over northern Europe/Scandinavia towards Iceland and Greenland.

So little sign of any marked milder air being seen over most of the UK. The outputs, including NOAA, all suggest this upper type of pattern. So cold seems about on average to be holding its own at 500mb and thus most likely near the surface for most parts of the country. With such a strong Atlantic flow then surface lows will figure in the equation most of the time and temporary pushes of milder air into the far SW and possibly some far western areas seems probable but most of the UK looks set to stay on the cold side thus precipitation could well be snow for a number of areas. As its a westerly flow at high level this may mean the so called battle ground type of situations develop from time to time. Some less volatile days to the rear of these lows with severe frost for those that stay on the northern side. Just where that boundary may be is impossible to say this far out (in the 6-15 day time frame) but I suspect it will move north and south, maybe as far north as southern Scotland at times and practically covering most of the country at other times.

The ECMWF-GFS link

http://www.meteo.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html done 2x daily

and below is the NOAA link

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php done 1x daily

and the NAEFS output done 2x daily

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

Remember they are ANOMALY charts and need careful regular study to get a good idea of the probable places where upper troughs and highs will sit but that should allow, with the contour flows shown on NOAA, ECMWF and GFS to get a fair idea of the general pattern expected.

One thing that needs a mention is that the 3 main charts do hold heights and suggest ridging between NNE and NW of the UK. It is possible that could extend further south again, as we have now, and a consequent colder effect on this part of the world.

I cannot see, as I've mentioned before, the CET coming in at anything other than at or below normal for January and the value further north is almost certain to be below average, possibly verging on meteorological 'cold'.