Model discussion highlights

[nick sussex]

You know things are a bit uncertain upstream to say the least when NCEP look to see what the ICON and JMA show . I’ve never seen those models mentioned before . Seems a bit desperate ! 

This last paragraph from them .

“An examination of the ICON and JMA models support a solution closer to the ECMWF/CMC/ECENS for fronts and pressures , so the forecast was hedged in that direction ...... more weighting towards the ECENS mean by Friday and Saturday.”

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4771459

[johnholmes]

Just a very brief post from me, Ill try and add the two models, but unable to sit at pc for long, serious bac k issues and b----y BT keep dropping my link, sadly my web provider is unable to stop them, anywayy

Ec shows trough 24 and 25 with -5 scottish borders 25/26 with 536 dm bity furter north; then 27 th with -5 central Scotland and 536 n of sottish mainland and its flow n of west. Noaa 6-10 shows flow s of west but with same conour height.

So not a mild outlook, maybe even rather cold in much of Scotland, any ppn snow over mountains and some hills but ppn rain for rest apart from highest n’ern mountains, in any ppn. No serious wind hazards unless prob far nw.

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4771602

[Kirkcaldy Weather]

On 14/12/2022 at 14:20, Kirkcaldy Weather said:

Really good signs as we head upto and beyond Christmas 

 

 

 

 

On 12/12/2022 at 07:54, Kirkcaldy Weather said:

I'm not sure what's so bad about the modelling, weather always has a constantly evolving nature even in blocked setups like we have currently, interesting how December 2010 also had a brief warmup before the 2nd cold plunge arrived. AO running similarly negative to Dec 2010 

There is high latitude blocking aplenty in the outputs which is likely to be getting a boost from the substantial +EAMT event setting up at the min and MJO progression through a number of phases. 

Possibly we see the US benefit most from a cold and snowy setup initially but could also see potential routes that provide us with a pattern not too dissimilar to current conditions 

With the above ingredients at play we likely should look for a high from the Pacific moving into the Arctic and towards Greenland 

ECM 

GEM Ensemble Mean 

And if we look at where we were 2 weeks ago ..

Those who were doubting the Greenland High development then as they were with the Scandi high beforehand might again be unwise to continue that downbeat attitude

 

We are now seeing the +EAMT show its hand

As mentioned above, High developed in the Pacific which starts to head into the Arctic (more on that in a sec). I've also highlighted the low pressure across Canada as this will be the low that comes our way for Christmas 

The Arctic blocking sure does look mightily impressive, potentially rivalling intensity records 

So the three biggest focus points for Christmas will be 

• Pacific > Arctic Blocking 
• USA snowstorm development 
• Atlantic troughing / low... negatively tilted, below AVG temps likely sinking south 

 It has been a very noteworthy period of below average temperatures and snowy conditions around the UK, plenty at -10C and below yesterday 

I had a lovely snowfall here yesterday too  

 

And plenty of signs to be expecting of further wintry outbreaks as December heads to the later stages and especially through the first weeks of Jan 

Progressing MJO movement through phases 4,5,6&7 over that period 

 

 

 

 

 

 

Mean from 06z GEFS beginning to sniff that out

Fascinating tweet 

January 1984 (Great piece by @BruenSryan ) ... 

January 1984: Unusually snowy and cold for zonality

BRUENER45.WIXSITE.COM

---

January 1984 was an unprecedented month. It was cold, it was snowy, it was stormy, it was wet. There is no month comparable to it, it is very unique. Westerly to northwesterly winds were...

Worth playing the vid here, highlights the more complex features that help set up the patterns discussed in this post 

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772001

[bluearmy]

this little wedge of heights sent south at day 5 is relevant on the Ukmo. It puts pressure on the low heights off the Norwegian coast by day 6 and actually introduces something interesting over scandi by day 6 - day 7 awaited to see where that may go 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4771927

[Mapantz]

Just to quell the debate; Zonal can be west to east, or east to west. If flow is parallel to the lines of latitude, it is zonal. 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772316

[bluearmy]

2 hours ago, CreweCold said:

They are. The sobering thing is the ops are constantly degrading in FI in terms of the TPV. Essentially showing that trough-ridge-trough is as good as it gets.

All to be expected really. The stratosphere had to be brought to heel for us to see any continuation of cold into January, which is why I was banging on about needing to preserve Siberian/Russian heights rather than solely focusing on Greenland heights. Greenland heights are usually the end game, and it has proved thus.

We're staring down the barrel of a big cold blob up above running the show into January-

I’ve been wondering about this for a good few days now since the gfs began to show the spv headed v strong high up and the ec 46 flipped likewise

At this stage we haven’t seen any convincing output showing that the downwelling of these stronger zonal winds makes a notable difference down at 500 hpa.   Infact this mornings gfs run shows the trop fighting back at the back end and beginning to ease the flow around 1000 hpa.   The ec46 showed that strong uptick high up easing back down to average by mid Jan rather than racing away at high levels - tomorrows update awaited in this regard.  I did note marco’s comments on Friday re coupling and I’m sure his intervention wasn’t based purely on dr cohen’s blog (which was gfs data). I suspect glosea is seeing similar. hence tomorrows 46 be8mg important in this regard. If later January loses the blocking signal on the 46 then that’s notable on the back of this strat stuff

2 hours ago, Kasim Awan said:

ECM been overcooking the Altantic for weeks now.

Have you see this weeks charts kasim??

I wasn’t overly inspired by the 00z output - Ukmo again looks hemispherically very workable but it has flattered to deceive these past few days late on in this respect.

the eps show a scenario like the gfs op where the cold ridge sinks se across us bringing a seasonal couple days middle holiday week. That could bring some surprises if it verifies but not a strong probability on snowfall if the sinking ridge does occur.  The clusters as referenced above do offer a colder set in decent numbers but awaiting the postage stamps to see how that is actually spread. 

into the distance of the extended ens and there is little to grab hold of - heights generally high across our sector but that includes to our south. Positive to take is that the main tpv looks to remain absent from the Greenland e Canada area although a daughter vortice could easily end up sitting there at this range.  
 

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772483

[carinthian]

@nick sussex Good summary . About sums it up. Just spoke to our team over here. Dead easy forecast for in Eastern Alps. Asked about Blightys prospects, almost impossible to call as of this instant. When pressed about eventual outcome, they think cold will eventually win out for most of the British Isles but timing appears the main problem. The deeper cold waiting in the wings up North stays put for most of this coming week. However, some weakening of the Euro high pressure is expected over the Christmas period and this should allow lateral transition of the Low. So its all about timing in this messy scenario and eventual track of the low. A sliding Low would be the best chance for many back home to release the Arctic chill and hence increase snow prospects. Its all a bit of a tease from the models but as of today still all in the lap of the Gods.

C

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772379

[nick sussex]

Any ridging will always topple as a chunk of the PV moves across to Greenland .

But what comes after depends on the mid Atlantic . You need the low heights southern Greenland to sharpen up and to dig as far south as possible to helps the jet track ne then back sw as the ridge topples .

You then can develop the Scandi high .

 A bit like what the GEM is trying to do on day ten .

It helps to have your original high as far north as possible as the toppling begins .

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772657

[IDO]

There is no sign that the vortex to our NW will setup there. It looks like it will pass through, in line with the last couple of months. The Arctic high moving to Siberia means that the tPV chunks will move towards Greenland/NE Canada for the interim. The mean suggests it is transient.

D8-11: 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772635

[Mike Poole]

ECM mean at T240 is quite promising for a longer term cold reboot:

Looking at the clusters, first T120-T168:

The question here is whether the west most low maintains a connection to the low heights from the N, as it does in cluster 1, contains the op.

T192-T240:

Cluster 1 proceeds similarly to the op run with a mild day 8/9 before cold returns day 10.  Cluster 2 is much more interesting, as the other low is disconnected, and an Atlantic ridge builds between - not really seen this on the op runs (that I can recall) but it has decent support with 21 members, and is probably the reason for the colder mean chart for the UK at T240.

T264+:

A variety of options here as you’d expect, not seeing any strong signal for maintaining the euro heights unless they are connected north e.g. cluster 3 into scandi.  But I think we need to get past the first impasse, and see what the MJO does, before we can have a clear idea what the path into the new year is…

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772445

[Penrith Snow]

2 hours ago, Ali1977 said:

ECM at 144, looks like it may be about to get a little better

The whole set up reminds me very much of the Christmas period in 1978, then as now a mid month cold spell relaxed just before Xmas as mild air swept north, a pronounced temperature boundary then developed over Scotland with a sausage shaped low pressure separating the air masses.

Eventually towards New Year the cold air moved slowly south bringing heavy snow to Scotland, by New Years Eve the cold was across the UK and a Channel runner gave Blizzard conditions in the South.

Interesting that a Iberian High was also evident throughout the period.

Andy

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772503

[nick sussex]

Here’s the day ten GEM .

Two areas in red .One low heights southern Greenland and that low over Iberia which supports that small high over the UK .

As you get the dig south of the first one this amplifies the jet ahead so you need that heading ne and then the jet loops back sw into the Low Countries .

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772684

[Cold Winter Night]

Some very strange posts this morning.

The outlook has improved IMO.
Perhaps not for a White Christmas, which I would love to have too, but let's be realistic, maybe expecting a certain rare weather type (snow) to occur at a very precise location (your residence) in a very narrow and precise time window (24/25 December) is setting yourself up for failure.

Yet, still, the further North in the UK you go, the higher the chance that this event really might occur this year, more than can be said about many a Christmas.

After Christmas, the latest ensembles have been trending colder. Both EPS and GEFS.
Good signs.

Some are talking about the Euro heights as if they have been there forever, the opposite is true, they are just building today, and 40% of the EPS remove those Euro heights again before Day 10 on the 0z EPS.

In the extended, blocking patterns are still very much prevalent.

The Dutch De Bilt plume is notably colder after Christmas than it was for yesterday's 12z.
Let's say I've seen worse plumes in December.

The knee jerking in here is more based on emotion than on actual model output, and tbh a bit weird after an already cold first 2,5 weeks of winter, with snow and frost and ice for many.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772762

[Eagle Eye]

1 minute ago, Paul said:

 this isn't Twitter you know...

 Best thing I've heard on here all day...

Well it's now one week till Christmas and sorry everyone but still a little ill so no energy for a long post but long term is looking very interesting. Almost every day it seems to keep getting upgraded. We've now started to see the initial -VE zonal anomaly setup forming in the 30W-0 area just above the Tropics which is around the Atlantic area so maybe the North America low will only have impact of driving the jet near it (and you can see that in the initial 90W-60W jet 'packet' moving across to the mid Atlantic area over time) but how much that seems to effect the zonal wind could be debated over as the other side of the coin is that It just pushes the other side of the zonal wind anomalies slightly further West.

 

And anyway, this isn't even in the area our weather 'takes place' it's just a good long term indicator. If we look at the meridional wind anomalies we can see the much weaker winds that almost perfectly line up with Greenland (pretty much bang on 45°) towards Christmas time and are getting stronger, in this situation it's not a west based Oscillation either but it's too far out to really take to much notice of the basing. So a possibility of a decently strong Greenland blocking just on from Christmas may arise.

Let's see how this evolves though because there's no real way this has got the forecast perfect of course, its just another way of looking at the weather just like the GFS is. I'm proffering it right now but that's because I find it easier to understand it as a basic pattern signal and I don't understand how to interpret models as much right now. So its great all of you offering insight onto each run.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772904

[Mucka]

On 16/12/2022 at 11:17, Mucka said:

Most notable for longer term prospects is probably the strengthening Atlantic blocking which although currently showing W based -NAO could go on to provide a Scandi ridge with improvements to the angular momentum of the low.

 

This post was from a few days ago when GFS ensembles finally started to sniff it but is one of several on the potential for an Atlantic ridge to not flatten but topple and form a Scandi ridge.

We are certainly not there yet but this shows that when looking at the output past 5 days or so we have to extrapolate and make our own interpretations rather than take the output at face value.

Sure we will get it wrong as well as right but if you have been looking at charts for many years you will see potential trends before the output catches up.

For example, here is GFS just 3 days ago. Where is the Atlantic ridge?

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773130

[Mike Poole]

The Christmas situation (and probably quite a bit beyond) seems to rest once again on how the models handle the lows in the atlantic in the days running up.  The 3 options seem to be as shown by GFS, UKMO and GEM at T168:

GFS leaves a very shallow feature that doesn’t impede the cold flow to the UK, UKMO can’t decouple this system from the rest of the mess of lows, GEM does decouple it, but it is still quite strong and attempts to put up a ridge ahead of it.  The behaviour of this influences the progress of cold to the UK, and also is indicated in inflating the euro high (particularly UKMO).

GEFS take at T168:

Mixed bag, but seem to me to favour the GFS take, which is consistent with the positive trend towards cold seen in recent suites.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773115

[MattH]

The situation for next week and into the Christmas weekend, in particular, is, simply put an asbolutely forecasters nightmare...

The better agreement within the GEFS for a fall through the 23rd/24th onwards is interesting, but as we are now all seeing the ECMWF once again continues to be a distinct 'scrooge' and just doesn't help the cause at all later this coming week - There is nothing fancy about this outlook, there is no hidden answers, it is simply about waiting for models to resolve what is a very (very) tricky evolution and those hoping for a potential White Christmas or, at a minimum, seasonal Christmas has to hope that on this occasion the GFS/GEFS are firmly more right than the ECMWF.

The phasing of lows within what is a clear baroclinic environment (an area of conflicting air masses) is what is causing the problems, as is the European higher pressure areas as well, again, which model has this correct is still not yet known and won't be for another few days - If someone was putting me on the spot and from what I've seen over the weekend, then my money is with the GFS, I think the likes of the ECMWF and the UKMO are complicating matters with the development of the low, to the point where a S or SW'ly remains possible, but clearly confidence in all this remains low, either way.

If and, for now, that is a big IF the GEFS is correct then for many it will be a cold and seasonal Christmas and for some the transitional phase, through Christmas Eve, especially across parts of Ireland, N England, perhaps Wales and the Midlands could also be a snowy one as well. There may well be a perfect 'sweet spot' with this evolution because any sort of frontal system or frontal wave sliding eastwards as cold air tries to come down from the north could, as the GEFS show, bring a White Christmas to some areas.

However, I remind all of the huge flip that both the GEFS and the EPS did a number of days ago after they both suggested that the fall in temperatures would occur on Tue or Wed of this week, let alone next weekend. Short and sharp changes in this setup can and will still occur, there is no clear 'form horse' here yet, but I do believe and think that the GEFS has this one, but time will tell next few days.

Cheers, Matt.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773259

[Allseasons-Si]

Guess who's back in town,...me and good evening all

a horrible trip back from Skegness this evening in all the rain and spray and so glad to be back

I see everyone's getting edgy with the models at present but i see nothing wrong with the gefs ens for here or London over the festive period

the ECM was an outlier again

and the latest from NOAA/CPC shows Atlantic height's to our W/NW and Scandi trough in the ext'd 8-14 day outlook

tis the season of good will so let's keep it friendly eh guys

C U l8ter for the 18z.

 

 

 

 

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773384

[Mike Poole]

ECM clusters, first the key timescale T120-T168:

Well, the ghastly ECM op is represented in the minority cluster 3 (14 members).  GFS solution or similar in cluster 1 (22 members).  Cluster 2 is somewhere in the middle, but probably mild for the majority of the UK.

T192-T240:

Rooting for cluster 2 here (22 members) which sucks the euro heights into an Atlantic ridge scenario.  Nice destination, this, after all the drama, should it come off.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773353

[Met4Cast]

The AAM has as expected fallen through the floor with a further strong -MT event & signs of westerly momentum returning to the mid-high lats. The UK likely to be on the boundary between cold/mild with snow possible (mostly in the N) before milder air eventually wins out.  i.e any colder periods for the remainder of this year are likely to be transient affairs but may still produce snowfall for many.

MJO prediction suggests renewed Greenland blocking end of 1st > 2nd week of Jan but my current thinking is it'll be more west based, i.e UK remains milder with probably low pressure sat over the UK rather than being forced to the south like this current cold spell.

Had the MJO cycled around into these phases during the second half of this month like early forecasts had suggested things would be very different, but the timing is off to support prolonged cold into the UK and of course is only one aspect of the global budget.

To add to the above.. the trop led running of things may be on borrowed time with signs of the stronger u-winds descending down from the stratosphere. SPV possibly setting up shop over Greenland again. Cold lovers *perhaps* living on borrowed time now.

No signs of an SSW in the forecast nor any sign of an SSW precursor pattern appearing on the outputs. Unfortunately I'm growing more & more confident that an SSW is unlikely this year, or at least in the next 3-4 weeks. 

So.. transient periods of colder weather but the trajectory does appear to be increasingly towards a milder one for the UK. Indeed, GLOSEA suggests westerly winds becoming more dominent as January progresses, fitting well with the above background signals.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773519

[SqueakheartLW]

19 minutes ago, feb1991blizzard said:

when the eps have come out on meteociel, check out the end of P3.

from 192 to 360 - the uppers

As we know us coldies like to see these very cold 850hpa charts that we often say or think BOOOOOOOM or BANK to but it's consistency of cold uppers that bring the coldest temperatures overall.

The perfect example comes from this very 12z ECM run

I have picked out this P03 you mentioned as well as another member that has an extended period of sub -5C 850hpa temps, P39.

P03

As we have seen above P03 has 2 dips into cold uppers territory with the first peak at -12.2C on 27th December before a warm up then the second peak on 1st January of -15.0C.

This results in a rather up and down 2m temp chart for P03 as shown

Although we see 2 dips in 2m temps at the same points as the coldest uppers it isn't consistent cold and any snow that may happen at these points will soon shift when the milder air makes its way back in again.

P39

How does this compare with P39?

Here we have the 850hpa chart again with both P03 and P39 on them. Unlike P03 which is very up and down with 850hpa temps P39 is more flatline and consistently at or below -5C at 850hpa very much from Christmas Eve right up to more or less the end of the run early in the new year.

This is the 2m temp chart for P39

As can be seen here once the run goes cold around Christmas Eve it stays very much cold right out to the very end of the run and any snow that falls during this period is much more likely to stick around despite the modest uppers due to the continuation of the cold.

Summary

We know how much we like to see these -15C or lower uppers charts but these usually only produce short cold snaps like BFTE 2018 as an example whilst less cold uppers can stick around for much longer like 2009/10 for example.

In the above example the 2m temp mean for the period 24th December to 2nd January is as follows:

P03 = 2.960C

P39 = 0.035C

Despite no extremes in terms of uppers it is P39 that averages out colder from 24th December to 2nd January due to the consistent nature of the cold and how the "home grown" cold effect can take place which means despite the uppers moving back above -5C at 850hpa at the end of P39 it registers a colder day at 2m than P03 does even though it has much colder uppers at this stage.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773429

[Eagle Eye]

@MATTWOLVES @offerman You two are great people who don't deserve to go through what you're going through and I hope somehow, someway things get better for you. I know Matt a bit better (but still only the least of it) and I cannot tell you how much of a great person he is, who doesn't deserve anything like what he's gone through. I think everyone on here should realise how much it takes to make someone like him.

If we take a look at every 18Z run since the 13th let's see if we can find a trend:

There is very little in the way of a trend there but it's clear that the North and Scotland are in the mix on most of the runs and except for the 1st one which was at day 12 only a few hundred miles south (which at this range is a possibility of course) and the midlands would be in play. In the south I wouldn't get too excited yet, we've only had 2 of the 6 in our favour but that doesn't mean we can't keep an eye on how it evolves from here.

What do the ensembles say?

No major trend but sort of the trend is for the cold to be taken further south through the UK and the Euro/Scandi/Eurasian blocking seems to be slightly further south. I think we could be in for a fairly cold Christmas day (yes I know these are the 850's) and there may be some conductive uppers for some snow as well. Don't know what's gotten some people down on here, maybe they think that the rain (according to radar it's pretty much all rain now) is pathetic fallacy for something or another.

I'm slightly less confident of my long-term Greenland block long-term forecast because it hung a bit on the AAM quickly rebounding and so phase 5 of the MJO helps us more (based off my unsupported hypothesis). Whereas here, the GWO suggests that AAM won't rise that well (green line is the forecast) and looks like it'll probably stay fairly lodged in the weak -VE state and act slightly Nina-Esque but at this amplification it shouldn't be too much of a worry, it just won't help build the blocks for a Greenland block.

Once/if after that small rebound happens we will probably end up with a more zonal pattern as the AAM slowly falls and these wave trains get less 'helpful' but I won't worry about that for now as that's unlikely to be too strong till we get to Teleconnection FI of 2047 early-mid January which should surely eventually wane the Greenland blocking if it does form but like I said I wouldn't worry about it for now.

But there's two sides to every 100-sided coin () and it's a possibility that energy is scattered fairly well for a Greenland block development despite the AAM and sort of the MJO signal. 45W is where you look at to find Greenland although how the zonal wind anomalies interact when it's 20-30N with the meridional winds depends on the circumstances.

A lot of confusion on the models but we've got a decent chance for a decent snowfall 'event' from Christmas onwards for the next few days it's just how the models track it from here that's going to be the problem because the flip flops keep flip flopping.

Then beyond that there is the signal for a potential Greenland blocking but to be more confident in it I would want a slightly more progressive MJO and AAM recovery to be better, otherwise I'm still fairly 50/50 as to how this could evolve. It's very interesting though and the conflicting signals make it nightmare forecasting so don't worry if you're confused.

The flip-flopping and crisscrossing probably means that even the Mets are finding it difficult to come up with a highly accurate forecast let alone any of us. So don't worry if you don't really have much of an idea what's going to happen on Christmas day and onwards, we can blame it on the flip-flops the models have put on.

Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4773573

[bluearmy]

1 hour ago, mulzy said:

Scandi high if FI is probably one of the options on the table (after seeing that ECM run).  Let’s see what the clusters say..

Eps control went that way with cold easterly later on 

the sheer number of eps clusters shows how fluid the next two weeks look at the moment. 

two things that has caught my eye last few runs 

a) is the tpv headed back to Asian for the new year 

b) the downwelling of the strat zonal flow seems to be moving back up once it arrives in the upper reaches of the trop rather than sticking around where it would be v unwelcome 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4773716

[TEITS]

Yesterday was a small step in the right direction and today its a much larger step.

What is happening on the model output is the low pressure you see at +72 in the Atlantic is now being modelled to track further S due to the forcing from the blocking to our NW. What the models are struggling with isn't just the exact track but also what happens to it. For example some models do not even have this travelling E across the country and instead takes the low S. This in turn allows the blowtorch S,lys.

However the step in the right direction is intially we thought Scotland was in the perfect position and then yesterday I thought it was N England. Today even the S could get to see some snow over xmas day. Note the ensembles for Cambs and how some members are bringing the much colder air S a few days ahead of the mean!

This happens simple because the low pressure swiftly tracks much further S and brings in the colder air. The ensemble below is a great example.

So in summary the chances of turning colder have increased and no location can be ruled out for this to occur on xmas day or before.

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4773751

[Catacol]

So - farewell to our cold spell. Warm, wet and windy here this morning...and always (for me) a sad feeling when the ice and frost depart. I would also say "snow" except I didn't see a flake and so that particular gloomy emotion I am spared!

While the waning of the pattern has brought in a milder snap there is plenty to consider going forward. I nailed multiple flags onto my "cold in the last third" pole a while back and that is going to prove incorrect. Timing is always the killer and the timing is off. However, the direction of travel is still the same. ECM for tomorrow:

Note the signficant and deep trough coming out of East Asia that is pumping up the Alaskan ridge and forcing it up towards the pole. This is the second amplification sector of the month underway - but about 5 or 6 days later than I thought it would happen. Que Sera.

By Xmas Eve the peak/trough shape is well established:

Note now momentum carrying through to the atlantic sector with a signal just appearing for heights to rise again over Greenland. For me ECM then loses the plot a bit - picking things up on Boxing Day with GEM we can clearly see that Greenland High being pushed up

Now....the big question as we approach the final stages of the month is whether this bout of amplification is enough to deliver a proper high latitude ridge, or whether the sub tropical high pressure belt in the Atlantic, and through to Europe, wins the day and prevents the southerly tracking jet that we were glad to see in the previous first amplification period of winter.

NWP ceases to be much use in these scenarios when we get up and over 144h (sometimes less) and human head scratching enters the fray. And this is where it gets really complex. I posted a really interesting 4 wave hemispheric anomaly chart not many days ago - take a look at this one now:

If anything it has become even more mind bending - starting to look more like a starfish than a standard hemispheric weather pattern and quite honestly picking the specifics out of this is nigh on impossible. The current ensemble trend is for the Alaskan ridge to fade away towards Asia quite quickly so that by the 27th the EPS looks like this:

Frustration perhaps for our Amis across the pond as low pressure heads back into the Aleutians and Alaska - no bad thing for Strat watchers overall though as this should signal the beginning of another round of strat attacks from the trop. Note also the signal for the Euro/Ural High building back in and edging north.

What to make of all this? Well - there's the trick. For me the runs and the ensembles are all showing signs of trying to resolve the strange starfish pattern back towards something more 'normal' but I'm not sure this is a normal winter. I'm looking at an MJO that is now bedding in at reasonable strength and moving in the western Pacific

and this will help promote more amplification as we approach New Year just when we need it to sustain the pattern. Mountain Torques have hit the bottom of another trough but from here there is only one direction they can go - and note that in East Asia we have not seen much of a retraction of pacific jet strength in recent days.

Overall AAM is slipping into negative territory and so we are creeping towards a context that says we ought to see a flatter second half of winter especially if the strat downwells - BUT we are on the cusp of a hemipsheric pattern that will put more stress on the strat and we have the MJO right were we need it next CPC expert discussion later today eagerly awaited.

Genuinely - I dont know. If this Nino-esque amplification pattern and current phase kicking off now gets enough punch to it then I could see us back in a cold airstream as we approach New Year. Or....if it doesnt quite have the penetration, and climatological bias towards strong sub tropical high pressure in a Nina pattern gets sufficient hold of things then we could be in average temperatures and looking at a very average UK shape with the north in cool cyclonic weather with the south a little more likely to see high pressure influence kick in.

But despite all this uncertainty I'm not ready to throw the towel in quite yet regarding a Scandy High. Signs of it in the ensemble forecasts at range...and if that monster alaskan ridge does decide to drift to Asia and take pressure off the trough sitting over Scandy at the moment then height rises there to me are quite possible.

So - I'd just sit back and enjoy the ride. I predict wild swings in Op runs - see GFS 06z on one end of the envelope and don't be surprised to see future runs of all models swing wildly in the coming days. Sod's Law and the usual UK climate picture would suggest that the coldest options wont appear and then we will be left desperately hunting for a SSW to do something in the second half of the season - but this is not a winter that has a usual look to it. All things possible....

 

Original post: https://community.netweather.tv/topic/98132-model-output-discussion-the-run-up-to-christmas/?do=findComment&comment=4773883