Model discussion highlights

[Midlands Ice Age]

 

3 hours ago, Met4Cast said:

Some won’t be happy until we see a return to snowball earth and even then I’m sure they’d find a reason to complain. 

Great modelling across the board this morning, the GEFS extend the cold (using -5C isotherm as the guide) another day or two with a tighter clustering of cold members. 

Details chop and change but the broad direction of travel remains the same. The GEM & UKMO are pick of the bunch for me. 

I think that I might qualify   in that category   

3 hours ago, Harveyslugger said:

People expecting an ice age

Well just look at my name....  Of course I am.                  Maybe not reaching the south coast... but the M4 will be OK.

Seriously though?...... I am waking from my 50 years of snoozing... My alarm clock went off early this morning when the sea ice extent figures from JAXA appeared and we have the highest amount of sea ice for the last 21 years. It is now greater than it was in the 2000's. 

There is enough cold air in the Arctic at the moment for everyone to share. 

PS... I have no idea why....... especially when apparently worldwide temps are so high. Even the Antarctic extent has rapidly caught up with its averages!!.

MIdlands Ice Age

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5000985

[Singularity]

 

The mid-stratosphere modelling has made for an interesting watch this past week and probably has played a role in the uncertainty regarding how strong the tropospheric polar vortex lobe over N. America will be, hence how strongly the Atlantic lows attempt to push cold weather out of the UK next week.

First off there's a week split this Wed-Thu, followed by a partial merger on Fri, followed by a more pronounced split Sat-Tue. It remains to be resolved how strong the vortex above N. America is, hence the uncertainty with what goes on below.

Incredibly, there are hints it may attempt to split yet again later next week, though the latest run wasn't as interested as the 00z.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5001066

[bluearmy]

37 minutes ago, IDO said:

The worry is that the other solution is also paved with twists and turns. See the GEM; it

has the surface high that the GFS 0z had, which delays the flow of the cold:

After that, the run falls to pieces, and GEM has been the poster boy for the GH potential on previous runs! There are many forks, and the GFS seems the best for a snow event, with the usual caveats. Remember the GH has a relatively short half-life, so getting an event in early would mean less worry.

Which is why I always prefer getting the cold trough across the U.K. and a bit further south into France - then the Atlantic trough can run into existing dense frigid air. It’s the best of all worlds. The trending on the ens is not in the right direction days 9/12 ref temps in association with the scandi trough not digging far enough south before it extends west. It could be that the models are over reacting to the renewed reversal above 70 N.  Fascinating watching but I have a nagging feeling that the stakes are very high for the south of England on this one.  Miss out next week and then we’re on to feb …….

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5001994

[Met4Cast]

In terms of where the polar boundary lies that is something that's going to shift north & south probably 100 times before we actually get to the period of interest, I wouldn't place too much focus on that. 

Returning momentum in the form of the jet stream edging back northwards seems a certain bet, it will happen at some point as the MJO continues it's progression eastwards and on the back of the recent (but brief) AAM tendency dip. How this looks synoptically will depend on how much blocking we retain to the north. It could be that the jet doesn't quite get into the UK and instead we remain cold for far longer (the 00z and 06z GFS det runs played with this scenario) or it could be, like the GEM we see a widespread, high impact snow event (perhaps multiple) as lows push up into the cold air across the UK. 

Current thinking is the 20th-25th for a potential Atlantic return (of sorts) and therefore increasing risk of high impact weather. Where? How? Who knows, that wont be resolved for a longgggg time.

In any case, we've already seen a return to +AAM tendency and frictional torque will soon return to +ve followed by another likely +EAMT event driving AAM tendency upwards, total GLAAM & GWO remain coupled with the El Nino base state. MJO progression likely through the Maritimes and back into phases 6 >7 around the end of January/beginning of February (MJO timing always difficult).

In essence, any waning of the block and Atlantic return will likely be temporary with renewed blocking likely into early February, perhaps Greenland/Scandinavia, more likely is we wont see the block to the north become completely eroded, cold air will never be far away. 

Very, very positive moving forward away from the chopping and changing of NWP outputs and attempting to nail down precise details 10+ days away.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002281

[Met4Cast]

46/51 of the 12z EPS had a technical SSW reversal.

If we do see a reversal then I expect modelling to be even less reliable than it currently is in the med-extended. There is a lot going on at the moment so getting caught up in every individual deterministic run searching for precise desired outcomes makes even less sense than it usually does. 

EC46 comes frustratingly close too..

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002306

[sebastiaan1973]

29 minutes ago, bluearmy said:

As I understand it (and @lorenzo is the go to person here in the strat), reversals in the upper strat generate several repeating waves over the following period up to a couple months. Because the current reversals are downwelling quickly, I would think it’s possible that the waves that follow will only repeat out to six weeks or so.  Say two waves - three weeks from now and six weeks from now (that’s very approximate) 

I'm not Lorenzo either, but I think you have to watch the work of Domeisen. In this chart you see the downwelling divided in 4 regimes. Right now we have blocking. This means there will be 2 significant downwellings after this one. This doesn't mean winter at the British Isles or at home in the Netherlands, but increased chance of negative AO.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002381

[Mike Poole]

2 hours ago, Scott Ingham said:

As ever if we don’t go to Scandi next the fun bit will be doing an autopsy and working out why to add into my scrap book of learnings these past 10 years!

Whats your call Mike? Where do you see us going next?

Well, that’s a question.  I am very persuaded by the arguments based on the GSDM that @Tamara, @Catacol, @Met4Cast and yourself have made very convincingly about the evolution of the troposphere.  They have for me, put the flesh on the bones of what the seasonal models have been hinting at for a long time - it gives me confidence when more than one line of reasoning leads in the same direction.  So that would imply a flatter pattern in late January, and the potential for more substantial blocking patterns again in February.  

Assuming that this cold plunge by 15th January happens without any further drama, I think any flatter pattern might in any case throw up surprises in terms of snow for some if the jet can remain south of where it usually is, and wedges of higher pressure and colder air remain in the mix, and no rampant PV takes hold (I’ll come back to that).  Or if the mild wins outright, the end of January could just be unsettled and wet.  Whether a Scandi high is part of the next phase of the evolution, I don’t know - they seem extraordinarily difficult to achieve in the depth of winter, but the hint is now there on the extended EPS.  You could say, if not this year, then when?  

I think what happens (or has happened) in the stratosphere will be important when the more amplified trop signal takes hold.  I think the weakened strat vortex due to the Canadian warming, and now the further warming just happened, have allowed the currently evolving pattern more amplification than might otherwise have been the case, which in turn has impacted the strat again with a possible SSW again in sight - this would be evolution rather than revolution in my view, but might again lend support around the time of the more amplified signal we expect in February.  With the weak strat vortex, I don’t expect a rampant trop PV to take hold during the flatter period end of Jan.

2 hours ago, Met4Cast said:

46/51 of the 12z EPS had a technical SSW reversal.

If we do see a reversal then I expect modelling to be even less reliable than it currently is in the med-extended. There is a lot going on at the moment so getting caught up in every individual deterministic run searching for precise desired outcomes makes even less sense than it usually does. 

EC46 comes frustratingly close too..

I don’t think whether there is a technical reversal will make much difference to the model performance, because I think that is already affected by the the complex interplay between the trop and strat during the whole of this evolution.  

2 hours ago, bluearmy said:

I’m not sure it will make much difference as it’s displacement  - we’ve already got ongoing reversed flow above 70N predicted for the next ten days or so. Having it get another ten degrees south could help to supress the jet a bit further south but I’m expecting reversal waves to head down into the trop out to the end of feb anyway. 

I think whether we get a technical SSW will only affect how this period of weather is referred to after the event, whether it will be put down to the Jan 2024 SSW or not, but the strat evolution has been important throughout this period and will continue to be so whether that happens or not.

All the best,

Mike

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002475

[Eagle Eye]

Could technically get very close to a reversal, maybe an actual reversal w/the flipped tropospheric pattern connecting up to Strat. If that does happen, could well mirror back down and re-intensify the poleward drive at the same time that the AAM budget is building in Atlantic.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002410

[Nick F]

Morning. Now the models seem to be settling on the cold northerly next week, thought I might start to post some thoughts. 

00z GFS looks a bit too bullish with the Atlantic encroachment from the SW next week, also it blows up a low south of Iceland early next week which phases with the Atlantic low system to the south - which the other models don't have.

Be interesting how well the models handle how far the south the deep cold gets and how far north milder air gets - the boundary bringing a high risk / high reward of heavy snow or rain wherever it sets up. 

Lots for the models to resolve next week, but think the 00z GFS looks a little too bullish with the Atlantic push, has a habit of blowing up lows too much.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002793

[Catacol]

32 minutes ago, Continental Climate said:

A good post in my view. If you look at the output say 5 days ago there was a much more robust signal for greenie blocking and the infamous shuffling high to the north was meant to just meander around giving us a prolonged cold period. That signal has evaporated. I've not heard a single mention of a shuffling high for days. Some people are quite rightly frustrated this signal has been dropped. This spell has been watered down last few days in my opinion. Will it get colder yes, will people get snow yes, will this be a period of snowy weather lasting longer than 6 days unlikely now in my opinion. There is no denying the blocking signal has faded last few days. 

A fair point - but I'm not sure the prognosis at the moment has really deviated from the overall shape of things that was probably best expressed by Tamara a couple of her posts ago. We have the wave break now that is being pushed up to high latitude at the end of the week, we then have the cold trough dropping in. We will likely have a slower breakdown from this than the models predict (because observationally models speed up breakdowns than is usually the case once it happens) and then we have - with the less favourable MJO phases and a drop in AAM - an anomaly chart like this to wrestle with:

First of all it is a very long way off - but if we take it at face value it reflects the progression of the drivers stated above but does not really give us a scooby as to what the synoptics will be. There is certainly a pressure contrast that is still suggestive of weak -NAO but quite where the cold/warm boundary will sit is very uncertain.

Then -  looking at the latest GEPS that, to my eye, has been a bit more accurate than GEFS from the 00z run we get this out in the very far reaches of ensemble modelling:

High pressure starting to build back into Greenland in line with the Nino background and drivers pointing to renewed momentum and amplification which then ties in with the EC weekly move back towards this:

So - some degree of relaxation of the cold was inevitable at the end of next week, but it does look temporary and - in any case - quite where the boundary between the warm and cold air will be is utterly impossible to nail down now. I think the overall pattern as described in that post of Tamara's remains solid.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002814

[Catacol]

ECM has just thrown out the most potentially snow charts across the UK from days 8-10 that we have seen since 2018. I'm in a rush - I dont have time to read the many pages of comments, though I will predict that some are very happy at these and some are bemoaning the marginal 850s in the south and sounding the doom-bell.

850 predictions at day 8 are utterly irrelevant. Look for the pattern. Cold trough, channel systems bumping into it. There are snow opportunities likely from both convective shower streams off the north sea as well as cold/warm boundary frontal events.

This is about as good as it gets. Happy days says this pig in sh*t. Enjoy your own day if you can and remember (contrary to my initial post yesterday!) that 12z forecasts are verifying better than 00z at the moment so let's build on this morning's foundation later on. 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002777

[johnholmes]

I suppose I will be talking to myself but comparing 06 to 00 at extended distances really is a waste of time. Compare like with like and you will get a better idea of where the particular model seems to be heading.

I'm in the middle of doing my usual 500MB output, will post it before long but they seem to agree with the overall outlook of cold returning over the coming weekend, but with differences in how cold.

re the how far north will any low get. Almost always IF the cold has been in place for 3 days or more then the initial modelling suggesting the Atlantic pushing the ridge/cold air away is very often too quick. The direction of travel of the depression at the surface and in the 3 dimension is fairly critical and is usually only seen accurately 24-48 hours out. Even then it can be several days before there is a real breakdown into genuinely milder gets there.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003059

[TEITS]

Have to say regardless of your location the current output is excellent and to be fair you will never get a set up that will deliver for everyone. Only the likes of 1947 do this when blocking alternates between Scandi & Greenland.

So the initial surge of cold N,lys around 14th/15th Jan looks likely despite some dodgy ECM runs a few days ago. At this stage snowfall looks limited but you never know what will develop in the N,ly flow.

Now onto my favourite part which reminds me of the late 1970s, 80s. The classic old skool situation of a blizzard for some, snow to rain for others, and then some seeing snow to rain and then back to snow again. At the moment impossible to say who will hit the jackpot but based on the current output and my own personal experiences I would say the bullseye is slightly further S than the ECM has this.

My reasoning is this. Note for my location the ECM operational is very close to the mean.

Now look for the S coast of England. This is way higher than the operational.

 

So the above combined with my own personal experience of these set ups suggest the main risk of heavy snow is further S with the N limit being around 30miles N of London. Subject to change though!!

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002842

[johnholmes]

Tuesday 9 th Jan

NOAA 6-10==15-19th, in other words inside the approximate date of ‘deep’ cold predicted some time ago.the 6-10 chart keeps the meridional flow across the chart, the shape is not the classic one but no signal for a developing mobile Atlantic, not on the 8-14 really. As usual the high +ve anomaly is much reduced but this is normal. IF this persists and the upstream becomes less conducive to another trough-ridge downstream then a change could be signalled but not so far and the 8-14 takes us to 17-23rd Jan?

ECMWF has never been as +ve about the deep cold scenario and its latest output for 15-19 Jan is pretty similar. The 850’s show the -5C extending during the period to cover all of the UK by the 15th then it is moved north again so that by the 19th is is predicted be N Wales to about the Wash area. This as the 500 flow backs more west or even south of west with time.

UK Met of course only shows surface and 500MB outputs for 3 days (13-15 th) but it looks to be on the same page for just prior to the two above from the 15 th. Ridge dominated both 500 and surface, over/just NW of the UK to a more trough dominated by the end of its run, again surface and upper air.

So overall then, after a temporary slight warming at the surface and height, over the weekend a deeper colder spell seem likely to occur. The direction of flow, initially, being N’ly not E’ly. Looking on Extra at the skew-T diagrams, the colder air seems to start arriving over Doncaster by 14 Jan and much colder air continues to advect into the area from a N’ly direction as far as the run goes=T+180. All the time with limited convection, to around 6000 ft. So even well inland it is ‘possible’ for snow to fall. This is way ahead of any reliability from the synoptic models so patience is needed as to just what will happen over the UK regarding snowfall. Be that from showers and any possible troughs in the flow or from the Atlantic trying to move in giving more general ppn.

To me it seems unlikely that milder air is unlikely to make much, if any, real progress against the cold airmass in the period under discussion on this post.

All really interesting though to see just how the actual weather will turn out.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003095

[nick sussex]

The track of lows into the UK tends to get modelled further south when you have a more stable block or when we have some wedges and a weak jet .

In the current set up the block position is more uncertain and the trend is for it to move west or at least change orientation to more ne sw .

Low pressure will attack the weak point and that’s currently near the UK.

Once the jet lifts ne the only way to effectively suppress that south again is renewed blocking .

As there’s no strong signal for that you must have any phasing of shortwave and low to the sw once the cold has had time to bed in and that needs to happen further east .

The stakes are high here because there’s a good level of cold to the north and the possibility of some heavy frontal snow as the different air masses meet .

These set ups are very complex with small changes making a large difference on the ground .

Throw in poor data coverage over the Arctic and the behaviour of the Arctic high and it’s really going to be a nerve shredding few days for coldies .

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003078

[Met4Cast]

15 hours ago, Met4Cast said:

In terms of where the polar boundary lies that is something that's going to shift north & south probably 100 times before we actually get to the period of interest, I wouldn't place too much focus on that. 

Returning momentum in the form of the jet stream edging back northwards seems a certain bet, it will happen at some point as the MJO continues it's progression eastwards and on the back of the recent (but brief) AAM tendency dip. How this looks synoptically will depend on how much blocking we retain to the north. It could be that the jet doesn't quite get into the UK and instead we remain cold for far longer (the 00z and 06z GFS det runs played with this scenario) or it could be, like the GEM we see a widespread, high impact snow event (perhaps multiple) as lows push up into the cold air across the UK. 

Current thinking is the 20th-25th for a potential Atlantic return (of sorts) and therefore increasing risk of high impact weather. Where? How? Who knows, that wont be resolved for a longgggg time.

In any case, we've already seen a return to +AAM tendency and frictional torque will soon return to +ve followed by another likely +EAMT event driving AAM tendency upwards, total GLAAM & GWO remain coupled with the El Nino base state. MJO progression likely through the Maritimes and back into phases 6 >7 around the end of January/beginning of February (MJO timing always difficult).

In essence, any waning of the block and Atlantic return will likely be temporary with renewed blocking likely into early February, perhaps Greenland/Scandinavia, more likely is we wont see the block to the north become completely eroded, cold air will never be far away. 

Very, very positive moving forward away from the chopping and changing of NWP outputs and attempting to nail down precise details 10+ days away.

FWITW the 00z ECM is highlighting where I broadly expect things to head as outlined in the quoted post from yesterday.

Cold air across the UK vs incoming disruptive lows = high impact snowfall events. 

I do think the ECM is being a little too progressive with the lows though, I suspect the first couple will "miss" and pass to the south, again still looking towards the 20th - 20th as a timeframe, although a day or two before can't be discounted given current modelling. 

The GFS is absolutely horrible when it comes to handling split flows in the Atlantic & disrupting low pressure systems, it depends to blow them up and barrel them through before correcting ever south closer to the time so I'd not worry too much about what the GFS or GEFS is showing for that matter. UKMO, ECM and to some extent GEM will give better guidance going forward.

All in all - No changes to the outlook. 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003036

[nick sussex]

Excellent ECM 06 hrs control run to T144 hrs . An upgrade on the earlier 00hrs run .

This might seem a very small change but this will make a difference down the line .

ECM 06 hrs run to T144 hrs.

 

ECM 00 hrs run to T150 hrs .

 

What we want is a straight flow from the north ne  , the bulge you see on the GFS is a sign that the blocking is going to start edging west and orientating in an unfavourable  manner .

GFS 06 hrs run  to T150 hrs .

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003233

[bluearmy]

Incidentally, the main 3 AI models seem less interested in bringing the Azores lows as far north as the U.K. 

Yesterday they were inconsistent so not deducing too much from this yet 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002845

[damianslaw]

1 hour ago, Nick2373 said:

06z well i don't know what Exeter are seeing but all I'm seeing on the 6z is just under average temps with a climb to just above from the 22nd onwards, South looks to be falling to just average conditions on every run, I cant wait for the 12z to roll out because quite frankly that's a rubbish chart if its cold and snow your after. 

 

What needs to be remembered when it comes to snowfall in the UK, especially in mid winter, which I class as roughly now through to mid Feb, is you don't need particularly cold uppers in frontal set ups to produce it. Indeed the heaviest snowfalls tend to occur in 'less cold air', provided dewpoints are on the right side of 0 degrees, heavy snow can fall with uppers as high as -2 degrees, even close to 0 degrees, evaporative cooling and lapse rates hold the key.

 

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003248

[Buzz]

12 minutes ago, Martz86 said:

It would be nice to have a model group just for those that know what their talking about, reading through this one is very confusing, shame really as I quite like reading the knowledgeable posts but it's becoming tedious filtering through it all. 

Do as I have done - add all of the problematic posters to your ignore list. It'll take a while but it's well worth it - I now mainly only see those posts which are actually useful. Reading this thread is now a pleasure, not a chore.

In addition to that there is of course the very useful Highlights thread, but that does rely on others actually marking posts from here as Insightful and not abusing the feature.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003040

[Nick F]

The difference between GFS vs UKMO and ICON are quite stark at t+144, so probably not worth fretting over mild vs cold boundary snow events next week at the moment. Best not over analysing beyond 6 days IMO.

T+144 GFS

T+144 UKMO and ICON

UKMO and ICON similar in having the straight northerly that digs further south, a stronger mid-Atlantic ridge north and east of the Azores low, which is kept more at bay and thus doesn't phase with the N / NE European trough.

Not sure who my money's on until the EC comes out though ... but suspect GFS maybe a tad too progressive with upper flow energy over the N Atlantic, particularly as it's pretty much a cut off low near the Azores that tend to be a sign of a weakening jet that disrupts.

12z GEM does follow a similar route to GFS, which makes me a little nervous to call UKMO and ICON more likely correct for now, but could it be the great N American wx models vs European wx models battle this evening?

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003476

[Bristawl Si]

4 minutes ago, MJB said:

You should know Exeter won't form an outlook from a GEFS chart ..............LOL 

UK MetO use a blend in their numerical forecasting system. And they defo wont fret every 6 hours over GFS output, unlike some of the NW members.

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003178

[bluearmy]

Whilst fi on gfs is very much just for trends and things to note down at the back of your mind, the NH profile is very much that of a distressed vortex and the way the low heights across the Atlantic drain away is reflective of downwelling reversal waves

all good signs as we head towards the end of jan. We’ve seen some fi runs which look very grim across the polar field so it’s nice to see runs which reflect what a bad place the vortex is likely to be in come late jan 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003578

[Met4Cast]

The bold green line is the GFS deterministic run that some people are looking at and calling winter over.

The rest of the lines are ensembles. Looking at the chart above the cold air hangs on across the UK until the very end of the run, the det whilst not an outlier has  very little support. The UKMO was very good. GEM was good, the EPS are good, MOGREPS are good.

There is more evidence to support a decent cold spell vs against. Could that begin to change? Yes, of course, but currently, today, it hasn't. 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003643

[Metwatch]

I'm not the best in making weather graphics, but I thought i'd do a quick sketch of the possible scenarios into next week as I am seeing quite a few elsewhere on the forum getting confused reading through this thread.

Scenario 1 and 2 at the moment both look possible, & which both could produce significant snow either further south, or mainly in the north. Scenario 3 I think is less likely as quite a few det runs show lows to push into the cold air in situ over the country early next week, similarly with various ensembles. Also possible with scenario 1 is that there would be a snow to rain event and mild comes in quickly after.

However with Scenario 2 that I can see as being possible, but not as likely. This will all probably change by Thursday / Friday as we get closer to the key period next week. I hope anyone less informed gets a better understanding of what could happen from this!

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003848