Model Output Discussion - 18z - 25th Nov onward

[Geordiesnow]

Oh don't get me wrong it would foolish to rule out another shot at cold at this juncture, it's just that it's now looking like we could well be back to chasing decent looking synoptics in deep FI with nothing more than average conditions in reliable bar an unlikely sudden turn around from the 12z's which is a really bitter pill to swallow after all the build up over the last week or so.

To be fair, even if it does goes to pot, we have not really seen many charts which scream of loads of snow potential nor has the -10hpa has never been forecast to strike parts of the UK so it was not like we were heading into a major cold spell to start off with.

What I have seen is a colder spell of coming up but a drier spell with wintry showers possible on the coasts. Only the UKMO has really shown anything to resemble the risk of significant snow.

If indeed it does goes wrong, then lets hope we can keep heights going across the North and hope it will be 2nd time lucky and who knows, the 2nd time may be a colder shot. I know that would mean starting all over again so to speak but its only the weather at the end of the day.

All said and done though, wait and see what the 12Z runs show, especially the UKMO and the ECM runs.

[johnholmes]

Dont look at operational runs - check means. The runs you get on wetter or meteociel are only a single representation of 20 or more parallel runs of the model, and statistically the mean pressure patterns of the full suite of parallel options is the best to look at for trends.

Interestingly it is true that the ECM means last night moved away a bit from polar heights and brought the vortex back together quite quickly, but if you pull up the ecm ensemble mean runs for midnight they have trended back to cold again. Gibby has mentioned the GFS ensembles in his post but not the ecm ones which is a bit odd. GFS ensembles last night were very cold; this morning not quite so much.

The overall message here for you as a new learner is that the models are picking up on the overall trend for high lat blocking and cold weather, but are having one hell of a job resolving what is going to happen in the short term with the low pressure system strengthening over Nova Scotia. If that system fires through due east then it will upset the cold pattern for a day or two, but not for the long term ("game over") posts which some on here like to throw out. The only thing that would bring back the zonal express of west to east from here would be a strong reformation of the vortex. All the background signals are against that happening, so whether the nova scotia low upsets things a bit and brings westerlies in for 24 - 48 hours it will be only a blip in a trend towards blocked and cold. To get to the trends run the mean ensembles for several days - that gives you the picture and will help you ignore the odd operational run that goes astray, or even the odd ensemble run that moves away from the general direction. Only get concerned about a change of pattern if 2 or 3 ensemble means start to go the same way: that might mean something. As it stands at the moment this has not happened - at least for the long term. I posted the 5 day cfs mean chart earlier - here is the slightly longer range one - there is nothing remotely zonal or mild on the horizon from this up to date mean analysis. In fact this is reverse zonality at its best!

Interestingly I suspect that the change on the anomaly charts (so far only 24 hours to go on) is due to the probability as chio has mentioned of the polar vortex either splitting or declining as it physically shifts east. This shifting east to me is the most probable reason why the unsettled rather cold westerly seems to be gaining ground in both the synoptic models and the anomaly charts

[summer blizzard]

GEFS looks good to me with the Jet still heading south east and the ensembles suggest that the op was repeatedly on the mild side.

I remain confident.

[london-snow]

LS, the weather has made mugs of supposed teleconnection signals many times before. The NAO particularly is a complicated driver so I would add a fourth zonal option, which is shown by both of todays GFS runs and the ECM later frames.

Hi Ian,

Am i right in thinking that the NAO goes with a blend of daily output and finds the net mean of this output and changes on a daily basis?

So for example -

Cold across the board model agreement = Negative NAO

Warmer across the board model agreement = Positive NAO

If this is the case then i think i would bin it until we see the pattern emerge within 120+ i.e do not waste any time looking into fi as it is utterly pointless until we see what happens with the positioning of that low.

My apologies if i am wrong as i am still learning as i go along.

[summer blizzard]

Hi Ian,

Am i right in thinking that the NAO goes with a blend of daily output and finds the net mean of this output and changes on a daily basis?

So for example -

Cold across the board model agreement = Negative NAO

Warmer across the board model agreement = Positive NAO

If this is the case then i think i would bin it until we see the pattern emerge within 120+ i.e do not waste any time looking into fi as it is utterly pointless until we see what happens with the positioning of that low.

My apologies if i am wrong as i am still learning as i go along.

The NAO ensembles are based on the GFS ensembles, as such whatever they show is what the ensembles show.

[johnholmes]

Hi Ian,

Am i right in thinking that the NAO goes with a blend of daily output and finds the net mean of this output and changes on a daily basis?

So for example -

Cold across the board model agreement = Negative NAO

Warmer across the board model agreement = Positive NAO

If this is the case then i think i would bin it until we see the pattern emerge within 120+ i.e do not waste any time looking into fi as it is utterly pointless until we see what happens with the positioning of that low.

My apologies if i am wrong as i am still learning as i go along.

its not to do with temperature but pressure differences roughly Iceland v Azores.

+ve NAO comes from the 'normal' pressure difference being low over Iceland and higher over the Azores, -ve is the revers when blocking you have been hearing so much about is likely to predominate

hope that helps

don't be afraid to ask questions.

[london-snow]

Oh don't get me wrong it would foolish to rule out another shot at cold at this juncture, it's just that it's now looking like we could well be back to chasing decent looking synoptics deeper into FI with nothing more than average conditions in reliable bar an unlikely sudden turn around from the 12z's which is a really bitter pill to swallow after all the build up over the last week or so.

Hi,

fi atm is at 120+ at the moment to my mind if not before. Its all down to what that low does if it heads north or better north west then it is game on. If it heads east then it will set up a battle between cold and mild although as other ' Experts ' have added the milder incursion will only be temporary.

[london-snow]

The NAO ensembles are based on the GFS ensembles, as such whatever they show is what the ensembles show.

its not to do with temperature but pressure differences roughly Iceland v Azores.

+ve NAO comes from the 'normal' pressure difference being low over Iceland and higher over the Azores, -ve is the revers when blocking you have been hearing so much about is likely to predominate

hope that helps

don't be afraid to ask questions.

Thank you ever so much for the replies both of you.

On the right path but wrong junction.

Edited November 26, 2012 by london-snow

[IDO]

Hi,

fi atm is at 120+ at the moment to my mind if not before. Its all down to what that low does if it heads north or better north west then it is game on. If it heads east then it will set up a battle between cold and mild although as other ' Experts ' have added the milder incursion will only be temporary.

Mr Snow, how far away will we be able to say 100% (or as good as) that the energy will head north rather than east? Is it a case that we will have to wait for the tell tale sign of movement or will there be another earlier factor that will preclude the ejection east, or is it just a case of trend watching? Its only five days away and I am surprised that there is no consensus as to the probability. Thanks in advance.

[andy_leics22]

I don't expect any big changes in today's 12z run, there will most likely be differences between the main models but I can't see there being a surprise big swing either way. I wouldn't be surprised to see quite big changes later in the GFS 12z run, after t144...There is just way too much zonal going on in the GFS 06z run for me, doesn't seem realistic. Between t0 and t144 though, not much change I reckon.

Let's be honest though, non of us really know what the Weather will be by the start of next week, we all have our own ideas but we are in the hands of the gods so to speak. So whatever the outcome is, don't get annoyed!

Edited November 26, 2012 by andy_leics22

[Frosty.]

Most of the VERY cold potential on the models never usually gets within 6 days range, the fun is in the chase but all talk of a rerun of 2010 is now pretty much laughable. It will turn colder but as gibby said this morning, no sign of any deep cold and snow mostly confined to northern hills but some occasional frosts, I think some of us have been duped by eyecandy charts, I keep telling myself not to get taken in by the super cold charts but I fall for it every time, it's what makes model watching so frustrating and exciting. The cold spell duration looks stunted as weather approaches from the west and southwest, still time for changes though, probably best to lower our expectation levels and then hope for a nice surprise from the 12z.

[Matty M]

I don't expect any big changes in today's 12z run, there will most likely be differences between the main models but I can't see there being a surprise big swing either way. I wouldn't be surprised to see quite big changes later in the GFS 12z run, after t144...There is just way too much zonal going on in the GFS 06z run for me, doesn't seem realistic. Between t0 and t144 though, not much change I reckon.

Let's be honest though, non of us really know what the Weather will be by the start of next week, we all have our own ideas but we are in the hands of the gods so to speak. So whatever the outcome is, don't get annoyed!

This is all pointless discussion as we have no idea, but i do think it is a crucial set of run.

The big one will be the UKM, it has been really really consistent, so if we see it stick to its guns at 4.20pm it is a MAJOR tick, if not then

things could be coming to an end for prospects of severe cold in the near term.

Before that we have the 12z which should give us an indication near 4pm of whether it is trending further towards the UKM or to a flatter pattern.

Crucial period from T84hrs-120hrs.

[Weathizard]

The GME trickles out painfully slowly, looking forward to this afternoon/evenings runs as hopefully we will either get upgrades or be put out of our misery

Edited November 26, 2012 by Weathizard

[nick sussex]

I think we have to be realistic given the upstream signals that the Atlantic will try and move in as that piece of PV over Canada moves east.

This however does not mean that a return to milder conditions is likely for the majority of the UK.

The angle of attack is crucial and much of this will be governed by high pressure to the ne in terms of forcing the jet axis nw/se, the important thing in terms of maintaining cold and snow chances is whether we see enough trough disruption to the west and so even though the medium term pattern is beginning to emerge we don't know yet the start point in terms of where the block will be before this.

This brings us back to the much talked about Canadian low, much of weather is like a domino effect and this is relevant, the further west and south we get the block initially the better chance down the road of a better angle of attack by the Atlantic.

So the track of that low does initiate a series of dominoes.

It is likely to be further east than originally modelled a few days ago but its whether we can see it make a good turn towards the north in time to give the block a chance.

We'll know soon....

Edited November 26, 2012 by nick sussex

[Jonan92]

GME 00z

GME 12z

Slightly stronger and back to the west

[Weather Boy]

GME 00z

GME 12z

Slightly stronger and back to the west

Really? They look identical to me!

[andy_leics22]

This is all pointless discussion as we have no idea, but i do think it is a crucial set of run.

The big one will be the UKM, it has been really really consistent, so if we see it stick to its guns at 4.20pm it is a MAJOR tick, if not then

things could be coming to an end for prospects of severe cold in the near term.

Before that we have the 12z which should give us an indication near 4pm of whether it is trending further towards the UKM or to a flatter pattern.

Crucial period from T84hrs-120hrs.

I agree, if the GFS and ECM stick to their guns, the UKMO has to back down eventually. Today's 12z run could possibly be a back track we see from the UKMO. I hope it isn't but I wouldn't be surprised if it happened.

I love snow like many others do on here, but sometimes you have to be realistic, even though the GFS has known to swing wildly after t144, it's usually a very solid model between t0 and t96.

[Jonan92]

Previous GFS run

GME run

They look different to me, GME looks better

Edited November 26, 2012 by Jonan92

[The Eagle]

GME looks fairly useful at 72hrs.

[london-snow]

Mr Snow, how far away will we be able to say 100% (or as good as) that the energy will head north rather than east? Is it a case that we will have to wait for the tell tale sign of movement or will there be another earlier factor that will preclude the ejection east, or is it just a case of trend watching? Its only five days away and I am surprised that there is no consensus as to the probability. Thanks in advance.

Afternoon Mate,

I am no expert and i am sure that the likes of ( SM,GP,JH,Chino will be able to give you more of a idea than myself tbh ).

However i will not shy away no matter how stupid i may look as its all part of a learning process.

We will take the 06z link here http://www.meteociel...gfse_cartes.php :

As we can see that low pressure system out towards the west which develops at 72+ and is fully developed by +120 so 5 - 7 days as you rightly say which is still a while away. Its from there that we need to see this travel north or north west to avoid crossing the atlantic and blasting through that ridge of hp and the cold to the east by which time is getting established in the uk. If that lp heads east then the milder air may win out temporarily going by the thoughts of Ian F however if that lp goes north then we are in business.

That is my take on things mate. As i said though i am no expert.

Just to further answer your question regarding probability's answer = Have you a coin preferably a lucky one

Edited November 26, 2012 by london-snow

[Weathizard]

GME looks more like its backing UKMO at t72 but my brain is confused by the postioning of the jet stream, as its quite different so could go anywhere

[karlos1983]

Really? They look identical to me!

If anything looks further east, and pressure was deeper on the 00z.? or have missed something..

[Backtrack]

Well the 12Z is now rolling out. Fingers crossed, this is a valuable run.

Let us pray.

[Weathizard]

Well the 12Z is now rolling out. Fingers crossed, this is a valuable run.

Let us pray.

Let us pray at the alter of Arctic highs, Greenland ridges and Cold air. 12z coming out now, squeaky bum time

Edited November 26, 2012 by Weathizard

[Jonan92]

If anything looks further east, and pressure was deeper on the 00z.? or have missed something..

In this run the low has 1005hpa and is near inland while in the previous run it was 1010hpa and a little to the east

Edited November 26, 2012 by Jonan92