Model discussion highlights

[phil nw.]

Now the dust is settling on the 12zs i think the overall picture remains of a cold Arctic flow heading south from Sunday followed later by Atlantic lows approaching from the south west from around next mid-week but with cold air in place.

This sets us up for one,maybe 2 battleground snow events later next week.The areas affected to be decided at much closer range but events like this usually affect quite a wide band of the country as they move in.Sometimes they bring in some milder air later or they can stall and even retreat if the cold wins out.

After so many poor Winters from a cold and snow pov let's relish what's in front of us,these synoptics do not appear that frequently.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003898

[bluearmy]

Fwiw, the control diverges from the op post day 9

the runner is fifty miles further south and day 10 system is 36 hours later and runs through n France 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003906

[Eagle Eye]

This pattern compared to predicted at the end of last year has been very well predicted in my opinion. I'll quote myself a lot here just to show how the basic pattern has verified. 

", the unstable inertia rules here due to the distribution of AAM appearing to continue to force the -VE NAM imprint on the Trop. Generally, a supportive sign for Stratospheric imprinting as well. As we go into mid-Winter, the built up momentum through the north Atlantic holding up the -VE NAM pattern is opposed by a loss in momentum budget over the Pacific where we see flip of the north Pacific mode also flipping the north American pattern "

Hence we got the cold a few days ago. Also, support for a SSW is possible again with the Trop wave driving either from this or the next event. With the very short, built-up momentum response, there was not much Stratospheric imprinting lost. 

"The Japanese signal is important to the evolution of the Pacific ocean as it's the transitional area between land and ocean and is also important for determining the distribution of energy between the Pacific and north America. Given a similar strength AAM to what we're likely to see, I'd rather an extended north Pacific jet and a retracted north American jet ripe for AWB just off the eastern seaboard which pushes the -VE NAO and Greenland high again. That's what's currently being modelled on the mean but it's low amplitude as expected and still a fairly weak winning signal."

... 

"linearly, it's more of the AO being flipped before the north American pattern due to the pre-supportive AO pattern flip that managed to work through the base US pattern due to the north-south split and the US pattern flips to an east-west distribution that works to being a positive feedback loop for the Greenland-Iceland pattern."

Hence the support for the Greenland high though I did expect more of a Greenland-Iceland high and it ended up being a UK high that retrogressed (sort of, I've forgotten the word I mean to say) towards Greenland. 

Also very impressive from the mean, though it is 14th vs 16th for what is being forecasted now. So in the end it wasn't a really delayed risk and the mean has been supporting it for a long time. 

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003963

[phil nw.]

Looking at next week on gefs anomalies.We can see the cold air has moved well south into the UK by,yes,15th so right on schedule.

The second and third images the 850s and mean sea level pressure anomalies for day 10-- the end of next week(uk/Europe view),

  

In spite of the ups and downs in the differing operational runs this Wintry pattern continues to be shown.There looks to be some real snowy interest next week,but where will this be is to be decided nearer the time.

 

 

 

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003964

[Cambrian]

12z ECM ensemble mean for days 6-10 paints the picture of a classical battleground setup. The challenge from the southwest is repelled by means of the low over the Azores ultimately being absorbed into the base of the Scandinavian PV driven trough, with the mild air making little progress - mean, anomalies and mean T850s. 

  

In the same way that the pole has relinquished one chunk of the PV to Siberia and ultimately Europe, there are signs by day 10 that the Canadian lobe is getting pulled southeastward through Newfoundland, the build of heights over the Pacific side of the Arctic maintaining the anomalous forcing of the Northern Hemisphere winter cold towards the North Atlantic and Northern Europe, with a further battle being set up for the ensuing days for the UK and Ireland.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004008

[johnholmes]

9 minutes ago, northwestsnow said:

I'm not sure how accurate the precip charts  are off UKMET but I've looked and it's basically dry with a smattering off snow N Scotland

144 as an example..

no ppn forecast of snow is accurate even at short times scales. Not that different to the summer forecasts of rain if you look back. How often even at T+24 or less was the ppn not in the right place/not the correct intensity etc. With snow there are  further 7 or 8 parameters to consider!

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003580

[Allseasons-Si]

I am back and i did miss the ECM run as i had to nip out and another cracking run it was too and just about anyone could see some snow over the next two weeks

i just thought i would add the NAVGEM below before having a look at some other stuff,a nice blocking high there on this run with no phasing issues with our northerly trough with the ESB trough

It is going to turn colder as we all know after the mild-er blip from the 11th-12th as the gefs and EPS ens show and i think that this cold spell is starting to have a bit more legs to it

the cpc still banging the blocking drum,...this has been consistant for some days now and you can see in the ext'd anomaly the lower heights to our SW,this is that feature that we see on the dets and to some extent on the means to heralding an approach of lower preasure from the SW under the base of our northerly trough,it does look to me that it slides south of the UK but this is just an anomaly but it looks good to me

EC ens graph 850's and 2m temps look cold with the op on the mild side of the pack of 850's but look at the 2m temps,this tells me that the op is still cold at the surface.

well that's my brief look at things,...on to the 18z we go them

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004085

[WYorksWeather]

Just going to have a bit of a chat around a few things that I think people are often conflating - there are different aspects of a cold spell that it's easy to confuse by only considering whether a run or ensemble set is good or bad for cold. I'm going to take the 12z ECM 12z vs. an older run to illustrate the changes we've seen over the last couple of days in a bit more detail.

There are four main parameters people are interested in as far as a cold spell goes:

• Depth - how cold will it be?
• Duration - how long will temperatures stay below average?
• Precipitation - is it dry cold or wet cold, and if the latter, will it snow, and if it does, will it accumulate?
• Location - where will the cold and/or snow risks be highest, either in absolute terms, or relative to average?

Precipitation is very hard to forecast, especially if it involves snow risk, so I'll leave that until the period of peak interest post 15th gets a bit nearer. Let's focus on the other three.

Here's today's ECM 12z, vs. Sunday's, for London. I've deliberately gone back a couple of days just to illustrate the change.

 

Now, the scales don't match, so you have to use your head a bit to match the two up. But it's easy to see the points where the chart crosses the mean. You can see that the 12z from Sunday was going for an 8 day spell cooler than average at 850hPa, whereas today's has extended it to around 9 days. So an improvement in duration of cold.

On depth, the key feature is that the risk of a quick return to very mild conditions (850hPa >5C) has fallen away, as has the risk of severe cold (850hPa <-10C). That's either an improvement (more chance of avoiding a very mild spell) or a disappointment (if you wanted severe cold).

Next, location. For the south, this probably feels a bit disappointing, as the deep cold which came in, getting the temperature down to -10C at 850hPa on Monday, now looks pretty unlikely to make a return, as it's not well supported.

But now, let's go somewhere much further north, and take a look. Here's today's ECM 12z, vs. Friday's, for Aberdeen. I can't show Sunday's, since I didn't save a copy, so the most recent one I can use for Aberdeen is last Friday's.

On duration, probably again a lengthening of a day or so, similar to London, with a tendency to delay the return of milder conditions on the mean.

So, if we have a look at the depth of cold, two things stand out. One is that the cold spell on Monday in London was significantly less pronounced further north, and the 850hPa temperatures only got down to around -5C, which for Aberdeen at this time of year is not really very notable. We then see a warm up, which has become more pronounced in the modelling in recent days, though less significant at the surface. Secondly, the cold spell post 15th has actually become more pronounced in recent days, now showing up as very cold on the mean, with 850hPa temperatures down to around -10C.

So, if you're in the north, the prospects of deep cold have actually increased in recent days, and since the first cold spell wasn't that cold, you've got more to look forward to if you like cold.

Summary

So, what can we draw from this? The answer is that the differing views of posters from the south and north at the moment make perfect sense.

In the south:

• Colder initial easterly than expected
• Return to mild slightly delayed on the mean
• Less risk of deep cold post-15th

In the north:

• Initial easterly not particularly potent
• Return to mild slightly delayed on the mean
• Greater risk of deep cold post-15th

Looking at those conclusions, it shouldn't be a surprise to anyone that your view on recent modelling will very much depend on where you are in the country.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004111

[Paul]

31 minutes ago, Scott Ingham said:

100% yeah this is all emotions and past disappointments scewing proper analysis of what’s going on. All the available data points in the right direction bar like you say the odd run.

Not wanting to pee on anyone's parade here, but proper analysis would surely be far more nuanced than that, especially going beyond the weekend in terms of specifics of the cold's longevity, how far south it reaches/stays & any snow risk around that. All the data points don't point in one direction. Many point in a similar direction, but there are operational runs (namely the GFS today) and plenty of ensemble members from various models which show differing solutions.

Yes, the colder outlooks in the shorter to medium term do look more likely right now and I'd certainly take the UKMO and ECM above the GFS 9 times out of 10, but that's not the same as the colder/coldest options being the only possibility on the table. 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004114

[MATTWOLVES 3]

There's no way that gfs is gonna out do mogreps ukmo and ecm..sorry its not happening..and I'm beginning to wonder now if this model even deserves air time.

We have Dr Amy Butler talking about enhanced Greenland blocking next week due to the recent warming yet gfs is clearly not seeing this..infact there's alot going on with the strat and I wouldn't be suprised to see it fall.

 

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004195

[Midlands Ice Age]

7 minutes ago, MJB said:

Easterly en route ???

 

THis is my take, but it facts what we have seen develop so far...

I have used the above chart to demonstrate that the whole of the NH, not just our portion of it, is involved in the change, and not because it shows an easterly.

Just look AT IT.....

What stands out ?

It is the huge fully rounded high pressure over the Bering Ocean and the Aleutians. that one cannot avoid.

If it is not this shape but a wedge shape then it will not effect what happens, because it will block the low pressures and not force them over the top.

This high starts to form at exactly the same time   (day 4 or 5)  that the atmospheric pattern starts to deteriorate on our side of the globe.

I have explained the process before, the high pushes the cold Arctic into North America which destroys any chance that our retrogressing high has of reaching Greenland.

This is EXACTLY the same pattern that the ECM had last week for 36 hrs, before it too decided it would not be a driver and reverted back to the other models situation

I suggest that exactly the same situation will happen with the GFS, as the models are known to flounder when a strat event approaches..  (however one day it will occur, but I suspect that most models will see it happening at the same time).

Has it called it correctly? . I expect that we will find out by Wednesday evening, when it will slowly start to drop the pattern, exactly as the ECM did.

If you want some  good news then it is that most routes seem to return us (the Atlantic) to a cold scenario, but necessarily blocked, which should enhance the chances of snow.

The big (IMO) question is what has led it along this pathway, and is up the wrong path?

MIA

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004313

[ghoneym]

10 minute read on model limitations and why ECM trumps GFS. 

ECMWF vs GFS. What’s the difference, and which weather model is more accurate - Windy.app

WINDY.APP

---

Learn about the difference between the ECMWF, GFS, and ICON13 weather models, from the experts of the leading pro weather forecast app

 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004351

[MATTWOLVES 3]

1 hour ago, Wilko999 said:

Cherry picking season again. Every time it's not favourable it's discounted. same old same old in here then. 

Your missing the point mate..its not cherry picking,me and a few others are stating that GFS as been largely on its own,that's not to say its completely wrong either. Ecm ukmo mogreps for instance all seem to go against it! It appears the met go against it as well,so do we accuse them of cherry picking cause that model is not showing the outcome they think is most likely!

The tweets from Amy Butler also points out how she sees Greenland blocking to gain some traction next week due to the recent warming! Again gfs seems to go against this also! And trust me she's a dam good scientist. It also points out how the strat is potentially coming under further rounds of warming looking ahead...so models will again struggle until this is resolved,yet it appears gfs is struggling more than others.

In all honesty I can understand why @Scott Inghamloses his rag at times because some can't see the woods for the trees. Its getting to the point that if 6 models all went cold,yet just one gfs went against it some would still say im not liking this trend one bit...its all going wrong..we can never get a cold spell in the uk anymore..next year im going on holidays to Finland...the list goes on.

Op runs are but one run amongst 30 members on gfs,and 1 of 50 on the ecm model. Yet some call the outlook on that one run before even viewing all the other data! Im not having a dig at the masses on here,cause the best posters know this and will want to view all the data over numerous runs and over several days before making a call or changing there minds. So I would call cherry picking a situation when 90% of the data goes one way with only that small cluster of 10% showing something more favourable being the one that gets pointed out for favouritism...not the other way around.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004361

[Weather Monkey]

I took a gander at the Model Discussion Thread back in late December 2009 to see how things compared. The discussions were quite similar to the last few days here but one thing I noticed, and l do remember from lurking back then, was having model agreement at 96hrs. This morning I highlighted comments from the pros over the pond in the NCEP discussion that "The UKMET was removed on day 4 due to its significant divergence from the rest of the guidance regarding the shortwave energy in the East Pac/Northwest U.S." Day 4 is of course 96h. 

So, where are we at as things stand at 72h and 96 hours from today's runs?  Are the models in agreement at this early juncture?

ECM 

+72h

+96h

EC Mean
+72h

+96h

GFS (I could only get the 18z so times adjusted to 66h & 90h accordingly)

+66h

+90h

GFS Mean

+66h

+90h

UKMO
+72h

+96h

GEM

+72h

+96h

And because IanF used to mention the JMA, here they are for the same time frames.

JMA

+72h

+96h

Finally we have the MetO faxes. The 84h+ hadn't updated on Meteociel when I looked so we can directly compare Sat 12z.

9.1 12z +72h

9.1 0z +84h

9.1 0z +96h 

And as a bonus here's tonight's ECM Op run in gif form.

The EC Op looks appears so well supported by the Mean that I had to check I hadn't saved the image twice. As for the rest, they have similarities at 72h but more differences by 96h. Events over the pond at that short timeframe make it difficult to call. Fascinating to watch though. 

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004360

[Bristawl Si]

17 minutes ago, Richard Fisher said:

Why is the border between snow and rain always the M4? Is this by chance or is there a geographical explanation why this happens a lot?

Partly, at least

Topography

A few miles north of the M4, from near here i.e. Old Sodbury, near the Bath M4 junction right along to past the Swindon junctions, we have the start of the Cotswolds or its escarpment.

Example: Heights go from 80m ASL in Yate, for example, to 150m plus, a mile or so 'up the road' In Old Sodbury. This happens all the way along the M4 to past Swindon.

Further East, past Reading, north of the M4, is the Chilterns, highest point 260m ASL.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004334

[carinthian]

On 07/01/2024 at 07:11, carinthian said:

Morning all from a snowy Salzburgerland , temp now dropping over here after a week or two of mildish weather . For some sort of consistency I have attached the 168t chart from UKMO . Um boys and girls make your forecast based at that chart ? Think inevitably there is going to be a clash or air masses, but where will this zone end up ? How far can the Arctic Front get south or will it be retarded coming up against the rise in pressure over France ? or will there be a middle ground ? Of course it could end up a clean cut sweep from cold to mild or cold wins out ! Fascinatingly , interesting winter charts to unfold. Its going to be a ride this week but for you lot back in blighty enjoy the colder drier spell for much of this working week , Still to far out to see what evolves by next weekend. Meanwhile the establishment of The Italian Low to produce some much need fresh snow to most of the Alps. To prolong any cold spell we all need its circulation to stay in put for much longer than some of the models show this morning. Enjoy your weekend and some may see a flurry or two.

C

Morning all. A bit of an update from my last post above sent on Sunday. Are we any the wiser for next weeks developments ? Meanwhile, we have an important World Cup Giant Slalom race on the local mountain in a couple of days. Cold snowy conditions look to remain before quietly warming up next weekend, So thats good timing. Back to the models and UK prospects. So again for some consistency, the UKMO extended still shows potential battleground but again with no clear cut route to depth in cold.  This mornings other models, especially ICON advance the colder air more quickly during Saturday night, that would be the best result to get the colder air in place earlier. The feeling over here from the experts is for that to take place as there is an expectation that the push from the Arctic will be strong enough to advance the front more quickly during this weekend. This should soon show in  outputs over the next couple of days and could again change the snow potential forecasts. Just as a bit of information showing on the snow model they use , has an up tick in snow for NW England by this time next week. Read what you want to in that .Happy model viewing, hope its not sending you crazy !

C

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5004449

[sebastiaan1973]

The sea between Sweden and Finland, the northern part of the Gulf of Bothnia. is frozen. This is quite remarkable. Please look at the extent. 

This can be important if the wind will turn to the northeast later on. In the weatehrmodels we see a persistence of cold (er than average) weather in Scandinavia.   

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5004647

[Man With Beard]

We're not used to pressure charts like this:

occurring in combination with uppers like these:

Although synoptically the GFS might not be precisely what coldies were after, it does deliver an alternative method of obtaining wintry weather in deep winter: Get the cold in first, and then any pattern that prevents mild southerlies pushing it out will be sufficient to sustain it. The cold gets in early next week (cross-model agreement getting better for that), and then a jet profile like the GFS is showing at D10 either locks the majority of mild air further south, or ushers it east before it can make sufficient inroads towards the UK:

 

As a result, a pattern than looked lost to cold at D9 recovers quickly to this by D11:

The moral of recent GFS runs, therefore: There's more than one way to crack a nut.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5004812

[TEITS]

Going to disagree with some of the posts today especially with regards to the initial N,ly and how far S this spreads.

If you remember for my location there was a lot of scatter with regards to the N,ly around 16th Jan. Now we have a solid cluster around -8C which for my location isn't bad for a N,ly. Also take note how even 11 days away the mean is still at -4C.

ECM ensembles for my location is also at -4C upto 20th Jan. This might not sound very cold but could be cold enough for snowfall, should fronts move in from the S.

 

Next take a look at ECM for N France. The mean suggests the operational was too far N.

So in summary. We begin with a N,ly, followed by a potential snow event next week (No idea where). Possibly turning less cold for the S before turning back colder again from the N into the following weekend with further snowfall opportunities. Into the following week i.e 21st Jan onwards the potential for an E,ly as I mentioned a few days ago. If this doesn't occur then still likely to remain on the cold side with further snowfall especially for the N as the pattern of blocking and a jet stream further S than normal looks the most likely outcome.

Just remember even during the classic winters of 63 (even though I wasn't born) at times the blocking did relent and briefly the upper temps increased but surface temps remained cold. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5004681

[Mike Poole]

A look at why the clusters were struggling, here’s day 9 from the EPS:

A large uncertainty!  Some cross polar rippers in there, some with a clearly defined ridge int Greenland in place, some with a declining ridge, and on some it has completely healed up.  

Let’s go back 3 days, day 6:

This is actually looking quite clear, most have the ridge holding providing a decent northerly to this point.  The ones that have a GFS style mess in mid-Greenland are few.  So I think we are further forward this morning.  The trend could still be that the block is underestimated, more runs needed.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5004648

[phil nw.]

Two faxs for Saturday.First is from yesterdays 12z and the second is from the overnight met run,the latest at t84hrs.

 

We can see little step forwards with the high retrogressing, setting us up nicely for the Arctic northerly hitting from Sunday.Cold front approaching Scotland already on that.

These are the ones to follow in the next few days for any developments that will be forecasted  in the flow ,and i dare say there could well be some disturbances heading south in that.

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005028

[Tamara]

Bom dia e todos

I make no apologies for yet again re-pasting this sequence originally posted just prior to New Year, because it has become an even more focused roadmap. Not just for the upcoming 10 day period, but indeed confidence increasing as a blue-print for well into the second half of the winter:

....................................................................................................................................................................................

With the Nino attractor phases fully engaged, the amount of westerlies propagated into the atmospheric circulation between tropics & extra tropics do, as you suggest, indicate a higher floor to the angular momentum budget in the 'lull' ahead of the next upswing as the MJO traverses the tropics during January. GWO Phase 4 is a good medium base floor level I would think.

If we were to take a diagnostic template of GWO Phase 4 (and account for a likely return shallow orbit through phases 0,8 & back to 4) during an intermediate 'lull', then that very intermediate lull phase you describe will likely feature the return of a flat upper flow extending towards Europe.

The difference to recently though with the Atlantic forcing will be the jet suppressed further south - and with a cold pool established then attritional forcing of lows against the blocking likely to be a feature. (This accounts for some of the thinking as expressed within my previous posts in respect of the sub tropical jet)

With a cold pool established, any erosion from the south/west into NW Europe is likely to be attritional and not likely to displace cold pooling totally.

Taking into account we are still now in the lag period for the effect of +ve momentum from FT/MT mechanisms c/o the recent tropical>extra tropical cycle, we are seeing the new convective signal come into the Indian Ocean. Sea temp anomalies are supportive of deep thunderstorm convection. This, allied to convection in the western Pacific, will generate further mean zonal west wind anomalies to propagate across the tropics into the sub-tropics. With the westerly wind additions generated in December still in the atmospheric circulation, total and relative angular momentum will increase sending the GWO back into a (potential high amplitude) phase 5 orbit.

This progression & evolution suggests a strong -ve NAO with positive height anomalies shuffling between Greenland > Iceland and Scandinavia. Meantime southern Europe wet & mild under the sub tropical jetstream.

Muito obrigada. Melhores Cumprimentos

......................................................................................

To update the template of this analysis:

A very starkly high octane angular momentum budget is emerging and prolific within the global-wind-flow budgets. This translates to stockpile ammunition supply levels for deeply sustained poleward amplification eddies taking on veritable tanker sized reserves.

Based on how much tropospheric led influence there has been on the NH pattern in recent weeks since the starting pistol was fired to destabilise the polar profile, these further poleward swathes of +ve momentum transport take on especially egregiously gargantuan proportions for future wholesale instability and implosion across the polar field. In this respect it is not hard to comprehend the latest sentiments of Amy Butler and how she sees the synoptic pattern imprinted

The copied post referred to a baseline phase landing place for the Global Wind Oscillation. This baseline, ahead of the strongest wind-additions yet c/o eastward progressing high amplitude MJO wave back to the Pacific has remained higher than intermediate phase 4 (as discussed in the copied post)

The latest GWO phasing, even under present lull stopgap at very low amplitude 5/6, reflects the remaining considerably high levels of +AAM anomalies within the atmospheric circulation as aggregate total AAM. (Phase 4 GWO would be more suggestive of flatter return of the jet and greater attrition from the Atlantic against blocking. (Though even this sharpens somewhat against late Jan/early Feb wavelengths)

This GSDM wind flow budget situation is significant. More on this shortly.

The GWO is a phase plot depiction of aggregate wind-flow within both the tropics (MJO related) and the extra tropics as a measure of how efficiently propagation of wind-flow is proceeding between the tropics & extra tropics. This matters, because it is a barometer for synoptic pattern (poleward) amplification potential and provides a diagnostic towards directional flux of wind-flow eddies.

Poleward flux has now become quite supercharged

What of the significance of this?

As the intraseasonally driven MJO crosses the Maritimes at high amplitude, then very strong +ve torque mechanisms will be re-engaged to over top a system already awash with +AAM anomalies. The GWO likely to drill upwards into very high amplitude Phase 5/6. Taking into account maximum winter wavelengths, then this teleconnects ever more strongly to entrenched -ve NAO (under chaotic stratospheric diminution to spotweld a deeply -ve Annular Mode).

How can this be visualised?

The upcoming next cascade of westerly wind burst propagation into the extra tropics creates white water rafting within the sub tropical jet from the Equatorial Pacific downstream to the Atlantic -at the same time as the polar profile becomes riven with -ve mean zonal -ve wind anomalies. Defining solid roadblocks for southward directive of a deeply unstable thermal boundary.

How can this in turn be visualised?

With deeper upper cold air ensconced north of the polar boundary, this leads to feedbacks of entrenched surface cold with time to feed an ever starker thermal boundary, This encourages and emboldens larger progressions of numbers of kayaks slipstreaming below it. This translates to trains of low pressure undercuts - and it is not difficult to envisage the potential for high impact weather events to unfold in such a scenario. 

The kayak posse delivers an "atmospheric river" of saturated sub tropical air and a large jump of temperature into the upper teens for my part of the world well below the thermal boundary at the same time as in contrast...

.... that is better left to the mercurial imaginations of any members who might be looking in from NW Europe.

Putting all this diagnostic analysis together, it is hard to see anything other than a tanked -ve Annular Mode relationship dominating much of the rest of the winter. However, and as ever, further analysis is wholly prudent to document how proceedings unfold.

Muito obrigada. Feliz quarta-feira

 

 

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005089

[johnholmes]

1 minute ago, Alexis said:

Must be mistaken then. Somebody posted the specs the other day. and I thought it was the 00z that was about a gig down on the total data.

Found this about weather balloons; certainly in my time world-wide ascents main times were 00 and 12Z for all data including balloons.

 Currently, the global radiosonde network includes about 900 upper-air stations, and about two-thirds make observations twice daily (at 0000 and 1200 UTC). The network is predominantly land-based and favours the Northern Hemisphere.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005208

[johnholmes]

4 minutes ago, Alexis said:

00z has less data, mostly from less balloon information. I wonder if balloon data is more important when it comes to gathering figures from less populated land areas, such as Greenland and the Arctic? Statistically it's not less reliable, but then again our weather comes from the south west seas most of the time.

Max balloon data is 00Z and 12Z

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005196

[Tamara]

10 minutes ago, Midlands Ice Age said:

@Tamara (and Met4)..

Would you think that the Met office/ BBC should send out a red alert for the upcoming?

(Or possibly not in the BBC's case as  would they even understand it?) 

I must say I am learning more and more from you on these connections with the Tropics. It gives a longer term (1 week or more), that we can view the atmospheric characteristics, and have a good chance of being correct. 

 Like Met4 , and although I am no expert yet, I really find your analysis interesting.

Lets hope that you are correct. Despite my 80 years of age I am happy (for the first time really) that despite the advancements in computer technology we are making real progress in being able to forecast for everybody - even in today's chaotic worlds. 

I have nothing against computers - I spent a whole career working with them - but unless you are absolutely spot on with your assumptions - they can be a long way out. Currently most of your assumptions are not handled by the large beasts at all, because  there is no way that they can mathematically be  programmed (just yet!). But I am sure it will come now.

With many thanks ..

MIA 

 

With the atmosphere now very tightly coupled to El Nino, +ve AAM westerly wind burst anomalies propagating from tropical convection traversing the tropics to the Pacific either usually manifest in

A) downstream blocking patterns across Europe in stable Annular Mode patterns (and other countervailing aspects that discourage poleward momentum transport)

or,

B) close to Iceland and Southern Greenland as under the present destabilised polar field and as assisted by E QBO Brewer Dobson circulation of tropical tropospheric air that ascends the stratosphere and augments poleward propagation of extra tropical +ve torque mechanisms and hence perturb the polar field and lead to an HLB outcome.

So though this is a deliberately generalised categorisation (and each situation has to be taken on its own merits)  - as already indicated, clearly this winter is meeting criteria B.

The present alert system seems well primed ahead of next weeks cold air advection. I cannot see this changing for a while yet based on, (and as my own little "at home" posts have been giving heads up for some time) there being still such an envelope of probabilistic outcomes for the first high impact weather zones and where the kayak procession first choose to navigate. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005280