Model Output Discussion - 18z - 6th December onward

[strathearn snow]

Click here to access the PDF version of the forecast.

Summary for all mountain areas

Severe upland gales across most mountain areas. Showers, of snow on the mountains will at time be very frequent, mainly eastern Scotland. But extensively dry southwest Scotland and Cumbria.

Headline, The Southeastern Highlands

Severe gales; frequent snow. Whiteout.

How Windy?

Northerly, mean speeds 45 to 60mph.

Effect Of Wind?

Walking widely difficult where exposed, from low levels upward in severe gales. On many higher areas, any mobility difficult. Severe wind chill.

How Wet?

Areas of snow showers, particularly east

Snow showers, or rain in some glens. The showers may be very frequent giving almost constant snow and whiteout for a couple of hours east of Glenshee. Least precipitation west of the A9.

Cloud on the hills?

Extensive east and north

Cloud at times below 600m in and around showers but a few breaks to 900m, especially west of the A9, and south of about Perth.

Chance of cloud free Munros?

10%

Sunshine and air clarity?

Little if any sunshine. Visibility varied but very poor in precipitation and at times near zero in snow, particularly east.

How Cold? (at 900m)

-1C; but will feel as cold as minus 19C directly in the wind.

Freezing level

750m but terrain from glens upward frozen or partly frozen and areas of ice.

Planning Outlook for all mountain areas from Saturday, 8th December, 2012

A brief milder period as rain extends southeast on Saturday and a thaw extends to higher summits in Scotland for up to 12 hours. Widespread severe northerly gales on Sunday. Very cold next week or perhaps longer. Terrain almost all persistently frozen to valley level from Monday onwards. There will be significant snowfall on mainly eastern mountains, and also northern mountains in Scotland, but for many areas, substantially dry.

I find this forecast the most reliable in terms of general trend. Looking good to me!

[mulzy]

ECM ensemble mean at 216 and 240 suggests that milder Atlantic air will break through (usual caveats apply at this range - confidence, spread etc.).

http://www.wetterzentrale.de/pics/Reem2401.gif

[TAFKAP]

Dave, I bow to your superior knowledge of easterly's but as another poster recently said, didn't the models do a similar backtrack for the 2010 snow event only to bring it back within a day or so of it actually happening?

I may be wrong and the synoptics may have been different but I distinctly remember this place going into meltdown for a few runs before the models got a grasp on things.

Indeed. Prior to major cold events the models have many times in the past (not always mind you) had a stutter late in the day. Think of it as a football team having a poor 10 minutes in the second half then coming back with a vengeance as the whistle approaches (I know the models aren't a football team, just a nice mental picture!).

Now things could go up or down from here. But the facts remain. Cold next week, maybe some snow, then FI as always remains FI. As Bishop Brennan pointed out an 88/89 winter would soon rein in the expectations of the more frivolous to realistic levels. We have a great winter ahead of us folks!

[nick sussex]

Oh dear!

The revenge of the shortwave, so we got over one and another one appears. Now that this has appeared its very unlikely to just implode.

If you look at the models they all agree on moving a chunk of the PV back to Siberia and this will cause lots of different solutions to pop up, its really not a time to be drawing too many conclusions from the later output.

However the GFS even amongst all the models at showing the least favourable early outcome still doesn't have the Atlantic winning within the higher resolution output!

[Frosty.]

The Gfs 00z op run has gone into full battle mode with the atlantic and the scandi cold block locking horns for most of the run but initially the upcoming pattern remains the same, a surge of arctic air spreading south westwards early next week with wintry showers to n/e areas and frosts becoming widespread, then winds fall light and the frost becomes persistent with ice days but a bit less cold in the far west as atlantic low pressure coming up against the block strengthens the airflow from the south, yes a cold southerly. However, I think the gfs op run is being too gung ho with the attempted breakdown, I feel it has underestimated the strength of the cold block and it won't end up being such a close call between cold and milder when the time comes. I would say though that the best areas for cold to persist in the next few weeks will be northeast britain but all parts of the uk will become much colder next week with a snow risk and widespread sharp frosts.

[weather eater]

We all want snow and blizzards, but personally cold and dry will suit me just as well, anything but the nonstop rain is a big plus and that’s the way things look like shaping up at the moment.

[sebastiaan1973]

http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2012020700!!/

The EC members at 168h, lots of disagreement, 5 clusters. Control and oper in a different cluster.

[TonyH]

So if its mild your after this mornings charts are an upgrade?

[Frosty.]

The 00z GFS is a massive downgrade

No it's not, next week would still become very cold and blocked and then there is a risk of rain turning to snow as it pushes into the cold air entrenched over most of the uk. And it's only an op run and probably an outlier.

[Snowy Easterlies]

We all want snow and blizzards, but personally cold and dry will suit me just as well, anything but the nonstop rain is a big plus and that’s the way things look like shaping up at the moment.

cold and dry is not as uncommon as people think and the GFS shows cold and frosty weather, even in FI snow reaches the west but then it dies out, albeit it stays cold for a while longer

http://www.meteociel...&ech=192&mode=2

of course it will change but this is what the actual chart shows, and not the "potential"

Edited December 7, 2012 by Snowy Easterlies

[Snowy Easterlies]

No it's not, next week would still become very cold and blocked and then there is a risk of rain turning to snow as it pushes into the cold air entrenched over most of the uk. And it's only an op run and probably an outlier.

when we say downgrade we mean downgrade for snow from the easterly, yes it stays cold but most on here look for snow not frost and sunshine as that is not rare like snow is, the control run is very nice in deep FI though, yet another bite of the cherry perhaps

Edited December 7, 2012 by Snowy Easterlies

[Ian Brown]

So if its mild your after this mornings charts are an upgrade?

Next week looks pretty cold even if the GFS comes off, the only model to bring the Atlantic back quickly is the GEM, supported by 4 GFS Ensemble members.

I think the general trend and a fairly clear one at that is to reintroduce the Atlantic by the end of next weekend, Ian F posted earlier that both the EC and MOGREPS go for this, although the timing of the transition is open to question.

[TAFKAP]

when we say downgrade we mean downgrade for snow from the easterly, yes it stays cold but most on here look for snow not frost and sunshine as that is not rare like snow is, the control run is very nice in deep FI though, yet another bite of the cherry perhaps

http://modeles.meteo...s-0-1-288.png?0

Speak for yourself. This isn't 'snow watch!' The synoptics being shown are rare and unusual and as myself and many others have pointed out would have been thought of as the stuff of dreams a mere few years ago. The stonking runs shown earlier this week were pure model porn and not to be taken as gospel. Potential for sub zero maxes and pale winter sunshine with sprinkling of snow are an order of magnitude better than a mucky and mild continuation of autumn. The 12z will bring changes and hopefully a little something for everyone!

[snowmadchrisuk]

The Gem still brings Wintry PPN in for most of England as from Monday next week , Normally I would discount it , but it is showing it like the Metoffice described

[johnholmes]

hi

This is an attempt having struggled through the past 4-5 pages of unfair posts both to one another and for new folk trying to make head or tail of what the models show.

below is an attempt by me to be as objective as I can from T+24 out to T+120 using the 00z output from UK Met, ECMWF and GFS.

I hope it helps some of you.

T+24=all 3 have Iceland low same place and ridge sw of UK similar again

T+48=slight differences in position of the low, 60-90 miles perhaps

T+72=and all 3 have it within about 1 degree of each other, and each has a 1015mb isobar within 30 miles of each other across the east of the UK, identical direction

T+96=identical positions for the low and the developing high to the NW of the UK

T+120=UK Met has a more definite ridge than GFS giving a flow north of east with ECMWF tending to more like UK Met.

So the charts for 00z are about as identical as you could reasonably expect 3 different models to be.

The T+120 Met Fax produced last evening is, in my view, as close as anyone this far out is likely to be with the surface set up bearing in mind what the models all show at T+120 00z this morning.

So some of the posts, comments in the model thread really are not that good at giving overall guidance to new folk in my view.

Can I also add regarding some posts commenting on the input from Ian F. PLEASE read the actual post or the copy made of it by Lorenzo, read it carefully, don't skim and see what you want PLEASE?

Edited December 7, 2012 by johnholmes

[Dampdorset82]

So it appears afrer the very cold model runs recently people have taken that as the norm and class 2-4c as mild!

The pattern appears different but the trend hasnt - Cold with potential for snow later in the run as fronts push in and stall.

The models are changing on every run - It has and will continue to do so even when the cold air is over us.

I am still very happy with the runs today and am really enjoying the uncertanty waking up and seeing whats showing next.

The facts are - The ens are all over the place later in the run

Colder than average temps still widely forecast for next week

FI is all over the place along with the PV which means THINGS WILL CONTINUE TO EVOLVE GREATLY AND THEY WILL!!

Just remember we are not seeing LP after LP soaking us so enjoy the fun and the unpredicable!

[afcone]

From reading this thread one would think the chance of snow has receded massively. But then I see the Met Office this morning states:

There is a 90% probability of severe cold weather/icy conditions/heavy snow between 0000 on Monday and 0800 on Tuesday in parts of England. This weather could increase the health risks to vulnerable patients and disrupt the delivery of services. Please refer to the national Cold Weather Plan and your Trust's emergency plan for appropriate preventive action.

Less cold over the next few days with higher daytime temperatures than of late so the mean temperature criteria is unlikely to be met this weekend, despite overnight frosts. There is now growing confidence that into the start of next week very cold air originating from the east or northeast will spread across the whole of England. An east or northeasterly flow at times will bring snow showers, particularly to the east of England, these sometimes heavy, and leading to locally significant accumulations. At present this spell of very cold weather looks set to last through much of next week and it is likely this alert will need to be extended.

[Frosty.]

when we say downgrade we mean downgrade for snow from the easterly, yes it stays cold but most on here look for snow not frost and sunshine as that is not rare like snow is, the control run is very nice in deep FI though, yet another bite of the cherry perhaps

http://modeles.meteo...s-0-1-288.png?0

I'm actually more concerned about the further outlook now because i've just looked at the latest gefs 00z mean and ecm 00z ens mean, both show a definate milder unsettled trend from T+192 hours onwards with the cold block being pushed away northeastwards and normal uk weather returning by T+240, that is a downgrade on recent times but the ensembles could be wrong.

[The Weather Dragon]

When will people learn regarding model output relating to potent easterlies. I have been on this forum since 2005 and have seen countless easterlies watered down by the models at short notice. It's not our normal weather and models struggle. Best to wait until 48 hours and then to concentrate on fax charts to be honest - would save a lot of let downs.

[Gibby]

Good morning. Here is the report from the 00zs from GFS, UKMO, GEM and ECM for today Friday December 7th 2012.

All models are clear cut on the weekend pattern but beyond that differences quickly emerge between the models. A cold Northerly flow over the UK today gives way to lighter winds tonight as a ridge of High pressure crosses the UK from the West. A slight frost will develop overnight tonight away from the coasts. Tomorrow will see a Westerly flow develop with cloud and rain and drizzle developing over Scotland through the day. The South holds on to drier and brighter conditions through the day. Sinday is a rather cloudy day for all with occasional light rain through Central Britain with drier and potentially brighter weather further South and North of this zone. There will be less frost and fog over the weekend than previously thought as winds remain rather stronger from the West and NW.

GFS then moves us into next week with a Low pressure near Denmark moving East and South into Germany with a chilly North wind over the UK giving way to light winds and calm conditions with frost and fog under High pressure midweek. Later in the week very cold air over Europe will seep West to the UK as a freshening SE flow develops with rain bearing fronts approaching Western Britain later. Into FI the South and West are at risk from rain and snow as fronts buffer up against the cold air while a SE flow over the North and East bring some wintry showers towards North Sea coasts. Through the FI period this morning the block to the NE holds firm and Low pressure becomes a cut off feature to the South while the High re-orientates its axis to favour a NE or East flow to develop over the South. The weather would be dry, cold and frosty for all with some freezing fog possible in the North.

The GFS Ensembles still show a cold spell to come although the longevity and severity of it seems to be tempered in more recent output. It also appears to become more unsettled after the coldest phase as rain and wind from the Atlantic breaks through the block by some members. there is huge scatter between the members though from the mid point of the run.

The Jet Stream shows the flow running SE or South over the UK over the coming days having ridge High up over the Atlantic before re-aligning to a point West to East well South of the UK later next week.

UKMO for midnight on Thursday shows Low pressure to the East and High pressure North of Scotland with an inverted ridge over the UK in cold air. The weather would be basically dry and bright with some wintry showers near the SE.

GEM shows a slack SW flow over the UK at the same time point, strengthening in the following days with cloud and rain preceded by snow sweeping the cold air away NE in the latter days of the run.

ECM shows a slack and increasingly cold airflow over the UK through the midweek days before an increasing SE flow develops ahead of Low pressure to the West brings a messy breakdown of snow followed by rain steadily across the UK late in its run.

In Summary this morning the cold weather is still on the way. However, it may not last long before it becomes under attack from an attack from Low pressure to the West. The spoiler Low which prevents the Easterly flow proper to reach our shores is also reponsible for allowing the Atlantic to get a foothold at least into the West of the UK later. Evenso, there is likely to be more twists and turns in this story over the coming days with cold weather never far away but conversely a period of deep cold and widespread long lasting snowfall looks somewhat less likely today.

[snowmadchrisuk]

Metoffice forecast for East Mids shows what they think ...

Becoming cloudy and windy with patchy rain during Sunday. Monday and Tuesday, becoming very cold with bright spells, but also with sleet or snow showers, some heavy, giving accumulations

[Snowy Easterlies]

Speak for yourself. This isn't 'snow watch!' The synoptics being shown are rare and unusual and as myself and many others have pointed out would have been thought of as the stuff of dreams a mere few years ago. The stonking runs shown earlier this week were pure model porn and not to be taken as gospel. Potential for sub zero maxes and pale winter sunshine with sprinkling of snow are an order of magnitude better than a mucky and mild continuation of autumn. The 12z will bring changes and hopefully a little something for everyone!

that is true the actual synoptics are rare for december, but if the GFS verified it would still be just dry and cold for most, i had a frost the other night in completely different synoptics its isn't always mild and zonal in december like people seem to think, i can recall many anticyclones spells or high pressure over sat over us in december with frosty nights but those synopitcs didn't look anything special but we still got cold days and frost

Edited December 7, 2012 by Snowy Easterlies

[WhiteFox]

Next week looks pretty cold even if the GFS comes off, the only model to bring the Atlantic back quickly is the GEM, supported by 4 GFS Ensemble members.

I think the general trend and a fairly clear one at that is to reintroduce the Atlantic by the end of next weekend, Ian F posted earlier that both the EC and MOGREPS go for this, although the timing of the transition is open to question.

"Mr atlantic, let me introduce you to mr block"

"Haven't we met before?"

Of course, Ian and numerous other posters are absolutely right. We really have no idea of the details of the synoptics for this time next week. We do know the atlantic will try and push back in: it always does. Fretting over every single nuance of a numerical forecasting model which frequently changes within 120 hours let alone 168 will lead you to early baldness.

The block may be weak by then, and the atlantic may swep aside all before it like a juggernaut racing through a puddle. Or the block may stand firm like a shining guardian of the east, hold firm and repulse the mild invader seeking revenge in the form of heavy snowfall. We dont kno2 and wont know for around 4-5 days! Next week, cold. Thereafter the models tell me it will be cold with a good chance of mild. There may be precipitation which has a chance of being snow or rain.

[Met4Cast]

No it's not, next week would still become very cold and blocked and then there is a risk of rain turning to snow as it pushes into the cold air entrenched over most of the uk. And it's only an op run and probably an outlier.

Did you not bother to read the rest of my post? I followed it on with an explanation. I'll post it again, for your benefit

I think we have to be realistic.

The 00z GFS is a massive downgrade with little in the way of significant blocking and a weak Northerly with high pressure stuck over us, the cold still gets into place but widespread snow and interesting, it's not. The ECM is a little better with stronger blocking but still no where near what we were being offered a couple of days ago or even this time yesterday morning.

Lets hope we see things upgrade come the 06z, if not, I fear this'll be yet another missed Easterly.

[chris55]

We are losing the link up between the Atlantic ridge and Scandi high with these shortwaves nipping inbetween, the trough to the east is to far north with the now almost cut off Scandi high slipping down the south east side of the trough with this "upside down U" shaped flow from east to west. This means we get a less potent easterly flow, we still get the cold air in though, just not on a stiff easterly wind.

ECM mean highlights this well

http://www.wetterzentrale.de/pics/Reem1201.gif

The pattern is almost a repeat of the failed cold shot last week, however the big difference with this is there is no energy coming out of the southern tip of Greenland and this is crucial IMO.

Instead of Low pressure forcing to the North of the UK and "toppling" the pattern we are clearly getting the energy undercutting, this is so much better for real snow potential.

http://www.wetterzentrale.de/pics/Reem1441.gif

http://www.wetterzentrale.de/pics/Reem1681.gif

Overall still a very cold period next week with the interesting scenario of the Atlantic undercutting any cold air we have in place. The Undercut rather than the Toppler is key here and is much much better for coldies.

http://www.wetterzentrale.de/pics/Recm1921.gif