Model output discussion - into 2018

[carinthian]

2 hours ago, carinthian said:

GFS would seem like that. It has support of some sorts with the US Navy model outputs. Clearly post 144t  these two models seem to be struggling to evolve the increasing cold  block over NW Europe this weekend. Endless progressive runs now  to advance some form of trough distruption towards UK from a more zonal type but the prognosis does not look right me in the period 144-210t.  GFS certainly grinding this one out going down screaming and shouting . If it wins out will be like goal of the decade !

C

The amazing stand off from GFS continues with this latest run as early as 144t. Digging its heel in with a set of runs that seemingly produce a very unlikely prognosis. Have never seen a difference as wide as this at 144t compared to ECM. Sure our experts will be baffled as well. Speaking to them soon and will report back with their analysis . This run sends shock waves into the heart of Euroland with African melt down in the Eastern Alps and makes me very nervous over here anyway. Think its time for a break and a bit of fresh air.

C

Edited January 3, 2018 by carinthian

[Wilxy]

Isn' it possible that ECM, GEM is over doing the blocking whilst GFS is being to progressive with the Atlantic there for we end up somewhere between. UKMO might be the model to follow from now until we see better agreement.

[carinthian]

2 minutes ago, tomjwlx said:

Isn' it possible that ECM, GEM is over doing the blocking whilst GFS is being to progressive with the Atlantic there for we end up somewhere between. UKMO might be the model to follow from now until we see better agreement.

Sounds about right to me. Maybe something in between, think tonights runs will be crucial  to see where we are going with this.

 C

[ThamesStreamer]

4 minutes ago, tomjwlx said:

Isn' it possible that ECM, GEM is over doing the blocking whilst GFS is being to progressive with the Atlantic there for we end up somewhere between. UKMO might be the model to follow from now until we see better agreement.

UKMO has come off the fence somewhat anyway, much more closely aligned to ECM/GEM now.

[West is Best]

5 minutes ago, tomjwlx said:

Isn' it possible that ECM, GEM is over doing the blocking whilst GFS is being to progressive with the Atlantic there for we end up somewhere between. UKMO might be the model to follow from now until we see better agreement.

Maybe but we don't know what UKMO is doing after T144 (or do we?) since at that stage it's identical to GEM and ECM.

UKMO fax charts look tasty by the way.

[Man With Beard]

T192 clusters - all have some sort of ridge to the NE, the majority would possibly see it merge with heights to the SE eventually (bit of guesswork needed here) - the op run cluster has similarities with one minor cluster - so not an outlier but not the preferred option after D8 in the extent of its blocking.

[feb1991blizzard]

1 minute ago, Man With Beard said:

T192 clusters - all have some sort of ridge to the NE, the majority would possibly see it merge with heights to the SE eventually (bit of guesswork needed here) - the op run cluster has similarities with one minor cluster - so not an outlier but not the preferred option after D8 in the extent of its blocking.

This still screams battleground to me rather than big convective -10c uppers Easterly.

[carinthian]

7 minutes ago, karlos1983 said:

someone posted it a couple of pages back, very under-cutty 

Looks plausible but without any upper air temp profile to view, its hard to say how potent any undercut will be, but looks to be heading along the ECM output at that time span for the time being/

C

[Ali1977]

3 minutes ago, feb1991blizzard said:

This still screams battleground to me rather than big convective -10c uppers Easterly.

Yeah, it doesn’t look ok like you can tap into any real Siberian air mass with these clusters!! 

[feb1991blizzard]

1 minute ago, Ali1977 said:

Yeah, it doesn’t look ok like you can tap into any real Siberian air mass with these clusters!! 

Yes - of course the battleground could get the majority of the country with 10 inches of snow and the Easterly might only get the country a few grains of snow in the SE (no accumulations) but obviously you wont be able to retrospectively look at both scenarios.

[bluearmy]

1 minute ago, Ali1977 said:

Yeah, it doesn’t look ok like you can tap into any real Siberian air mass with these clusters!! 

Tbf, it’s way too early to make this judgment, especially as the Icelandic clusters don’t even show all of Scandinavia, never mind w Russia. 

Noting a trend from the latest eps to drive less Euro troughing (which would mean less CAA ) but with so many clusters it’s still a case of watching and waiting although the broad pattern is settling down nicely with the ec op still leading the way along with the GEM. Still think we haven’t yet seen an op throw out the correct evolution days 5 to 8.

[Catacol]

2 hours ago, Matthew. said:

One thing what is puzzling me is how are we getting all this blocking to the NE with zonal winds are 52m/s although they do drop off to 40m/s in a week but still

Winds forecast to moderate in the upper trop at all northern latitudes. By Thursday next week any sense of a zonal train has faded..

Wave 2 warming signs beginning to show next week

 

with lower strat vortex showing signs of stress as alaskan and scandy ridge impact 

@chionomaniac might be able to add some flesh to this in the strat thread as we move forward towards mid Jan, but for the short term at least zonal winds dont look to be a problem - if the modelling is correct of course.

 

[Weathizard]

Day 5 mean comparison, fairly similar actually.. GEFS insistent on sending more energy over though.

[SMU]

But ^^ 06z mean V 00z mean shows more & more Easterly component - 126/132

Note the mean of the eastern end of the block less saggy = more recarving SW

Edited January 3, 2018 by Steve Murr

[karlos1983]

A lot of the GEFS Purbs at 144 look like they will undercut. 

[frosty ground]

Ensemble 1 shows what we want from the Jet, Curved back South West.

Edited January 3, 2018 by frosty ground

[SMU]

Last one from me

156 mean - first GFS mean to show a parcel of breakaway energy moving SE splitting off the main flow

just SW of UK

[Catacol]

1 hour ago, ShortWaveHell said:

I shudder to think what this thread will be like if this easterly does a Devon Loch 

It's happened before.... in a December not so far far away......

Easterlies are notoriously difficult to get in place: insufficient support from underneath and they sink, too much northern jet and they sink or fade to the east. What we need is sufficiently robust heights to encouraged significant trough disruption to the west of the block with as much of the split energy as possible going underneath rather than over the top. This helps pump up the block via low heights over France/Spain and in the perfect scenario the block will then "retrogress" to the west. 

Note that the precise location of these blocks, and how they interact with the jet, in my opinion becomes removed as a science from teleconnective forecasting in the microscale forecasting world of days rather than weeks. We have a period of northern blocking on the horizon now and exactly how the block orientates and which air source precisely it taps into is a matter for the short term experts like Steve Murr to analyse. Experience of model watching tells us that GFS is often overly progressive with the jet and blows blocks away too quickly; ECM at the same time has had a habit also of over emphasising mid atlantic meridionality and hence those calling for a "blended" solution of the two have their feet on some solid historical ground. To my eye UKMO often offers the closest to that mid-ground solution when it comes to the UK backyard so a close eye on UKMO is a very good idea. It also makes it frustrating, however, that we are generally restricted to T+144 for UKMO rather than 10 day range analysis for GFS/ECM. Adds to the mystery a bit I guess!

How do we get snow? If the isobars are tightly packed enough giving a good flow over the North Sea then the east coast will quickly pick up "streamers" - effectively lines of convective showers that can merge into some quite significant falls. These are at least partly dependent on the precise angle of the flow - the longer the sea track the better. For those on the western side streamers tend to dry up... so instead all attention becomes focused on "bumpers" - systems that grind up against the block from west or south west. Again - precise angle is important because the flow needs to stay east enough of south as they come in to allow a cold dry continental feed to main optimal conditions for snow. These bumpers are, in my opinion, harder to get than the streamers in the east... and it is rare to get them aligned perfectly. However when it happens the snow that falls can be heavy (see Feb 96 and Feb 82 for my region) and probably outstrip snow quantities the east can get. So east gets more action more regularly... but when west gets it the action can be big! Feb 96 example below

One linked scenario is the Feb 91 setup where the trough to the south is deep enough and active enough to send weather fronts south to north into the flow. In 91 the undercut was very effective and fed a low over Genoa that was active enough to throw significant fronts on a south to north trajectory. Others will need to correct me on this - but I think Feb 91 is the only modern example where this has happened? Would be interested to know if there have been others I havent spotted.... Again - Feb 91 graphic below

 

Is there a negative side to an easterly? Yes. If the trough to the south is too shallow then the isobars drift apart... the high becomes "flabby" and the flow from the east insufficient to give anything other than drab, grey, bone-chilling cold. If we are honest this is the most common evolution of an easterly and can be a real hope killer - to see such cold in place but be unable to get any proper convection action going is grim. Bumpers can still occur - but if heights are not low enough over France then it seems harder to get the undercut - so a weak flabby high will tend to sink and the energy ride over the top.

So it is absolutely key we get energy undercutting to the south via trough disruption to the west of the block as the first stage to a winter wonderland. If this doesnt happen then the deck gets stacked against any significant snowfall. And teleconnections mean little to nothing for events at this short range under the UK hemispheric microscope.

[The Northern Ramper]

53 minutes ago, karlos1983 said:

someone posted it a couple of pages back, very under-cutty 

The midlands will get plastered ?

[karlos1983]

1 minute ago, Ramp said:

The midlands will get plastered ?

I'd be surprised if anywhere away from the Channel Islands saw any precip from that, more likely to miss the UK, if that indeed verified.

[karyo]

5 minutes ago, karlos1983 said:

I'd be surprised if anywhere away from the Channel Islands saw any precip from that, more likely to miss the UK, if that indeed verified.

Agreed! But I wouldn't mind if a proper cold easterly followed. 

[warrenb]

I don't think the GFS can override the La Nina pattern, and is purely going with it.

[The Northern Ramper]

11 minutes ago, karlos1983 said:

I'd be surprised if anywhere away from the Channel Islands saw any precip from that, more likely to miss the UK, if that indeed verified.

Sorry I should have posted this in my thread.

[alexisj9]

6 hours ago, Ali1977 said:

It goes look strange but look at that blast of WAA heading up from the Atlantic, could reinstate some form of Scandy high , and should keep that low pressure in the MED.

That' fantastic. We are stuck in very cold easterly if that happens. High over the top keeping the low to the south stuck. Could get dry though. But no thaw at all.

[johnholmes]

8 minutes ago, warrenb said:

I don't think the GFS can override the La Nina pattern, and is purely going with it.

Neither GFS nor any other synoptic model is aware of such a thing.

All set off with the basic observations at the set time of, 00, 06, 12, 18 and are then run out to the end time of the particular model using complex mathematics on the main physics used in meteorology. No other input as far as I know.

Not the same with climat models.

this link has useful information

https://www.metoffice.gov.uk/research/modelling-systems/unified-model/weather-forecasting

 

Edited January 3, 2018 by johnholmes