Model Output Discussion 18th Nov.2013-12z onwards.

[Methuselah]

Does anyone know if the models take account of the amount of Northern European snowcover? If I remember correctly (chio?), isn't extensive snowcover thought to feed back all the way up into the stratosphere?

Edited November 20, 2013 by A Boy Named Sue

[Man With Beard]

The 12z GFS run does not let the atlantic get aboard at all and builds the mid Atlantic high nicely in FI.

I know its FI but it may well be the start of a trend. Fingers crossed

I feel that most good cold spells are first picked up on by GFS T300+. If a trend is shown several times (and I stress, several) in this time range, I take note. Strangely I think they then get dropped somewhere before T192 but then reappear a bit nearer to the event. Of course it's no guarantee but I'm sure it's often happened.

[Mucka]

The weak signal for a mid Atlantic ridge to form ushering in colder air early December just about visible at the end of the ensemble graph

 

Disclaimer:

 

To view product as advised rose tinted spectacles are required - spectacles not included

 

http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=256&y=53

Edited November 20, 2013 by Mucka

[MR EXTREMES]

a boy name sue I think you are correct I think there might be something about this in the snow and ice northern hemisphere thread.

[John Cox]

Agreed,

 

People talk about wanting the HP thats due for the nearly next 2 weeks to be over sooner and to let the Atlantic back in. .... And then to have a new shot at some "snowy potential".

 

I, for one, am quite happy that the HP is due to sit around for a while. I think it has a better chance for some very cold weather compared to letting the "westerlies" getting going. Of course it could go the "Bartlet" way. But hey, I prefer to gamble on this one.

Edited November 20, 2013 by John Cox

[radiohead]

I feel that most good cold spells are first picked up on by GFS T300+. If a trend is shown several times (and I stress, several) in this time range, I take note. Strangely I think they then get dropped somewhere before T192 but then reappear a bit nearer to the event. Of course it's no guarantee but I'm sure it's often happened.

 

The idea of an Atlantic ridge was picked up quite far out in FI. This isn't quite what we ended up getting, but it's still not a bad effort from 324 hours out.

 

12Z GFS from 12 days ago :

 

 

Today :

 

[Ian Brown]

Agreed,

 

People talk about wanting the HP thats due for the nearly next 2 weeks to be over sooner and to let the Atlantic back in. .... And then to have a new shot at some "snowy potential".

 

I, for one, am quite happy that the HP is due to sit around for a while. I think it has a better chance for some very cold weather compared to letting the "westerlies" getting going. Of course it could go the "Bartlet" way. But hey, I prefer to gamble on this one.

 

Yes John, when people talk of a reset ie to zonality they need to be careful what they wish for as such set-ups can last weeks and months.

[bluearmy]

hmmmm -  a quick look at the NH plots of the GEFS through week 2 reveals there isnt much appetite for a raging trop p/v. infact the majority of the members are amplified and most split or displace the p/v convincingly. remember that it was the gefs a couple of weeks ago that first spotted the current period of amplification. it may have become a damp squib as far as we are concerned (the shortwave 150 miles west or east and we'd likely be snowcovered now), but the states and eastern europe will not be saying that by this time next week.

[forecaster]

Does anyone know if the models take account of the amount of Northern European snowcover? If I remember correctly (chio?), isn't extensive snowcover thought to feed back all the way up into the stratosphere?

 

Yes, they will take it into account. They try to get the initial conditions as good as possible; a lot of effort goes into that.

Not sure if the stratospheric response occurs on a timescale small enough to become apparent to most models though. 

[Matty M]

Quite a significant difference from today's ECMWF 96hr chart to yesterday's 120hrs, if youre in parts of Germany/Denmark etc..

 

I think a small trend tonight and would not be surprised to see some cold upper filter into parts of eastern England by T0

 

All we need is for a big surprise Azores Low to pop up

Edited November 20, 2013 by Matty M

[SP1986]

I can certainly see the potential for a split in the PV later on, from where I'm sitting, any attempt of the Atlantic moving back in will potentially displace that vortex and allow a link between a developing Greenland High and a mid-Atlantic block. However it depends whether the low west of Greenland is hot on it's tail, as to whether it becomes a sustained block or a toppler. 

 

That said I don't foresee any great Atlantic resurgence, but that little bit of attempted resurgence might be the ticket to the split many have been expecting in the last few weeks.

[nick sussex]

If high pressure is to hang around then from a cold perspective even if you can't get an easterly you'd want the centre to be to the east of the UK to pull up a more se flow which would likely be clearer and still bring some nice sunshine and frosty nights. If the high edges too far west you could get a lot of cloud being pulled into the circulation.

 

Regarding any possible reset for those wanting a fresh start so to speak as Ian B mentioned this often ends in tears. Generally these set ups go one of two ways either the high hangs around and the upstream pattern becomes more favourable so you get some retrogression or the PV forces it south and you end up with a zonal mild sw flow.

[MR EXTREMES]

ecm t96 needs to be in the cat litter tray its the odd one out in a massive massive way. 

[shaky]

Quite a significant difference from today's ECMWF 96hr chart to yesterday's 120hrs, if youre in parts of Germany/Denmark etc..

I think a small trend tonight and would not be surprised to see some cold upper filter into parts of eastern England by T0

All we need is for a big surprise Azores Low to pop up

thats a massive shift west and south in cold uppers and that at a relatively short time frame.the gfs has pushed the cold uppers West aswell

[Matty M]

It's such an evil shortwave near Iceland around T120hrs.

 

But look at how it was progged on yesterday's 12z, and then on today's, much weaker, what will tomorrow's show?

 

[Matty M]

A final comparison of the big changes that can happen in 24 hours. In this case not really making a difference for us, but major different for parts of Europe.

 

 

[MR EXTREMES]

you can almost touch that cold air although some of the other models are close to the ecm but after lastweeks drama im going to suggest bin it but if its correct a little correction north and west could manage an easterly but ive seen enough times this could go drastically wrong.

[Matty M]

The big three in almost complete agreement at 144hrs for the high.

 

Unbelievable!

 

It can only mean one thing, major changes are a foot! 

 

 

 

Edited November 20, 2013 by Matty M

[Summer Sun]

ECM maintains the pressure rise this evening

 

 

More a less in line with UKMO and GFS at t144 agreement at last!

 

 

ECM following its 00z run so far

 

 

Frost and freezing fog likely to become a hazard into next week

Edited November 20, 2013 by Summer Sun

[MR EXTREMES]

ecm t168 bye bye vortex that's showing on a few models to.

[Gael_Force]

I noticed 1962 in the analog years - a lot of similarities to current output - no need to think December will be a duffer.

 

now

 

 

6 days later.

 

[MR EXTREMES]

the 192 ecm could be intresting.

[Tom Jarvis]

ECM about to give us a northerly

[Cloud 10]

Yes,interesting ECM 168 hrs.

 

 

Maybe we can just skip ahead to the mid-atlantic ridge?

[Cecil Hogmanay Melchett]

ECM about to give us a northerly

Hmmm not theECM im looking at.