Model Output - General Discussion

[BLAST FROM THE PAST]

With the charts now working on the detail of this arctic Blast from the Past FI detail is probably more futile than normal. However, on that there is a signal for the Atlantic to pep up and send some very tasty storms towards the UK. I feel that is likely to happen as there is a major signal for a major storm around New Year. This cold blast looks tastier than expected for sure and IF the Atlantic plays ball and fires up how it interracts with the northern blocking and cold air....I just don't know. Set ups like this cold one tend to not go too far away before coming back [which I certainly think it will in early Jan if it is shunted away] but as some have said there are signs that we may not really lose it at all.

Anyway pure conjecture for now as we have a cracking very cold week to come....let's enjoy...and keep an eye for your elderly neighbours.

BFTP

[Eugene]

I just can't buy the atlantic breakdown going from very cold northerlies to warm southwesterlies within 5 days is just not likely IMO.

Anyway pure conjecture for now as we have a cracking very cold week to come....let's enjoy...and keep an eye for your elderly neighbours.

Yes very wise words, it's easy to forget as the majority on here are under 50 of people of a more senior age who don't like the cold at all, even now it's a too cold for them.

[TEITS]

On Friday and Saturdays runs a strong easterly was progged for Tuesday/Wednesday and even yesterday a strong easterly was progged by both ECM and UKMO for Wednesday and Thursday.

Nothing has changed in my opinion. If anything over the past 48hrs the UKMO/ECM have upgraded the E,ly.

Into the medium range and the models have certainly upgraded. Remember that dreadful ECM 12Z run that had our HP sinking with low heights to our N? Now we have excellent agreement for a real Greenland HP and an Arctic blast.

This cold spell has followed the usual pattern really. Fantastic charts at first, downgrade, upgrade within reliable timeframe.

[Cecil Hogmanay Melchett]

Well undoubtedly some places are going to miss out,of interest on 06z is that we only get about a day or so

of the really cold uppers.Thats not a grumble as the air should be still cold enough for most but places further south

west could just end up with a cold dry spell with little or no precipitation.

As Teits says the flow from the East is looking quite slack and we want it to be as strong as posible for the

showers to really penetrate across the country.

The Se looks good at the end of the week,through the weekend the threat transfers North as the winds veer

North.

At the moment its pretty difficult to call but going off 06z i'd say the SE looks very very good for some

snow cover.

Just watched bbc n24 and the presenter said 'wintry showers' wed thur and fri.I suspect altitude maywell

play a bigger part then expected here.

Edited December 14, 2009 by happy days

[Optimus Prime]

As I made perfectly clear the 06 and virtually every other run remains choc full of wintery potential, but I also stand by my call that the arrival of the coldest air has and continues to be delayed on virtually every run.

I really don't understand what you're trying to get at. The easterly is well within the timeframe of reliableness. The easterly and cold air starts filtering in from Wednesday with the cold air dragged in on Thursday and with the coldest air over us Friday/Saturday.

This happens all between 120 hours. I can't see much changing now. There's mass agreement that it will turn cold/very cold from Thursday.

Edited December 14, 2009 by Optimus Prime

[snowking]

Just watched bbc n24 and the presenter said 'wintry showers' wed thur and fri.I suspect altitude maywell

play a bigger part then expected here.

I think you may find that this refers to the fact that its likely to be a sleetier affair right on the coast (as is suggested by Met Office forecasts), where as further inland its more likely to be snow. You probably also find that given some of the convection we saw even yesterday theres likely to be some showers of hail.

Anyway some cracking runs overnight, I still struggle to see why the pessimism is still occurring here, I think perhaps people are getting a little greedy now. Suggestions ive seen this morning od 850's now not cold enough for snow just show once more some people need to brush up on some of their model skills. For example where 850's are at times on the gfs only at -3 to -4c, they have neglected to consider both a) downdrafts given the convective nature of the showers and b ) the thicknesses which are sub 528DAM. We also have favourable dew points and some fairly favourable temperature profiles. If we're going to see maximums of 4c then many parts will be more likely at 2-3c, with noticeable drops during any showery activity during weds/first part of thursday

Loads of potential in the short term, never mind the mid term towards the weekend and beyond, people need to realise we are seeing some great synoptics currently and perhaps think back to winters such as 2006/07 where we would have sawn off a limb to get charts like we're seeing at the moment!

Kind Regards

SK

Edited December 14, 2009 by snowking

[cooling climate]

Well Christmas has certainly come early this year for us winter weather enthusiasts, excellent, excellent

synoptics on display again this morning.

My take on this mornings models, for east Midlands, east Anglia and the southeast is snow risk from tonight

through to Friday with daytime temps around 2-3c at best.

Friday night onwards becoming very cold with ice days and any precipitation to fall as snow (no marginal situation

here) and a good old fashioned winter freeze to set in.

With all of that to look forward to I couldn't care less about t168 until the weekend at least.

Just to add with the synoptics we are seeing I don't think anyone is going to miss out, at least I hope not.

Edited December 14, 2009 by cooling climate

[Guest North Sea Snow Convection]

The GFS before last weekend was predicting upper temps nr -10C and snow shower potential for Mon/Tues this week. Whilst the snow potential hasn't been realised it is not too far wide of the mark for temps in this SE corner as there is a pool of sub -5 uppers cold continental air here in the clearer air away from the rain and sleet band

Regarding the easterly towards the end of the week - the general modelling has remained consistent for most areas to turn colder with lower uppers moving south westwards for the Thurs/Fri timeframe - I don't think this has been put back at all. Indeed, as stated by a few, it appears that a slight upgrade in the easterly is occuring.

Finally, we also have the northerly incursion with another swathe of cold uppers to look out for from the north. At this time, the general modelling is being consistent about that too.

For sure, there have been some outputs which have shown -15 uppers and huge waist high stormstorms sweeping the UK - but on the whole, I think that realistic expectations about this cold spell have been realised by the models and on that basis imo I think that people's expectations *should* be managed easily enough

Synoptically this cold spell is truly remarkable for the early winter period - and I mean that when compared historically as well.

Edited December 14, 2009 by North Sea Snow Convection

[Iceberg]

Meto 06Z makes more of the LP now as well the chances of precip particularly Thursday are increasing.

The wintry mix of it will be very difficult to call, (even by Wed).

The warm sector will likely be confined to the SE of England as the LP exits across Dorset, however even here it should turn readily to snow even at lower levels.

Prime places would seem to be the midlands and cotswolds again where it might be entirely sleet or snow and should settle readily on hard cold ground.

Evalation will be important for the first few hours.

Anyway thats just an initial stab going on the METO and GFS 06's, but this will likely change.

If it's still there on the 12Z then this will get very interesting.

The ensembles will be interesting in the next 10 mins,particularly the pressure temp ensembles for the midlands southwards.

[AtlanticFlamethrower]

Synoptically this cold spell is truly remarkable for the early winter period - and I mean that when compared historically as well.

It hasn't happened yet!

I'm concerned about the amount of cloud cover projected during the week. This has raised dew points and keep some overnight temperatures above freezing.

I'd prefer to enter this spell with a frost. It still feels like autumn outside. So I'm guessing there is still potential for damp squib in many areas in the South and on the East coast.

Also, previous ensembles for London have shown -15C at 850hpa around Thursday. Now the spread is between -4C and -10C (00z).

I'm disappointed that I'm still worried it will be a marginal event for many, this being entirely due to the warm North Sea (IMO).

Edited December 14, 2009 by AtlanticFlamethrower

[MR EXTREMES]

Also, previous ensembles for London have shown -15C at 850hpa around Thursday. Now the spread is between -4C and -10C (00z).

and thats not good enough lol.

have you looked at the latest models ?

and read jh blog nothing is any different to yesterday if anything its better.

Edited December 14, 2009 by badboy657

[Frosty.]

If i'm not mistaken, the gfs 00z yesterday was showing the mild air breaking through before xmas day and the 06z showed the cold lasting longer, today it's the other way round. The GFS 06z is yet another in a long line of wintry runs just tainted slightly by the late FI charts but the next 7-9 days look increasingly cold with a taste of siberian air followed by a blast from the arctic, as to whether it will turn less cold / milder before the big day, I don't think the models really know yet and the deeply entrenched cold airmass might hold on.

[Cecil Hogmanay Melchett]

Severe downgrades for the south today it is fast becoming a northern and north eastern event, we will end up with the north and north east getting several feet of snow by sunday night and the south getting at best a wintry mix. Very disappointing, guess am ging to have to go snow chasing later in the week

Hi mate,

I wouldnt say severe downgrades for the south at all.It does look likely that the REALLY cold uppers wont be on our

shores for more than 24 to 36 hrs max but im sure we'll be ok,that said i didnt like the refernce to 'wintry

showers' wed thur fri,i must admit that phrase isnt what i had in mind when looking at the ,odels.

I do have a suspicion though that elevation might help folk out here later in the week.With the NSea very

warm for the time of year their will be modification for those esp near the East coast.

I'd hope bbc start showing maxima of 1 and 2 come Fri,i think the latest one i saw has 3 and 4 on thur which

is a bit high for my likng.

Best keep an eye on the bbc

[nick sussex]

The latest ecm ensembles for the Netherlands show the ecm operational run a mild outlier for days 9 and 10:

Today we're lucky in the the freebie ecm info is all 50 ensemble members upto 168 hrs. Quite a range of outcomes with the operational run trying to build pressure over southern europe, IMO this is a wrong call by the ecm and not supported by the general guidance.

http://www.wetterzentrale.de/pics/Recm1681.html

Then if we look upstream alot of uncertainty, NOAA are dubious of todays operational models past day 5 with doubts about what happens to the Greenland high. I think given all this the ecm later output is likely to be barking up the wrong tree or has overreacted to upstream signals.

Edited December 14, 2009 by nick sussex

[kold weather]

The long range ECM also show the hallmarks of a return to some sort of normal zonality, but the 0z op run was one of the fastest with breaking it down out of all the runs, expect the next run to be a little slower in the breakdown:

http://www.knmi.nl/exp/pluim/vijftiendaagse/Data/15DAAGSE_06260_NWT.png

Does look like xmas will be something of a washout compared to what could have been, indeed quite a few of the GFS ensembles have a very rapid breakdown...we will see but there is a good sense of general agreement now. Sadly the synoptics we are seeing modelled would strongly suggest we will get a SW airflow as the Scandinavian vortex gets absorbed by the strong Atlantic low and pulls westwards opening up a SW airflow, that set-up also wouldn't be that snowy either...

[nick sussex]

If Im not mistaken I have not read such rediculous comments for a long time. They really have no place in the forum.

Best wishes

Have you quoted the wrong post? Frosties comments are perfectly valid, theres alot of uncertainty in the extended outlook!

[Guest North Sea Snow Convection]

It hasn't happened yet!

I'm concerned about the amount of cloud cover projected during the week. This has raised dew points and keep some overnight temperatures above freezing.

I'd prefer to enter this spell with a frost. It still feels like autumn outside. So I'm guessing there is still potential for damp squib in many areas in the South and on the East coast.

Also, previous ensembles for London have shown -15C at 850hpa around Thursday. Now the spread is between -4C and -10C (00z).

I'm disappointed that I'm still worried it will be a marginal event for many, this being entirely due to the warm North Sea (IMO).

Irrespective of the detail to come and whether or where or when it snows - there is solid agreement for the synoptical pattern which we have come into and for which the easterly later this week and reload to the northerly, in the classic style that Greenland H pressure brings, to take place. There is no question about the broad synoptic pattern - the only questions remaining now are the details which will be filled in as the week goes on.

Edited December 14, 2009 by North Sea Snow Convection

[Altohumorous]

I don't think to many people took that dreadful ECM too seriously last week, it looked wrong at the time and so it was proven.

This cold spell most certainly hasn't followed the usual pattern either IMO, as hitherto the usual pattern was cold blast at 180hrs, downgrade at 144hrs and then vanish without trace into Scandi at 72hrs...

As I made perfectly clear the 06 and virtually every other run remains choc full of wintery potential, but I also stand by my call that the arrival of the coldest air has and continues to be delayed on virtually every run.

I dont think it's delayed, it actually doesnt happen properly at all according to this morning's runs, IN COMPARISON to what they were mostly showing the last couple of days (at least in the case of the northerly). I never felt that the easterly looked like bringing much of the very cold air that came with the Arctic highs that are over/coming down over Scandinavia and East Europe.

IMO the coldest air that had been forecast to hit these islands is now not going to, with the exception of the south east corner of England. ColdER air does filter through to all parts IF that last short wave gets its act together as forecast, but the air that actually ends up over us is a (and looking somewhat slack) remnant of air that is currently over Scandinavia and the Low Countries. The isobars by friday make it look like the air is coming from Russia with love but that set-up doesnt last long enough for us to get the feed from further east than I've said, before pressure rises, and then the northerly.

The penetration of the real cold from that northerly now looks to be held back to our north, we get a bit of it in what looks increasingly like a situation where instability over the ocean just to our north will take over and prevent the advection of the very cold air from the north.

Of course it's a long way off, but the trends seem to be showing that to be very likely.

And of course again, the air we get in the end is overall very cold by our standards, cold enough for snow which will hit eastern England to some extent on thursday/friday, and then from whatever showers/short waves that hit and form during the northerly, mainly in the north and northwest, possibly further south and east if the low penetrates.

In the meantine tomorrow and wednesday look to have snow potential in England as the first short waves engage and generate some colder air during precipitation. It will be interesting to see what way the models go the rest of today and tomorrow, but agreement now looks strong for the next week.

In summary for most, a bit of wintryness in the next 3 days, possibly more in east England if the shortwave potency increases and if the easterly delivers on the coast, which it looks certain to for a day or possibly two; increasingly frosty for all, then possibly some significant snow for the northern half of these islands at least over the weekend IF both the cold AND unstable air make it far enough south. My hunch is that for most it will stay mostly dry with high pressure blocking instability. Then when the high declines from us, it's very unclear what it leaves.

By the way, the warm sector of the arctic low hits Scandinavia but it's very unclear how it might affect us. If the cold front is held up by lack of penetration and instability forming just to our north then it will just be assimilated into the overall. If the cold front penetrates then I think the warm sector will in any event stay away to our north and northeast, possibly clipping the far north/east of Scotland. That part of the warm sector becomes, in effect, the air that is just north of these islands on friday, the southerly bit of the Greenland high, which of course is warmer than the air behind the cold front anyway.

[SP1986]

I Having looked at some the GFS forecasting of 2m temperatures in the mid range, they do leave alot to be desired. There are some bizarre predictions there, especially for northwest facing coasts in a northwest wind - perhaps for inland areas it's possible to have -5C but even in those cold condition you have to question the GFS potential accuracy (or rather lack of), in terms of local scale modelling.

[azores92]

im sorry kw, but christmas day is still 11 days away, so saying it looks a washout at this range is nothing more than a guess really. the models might hint at a breakdown, but the fact is, recently breakdowns of this upcoming colder spell have been put further and further back, and some of the elders of the mod have implied that the models are being over progressive in bringing the atlantic in.

[Buzzit]

Hi All

Thanks for the FI interpretations but I really cant see anything beyond the end of my nose (+72)

Im not sure the models are currently seeing past +72 either, too many unusual variables....

In general I feel the models are preprogrammed to accept certain variables more than others

etc (the weighting factor) which is why we rely on people rather than models.

I know we talk about models breaking patterns etc too quickly in FI. But I also wonder whether at

the closer timeperiods do the models also throw a wobbly if they see patterns they are not

programmed to expect ? (Some form of built in bias even at shorter ranges ?)

I feel a deep set cold is on the cards until 2010. Too much momentum around the pole for their not to be...

Thanks

[kold weather]

What is very uncertain is just how far south the upper low over Scandinavia gets, the GFS suggests in the last few runs that uit can gt decently south, the ECM meanwhile only just gets the cold air in place in the south and is nowhere near as unstable as the flow the GFS runs would have been, also if we don't get it then it really reduce the risks of getting much snow at the breakdown.

There is a risk we get caught in the middle of nothing, in other words the jet runs to our south and the fronts stays outh, the upper low stays too far north and doesn't quite bring down the coldest and most unstable air, then the low pressure in the Atlantic absorbs the low and a SW surge comes up, a few hours of snow and bang back to rain and the same old story...thats a real risk IMO, something to keep a close eye on!

[Cecil Hogmanay Melchett]

What is very uncertain is just how far south the upper low over Scandinavia gets, the GFS suggests in the last few runs that uit can gt decently south, the ECM meanwhile only just gets the cold air in place in the south and is nowhere near as unstable as the flow the GFS runs would have been, also if we don't get it then it really reduce the risks of getting much snow at the breakdown.

There is a risk we get caught in the middle of nothing, in other words the jet runs to our south and the fronts stays outh, the upper low stays too far north and doesn't quite bring down the coldest and most unstable air, then the low pressure in the Atlantic absorbs the low and a SW surge comes up, a few hours of snow and bang back to rain and the same old story...thats a real risk IMO, something to keep a close eye on!

Its a real risk Kold and a growing one IMO.

I'm having a few doubts now to be honest,not about the pattern in general but the trend away from the -10 stuff

hitting us.We need that colder air to bring the snow,anything less with a warm North sea could see modification.

Places with altitude should be OK,but low lying areas near coasts MIGHT struggle.

Edited December 14, 2009 by shuggee

[kold weather]

im sorry kw, but christmas day is still 11 days away, so saying it looks a washout at this range is nothing more than a guess really. the models might hint at a breakdown, but the fact is, recently breakdowns of this upcoming colder spell have been put further and further back, and some of the elders of the mod have implied that the models are being over progressive in bringing the atlantic in.

Sure it could be put back I'm not ignorant to that possiblity, I'm just suggesting that when you've got the ensembles from both the GFS and the ECM suggesting wetter conditions, then it just comes down to the exacts of the synoptics. What I wil lsay is the 0z ECM is almost certainly too progressive, both sets of ensembles suggest 22-23rd being the breakdown dates BUT obviously don't need much od a delay to bring xmas into play.

Certainly more then a hint of a breakdown though is what I'd say, more like a screaming warning sign. I'm still thinking this is progressive as well FWIW but models do suggest a washout...thats all I was saying.

[nick sussex]

Yes I quoted the wrong post sorry to everyone If I caused any offense !

No worries Regarding the models yes they seem to be painting a confused picture, in terms of inbuilt model bias, there are some that have been noted with the gfs, this model does have a tendency to overdeepen low pressure and bring the cold air too far south in its later output.

The problem perhaps isn't so much bias but a complex pattern which shows the models up,perhaps we're asking them to do too much here. Given the upstream doubts there are bound to be more changes so in terms of detail which is so important in terms of snow potential its very uncertain.