Model Output Discussion - 8th December Onwards

[Snowly does it]

i would urge a note of extreme caution here. The MetO 6-15 is now following the trend of up to the 12zs yesterday and is going for average to milder in the south and wet. Of course they could just as easily have been caught out as anyone but this still has the capacity to follow the milder path.

The 06z is a grea demonstration of the obstinacy and power of a decent high latitude block, but you gotta get those trigger lows....

Would hate to have to call this but still favour LP, wet and average to milder conditions for the week after the cold spell

[IDO]

Latest short ensembles:

http://modeles.meteociel.fr/modeles/gens/graphe_ens3.php?x=306&ext=1&y=141&run=6&ville=Londres&runpara=0

Closest we have seen to agreement for a while, so the 06z is probably very close to the final picture. 15% bring the Atlantic in earlier, same hold the block a little longer. The mean then trending into positive uppers so southern Uk looking to average temps for a few days.

The ensemble mean at T192:

Op run:

The block makes significant less progress west than the op run, which in all probability is a cold outlier (or colder solutions). A north/south split most of the run:

The north certainly holding onto colder uppers most of the run (up to 192). But the south average up till then.

[EML Network]

Running through the various GFS runs, it's clear that the Russian High isn't going to budge, but at the same time the Atlantic seems to have an arsenal of Low Pressure systems it just wants to keep firing at us, coming off the Eastern Seaboard , so as much as I'd love to see the Russian High Retrogress , I'm seeing a stand off, with the meeting of these two forces well out to the East, the end result is that the UK is locked in a constant South West, to West zonal pattern, windy, wet, and until the Atlantic runs out of steam, I'm not seeing a potential cold and snowy possibility before 20th Dec at least.

With High Pressure to the East and around Greenland, what are the chances that these Lows are simply going to rotate around each other for weeks upon end, occasionally getting an injection of new energy as new Lows join the party off that Eastern Seaboard and we get stuck in a rut until the new year ??

Edited December 9, 2012 by EML Network

[Frosty.]

Well yesterday I thought the fat lady was clearing her throat and about to burst into song but today it's revenge of the cold block giving the mild atlantic a good kicking, a real battle looks to be brewing and there is a good chance the upgrades will continue on the 12z. it will create more of a headache for forecasters compared to yesterday where it looked like turning milder, wet and windy, could be a snowy spell ahead with the cold block much more stubborn, especially for the north.

[Froze were the Days]

Impressive consistency from the GFS because although obviously their are slight differences between the 0Z/06 in distant FI the overall trend of blocking is the same with a resulting E/NE,ly flow.

Fasinating spell of model watching to come I feel regardless of the outcome.

12

Wasn't the GFS pretty consistent for the 2 previous 'faux' cold spells though medium to lo-resolution runs? a lot of folks are now treading very cautiously when a potential easterly shows up but agreed incredible model watching even though no significant cold has shown up just yet, infact I can't remember such a non-zonal period well since 2 years ago!

Edited December 9, 2012 by Froze were the Days

[IDO]

Running through the various GFS runs, it's clear that the Russian High isn't going to budge, but at the same time the Atlantic seems to have an arsenal of Low Pressure systems it just wants to keep firing at us, coming off the Eastern Seaboard , so as much as I'd love to see the Russian High Retrogress , I'm seeing a stand off, with the meeting of these two forces well out to the East, the end result is that the UK is locked in a constant South West, to West zonal pattern, windy, wet, and until the Atlantic runs out of steam, I'm not seeing a return to cold and snowy before 20th Dec at least.

With High Pressure to the East and around Greenland, what are the chances that these Lows are simply going to rotate around each other for weeks upon end, occasionally getting an injection of new energy as new Lows join the party off that Eastern Seaboard and we get stuck in a rut until the new year ??

That's a classic blocking Icelandic low bringing a zonal flow to the UK. Hopefully other synoptics, like a mobile Russian High, or Northern Blocking will force this out of situ.

[joggs]

Just a quickie peeps(sorry mods) interesting rumblings in the strat thread maybe to start showing in FI. Regards

[bobbydog]

Running through the various GFS runs, it's clear that the Russian High isn't going to budge, but at the same time the Atlantic seems to have an arsenal of Low Pressure systems it just wants to keep firing at us, coming off the Eastern Seaboard , so as much as I'd love to see the Russian High Retrogress , I'm seeing a stand off, with the meeting of these two forces well out to the East, the end result is that the UK is locked in a constant South West, to West zonal pattern, windy, wet, and until the Atlantic runs out of steam, I'm not seeing a return to cold and snowy before 20th Dec at least.

With High Pressure to the East and around Greenland, what are the chances that these Lows are simply going to rotate around each other for weeks upon end, occasionally getting an injection of new energy as new Lows join the party off that Eastern Seaboard and we get stuck in a rut until the new year ??

looking at the bigger picture, i think the key here is the movement of the PV to siberia. russian the block won't move, as you say, however, when the PV shifts (as its modelled to and i think GP and others have been saying it should) this shunts the block westwards, possibly even allowing greenland retrogression. this strengthens the block nearer to us which keeps the atlantic at bay and puts us in a much better position from a wintry perspective

[IDO]

All in FI but Control run (T324):

Op run:

Mean:

It looks like Christmas or the following two week pattern could be mild or v.cold. The mean suggests around 50/50 either way. Keeping an eye on this trend and hopefully it will edge towards the colder option.

[nick sussex]

Still alot of uncertainty in the shorter term which will impact on the medium in terms of the orientation of troughing to the west.

Overall from a cold perspective and potentially moving forward I think we can say theres been a little upgrade today.

PS. As you all know I moved down here a few years ago, hopefully my rather poor attempt at photography will give you an idea why I chose this region. This is the view from my terrace taken a few days ago early in the morning:

The second one is with a little zoom taken today.

[mulzy]

Think we really need to keep our feet on the ground - even though there are tentative signs for undercut and the block eventually winning through in the op runs of the major models this morning, there is also the possibility that the residual energy of the PV spilling into the Atlantic could fuel the Atlantic for quite some time (as indicated in most of the ECM and GFS ensembles).

[Weather Boy]

I know that the great and the good tell us not to compare a GFS with the following run, but rather a particular run with the previous days, but with NW's 'previous run' button I can't quite resist, and I see some interesting differences between the 0z and 6z.

At a reasonably early stage in the run there are some significant differences, perhaps illustrating the high degree of uncertainty.

Here we have the 0z:

Look at the little low developing to the south and threatening to be a cut-off low. This is absent or at least less pronounced on the 6z:

So, at this stage, it looks like the 6z is going to be worse from a snow-lover's perspective. But then:

The low in question on hte 0z is not cut off and actually causes trouble, delivering cold weather to Scotland only, whereas its absence on 6z allows a deep channel low to develop and threaten snow for the southern half of the country and a short-reach SE flow for all:

Then in deep FI both runs end with a stiff easterly flow, although the 6z is fierecer:

So clearly nailed then! (Smily surely not necessary with that comment).

What do we learn from this? Well there are trends but anything is possible and cold solutions are on the table following the Atlantic's initial push in which will surely happen at some point. Who would dare say more than that at this point?

Edited December 9, 2012 by Weather Boy

[IDO]

I notice the UKMO update suggests average/mild (south, at times) and wet right up to Christmas. To do a sudden U-Turn like that I suspect it is of lower probability for anything cold in the medium term. So despite the odd good run today for cold, really nothing has changed.

As I thought the OP is a cold outlier:

http://modeles.meteociel.fr/modeles/gens/graphe_ens3.php?x=306&ext=1&y=141&run=6&ville=Londres&runpara=0

Still lots of spread, so wriggle room for a sea change, but little confidence.

[lorenzo]

Interesting runs so far today and the game over perhaps as gone on to be a third replay.

Fax charts are fascinating today. I like the 72 - 84 hrs step where 3 Atlantic fronts come in and one decays, also you have at 96 hrs a trough heading into southern Norway and one on the way back 300 miles North of it, all signs of Atlantic being repelled or eroding the block.

This period has definitely made me think more about what the models are showing in terms of how can we trust the output and at what range. 41/51 ECM Ensembles was a very strong signal to dilute as it did. I do however think that a lot of this volatility is down to the Vortex shifting, even the Strat charts from ECM have interesting variance within them and they are normally subject to less full on changes.

Have learned a whole lot in the last few days which is a great positive when a lot of what we were seeing on the models was less than pleasing for cold weather fans. Model flips whilst frustrating are pretty damn exciting for drama.

Looking at the GEFS panel for 850hpa it would seem it really is a run by run diagnosis of what could happen next between the Atlantic moving across to our shores. BA analysis post at the front of this thread - top class. Looking forward to messrs Sussex & Murr disect the Atlantic progress on the 12z and FI therowing up Xmas presents . Nice pics Nick !

[itsnowjoke]

I do believe that the bookies could be a little bit poorer.......

First Christmas Day chart.

i hope not as much as i like snow it would cause travel disruption.

[washtalk]

Hello all, bit of a lurker but very interesting watching and seeing all of the highs and lows (pardon the puns ) on this forum. Charts, IMO, looking more interesting this morning further down the line for some cold weather BUT we have all been there before so patience just may be the key word today.

[PubliusEnigma]

This is the most convincing frame that Ive seen all winter. It doesnt rely on the fickle Arctic High or the Russian High providing a feed, but the Greeny High developing. Our friend of recent summers that resides from May till September and then buggers off in November and December ..

The Siberian Polar vortex is a tad too far east to affect the backstream weather across the UK If . If the Vortex was

located 1000 miles further west, there would be a chance of the Siberian High drifting west into Finland with a far

greater chance delivering very cold easterlies to us. Could well be a snowy Christmas Eve in the south if that came off.

Edited December 9, 2012 by PubliusEnigma

[Summer Sun]

Before people get carried away Ian Ferguson has posted this in the south west thread

Well, latest analysis just in from Exeter as we look into the next fortnight. They're not suggesting any return of blocked easterly or such-like: indeed quite the opposite:

Days 8-10, Sun-Tues: Unsettled and often windy with bands of rain crossing the UK, with clearer/showery interludes in between. Still a risk of some snow over high ground at times in the N, mainly Scottish mountains. Temperatures mainly close to average, occasionally mild in the S, but with still a risk of overnight frost in clearer, quieter interludes. EXTREMES COMPARED TO CLIMATOLOGY: Nil CONFIDENCE: High confidence for cyclonic SW’ly type. Low to medium confidence for the heaviest spells of rain to be across the S and W.

Days 10-15: broad continuation of conditions and synoptics described above with little change expected."

BBC weather forecast for the week ahead on BBC just a few moments ago

BBC weather for the week ahead

Dry and cold

Widespread frosts till Thursday

Snow showers along the east from Monday (high levels of Scotland down to the north york moors possible further south later in the evening) all levels from Tuesday

Greater uncertainty from Thursday

Possibly milder and windy from Friday but very uncertain at this stage details will change as the week goes on

Edited December 9, 2012 by Gavin.

[Catacol]

I notice the UKMO update suggests average/mild (south, at times) and wet right up to Christmas. To do a sudden U-Turn like that I suspect it is of lower probability for anything cold in the medium term. So despite the odd good run today for cold, really nothing has changed.

As I thought the OP is a cold outlier:

http://modeles.meteo...ndres&runpara=0

Still lots of spread, so wriggle room for a sea change, but little confidence.

Little confidence in anything would be the wise call at the moment. These ensemble graphs have changed hugely for the end of the week in the last few days, so for once I have lost a little confidence myself in their ability to pick up the scenario for a week's time. What we DO know is that there is a cold high to our east that is going to increasingly ease westwards due to the repositioning of the vortex, and a residual segment of vortex left attacking from the west. Result? Good question... ensemble means show this pattern but do not currently show the result - the UK is slap in the middle of the fight.

For me it all hinges on how much energy is actually left behind by the vortex, but I strongly suspect that the models will have a hard time right up until the 24 - 48 hour range actually determining what that will be because the vortex itself is so mishapen and in distress. Go and surf a few winter NM vortex charts and compare our current shape, and shape over the last couple of weeks - it is not conforming to "normal" at all.

ECM currently has the vortex repositioning accelerating through Tues/Weds so I think we can expect some big model variation between now and then until the speed shape of that transfer is clear.

[chiffer]

Before people get carried away Ian Ferguson has posted this in the south west thread

I wouldn't have expected them to say anything other than that, just echoes what we already know they think. The models are showing a milder turn albeit still not as bad as last year, however there's room for change either way whether it be above average or below. You can have gut instincts but what the charts suggest are milder spells and that's what id forecast unless there is considerable change which could still happen at any time. Just got to keep an un biased view and a search for nothing until its right in front of us.

[Catacol]

Before people get carried away Ian Ferguson has posted this in the south west thread

Yes, but bearing in mind that the MetO itself was touting the cold blocked scenario with harsh frosts etc etc not that many days ago, I think we take this with a pinch of salt too. Ian himself stated that the Met are not particularly interested in anything beyond the 10 day range, and they use a combination of the EC and Mogreps models to come to some kind of conclusion. I suspect that this probably involved a single forecaster staring at a screen of model output and taking a best fit line. These models are better than the ones we have access to, but recent events have shown them to be flawed too.

I think we might have a better idea of the shape of things by Fri: by then the vortex repositioning will be clearer.

[snowking]

Before people get carried away Ian Ferguson has posted this in the south west thread

BBC weather forecast for the week ahead on BBC just a few moments ago

BBC weather for the week ahead

Dry and cold

Widespread frosts till Thursday

Snow showers along the east from Monday (high levels of Scotland down to the north york moors possible further south later in the evening) all levels from Tuesday

Greater uncertainty from Thursday

Possibly milder and windy from Friday but very uncertain at this stage details will change as the week goes on

I still don't give much creedence to their longer term analysis when it's based upon the MOGREPS - a model which, from the info provided by Ian in recent weeks, has always seemed a little slow to follow potential new trends. That isn't to say that the 0zs are definitely a new trend, but if they prove to be the case then I always find the longer terms Met Office guidance a little slow to react (in fairness to them, that is because they wait for strong guidance either way on a scenario, rather than flipping between scenarios with each run).

I await the 12z but actually recent history has been GFS picks up something new, and the others follow a short while after.

Obviously we could be back to yesterday's standing come the 12z, but I wouldn't be taking their view on thins as gospel....the can only suggest what the models have been showing in the past 48hrs, and as we all know that has been subject to much change in recent days

SK

[nick sussex]

Think we really need to keep our feet on the ground - even though there are tentative signs for undercut and the block eventually winning through in the op runs of the major models this morning, there is also the possibility that the residual energy of the PV spilling into the Atlantic could fuel the Atlantic for quite some time (as indicated in most of the ECM and GFS ensembles).

Thats a good point and means we can't take any output at face value till the main PV has relocated to Siberia.

At the moment the models are deciding how much of it goes and how much residual energy is left over, that impacts any troughing near the UK, if the models overstate/understate the left over energy this makes a big difference to the chances of any undercut.

[Methuselah]

There's only one solution IMO: the one that happens...Unfortunately for us, no computer model is capable of finding it, may never be able to find it?

What's more, the weather (outwith the quantum-scale, of course) is not digital...

[Frosty.]

Well the latest meto update makes no bones about it, saying it will turn milder in all areas by next weekend, that shows high confidence considering the backtrack from the 00z runs this morning, it's almost as though they haven't even reacted to the latest developments or just dismissing them. The further outlook is then average/mild zonal but it sounds like they are still on saturdays models rather than the more complex situation now with the battle lines being drawn as I type this, hopefully a backtrack from the ukmetoffice tomorrow.

Edited December 9, 2012 by Frosty039