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Paul

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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

Next weeks pattern is a very good match for zero lag MJO phase 5 composites all the way from eastern N America to East Asia.

Most model runs then move the MJO into phase 6 which corresponds to below normal heights over Europe. That implies that we should see the Atlantic storm track tend to head further south as we approach the new year.

So far this has only been hinted at in the modelling with slight adjustments south bringing the polar boundary down to central UK at times.

Question then is whether the MJO is strong enough to force sufficient deceleration of the Atlantic westerlies for a high to establish N or NE of the UK via a stalling trough that disrupts into Europe. Again, only hints of this in the modelling.

We often see westerly regimes extended until further notice by the modelling due to their relatively high stability, only for a change to manifest at the 7-10 day lead times having barely been represented beforehand. So… we’ll see - I’m not (yet, at least) convinced that a predominately westerly regime is going to lock in for much more than a week.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776134
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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)
23 minutes ago, northwestsnow said:

Thanks mate I hope you weren't offended TBH your posts are always appreciated.

Quick one with the storm   hasn't the track changed to basically promote a surge of the jet into the N Atlantic thus flattening the pattern in our sector ?

None taken, I understand the frustrations that can arise when the modelled forcing shifts significantly before our eyes.

I believe the behaviour of the storm has been affected by the phase 5 MJO in a way that the models took time to fully catch onto, though most got there by Tue (GFS the glaring exception).

Y’know, I’d not be surprised if the MJO-polar vortex battle played out broadly similar to how it did last January, with mid-latitude blocking early next year, though perhaps centred a bit further east this time. UK mainly settled especially in south where temps lowest, chance of sneaking in a cold E to SE flow depending on how the high orientates. 


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776148
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Posted
  • Location: Solihull, Midlands. (Formerly DRL)
  • Weather Preferences: Sunshine, thunder, hail & heavy snow
  • Location: Solihull, Midlands. (Formerly DRL)

It looks like tomorrow, a spell of rain will spill up North through the UK from the South-West as the models (GFS 06Z as an example), shows Low Pressure directly to the West of the UK flinging a disturbance North-East:

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This could be wintry over some Northern peaks and over the high ground of Scotland, as the Atlantic Low runs into colder air further North. Flow will increasingly back from the South-West tomorrow as the rain and hill snow clears North-Eastwards with brighter weather moving into Southern areas, probably with a few showers into Western and South-Western areas. Cold over Scotland, especially over Northern parts and rather mild towards the South (albeit Central areas of the UK may stay just below double figure temperatures). 
 

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On Christmas Eve, the Atlantic Low will arrange itself in a South-West to North-East position and gradually start shifting North-East to the West of the UK. Centre of the Low moving closer towards the West coast of Ireland. It will be bringing a South-Westerly flow through the UK. Some showers at times over Western and North-Western areas of the UK, with a few towards the South-West. Generally brighter and drier towards Eastern areas of the UK:

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Rather mild again in the South, particularly far South with double digit temperatures. Cooler further North, and cold over Northern Scotland, where some showers towards Western parts of Scotland could be wintry over the hills. 

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Christmas Day has the Atlantic Low making further trips North-East with the Centre of the Low hovering close by to the North of Scotland. Compared to what it would have been like tomorrow, the Low has shrunk a little bit in size, but… it has become moodier as it deepens to the North and becomes tightly wind up! A fairly complex disturbance lining up to the West of the UK tracking East through the day bringing some bursts of rain across some Western and Northern areas, probably falling as sleet or snow over Northern hills and the Scottish Mountains and the possibility of a more organised area of heavy rain heading North-East through South-Eastern UK. (Have to call in the snow witch and cast a wintry spell on the precipitation ✨). 

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You’ll see, however, that colder North-Westerly winds will tuck in behind the spells of wet weather to the West of the pointy disturbance - possibly a chance of wintry showers across the far North-West. 

Fairly mild again across the South, and cold again over Northern Scotland. Cool(ish) over Ireland but becoming chillier over that part later on into the day:

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Boxing Day could then see a chilly Polar Maritime flow invading all (or a large chunk) of the UK as the Atlantic Low continues to go on a voyage further East and North-East. The Centre of the Low now just of the North-Eastern Scottish coasts. Chance of it bringing strong winds over Northern Scotland (although it’s possible the moody Low could be more relaxed on the day itself, plus a few adjustments are possible at that range).

A chilly day for many, though, in the nippy North-Westerly flow. Some showers, wintry at times, especially over high ground, for North-Western areas of the UK. 

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It’s at this point you will have noticed that the Greenland, plus the Northern West to Mid-Atlantic, ridging gets knocked down South to the West of the UK thanks to Low Pressure to the West of the Northern Atlantic ridging (around the Eastern Canada area) flattening the ridging. 

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We then get this (examples from the GFS, ECMWF and UKMO - around the 138 to 144 hour mark), for early Wednesday next week:

GFS

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ECMWF

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UKMO

58B5AB4F-B37A-46CE-9E26-ECB162B44BCF.thumb.gif.5c7e016cb9dfb984c36b2457d963765f.gif

Band of High Pressure and high heights across the South of the UK and low heights across the North of the UK. A flow dominated from the West towards the UK. There is a bit of a shallow surface ridge just to the North-East of the UK on the GFS trying to interrupt the Westerly flow over the UK on that run for that time. Also, as some did note earlier, however, the Vortex isn’t having a party over North Eastern Canada. Mostly rather compacted over the Arctic and Pole area (the purples). Maybe over time, things might become more amplified upstream. At the same time, some of the troughing over North-Eastern Canada may keep the pattern downstream towards the UK, flat (at least until the troughing shifts East out of that area). 

The ECMWF did attempt a Northerly/North-Easterly outbreak out West of the UK later into next week as heights rose in the Western Northern Atlantic. But some of the high heights fairly nearby to the East over South-Eastern Europe made it a bit of an obstacle for the strong Northerly to reach the UK (more of a slack North-Westerly for a time over the island). Developments upstream with the shallow filling Low over the UK linking with Low Pressure over Iceland got in the way of the mid-Atlantic ridge getting further North. There was also the fact that a developing Low over the Western Atlantic to the West of that ridge just piled everything further East and the UK ended up in a mild South-Westerly flow, along with more sturdier ridging directly to the East of the UK. 

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I could probably see how something like this might lead to Scandinavian High developments. Low Pressure out West being more vertically aligned to toss up a lot of Warm Air Advection (WAA) Northwards through the UK area could assist in pumping a block to the North-East of the UK giving the Vortex further North/North-West big slap. 

Quite far out to put much trust in something like that yet. It might be a possibility at some point. 

Both the GFS and ECMWF ensemble 500mb and Sea Level Pressure means for early Wednesday next week (in that order below) does show the UK under a broad West to South-Westerly flow, so fairly mild, more especially across Southern UK areas:

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Main area of the Vortex across the Pole. Worth pointing out again, no strong Vortex to our North-West around the Northern/Eastern Canada area - surface ridging over Eastern parts of Northern America and Canada, plus a surface Low dropping quite far South to the West of that ridge over Western parts of Northern America and Canada.

It may look as though there wouldn’t be much to fuel the Jetstream upstream to the West of the UK - the lack of a strong Polar Vortex to our North West towards North Eastern America/Canada. Saying that though, there is a fair amount of cold upper (850 hPa) air still spilling South out of North-Eastern Canada (via lingering Low Pressure along the North-Eastern Canadian coast). That colder air meeting the warmer air further South in the Western, mid and Eastern Atlantic pushing a robust arm of the Jet towards the UK. Making ridging of High Pressure in the mid Atlantic a challenge to pop about keeping things flat in that area:

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In fact, just pushing the toppling Western and mid Atlantic ridging we will be having the next few days further East.

Not to say it’ll stay like how the chart shows above forever (to be fair, nothing does). The pattern may become more wavy and amplified again at some point. Because although models can be prone to over-amplifying patterns, they can possibly overdo the flatness of the pattern as well. Have to see what happens. 

Nonetheless, the NOAA 6 to 10 day 500mb chart below has the UK under a Westerly to South-Westerly upper flow. A string of lower than average heights extending from North-Western UK Northwards through to the Pole and towards the North-Western parts of Northern America and Canada. Higher than average heights over South-Eastern UK and South-East into mainland Europe, reflective of the high heights models show in that area. Plus, some higher than average heights over Eastern Canada:

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https://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

So an Atlantic Westerly spell does look likely and generally fairly mild I would say, probably with some cooler fleeting bursts from the West, especially for North-Western UK. 

The 8 to 14 day 500mb chart from the NOAA, while still maintaining a South-Westerly upper flow, has higher than average heights becoming somewhat more influential over the UK from the South-East. Therefore could become more milder with any cooler bursts from the West or North-West becoming less likely. In a way, it fits in with what operational models such as the ECMWF and GFS show deep into their runs with the European heights becoming a little more controlling for the UK:

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https://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

Although none of us can, for certain, know what could happen in a week or 2’s, time (always the way really), at the moment another big cold spell does look very unlikely, bar some chillier interludes from the West or North-West at times. Perhaps as we go towards, or into, the New Year Santa might start delivering some late surprises for the cold weather enthusiasts in here. Just doesn’t seem much appetite at the moment for anything particularly white away perhaps from Northern high ground and hills. 

For those who rather it would stay around average to generally mild, especially those of you in the South, then the outlook should be quite pleasing. Would mean saving some costs on the heating at times. So could argue, a positive on that front as much as most would love to see that sparkly white stuff.

It’s the sort of outlook where North-Western areas see the most unsettled conditions with areas further South and East seeing more in the way of drier periods at times, particularly between the bands of precipitation. 

This will be my last post on here in a while as I admit to wanting a break too (not necessarily due to what the models currently show, but could say part of it could be that) and focus on other things. I appreciate that some of the aspects mentioned above will have very likely been covered earlier in the thread and my post might not be free from bias, particularly compared to those will deeper knowledge. Despite everything I’ve written, still feel I have more to learn.

I like to wish everyone on Netweather a…

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…hope it’s a fab one and is filled with warmth, comfort and joy. For those where it’s a struggle, I pray you’ll get through it okay (we’re always here for support - never have to feel you’re completely on your own), and that the New Year will bring a more promising start for the weather many desire. 🎄


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776273
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Posted
  • Location: North West
  • Weather Preferences: Anything but the prevailing wind!
  • Location: North West

The January blocking signal on the ec46 is consistent now. @northwestsnow in answer to your questioning its  worth.. what else should one use ? Gfs extended? JMA weeklies? The cfs? Or should we simply abandon sub seasonal forecasting altogether? It may be the final frontier but it is my area of interest. IMHO The 46 is the best we have and right now it holds significant  interest for coldies into January. 
 

Notably, it weakens the zonal winds at 10hpa slightly below average in the first half of Jan. The GEFS are similar and we also have consistency from its previous run. Seen as the upcoming quasi zonal spell is likely trop driven anyway there remains no convincing evidence that a pv of doom is on the horizon nor a consistent signal for coupling. @jules216 you’re right it doesn’t show an ssw but it wouldn’t yet and the trop patterns it advertises, especially late Jan with a decent Ural block, could perhaps set something significant off into February. (It does look like that’s when one might occur now).

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We can therefore examine any blocking forecast with less scepticism than would be the case under a strong, coupled strat regime.

The precip charts for weeks 3 - 6 show the unsettled weather favouring a southerly track

W3

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W4

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W5

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W6


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The MJO passing through 7-8-1 would also support a more blocked pattern. This is indeed what is advertised.

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The JMA weeklies hint at an MAR for the latter half of Jan

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@CreweCold You’re very downbeat at present mate (you don’t need to explain why to me 😉) but are you backing the cfs over the eps for the 2nd half of Jan?

So it’s a case of continued intrigue into January, though a 15+ day of westerly winds does look likely in the interim. My punt is that cold chances resume around mid month.  Another westerly spell in early Feb followed by an ssw. If it’s an absorptive event then an epic late Feb / Early March could follow. 
 

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Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776508
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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

These nudges of the polar jet further south along with reductions in zonality might yet prove to be a big deal by the early days of Jan.

Scandi highs are rarely picked up on at long lead times due to models having a propensity to keep troughs too neat and tidy rather than disrupt them.

The further south the storm track and slower moving the main lows, the more likely trough disruption becomes.

One thing that really keeps my confidence down at the moment, though, is EC42 consistently showing a classic MJO phase 7 response halfway through Jan. It’s as if there’s something in play that can add 5-7 days to the usual 4-10 days lag time for pattern response to the MJO. What could it be…?


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776577
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Posted
  • Location: st albans
  • Location: st albans
35 minutes ago, Ali1977 said:

Something to look for, signs of a SSW in a few weeks. Could contain: Plot, Chart
 

Current GFS FI as a marking point!! 

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Control a little stronger 

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Ec 46 was showing broadly this for end week 2 and into 3 - very few members went v weak through the rest of the month. 


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776659
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Posted
  • Location: Lincolnshire - 15m asl
  • Weather Preferences: Frost and snow. A quiet autumn day is also good.
  • Location: Lincolnshire - 15m asl
1 hour ago, SnowBear said:

 

The last few years we have seen more anomalies than usual, we now see another playing out in the US with the winter storm there and the apparent forecast of a fairly quick change to warmer weather soon after. 

That plunging cold is forcing down into the warmer latitudes so the warmer air has to go somewhere, and I suspect what we are seeing is the outcome of that with this warmer period here. 

But, will it stay that way as short or as long as the models think it will? 

Good point. It does look as though the amplified pattern is going to fail to bring about a favourable block before the inevitable waning of that phase kicks in. 

The US cold storm is the product of extreme amplification. Not the first time in the last 10 years we have seen this with the US getting a frigid influx of cold as a result of Pacific jet extension and a semi permanent north Pacific high sitting in just the right place to be amplified further and then open the flood gates.

Running the models today what seems to be happening is that this very cold trough pushes into the Atlantic but the Euro High sits tight and puts up the stop sign.

CC modelling consistently sees pressure increases over Europe becoming the norm. We see this pretty much every season with our own eyes already and as a result we see a trough anchored to our west with nowhere to go. Mild and wet. Model watchers over many years have seen this over and over. In the past, when pressure was not so anomalously high over Europe these systems would push through more often. More Scandy Highs as a result. A genuine Scandy High is becoming rare these days.

I find myself thinking - once again - that without a SSW our chances of winter snow for lowland areas of England are slim and getting slimmer. Our summers and winters are increasingly impacted by high pressure over Europe. 


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776777
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Posted
  • Location: Lincolnshire - 15m asl
  • Weather Preferences: Frost and snow. A quiet autumn day is also good.
  • Location: Lincolnshire - 15m asl
24 minutes ago, Don said:

Sounds like you are not optimistic for a colder mid January period?

Proper deep cold will need a significant intervention. SSW or significant +EAMT. Both are possible but not easily predictable. Without one or the other I would expect AAM to continue to fall as per a typical Nina season and the pattern to flatten out as a result. Should the strat have a clear few weeks then by mid Jan some degree of downwards coupling would also be logical. Westerly +NAO February as a result.

But there is a lot to happen before then. Another bout of amplification should occur in the first third of January and perhaps it can gain enough traction in the Atlantic sector to produce a ridge in the right place. MJO will be in the right place to add weight. If the strat can remain disconnected from the trop for a while longer, perhaps aided by the return of the Ural ridge + Aleutian trough modelled in the medium range ensembles, then another burst of cold in January is possible. 


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4776802
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.
1 minute ago, Allseasons-si said:

Yin-Yang...

getting a bit toasty atop...

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Signs of  pressure being put onto the Strat long-term should start cropping up fairly well but that pressure needs to be sustained of course. I'm holding out hope that the Trop pattern will support that and we keep getting rebounds of +VE AAM so that the Trop remains relatively unstable and thermal transfer can migrate both 2D vertically and 3D vertically. What all this means is that we need a sustained temperature gradient (from an oscillating jet stream, probably from either one strong mountain torque events or multiple smaller ones) because that's how Rossby waves move up as they try to link back to local thermodynamic equilibrium, their dynamic response is to typically move up. Then they impart an easterly force onto where they propagate hence we see a weakening of the zonal winds by where they reach and they can refract the Strat away from it's normal which unevenly distributes heat. As it does so, that could potentially cut of the Arctic flow and significantly warms it quickly as the warm air spills and and we see the zonal wind reverse due to this.  That's a quick snapshot of how a SSW works if anyone happened to be interested. Right now, it's a long shot as the zonal mean in the Strat is quite clearly fairly strong and trying to connect up with the Trop pattern but there's a small AAM rebound and an anomalous Pacific jet which is helping to increase the local temperature gradient as the centres of systems amplify yet the jets energy is fairly differentiating around the globe. So torque increasing events have helped thermal Eddy's transfer energy and slowly we should see that leak into the Strat by the New Year with the weakening of the zonal winds. Throw in the MJO phase 6/7 lag and you've got yourself a fairly amplified Eddy flux pattern long-term and hence why we're seeing charts like this with some downwelling of the Strat still trying to occur but you can see the Eddy's vertically upwelling from the trop pattern and translating themselves into a fairly Wave-1 dominant system.

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It's clear that the upper Trop is shunting away from the Strat at the end of the run after a fairly brief attempt at a strong connection but how realistic is this? Well, the main way of finding that out is thinking about hoe the upper Trop evolves through zonal wind profiling to suggest how Eddy flux should evolve.

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The zonal development whilst it foes look fairly slow and conductive for an oscillating jet (of course we won't see the Trop effects from it that much yet, although it's clear that we can rule out the Eurasian or more specifically, African/Arabian feedback wouldn't result in a jet that could be fairly helpful in developing some sort of Euro/Scandi block perhaps initially UK based but that's just looking at the models and relies on the upwelling of the feedback to further North but I'll go more in-depth later) is probably not the best way to look at it because the thermal gradient at that area matters less in my opinion.

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Looking closer to home for some wave-trains and we do see something of the sort evolving. Not sure if it's classified as a wave train in itself but that's a fairly interesting look at the wind and could see a decent thermal gradient and is at least renewed flux between blocking/ridge attempts that looks similar to late November. Once again, how this evolves closer to home, I'll go over later but for the Trop-Strat pattern it's fairly good and I think shows that an anomalous energy distribution from how the East Asian jet works (whether it be extension or retraction) can affect how much the fluctuations in Eddy's can occur downstream. That's important for forming that upward wave movement which is in turn important for increasing the "riding outer wave" as Chio describes it. This isn't really an upwards split, more seems to me to be upwards wave distribution which is helpful for downward wave reflection from the Strat under SSW circumstances. Decreasing the chances that it's a minor SSW which may not affect us as much, hence why it's probably a better way of evolving a SSW than an upwards split though of course with an upwards split, the Trop pattern is split initially so without the AAM going -VE it can still be good for amplifying the downwards split, even with a 'minor' wave reflection. Yet, I still l don't think this will be enough as the unstable inertia going into the Polar pattern decreases through a relatively stable AAM compared to before, the actual fluctuation of Eddy's and thermal gradient is likely to be slightly weaker. So I think the apparent large 'disconnect' between the Trop and Strat in FI is slightly over-exaggerated. Although, that will depend on whether the AAM rebound props itself up slightly stronger and the MJO slightly more progressive and amplified. If that is true then the signal may be picking up an early 'disconnect' between the two more amplified than my current thinking.

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Even then though, we should see some 'disconnect' between the two akin to thermal Eddy's slowly migrating up the Trop and into the Stratosphere because the upper Trop pattern response to the East Asian Jet Extension should be different to the Strat's reaction to the downstream energy scattering and Eddy vertical propagation simply because it is moving. Essentially what I'm saying here is that the Trop is getting moved earlier than the Strat and because the Earth is rotating the effects can look over exaggerated to what you would imagine. This is where the Earth's rotation helps us because it holds strong the unstable thermodynamics between the Trop and the Strat as energy cycles up the atmosphere and some cycles back down. This would distribute the Strat slower than the Trop and also mean that there is almost constant support for Wave-1 to at least keep it's strength slightly further beyond if/when the amount of Eddy flux starts 'drying up'. Eventually, this would lead to a radiative dampening of the Strat and the Strat and Trop connect up again so without a SSW or at least a large split, this could make the weeks worth of work and pressure on the Strat 'useless' so clearly we need to keep a large thermal gradient up as long as possible. Best things for that would be an extratropical 'wave train', an increase in AAM and/or MJO phases 6 and 7.

I don't know how this will evolve of course but I can see it going one way where we get close but not close enough and people are getting 'on top' of the people predicting a SSW could occur. Or the people saying a SSW won't occur will be told how wrong they were if one does occur. Please, don't do that anyone as you could dishearten the person. Right now, it's a 20-25% chance of one in my opinion as we don't know how the Trop will evolve by day 5 let alone by mid January. Hence we could see a return to the Strat downwelling into the Trop as the Eddy's 'dry up' too quickly but we have seen most forecasts keep up the Eddy's strength right up till the end of the run so good support to keep it going for a while but how it'll evolve beyond then is important as it needs to become a sustained signal for the warm air to 'leak into' the Strat PV. This whole post is just my best guess and I've left a lot open but have tried to remain positive throughout it so far. Simply put, it's too far out to fully understand for now so I'm not willing to make a call whatsoever.

Looking FI into the NH Strat and you can see that high putting pressure onto the vortex but how much pressure it can put will of course determine the eventual outcome. That wrapping up looks pretty tight and considering how the Strat normally evolves and the high also probably evolving fairly normally but simply put, more runs are needed as it's way too far out to worry about positioning. The wave essentially rides the vortex but the vortex is fairly strong and wrapped up nicely, it's difficult to work out how the high would evolve from there. If I were taking it as entirely correct then the best chance would be a leaking split right through the Greenland area with the high riding pretty much all the way around the vortex as it starts in Eurasia and ends up back near Europe. On the other hand though this is out in FI for now so we're just going to have to wait and wait and wait and wait for nothing or something to occur. Interesting times Strat wise, a genuine possibility but it's also fairly far out in the distance that we can't really know what will happen here.

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The 1hPa is very hard to work out but that's at 384 hours so I won't worry about trying to work that out 😆.

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A SSW is unlikely but cannot be ruled out to summarise all of that...

Onto closer to time and closer to us...

And looking for a cold pattern evolution is difficult but not impossible. Compared to the last few days the GFS is feeling the festive cheer by evolving us a UK/Scandi high going into the New Year and this sort of makes sense of the travelling of the energy scattering of the 'wave train' showed on the meridional winds earlier with weaker winds going into the Atlantic which could end up moving closer to Europe and the high rides the oscillating jet stream due to that fairly well (note that I'm looking at a slightly different level of the Atmosphere here). I'm not sure how much amplification can come from this though but one can hope.

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Whereas the ECM is slightly less keen but still amplifies it into an alright position just may have to hope. that it doesn't act like a Euro ridge (which now that I've said that, it probably will 🤪🤣) and flatten itself out. With this setup, there's not much cold bottled up to the East so it would have to be long-fetch which is unlikely but if things do evolve wel; we should at least get some decent cold and perhaps something of a good event for those further North and Scotland but only if all goes well.

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GEM is is the least interested and I see where it's coming from but I think the fact that we've had that air drawn up originally probably favours the ECM's stance on this. It would still be good away from the south and maybe Midlands for cold and maybe snow prospects depending on how things evolve. I think we forget the North and Scotland because apparently they 'get a lot' but I'm pretty sure I've heard about areas there which seem to come with their own mild and don't get that much snow and are perhaps on par with how much the south has typically got over the past few years.

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I think out of the three of them the ECM is most likely to be correct but that's simply my ECM bias that I developed after it got a Storm system pretty much spot on in the Summer even when Convective Weather was struggling to understand where it was coming from (low/slight risk and ended up being quite a large squall line I'm pretty sure) and I hold Convective Weather in very high regard.

I noted the large amount of moisture still left to transfer in the North Atlantic a few days ago and the ECM seems to be picking up on a signal for another potential Atmospheric River which if shunted further North could combine with the potential cold for the North and Scotland and bring them a lot of snowfall. So let's see how this evolves as well. GFS keeps it more vertically elongated and holds it back, GEM also seems to hold it back but then brings it in with a vengeance.
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P.S 

@Allseasons-si I'm quite a slow typer (yet seeing as I use it for school as my handwriting is awful you would think I would be quick) and thanks for the kind words, much appreciated.

This is Eagle Eye signing off for the night(or actually early morning)and if I can't get on later today then Merry Christmas to all of you lovely people but I'm going shopping apparently and where we're going has got WiFi so I'll need a distraction from adults talking about cheeses 🤣.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777110
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Posted
  • Location: Eastbourne and Larnaca,Cyprus .
  • Location: Eastbourne and Larnaca,Cyprus .

Interestingly the GFS06 hrs run supports the UKMO .

Its a shame the ECM isn’t interested in this type of evolution .

You can see the UKMO 00hrs run first for T168hrs .

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Now the GFS 06 hrs run for T162 hrs .

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As the upstream trough digs south the jet will bounce ne or n  ahead of it .

This will try and force a ridge between that troughing and the low near the UK.

You need as much dig south as possible and the troughing to sharpen up because you need the ridge sufficiently north and the jet to cut back sw towards the Low Countries .

So a negative or at worst more neutral  tilt of the upstream troughing and elongated not rounded in shape .


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777198
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.
19 minutes ago, Battleground Snow said:

Another toasty run for the strat.

How much more realiable is a strat forecast compared to  the 500mb pattern ?

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As a base pattern it's more reliable and I've seen it generally verify more than the Trop. The warmth of the Strat can be quite wrong but the general direction of movement is modelled rather well. A large Wave-1 dominance looks likely as I said earlier this morning and the Trop pattern in a few days time with increasing Eddy's supports this setup so this Wave-1 and Eurasian/North Pacific Wave is probably the most likely at this stage. I think the GFS is modelling the area really well its just how well it models the warmth of the wave riding the vortex and the inner bands of the riding wave is difficult to tell. It may be overdoing it as I think its being overdoing the thermal gradient for a while now but at this range who knows. Like I said, I think it's it's the area and strength relative to the Euro warming pretty much spot on but the strength of the main warming may be slightly overdone (or it could be undercooked depending on how the upper Trop handles the Eddy's from the energy scattering due to the East Asian Jet Retraction). So right now it could go either way on this one and I think it's a case of waiting for now.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777227
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Posted
  • Location: Wantage, Oxon
  • Weather Preferences: Hot, cold!
  • Location: Wantage, Oxon

Not posted much lately, but now there is something to get our teeth into again showing on the model output, I’m back!  I think some of the runs yesterday were starting to show the MJO phase 5-6-7 response, that is the most likely (and shortest) route back to cold.  This is the euro high (phase 5) through to Scandi high (phase 7) evolution shown below:

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Today’s GFS 0z illustrates this very well, T192, T330:

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The same evolution is putting pressure on the strat vortex, via approximately the Ural high, Aleutian low combination.  Well the Ural high is approximate, but the Aleutian low is quite consistent on the model runs.  It’s been at the back of my mind what’s with the Met Office prediction of cold returning mid-Jan, and I don’t think they are seeing a SSW - not showing on the ECM 46, and there wouldn’t be time, even with the quickest of quick trop responses for that to cause a cold outlook by mid-Jan.  Good to see the pressure being put on the strat vortex so consistently now, though.  

So I’m guessing, the prediction of cold must be down to the MJO.  Let’s hope it delivers, not entirely comfortable having all our eggs in the MJO basket, as in my experience it has an annoying habit of retreating to the COD just as things get interesting, but in the MJO we must trust!  Bring it on!


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777138
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Posted
  • Location: Lincolnshire - 15m asl
  • Weather Preferences: Frost and snow. A quiet autumn day is also good.
  • Location: Lincolnshire - 15m asl
2 hours ago, northwestsnow said:

Strat is waaaaay beyond my comfort zone ..

@chionomaniac @Catacol

Ed knows more than me....but ensemble forecasts support the return of low pressure over the Aleutians and a high anomaly close to the Urals. Therefore strat stress as we move into 2023 looks certain. We will need to wait and see whether this second round of attacks can bring it down. First half of December we saw strong warming that distorted the upper vortex hitting it pretty hard at the very top - but it has been recovering in recent days. 

Give it a bit of time. Too far out to be sure of specifics at this stage. NWP next week might be revealing.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777301
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.
19 minutes ago, lorenzo said:

Why wouldn't you be interested in an SSW when the vortex currently looks like this...

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And, FTs are doing this...

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Gonna be a fun slingshot out of this NAO+ pain..

Absolutely, vertical thermal Eddy's increasing in the reliable now putting large pressure on the Strat not to mention the GFS underdoing the strength of the AAM rebound. 

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Caution

A lot of writing coming up...

As we go into the New Year Trop pattern,  the plausibility of an MJO driven signal also backed by the AAM is looking fairly reliable. I expect phase 6/7 to show by mid January (ish) in the NAO state as long as the AAM doesn't take a large downturn to a -VE state. Assuming horizontally and vertically stretched Eddy transfer in this 2D look at the Trop, especially the upper Trop then the transfer around the Earth of signals for blocking should be fairly good. The transfer of Poleward Eddy's relies on a holding of cn unstable inertia pattern preferably held by a fairly sustained +VE AAM signal that we might be entering now. This pattern combined with the MJO may support some form of Greenland blocking later especially if the East Asian jet retracts slightly and we can hold an amplified Rossby Wave pattern. Plenty to be cheerful about and it's Christmas time but it's still fairly far out and the strength of poleward Eddy's is yet to be determined really.  Whether the GFS is overdoing the MJO signal and therefore overdriving the poleward thermal transfer or not you can argue about. Personally, it's been underdoing the AAM and MJO signal for a long time and has tried to slow down the MJO signal for a while. So I think it may be overdoing the signal beyond the end of its output slightly in terms of Eddy's and that may show in a few days time. It could also be underdoing the signal by under amplifying the forecasts and hence we may be in better luck than we even think now.

Right now, I can't really tell and I won't know till after the event but looking long-term and I think a Greenland blocking signal could start showing itself in the output when we get into January. I won't go too much over the Trop pattern as of now but the AAM rebound bring stronger than initially forecast has given me hope that it can sustain itself for longer than forecast. If it can do that then we can look closer to home other than a potential SSW for colder prospects. Its a lot to ask from the AAM but I remain hopeful that it's festive cheer will keep up till my birthday on the 24th January.

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Looking at the arguably more impressive Strat though and there's a lot less IF's.

The zonal wind is on its way down into the New Year, after the initial Vortex Intensification (VI), the Eddy's start to reach the Strat and the warmer air gets distributed away from the normal and Rossby Waves imparting easterly force and the zonal wind will weaken. Its as simple as that. 

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Eddy's clearly strengthening into the New Year and the Wave-1 response is very clearly. This could potentially put a lot of pressure on the Strat.

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Seeing as it's essentially the same as earlier today I'll quote myself quickly

" we should see some 'disconnect' between the two akin to thermal Eddy's slowly migrating up the Trop and into the Stratosphere because the upper Trop pattern response to the East Asian Jet Extension should be different to the Strat's reaction to the downstream energy scattering and Eddy vertical propagation simply because it is moving. Essentially what I'm saying here is that the Trop is getting moved earlier than the Strat and because the Earth is rotating the effects can look over exaggerated to what you would imagine. This is where the Earth's rotation helps us because it holds strong the unstable thermodynamics between the Trop and the Strat as energy cycles up the atmosphere and some cycles back down. This would distribute the Strat slower than the Trop and also mean that there is almost constant support for Wave-1 to at least keep it's strength slightly further beyond if/when the amount of Eddy flux starts 'drying up'. Eventually, this would lead to a radiative dampening of the Strat and the Strat and Trop connect up again so without a SSW or at least a large split, this could make the weeks worth of work and pressure on the Strat 'useless' so clearly we need to keep a large thermal gradient up as long as possible. Best things for that would be an extratropical 'wave train', an increase in AAM and/or MJO phases 6 and 7."

And the latest run still supporting my view (although still fairly far away of course but it's a well supported view) on how the 'disconnect' shows increased thermal Eddy vertical profiling.

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Lots to be interested about going into the New Year and I'll keep updating everyone about it. Merry Christmas to this great forum and here's to a potential SSW in January (ish) if all goes well for us. Cheers.

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Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777442
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.

East Asian Jet Retraction (EAJR) clearly showing in the forecast now (120E-180) and that halts the progression of the Pacific jet for the time being and may help oscillator the jet downstream allowing clearer transfer of an amplified MJO. The MJO lag should be roughly phase 6 which is one of the positive signs for a -VE NAO and further progressive poleward Eddy's going into January time. If we see the development of this and a fairly sustainable MJO phase 6/7 and the high over the southern US/West US then that may be drawn up by the combination of multiple slightly supportive factors of the MJO/ +VE AAM/EAJR and we could see some WAA priming interacting with with warmer air over that area and professing it poleward towards Greenland. As the atmosphere tries to balance itself, it would have no option but to draw that WAA towards the -VE NAO space through unstable inertial patterns helping force the AO more negative and also increasing vertical Eddy's. This Trop-Strat upwelling of thermal waves may only be the start if these background signals happens to collide into a Greenland blocking/ or the EAJR interacts with the Euro high and draws it up towards the UK/Scandi but the timing has to be perfect and right now my personal view is that it's a little bit off. The AAM downtrending due to a slight loss of torque on the GWO before it uptick again with a gaining of mountain torque/frictional torque but the timing of that re-gain may just be off. There's a lot to be hopeful for going into mid January especially though. If all goes well the Trop pattern could support WAA into Greenland or in a more progressive system a Euro/Scandi high and the Strat looks to be naturally increasing in Wave-1 strength splitting the upper Trop and Strat fairly significantly and distributing warmer air towards the Eurasian/North American area and putting pressure on the Strat vortex. For now, how much upwards wave flux there will be so that we can determine the refractive/reflective properties of the Strat and hence how much it could potentially benefit us in the downwelling to the Trop if a SSW does happen, is very difficult to tell because we haven't seen them go up yet.

u_200_anom_30.20N-30N.thumb.gif.ab5ee67877142a9946a359c2b4018b96.gif

The models are handling this very badly though. The return to zonal through VI downwelling slightly to the Tropis fairly well modelled but for how long and how strong is difficult to tell. I think that around the New Year they disconnect again as the background signals start showing signs of adverting poleward and hence thermal gradient increases and so thermal vertical movement flux starts going ⬆️ and the zonal winds start going ⬇️ in the Trop and the Trop-Strat upwell should weaken the zonal winds in the Strat as currently forecast. Good signs in the Strat but I don't personally think (at the moment) that the Trop pattern will favour us in mid January. Instead the zonal Atlantic setup could be favoured by the energy scattered more towards the Eurasian area if we have the Eurasian feedback backing too much East but it depends on the timing of all the Teleconnetions like I said earlier. Hope I'm making up at least 1% for Tamara's genius.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777722
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Posted
  • Location: @scotlandwx
  • Weather Preferences: Crystal Clear High Pressure & Blue Skies
  • Location: @scotlandwx

Why wouldn't you be interested in an SSW when the vortex currently looks like this...

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And, FTs are doing this...

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Gonna be a fun slingshot out of this NAO+ pain..


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Posted
  • Location: Scunthorpe
  • Location: Scunthorpe
2 hours ago, Bricriu said:

It's disappointing the GFS is downgrading the warming in the Strat on each run . I hope we are not relying on Euro High going far enough North, that  is difficult to achieve. I see the UK Met Office  are now only talking about brief cold spells. I wonder do they think the MJO phase will not be good enough this time to bring about a robust block. 

Better not to just take what the Op run is showing and the Op run only. Each of the ensemble members throws up some wide variations. There's some decent warmings in there on some of the members and at least every single member is showing a warming of varying degrees and some are even throwing a second warming shot after the first one.

All of the below from the GFS are better than what the 12z Op run has shown. P07 is my favourite one for obvious reasons.

Could contain: Plot, Chart, Outdoors, Nature, Map, Atlas, DiagramCould contain: Outdoors, Nature, Plot, Chart, Hurricane, Storm, Face, Person, HeadCould contain: Outdoors, Nature, Plot, Chart, Hurricane, Storm

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Even the GEM 12z is coming out to play too

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Not sure I could say at this stage that the warming is downgrading when the range of warming peaks is very much consistently in the -20 to -16 range with some less warm outliers as well as the above warmer outliers.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777819
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.

AAM amplification nearing late November +VE states and so should slowly start driving poleward Eddy's somewhere soon (depends on the MJO background though). So it won't be long till we see the lower Strat start weakening fairly well. First signs of increasing thermal Rossby Waves pushing into that area of the Strat. I'll be monitoring how this all evolves...

Also hence why as @bluearmy says, the NAO and the AO are both heading more negative by early(ish) January...

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Edit

I should spell check before posting.


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Posted
  • Location: Hoyland,barnsley,south yorkshire(134m asl)
  • Weather Preferences: severe storms,snow wind and ice
  • Location: Hoyland,barnsley,south yorkshire(134m asl)

I know this doesn't look much ATM but you can see the Euro heights starting to edge northwards in the ext'd,it is an amplified pattern out of the states with that +ve anomaly in NE America,...just need to back it further west so that we can get the Euro heights to amplify further to our N/NE just like the latest gfs run shown,what strikes me though is that the jet seems to be firing up on the other side of the NH in the N Pacific which in turm amplifies the pattern in the states

610day_03.thumb.gif.b63e819964334345fb2fd233754d99d2.gif814day_03.thumb.gif.ce23669918831c3258565a1f8d1072f8.gif

let's slow that trop pv down again,@trop pv,...you had your mini break now give us one he he😁

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the gefs still favouring an decent amplitude into phase 7-8 mid month> but the ECM is less inclined though,when has it shown any better than the gefs,...never has IMO

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so a conclusion here then,...a holding pattern for now with some unsettled weather briefly coming in off the Atlantic then a reduction of westerly momentum as we go into Jan mid month looks likely with the NAO/AO slowing down a tad into neg values again thanks to the jet firing up north side of the NH amplifiying the pattern out of the states.

 

 

9 minutes ago, feb1991blizzard said:
CHARTS.ECMWF.INT

 

Oh!!!,...i have that site already ha ha,just didn't look at the strat charts,...doh!!!!


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4777861
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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

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So the very important MJO action has corrected a bit weaker during the weekend, reducing the strength of push toward a Scandinavian high - hence we’re seeing a lot of Euro highs in the modelling as the amplifying ridge becomes trapped over central parts of the continent.

Still enough spread across stronger MJO outcomes that we could yet see a Scandi high emerge, but probably of the ‘saggy’ variety that requires a narrow range of orientations in order for cold continental air to reach the UK much - or at all.

Failing that we have the SSW possibility but honestly, that has to be mainly wave-2 driven to capture my interest. When wave-1 dominates as modelling currently suggests, the resulting displacement type SSW tends to put notably cold weather across N America while we get at most a 10 day cold spell but are just as prone to abnormally mild weather depending on the finer details of the displacement.

Wave-2 type SSWs are more common during a La Niña so you never know… but at the moment and for the foreseeable future the atmospheric state is being pushed so far from La Niña-like that I can’t see typical La Niña tendencies being a useful guide for most or all of Jan 2023.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4778009
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.

I've been focusing on the Strat for a while now and I've almost completely forgotten the pattern signals away from it.

Looking fairly flat right now hence the general displeasure with how things are going but tentative signals long range that we might see a more amplified Euro ridge moving towards a UK/Scandi blocking. This is so far out that it's unlikely to verify exactly but what is the general pattern looking like?

I think its too early for now and the progression of the Trop is over modelled on the GFS but slowly there are signs of a second EAJR that looks to be linked with a loss of mountain torque over the next few days.

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The last time the energy scattering displaced itself from normal it interacted with the African high to draw up a Euro ridge and ended our return of cold chances as the Eurasian feedback to the EAJR ended too early and we saw a waxing of the Eurasian jet which in turn extended the Pacific jet and we ended up with the more zonal Atlantic despite what initially looked like it could be a Greenland blocking potentially forming I think it just took to long and the -VE zonal anomalies were just brushed under the carpet by the jet extension across the Atlantic. This time the waning of the 120E-180 and the feedback just beyond 60E (to the right) is looking fairly sustainable and so energy is likely scattered fairly well downstream but note the zonal setup over 60E moving further West and the weakening of the first Eurasian feedback. Not that that should matter that much as that wasn't a feedback as such just a form of energy scattering so it should end up waning. Beyond that though, the strength of any Eurasian feedback will therefore be difficult to determine because the zonal signal may override the EAJR signals feedback further East. Personally my view is that the Eurasiann feedback to the -VE mountain torque event is likely to be what that 120E event is and as that slowly spreads East, the building blocks of a Eurasian block will be slowly spread West and connect up with the far East of Europe towards the first week of January sometime. This feedback should stay fairly steady and then we're relying on the EAJR to scatter energy well enough (perhaps aided by the MJO because the timing is well enough with phase 6 that Rossby thermal transfer favourable for an unstable poleward Eddy's transfer may start increasing hence the chance of -VE AO starts increasing on the Models) that it will interact positively with the Euro high to start drawing it up (WAA) towards the Eurasian feedback and when they interact a Scandi high is possible. However, the initial zonal steady state across Europe may hinder that so I'll be watching how that evolves with a keen eye. Note that the Euro amplification in the models for later this week is shown by the Eurasian -VE anomaly over the next few days but I don't personally think that will be enough at the moment to form a Scandi high unless the Eurasian feedback forms quicker than my current thinking.

250587646_u_200_anom_30.20N-30N(1).thumb.gif.c316cb2ec6c895015043abda49efd1c0.gif

The MJO losing amplification over the next few weeks though so hopefully we can regain some AAM as we start losing it over the next few days otherwise I'm worried about keeping up poleward Eddy's. Phase 6 looks fairly amplified on the models but as we try and move towards Phase 7 we start losing the 'signal' for a strong amplification and so the downstream effects may be slightly minimised. Hopefully it's just being undermodelled at the moment.

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And thank you @knocker I will read through that when I get back to my laptop later today as as phone won't open it (does that with a lot of files that I don't have the apps for, for obvious reasons of not having the right apps 🙃).


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4778076
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Posted
  • Location: Wantage, Oxon
  • Weather Preferences: Hot, cold!
  • Location: Wantage, Oxon

Well, the time has come for the MJO to stand up and be counted.  Here’s ECM take (GFS similar):

Could contain: Plot, Chart

At the moment as of now we are in phase 5 with decent amplitude, but the model hits the COD by 27th.  If this proves by actual data not to be correct, then we can expect some more amplified solutions appearing in the model output, so I will be keeping my eye on this chart for the next few days.  

Meanwhile, the extended T264+ clusters shows promise right at the end with the demise, one way or another, of the southern euro heights.

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Cluster 2 has most promise, but all continue to show evidence of blocking of some sort.

 


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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.

Small signs of a better shunting of the upper Stratosphere and Stratopause vortex with the warming signal over Eurasia backing up the Pacific Wave-1 signal so small hints of a strong Wave-1 signal stretching right up into the Stratosphere and really shunting up that aspect ratio. I would prefer to see tentative signs of Wave-2 to backup the Wave-1 signal as Wave-2's are much more linked with major SSW's but that's if one were to happen in the first place. I'm still being cautious though the disconnect between the Trop and Strat vortex is clear to see, it remains fairly far out for now. Notice the strong amount of EHF reaching the upper Strat and into the Stratopause on today's update as they are looking to back up the wave pattern. Notice the clear displacement in the Stratopause; if that can force reflection down to the upper Stratosphere (especially 10hPa) area then we can start to get fairly excited but like I said, I would prefer it if we did see Wave-2 increasing as the upwards wave flux activity may wane slightly early which would weaken the reflective Strat properties without Wave-2. It's a good update but still too far out for my liking and it'll be a long wait to see how things evolve. The thermal gradient and change in vortex placement is what I'm going to be looking at as things get closer as they will have a big impact on whether or not a SSW happens in the first place. Beware that a minor SSW is a possibility unless upward wave flux doesn't wane or Wave-2 comes out of pretty much nowhere and that's if we see a SSW happen. It's still unlikely but based off how the upper Strat and near the Stratopause is evolving there are tentative signs that we're moving in the right direction for one...

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Posted
  • Location: Barnoldswick, Lancs, 500ft
  • Location: Barnoldswick, Lancs, 500ft

Hi. Hope all are having a good Christmas period...

Since my last post the outlook has most certainly shifted in a mannor that, overall was underestimated and that is clearly towards a more cyclonic spell. Therefore, I wanted to try and see if we could figure out why such a change in quite a short-space of time. I think the two variables that have influenced the outlook has been the MJO, initially in the 'wrong' phases but an understimation for more of a strat and trop connection, something which I didn't expected so quickly - Some may agree or disagree with this analysis and it is difficult to say for sure, but, as ever, 9 times out of 10 if the AO and NAO change state and the N Atlantic becomes far more mobile and cyclonic then it is usually down to influences from the strat on the trop. It is also worth remembering how prolonged the cold weather was during the first half of December too, as some years we may had this cyclonic pattern in place since late November, that hasn't been the case.

A few pieces of evidence that relate to the above are as follows;

The MJO, while not obvious on RMM plots did move through the I/O and into the Maritimes with reasonable amplitude, at this time of year phases 2-3-4 are not great for the UK and it is interesting to see how looking ahead some of the composite plots match this evolution. When compared with the up-coming short-term anomalies as well through into early January from the latest EC Monthly, the key area of low pressure over the N Atlantic, coupled with the zone of high pressure over the NE USA across the sub-tropics and into Europe and Russian match that MJO retrogression plot well.

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The other underestimation, which I certainly got wrong, was the short-term and quick development of a greater influence from the strat on the trop, despite variable AAM regimes, I'll touch on those shortly - As we all know the strat influences on the trop can often dominate all others, especially under certain circumstances and, IMO, there has definitely been some downwelling of stronger W'lies from the strat to the trop and just the below few plots highlights this. The key feature here is the highlighted section for zonal winds at 100hPa through Nov and into Dec, note how into early Dec the zonal winds were at record low levels, not just at 100hPa either. However, note how that has reversed over the last week, rising above the climate average, while uWinds show descent as well.

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The frustrating aspect to all of this is that this has occured when the long-predicted rise in AAM has taken place again with some highlly impressive plots making an appearance over the last week, with E'ly AAM anomalies dominating the mid-latitudes, while AAM transports continue to show favourable patterns as well - Therefore, we seem to have entered into a period whereby there is an overriding factor in play as I would put money on suggesting that if this were early December again, with lower zonal winds and less influence from the strat, then we would have had likely seen a return to amplification. AAM will now ease away looking ahead.

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Where we go from here is problematic - If we continue to see greater influences from the strat onto the trop then the long-predicted seasonal data suggesting a +ve NAO regime through mid to late winter may well dominate. An SSW is and does remain a distinct possibility, but, as ever that is often influenced by the troposphere and nobody knows for sure, it doesn't look like happening now before the end of January. Can the MJO getting through into phases 5 and 6, perhaps 7 looking ahead alter the pattern? - The simple answer is it could, but we need to be mindful of the strat and trop connection as a continued overriding factor.

One thing that is for sure no significant winter synoptics are on the way within the next week, at least, perhaps 10-14 days. Beyond and all is still the play for, those now writing off January and suggesting Feb is our 'only hope' are mistaken, it doesn't work like that, so caution on jumping to Feb and Mar already on the 27th/28th December.

For now it is more standard fair synoptics for the British Isles, with often mild, wet and windy weather the dominant feature - Good for those who don't like cold, bad for those we have flooding concerns as some increasingly large rainfall totals are on the way, as ever always a positive to a negative and vice versa. If someone was putting me on the spot for potential changes then I would suggest somewhere between the 7th and 14th January for amplification, but with low confidence. For the cold, winter fans out there the key thing to hope for is that AAM doesn't fall away significantly and a more coherent strat and trop coupling arrives through January as that would write things off for some time.

Enjoy the rest of the Christmas and New Year period.

Matt.

(NB: Apols for any spelling errors, tried to fire this out while working as well, so no time for grammar checks!)


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778371
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.

Todays 00Z update shows the development of the polar-night jet looking fairly substantial now hence the VI from the Strat pushing down into the Trop and we're getting a fairly zonal pattern evolving but the Eddy driven subtropical jet is also forming rather well and upwelling making for interesting viewing as it's possible that it can help driven the PJO (polar-night jet oscillation) which can really drive the Strat thermal gradient rather well in the long-term which is essential for the potential early onset of a SSW with a polar-night jet in place (I do think final warnings have such of a problem). Note that this is not a time series so each image is just a latitudal map at that time. Unfortunately, the strongest driving of Eddy's into the polar-night jet is still out in FI so we're quite finely balanced in terms of a SSW or at least a weakening of the polar-night jet. We know that these things can keep getting pushed back until they can't happen anymore and we've got to hope that doesn't happen this time around as the Trop thermal Waves try to drive themselves up into the Strat over the coming days and further on.

Now

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Early-mid January 

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What a polar-night jet is.

ZonalWind.thumb.gif.80845ef0ac45bc29d36db30b07b67d3f.gif

Edit

I'm going to add on instead of writing a whole new post:

Personally, this recent significant development of the polar-night jet has downwelled and connected up with the main vortex and overriden the AAM signal because despite its amplification it hasn't been sustained enough yet to cause poleward heat transfer and so right now won't be counteracting the downwelling of an intensifying Strat jet. As the subtropical jet develops though we could see this slowly change as over time the AAM has more of an influence as well as the MJO phase 6 lag slowly showing as we go into January as it only loses its signal and strength partly ad I tries to enter phase 7; phase 6 is still at a fair enough amplification to drive waves and thermal transfer poleward along with the +VE AAM. Slowly this develops an Eddy-drigen subtropical jet that can counteract the downwards strength of the polar-night jet and these can drive upwards wave flux into vertically integration into the Strat and we see a large thermal gradient development from this, probably in the form of a Wave-1 initially. Large thermal gradients are responsible for Rossby thermal and zonal wind transfer and Rossby zonal transfer imparts an Easterly force on the zonal wind slowing the VI down and potentially onsettimg a PJO upsetting the natural balance of the Strat temperatures further weakening the zonal Strat. This would be how a SSW would develop right now. I will go more in-depth later though.


Original post: https://community.netweather.tv/topic/98132-model-output-discussion-christmas-week-and-beyond/?do=findComment&comment=4778388
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