Model Output Discussion - cold spell to end Autumn

[Winter Hill]

8 minutes ago, Singularity said:

Alright, no need to scream 

 

 

At this range the details are of little concern but it is of note how the Pacific ridge is not as sharp on this run (left chart) which increases the risk of the Canadian trough breaking loose. On the other hand, the seed for the deep trough is shallower and more stretched out which makes me wonder if that will evolve into such a 'pushy' system.

Given the 00z ECM this is just speculation with respect to this particular run (for the fun of it, if I'm honest!).

PV looking very angry over Eastern Canada & Western Greenland 

[SMU]

Morning -  I see yer more drama on the 06z ... Time after time its 'South west'... yet   Some members still question why some of us document in advance the reasons why-

The models are now 'resolving' the visibility of the ridge that sits to the south of iceland at T96 that little 'sausage' is becoming more & more apparent which is in turn increasing the trough disruption & track-

The low is elongating so much that we are now also beginning to lose the onshore flow that for the S/SW & SE is the killer

here side by side is the 18z V 06z

you will now the negative tilt & south Easterly flow on the 06z v the more positive 18z ...

Its all getting rather interesting... 

Wales > Cotswolds in the £££ seat or just the hills in Devon if it holds true to form & history!!

S

[Kentish Snowman in Yorks]

10 minutes ago, bluearmy said:

We are now within the timeframe (T120) where the ops verify better than the ens mean on heights. 

But the eps running at 14km are a very good tool compared to a few years ago 

i am intrigued by the second feature which is now consistently modelled to approach on a more west to east basis rather than sliding or diving 

I take it that is not such good news in terms of prolonging this cold spell?

[snowice]

2 minutes ago, Steve Murr said:

Morning -  I see yer more drama on the 06z ... Time after time its 'South west'... yet   Some members still question why some of us document in advance the reasons why-

The models are now 'resolving' the visibility of the ridge that sits to the south of iceland at T96 that little 'sausage' is becoming more & more apparent which is in turn increasing the trough disruption & track-

The low is elongating so much that we are now also beginning to lose the onshore flow that for the S/SW & SE is the killer

here side by side is the 18z V 06z

you will now the negative tilt & south Easterly flow on the 06z v the more positive 18z ...

Its all getting rather interesting... 

Wales > Cotswolds in the £££ seat or just the hills in Devon if it holds true to form & history!!

S

I see from 06z could big a big surprise over here

[Methuselah]

Looks like a whole week characterised by 'marginality' - which, lo-and-behold, is an actual word...So why 'zonailty' isn't is a bit of a mystery: 

 

[snowice]

It's the north westerly train not the zonal 

South westerly.

[shaky]

13 minutes ago, Nick F said:

06z GFS keeps the secondary low dropping SE on Sunday completely separate from the parent low wallowing around the Norwegian Sea further north, hence it has its 'freedom' to wander further south on this run. Look at the frames on the EC and UKMO det. run and Sunday's slider low merges with the low to the north (which loses its identity eventually) - perhaps this merger with the other low tending to pull it on a more northerly track than GFS.

The tracking of this low wouldn't normally be so fixating if there wasn't cold air entrenched before it arrives! My money's on a more northerly track like the 00z, but I would love to be proved wrong!

Nick everything has moved south!!this is what i mentioned last night!!even the midlands could get lucky at this rate to even get any snow at all!!

[West is Best]

22 minutes ago, snowray said:

Big shift south on the ICON 06z, not as far south as GFS but close. ICON tends to follow the ECM idea by the way. Here are the two PPN charts, 00z and 06z for comparison.

 

Indeed. It's worth bearing in mind that whilst marginality is nail-biting, it's also historically the setup that produces the heaviest snowfalls.

I'll wager that many of us on here would prefer to see boundary snow events, which occasionally over step the mark only to re-load from the north than endlessly bone dry cold days like February 1986? The winter which stands out for me is 1978/9 when we had prodigious snowfalls from occasionally precarious setups.

[swfc]

Morning

Seems "slider gate" has kept the headlines again today!So not seen much comment on the gulf between gfs and ecm be it at 240hrs? ?? Looks huge imo and ecm looks unlike the 6z gfs keeping the colder theme going

Sorry if I seem off topic

[Frosty_wsm]

33 minutes ago, ICE COLD said:

I'm liking the 6z moving the snow boundary south . Means I'm gonna get some snow in Hertfordshire. Like people have said it will probably miss all together . 

Beautiful chart that, just a little more correction south and west would be even better although  as others have mentored on here these 'sliding' lows often do correct sw nearer the time.

[Singularity]

14 minutes ago, Steve Murr said:

Morning -  I see yer more drama on the 06z ... Time after time its 'South west'... yet   Some members still question why some of us document in advance the reasons why-

The models are now 'resolving' the visibility of the ridge that sits to the south of iceland at T96 that little 'sausage' is becoming more & more apparent which is in turn increasing the trough disruption & track-

The low is elongating so much that we are now also beginning to lose the onshore flow that for the S/SW & SE is the killer

here side by side is the 18z V 06z

you will now the negative tilt & south Easterly flow on the 06z v the more positive 18z ...

Its all getting rather interesting... 

Wales > Cotswolds in the £££ seat or just the hills in Devon if it holds true to form & history!!

S

Brings back memories of the Jan 2013 'wedge' which I seem to recall you were expecting to become more influential and with good success 

This cut-off ridge in this case is so closely entwined with the way the trough shapes up in the first place, though, that I'm not sure which is leading the other. One could side with the upstream dictating the downstream but I have see these ridges also be influenced by Arctic Highs (and a strong one is in the frame on this occasion...) plus lower-stratospheric patterns (not sure about this one - anyone got charts at 100 hPa? TIA).

[chris55]

16 minutes ago, Steve Murr said:

Morning -  I see yer more drama on the 06z ... Time after time its 'South west'... yet   Some members still question why some of us document in advance the reasons why-

The models are now 'resolving' the visibility of the ridge that sits to the south of iceland at T96 that little 'sausage' is becoming more & more apparent which is in turn increasing the trough disruption & track-

The low is elongating so much that we are now also beginning to lose the onshore flow that for the S/SW & SE is the killer

here side by side is the 18z V 06z

you will now the negative tilt & south Easterly flow on the 06z v the more positive 18z ...

Its all getting rather interesting... 

Wales > Cotswolds in the £££ seat or just the hills in Devon if it holds true to form & history!!

S

Yes Steve

its key to keep it cut off from the trough to the eas with that little wedge of high pressure more apparent on the 6z, keep it clean and you lose the warmer flow, and bring the snowrisk further south.

[bluearmy]

1 minute ago, Kentish Snowman said:

I take it that is not such good news in terms of prolonging this cold spell?

Given the eps appetite to amplify the jet again I’m not convinced re the transition period at the moment on any model !!

 

[SMU]

18 minutes ago, chris55 said:

Yes Steve

its key to keep it cut off from the trough to the eas with that little wedge of high pressure more apparent on the 6z, keep it clean and you lose the warmer flow, and bring the snowrisk further south.

Yep happy with the local elevation here as well - 

certainly not nailed yet- Just waiting for the 06z JMA etc not for definitive tracks but for all models to be making adjustments...

[nick sussex]

I see the slider continues to cause major drama!

As Nick F just mentioned phase timing or no phasing with the trough to the east is critical, the normal effect of phasing is to pull the upstream system further north and east so no phasing or later phasing will alter the track.

I wouldn't trust any output until the slider is within T72hrs range  because of that.

Later on the GFS tries to flatten the pattern but  its view upstream isn't what NOAA expect, a blended solution with the ECM to address both biases should see the cold continue for longer.

 

 

[Man With Beard]

Rather surprised to see the GFS revert to a SW slider!!

I also note that the latest JMA/ARGEPE, though not fully out yet, have adjusted by D3 slightly in favour of a more SWly slider.

Steve M - I'm not sure the models always get the sliders wrong in this kind of set-up - I think they get them wrong more often when there is a better block directly to the E or NE. I thinking the outcome is more to do with whether the low to the E will phase with the slider low to the W, and if so, when. The ECM op phases them, the GFS 06Z doesn't. We'll probably see this resolved in the next 24 hours.

[Nick F]

To give some credibility to the 06z more southerly track for Sunday's low, the 00z GEFS stamps had a fair few southerly tracks for the low too

Be interesting to see what the 06z GEFS stamps show too, though as others have said, the high res runs should be a better guide than the ens mean or clusters at only 5 days out. Though there are six EPS clusters as early as 00z Monday:

 

Edited December 6, 2017 by Nick F

[Geordiesnow]

Very nice too see the slider modeled further south and west, slightly surprised by that but this gives more room for error that at least somewhere across the UK will see some frontal snow on Sunday but its still far too early to nail down the details thats for sure.

I don't think the ECM is that bad regarding the slider, very low thicknesses and a slack flow which results at least some places seeing some snow I feel despite the uppers looking a little underwhelming but all in all positive runs this morning imo.

[Derecho]

So, another day and yet another messy picture

To summarise we have some very cold air from the NW on Friday but what next?

Do we get a soft exit from the cold spell and see the cold air over Europe over parts of the UK still?

Or do we get a hard exit with the colder European air displaced with lots of rain?

That is the £50 billion dollar question and the key is the area of low pressure entering northern Ireland. There is no agreement yet.

If this passes a little further south then there could be snow for the many and not the few for England.

However further north and the snow event is limited to much more northern areas. Rain means rain for others.

Very difficult to call in my opinion as seen by the percentages, maybe it will cross central England but that result is not binding and could easily change. The last two GFS runs have crossed it over Southern England now due to a weak wedge of heights over Greenland.

                          48%                                                           52%                                                          
  * and northern England

Once the low clears we are stuck in a col of somewhat cold air which is capable of a wintry mix in some areas. However naturally people will look at the next potential route for cold. Here are three options. I rate a Greenland high as less likely at the moment which I shall explain.

Lets start with the Eastern USA and Greenland, cold pooling is possible in the eastern US and NE Canada. Off the Eastern seaboard however are warm SSTs and this fuels areas of low pressure to form and cold air is allowed to build freely off the west coast of Greenland... unless the arctic high throws a spanner in the works.

  
                          20%                                                            40%                                                           40%
  

A strong and stable Greenland High would be quite difficult at this point and obviously requires a helping hand from the arctic as the ECM shows.

The option I’d like to see is to remain in more European based cold. Maybe we should look to Norway and build some high pressure there and import the colder European air. It would take a bit of time to get the really cold uppers, but it would be cold enough at least for a good taste of winter. The advantage of this pattern is heights in the Atlantic are less important so cold over Greenland may not get in the way of a wintry spell of weather here.

The last place we want to look to is Switzerland for high pressure. Late GFS 00z shows this scenario and it may be possible. Though this is a long way out and it may not be as mild as that.

These are just a set of scenarios which could occur under the current synoptic situation. In the end the British weather will do what the British weather does. It’s the will of the weather gods. Lets hope they change their mind from the zonality of recent years and we remain in the cold European air!

[bluearmy]

The number of eps clusters early on tells us that it’s pretty pointless second  guessing this 

on the extended, the clusters reveal a binary evolution between a fairly zonal solution and more amplified with the more amplified cluster ending up with a distinct  ridge to our north and euro trough maintained (as much as one can see on the Icelandic output)

[ukpaul]

Ensembles have the first slider hitting pretty much anywhere in the British Isles, no pattern at all yet defined. One even misses the south completely while the rest have snowfests to marginal further south, west, east and north!

[snowking]

Just to show the minute variance which makes all the difference, the low on the 6z control is about 5mb deeper, which helps to pull it a little further north and merge somewhat with the low to the north - net result is pretty good continuity with the median position of the potential snowfall from the 0z EPS (Wales, Midlands primarily, most of it to the north of the M4)

[Man With Beard]

22 minutes ago, Nick F said:

To give some credibility to the 06z more southerly track for Sunday's low, the 00z GEFS stamps had a fair few southerly tracks for the low too

Be interesting to see what the 06z GEFS stamps show too, though as others have said, the high res runs should be a better guide than the ens mean or clusters at only 5 days out. Though there are six EPS clusters as early as 00z Monday:

 

And look at just how evenly spread the ECM clusters are - only 10 in the biggest cluster, 6 in the smallest. All with different interactions between the lows to the NW and SW!

This slider is absolutely not call-able yet.

One thing in my mind though - troughs to the NE are often correcting a little further NE nearer T0 - such a trend might favour the SW route?

Regarding longer term, there continues to be excellent continuity for 15-16 December with two-thirds of clusters a renewed Atlantic ridge by the 16th:

however, as BA alluded to, the less blocked solution becoming more evident between D12 and D15, up from 30% yesterday to 50% this morning. Still a very large cluster with a ridge to the north and potentially east ( @ShortWaveHell yes, this latter theme has been the most evident one in the past few ensemble runs, and interesting to hear Glossea going this way too)

  

 

Edited December 6, 2017 by Man With Beard

[EML Network]

The same posters on here always trying to see what they want to and hopecast. 

I have to chuckle when I see so much attention on one LP system, of course it's path is going to be modelled differently from run to run and I understand why so many people are interested, but the path is more or less clear..this will move pretty much straight across the UK from NE to SE cutting a thin sausage shaped wedge, Snow more likely from Wales in the West drawing a line to Lincoln in the East and anywhere North of that is in the firing line. 

 

Those like me in the South really aren't going to get much out of this from Sunday onwards...those in the South and South West...your best chances of seeing snow is prior to Sunday, with Friday being your best opportunity and this has been consistently modelled for some time now. 

 

 

If you like cold zonality and lots of rain then you're in for a treat next week, I really can't see how anyone see's it any differently ?

 

As it usual from cold Zonality, N.Ireland, Scotland or NW England coastal areas are where you want to be. 

If you want a UK wide snow event then you need an Easterly or a North Easterly and until that happens the majority of us on here are going to be in for a let down...personally I can't stand nothing worse than cold, strong winds and rain...and that's what most of us are going to see from this set up AFTER the weekend. 

 

So enjoy what is to come from Thursday through until Monday IMO, but by all means feel fee to see what you want to and ignore what is actually being modelled

[Daniel*]

Sod’s law the slider low will go too SW and miss England altogether & skirt the extreme south coast instead hitting Northern France and the Channel Islands. I’d say that is highly unlikely not too surprised by southerly track by GFS 06z seen it time and again, would be good to see some consistency in the 12z.