Model Output Discussion - cold spell to end Autumn

[Daniel*]

1 hour ago, MattStoke said:

People commentjng as if the ECM is spot on with the slider low. You really think a model will be spot on with such a complicated setup this far out? Ridiculous! It will be days before that one is resolved. The huge difference in the handling of it by the various models over the past few days should tell you that. Come on, people!

Spot on to demonstrate the last four runs from GFS in ascending order. What does that tell you? *HUGE* uncertainty it will not be till Friday until the models truly have a good handle of it.

[Chesil View]

Just now, Daniel* said:

Spot on to demonstrate the last four runs from GFS in ascending order. What does that tell you? *HUGE* uncertainty it will not be till Friday until the models truly have a good handle of it.

Greav post Daniel

[Mr Frost]

Absolutely fantastic Metoffice UK 6-30 days update today -  every year I would always hope December would be cold throughout with the chance of snow as it adds to the festive feeling! 

With what the models are showing for the foreseeable and the background signals it really is an exciting time of model watching. (If cold weather is what you are after)

Looking forward to seeing all the pictures from different areas of the UK and Ireland this month.

Hoping the GFS and ECM start to look similar today and tomorrow with regards to the upcoming cold spell this week. 

Most folk have a bias on here when posting thoughts on different outlooks but why would they not? (It’s a weather enthusiasts forum after all) 

Thank you to everyone who posts on here all year round or during particular seasons - I have been a member since 2009 and still learn new things every year! 

 

 

 

 

[georgiedre]

I agree with Joe b regarding mountains holding and moving the slider's as they cross from the west that's why I think a line from northern Ireland,Wales and SW England will be furthest the slider will get to . Could be wrong but that's my guess

[Timmytour]

1 hour ago, johnholmes said:

re this comment

Maybe the experts could refresh us on how sliders are modelled in regards to their biases? This might give us a hint of what to expect in a few days? 

No model has any bias, all are run with the mathematics to deal with the laws of physics as applied in meteorology. Lows and highs appear/disappear on this basis.

At the risk of causing some dissent another point worth trying to remember. That is compare 00z to 00z and 12z to 12z, not the most recent, that is until the time period gets below, usually, about T=96. Around this time then the more recent data increasingly tends to outpoint this method. 

I quite often see the comment that the models have a “mild bias”

 

I don’t really understand how this can be since it appears to me they deliver us, in terms of percentage returns, many more “snowmageddon” runs than the actual weather ever ends up delivering us.

 

One would hope that if the models are programmed with the right algorithmns, they would deliver us the same proportion of the all the weather types we end up getting as they project from however many days out. But, to me, they have a “cold bias”. I cannot help but think there is more excitement to be had from model watching over the years than from watching out of the window!

 

 

Let’s hope that this time the weather delivers us what the models, on so many runs, have projected for us in the way of snow.  It will help  avoid the “cold bias” getting worse!

[igloo]

im not sure the last run from the GFS had this slider crossing the midlands the ECM has been consistantly modeling this on the same path for the past 3 days if you look back a few days the GFS had storm caroline smashing in to northern france which was also wrong its only starting to catch up to the euro models as always

[Singularity]

 

06z then 12z. Slightly lower on this run with a little more of a ridge ahead of it. Could try for something akin to the 00z UKMO run?

[frosty ground]

Heights further north and a better south north alignment of the disrupting low.


Low slight further North, therefore boundary is further north.

Edited December 5, 2017 by frosty ground

[mpkio2]

On 29/11/2017 at 18:51, mpkio2 said:

And so, what do they models see now? What's been the trend/theme over that past few days?

12z GFS 29/11 t144:

12z UKMO 29/11 t144:

12z GEM 29/11 t144:

0z ECM 29/11 t144:

Very good agreement between the models!  (Especially the GFS/UKMO!) The THEME is for heights in the Atlantic to further ridge up to Greenland (Look at that WAA!!! ), Trough over Scandy, Arctic High STILL in place, trough over NE America, Low off Newfoundland (Helping with WAA to build GH! - Hopefully! ), high building NW of America (Alaskan High?) and high over Russia slowly building too! @chionomaniac  Is that a 3-Wave Tropospheric pattern emerging? )

Of course, the models don't have the details down yet of what will happen after, seeing how previous runs have built a GH successfully and some haven't, with inter-runs showing different outcomes after the t144 period (Which is around the timeframe (6th - 12 Dec) of @Steve Murr 's potential for Blocking to form around Greenland! ).

Asd many have already said, it's knife-edge stuff for the UK (When isn't it, though, really? ) and a case of "Wait and see".

 

ANOTHER EPIC POST INCOMING!!!

Hello all once more!

I've been monitorIing and lurking in the background, taking in what has been said on our current winter prospects. Much has been a-going on, huh?

Anyway, as can been seen from my post above from last week, I mentioned that the THEME going forward was looking good with "heights in the Atlantic to further ridge up to Greenland (Look at that WAA!!! ), Trough over Scandy, Arctic High STILL in place, trough over NE America, Low off Newfoundland (Helping with WAA to build GH! - Hopefully! ), high building NW of America (Alaskan High?) and high over Russia slowly building too! "

And where do we currently sit?

0z GFS 05/12 t12:

Hmm, not bad predictions from all models on the GENERAL pattern! Arctic High, heights in Atlantic, Trough over Scandy and NE America, Alaskan ridge and slowly building Russian High is all that is currently occurring, as the models predicted!

What they didn't get right is the amount of low pressure in the Atlantic the currently is which, ultimately, stops a stronger Greenland High from establishing due to low WAA. I advised not to take any model seriously after t144 (At the time!) all too seriously as the models didn't have the pattern nailed (Most were showing strong Greenland Highs! but some wern't) and, as can be seen where we currently are heading, it was right to do so!

Upcoming Cold Spell!

Cold incoming on Thurs into weekend looks nailed by all modles!

0z GFS 05/12 t72:

0z GEM 05/12 t72:

0z ECM 05/12 t72:

0z UKMO 05/12 t72:

Looks like a classic cold, artic blast to me!!!

Very good cross model agreement (Is what we want - if cold is your thing! )

Model Violity - What Will Happen After The Northerly?

The real problem is what happens after the intial northerly and wheether a preferbale "slider" sceanario will occur for the UK, as ala the GFS has been hinting in some of its previous runs over the past few days.

Heres what all models are showing for t120 (Sunday 10th December)....

0z GFS 05/12 t120:

0z GEM 05/12 t120:

0z ECM 05/12 t120:

0z UKMO 05/12 t120:

GFS/GEM both appear to have the "slider" low coming off the Atlantic further south (Back edge snow showers on the North of the low!) than the ECM does. UKMO appears to ba a midel solution.

Like many, I thought ECM looked horrible, but the more I studied it, the better it looked, especially if you understand the evolution.

From t120 to t144 the low south of Greenland falls down on NW - SE axis and joins the trough over Scandy resulting in a strong NW'ly flow....

0z ECM 05/12 t144:

Which then allows for an Atlantic ridge to build behind it...

0z ECM 05/12 t168:

Which ultimately leads onto this....

0z ECM 05/12 t240:

Which, actually, the 0z GFS t240 looks awfully similar to....

0z GFS 05/12 t240:

In fact both the GFS and ECM look rather similar, if you ask me, esepcially if you compare them side to side!

Both contain an Atlantic ridge, Scandy Trough, NE America Trough (-PNA signature!!!), Alaskan High, PV Troughing out to the East of Russia, Russia high, Artic high STILL in place! Obviously both look different, but both have same TREND/THEME!!!!!

And as I've noted over a month now, Trends and Themes are out freind this season!

Especially the whole "slider" discussion between GFS and ECM!!

ECM appears to look badly in comparison to the GFS because with GFS you can see its evolution of the low coming off the Atlantic from t144 to t168 where it slides under and phases with the trough over Sceuro - (It lowers the heights in Europe!). But with ECM, you can't see the evolution of where the low goes and whether it "slides" or not. Because you only have t144 to t168 to work with to see.

0z ECM 05/12 t144:

0z ECM 05/12 t168:

Lowers heights over Europe,meaning either the low went south of us, or phased with the intial trough sitting over Scandy. Becasue how do you know that the low didn't go south between t144 to t168?? Next few runs might show this better!!

Either way, there are some good TRENDS going on in the models, hinting at a "waxing and wanning" of a Atlantic ridge, Scandy trough, NE America trough, Alaskan High combo still to play for upto mid-Decemeber - its a TREND they are showing and nothing more!

To be honest, anything and everything couldpossibly be happen after the inital Northerly, but a colder pattern looks likely as being sustained (For now anyway! )

Also, I wouldn't get too caried away with uppers and moaning of where it willsnow and will it snow and all that really. As many on here as alredy noted, these finer details are likely to change constantly through intra-runs. Also, its possible to get snow showers even with -3 850hpa temps, as long as dew points and cold underneath too - it happened for London in Dec 2010 in one instant and, as many a few knowledgeable posters will tell you through expereinced, has occured in previous "Battleground UK" sceanarios in the past.

The battle continues and the roller-caoster doesn't llok like its gonna stop any time soon!

Exspect a few surprises in the coming days and the mdoels to chop and change regualyl!

Eyes down for the 12zs!!

~mpkio2~

[Day 10]

A correction west on this run as it stands here:

 

[SMU]

GFS much better for more snow

UKMO rain for pretty much everyone @120-

so no resolution yet

[karlos1983]

UKMO not great at 120 for slider #1

Should we be worried about the PV lobe? 

Edited December 5, 2017 by karlos1983

[frosty ground]

Very snowy for Manchester North, Everything is slightly sharper than the 0z run and a correction south for the Snow/Rain line.

 

[Singularity]

  
Hmm not quite eh?

That is one long trough going on right there! At least the sliding portion is weaker so less milder air drawn into the situation. With heavy precipitation and the wind kept from the SE across the northern half of the country, quite a large portion of the UK sees a substantial fall of snow although it looks a bit mixed with rain at times at lower levels outside Scotland. 

[snowray]

Liking the look of the 12z, could be very snowy from the Midlands north on Sunday on this run. 

[Summer Sun]

UKMO t120 colder air clinging on in the east less cold out west

[warrenb]

1 minute ago, karlos1983 said:

UKMO not great at 120 for slider #1

In fact, not just for the slider, UKMO is flattening the pattern

[Dean E]

GFS 12z and UKMO both differing again this afternoon, still 5 days out currently.

Models are bound to continue to chop and change as this is unusual setup for the UK.

[Weathizard]

UKMO at 120 is pretty ghastly

[Southender]

Yep as others have already mentioned, slightly better alignment on the slider on Sunday on the GFS. Still looking promising for North of the Midlands. Down South....meh.

UKMO = rank.

Edited December 5, 2017 by Southender

[Singularity]

Turned out a little better than I imagined with the closed low forming in not a bad position for cold air to filter back in and produce some more wintry weather.

UKMO is pretty ugly this evening as it even looks tricky to get the Euro trough dug-in far south enough from the +120. Feels like we're picking solutions at random out of a hat for the time being.

[Duane S.]

GFS 12z an improvement on the 06z, not as good as the 00z, smack inbetween with the slider.

UKMO, not particularly pretty

 

[Singularity]

6 minutes ago, warrenb said:

In fact, not just for the slider, UKMO is flattening the pattern

A lot riding on the -EPO ridge pulling the western flank of the Canadian vortex back toward the central States. That's what the 00z ECM did from a very similar position at +120.

Edit: Nobody need worry, GEM knows the way 

You never know though... but yes, not the horse I'd bet on if I'm brutally honest.

Edited December 5, 2017 by Singularity

[terrier]

Correct me if I’m wrong but I’m struggling to see the excitement here. Yes the gfs at 120 offers snow opportunity’s for others but quickly turning back to rain away from the highest peaks. The ukmo is flattening the pattern already. So after the northerly this weekend can’t really understand we’re the excitement is coming from. Will it be cold yes. Will it be widespread snow and locked in cold spell. From my eyes can’t see it. Think looking at the top 3 models the majority of us will be wet and wild. Not snowed under. 

[frosty ground]

I think it will have another go later..... not that it will look anything like this in the morning.