Winter Season: Model Output Discussion Highlights

[LRD]

Going to allow myself a little smug moment and say that I warned folk not to get carried away with "cold zonal" runs. I was even more sceptical when the GFS ensembles were in total contrast with MOGREPS on the 12z runs

How many times have hopes been raised during an evening only to see it all crumble in the morning? A rhetorical question of course - we all know the answer... lots

Speaking of MOGREPS:

Christmas isn't in view on these graphs yet but the trend is clear. It's been showing an uptick in 850s for a few runs now for next weekend after a chilly end to the working week

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5184584

[Uncertainty]

I don’t normally analyse the clusters in detail - @WYorksWeather @Mike Poole and others do a great job - but the eps clusters  between days 8 and 10 are not at ‘oblivion’ level. In fact, if you offered them to me 3 months before a random Xmas period, i would probably take them.

The key takeaway is the euro trough. As long as that’s in play, scenarios in the realm of yesterday’s gfs 12z will remain possible. If the models, especially the eps, are underestimating the mjo’s phase 6 progression, then maybe the Atlantic will play ball. Webb has just put out a very illuminating tweet on this matter.

I’m not being optimistic for the sake of it, but I’m just not seeing enough evidence to write off the next 4 weeks. No, I’d doesn’t look like narnia, and the outlook isn’t great, but the below charts reinforce my feeling that the course towards oblivion can still be altered.

GEFS FI

EC46 weeks 2 and 3

cfs mjo

Bom extended mjo

December neutral and Nina composites for phase 7

 

@CoventryWeather the extended clusters look quite interesting, but Xmas day does look flatter.

Keep the faith; for now.

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5184609

[bluearmy]

 knocker  the vortex pattern is pretty much in the same locale (atop the pole) all the way from the bottom of the strat to the upper part.  So the upper and lower strat looks well coupled when looking at that and the zonal flow at 60N.  That zonal strength also dips down into the trop in around a weeks time.  As I said a few days ago, coupling has quite a range of definition. It seems that on here we use it to reference when the strat and trop are both strongly zonal at the same time and around a similar vortex ‘shape’.    So far this season it seems that the trop has held sway over the strat. This upcoming ‘coupling’  could well be more of that. But the cross flow chart seems to indicate the stronger flow dipping down. the message has been that this will be temporary. Cohen will update his thoughts this week and I think these will be significant in the respect.  I’m hopeful that we will see a resumption of the upper strat/trop disconnect by years end. 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5184622

[knocker]

 bluearmy To my very untutored eye it does not look to me that the "coupling" is definitely established. That 100mb chart has the trop signature all over it 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5184601

[bluearmy]

There is some momentum to pretty much remove the Canadian vortex from Canada where it affects the Atlantic sector in a couple weeks time.  Whether that’s part of a reconfiguration towards a broad large tpv centred around the pole or a movement of the tpv towards the pole/asian side isn’t clear atm.  Something else to watch. 
 

just to add that heights remain low of n Greenland in all events so a proper greeny block is not on the agenda out to new year 

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5184773

[Cambrian]

I’m beginning to like the look of this European trough more and more, here on the 12z ECM op. Its development has been signalled in the ensembles for many days now but this is the first time we see such a clearly staked out evolution within the 10 day timeframe.

The transformation between day 3…

 

…and days 5 and 6…

  

…as the trough drops through the UK and Ireland and then proceeds to clear the heights out of Europe, setting up a northwest - southeast corridor for the next, more active low pressure system to move down through the UK and Ireland, delivering a packet of low heights into the base of the upper trough, aiding the further development of the cold pool and cut-off system over Europe.

Days 6-10 animations:

  

Even the T850s are holding interest. Impressively cold uppers, around -18 degrees over Scandinavia at day 6 hold firm there and ultimately mix in to the circulation over Western Europe.

For those looking for a more seasonal flavour to the weather leading up to the festive period, this is the most promising run from the ECM for several days and the crystallising prospect of development of the cut-off European low - at the same time as quite paradoxically, the drawing of even lower heights into the core of the Canadian PV helps to pump up a bridge of heights building northeast from the Azores through northern Scandinavia to western Russia - might prove to be very timely indeed. 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5184956

[Mike Poole]

 sebastiaan1973 Just thinking aloud, but one thing that has become noticeable on these plots recently is that the strat vortex is now forecast to spin at well above average speed throughout the run.  It may be that this increase in the zonal winds from the position as of now, is actually a reflection of failing to properly couple with the trop and running free once again in a substantial number of ensemble members.  

It does look increasingly unlikely that a SSW will occur on a timescale to affect winter, and I’m sure nobody wants another spring ruined by one anyway.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5184992

[Jordan S]

Quite a mixed outlook next week onwards.

Most likely outcome is a fairly straight west to east flow overall after an initial south/southwest flow at the beginning of next week, largely unsettled mid week with potential strong wind gusts in the south in association with a possible disturbance /small area of low pressure swiftly moving east/northeast beneath the dominant low to our north, with 30-40mph gusts, along with rain at times for most/all, some of it heavy, brief hill snow possible for parts of the north but primarily parts of Scotland.

Potential strong north-northwest/northwest winds in the northeast of the UK around Thursday time with gusts of 50mph possible, perhaps especially for Shetland, remaining unsettled at times everywhere later next week onwards in the run up to Christmas with westerly/southwest winds, generally fairly mild overall though with further hill snow occasionally possible in the north along with a more northwesterly airflow on occasion, higher pressure closer to the southwest perhaps late on.

As we go through the Christmas period itself and slightly beyond 24th-28th a trend to less unsettled conditions in the south/southwest is possible due to higher pressure closer by here, but possibly remaining much more unsettled over northern parts of the UK with the risk of gales/severe gales by this point in places, courtesy of a possible increase in temperature gradient, along with potential further hill snow occasionally, winds generally from the west/westsouthwest over southern half of the UK and northwesterly/ west/northwest over northern parts is the most likely outcome at the moment for this time period, temperatures a little above average for southern UK overall and generally around average for northern UK is more likely.

Any hill snow at this time perhaps temporarily to slightly lower levels in showery periods in the north behind low pressure systems which may be deep moving on a southeast directory over the north sea bringing temporary somewhat colder air southeast, this would coincide with high pressure building even more strongly than the preceding days just to our west/southwest, which could make way for less mild conditions everywhere with the timing of this being more likely just after Christmas day.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185032

[Cambrian]

A case of Paradox Lost on the 0z ECM op compared with yesterday’s 12z run. The PV is not on this occasion modelled to be centred over northeast Canada, rather it has begun its transit east that has been a feature of the ensembles in the extended range for a good few days and so is instead centred over the very north of Greenland. Yesterday’s 12z / today’s 0z.

 

This closes the gap of opportunity we saw on the 12z and prevents the build of heights just to the south of Iceland through to northern Scandinavia to form the cut-off European low and also injects more eastward momentum into the trough, which is as a result is a good deal further east, dropping down into Greece. 

This day 10 setup is supported by the 0z EPS and GEFS, the Azores high extending eastward into Biscay rather than northeast toward the Faroe Islands. 

 

Looking at the Christmas period through to the end of the year from here is fraught with conjecture but it appears that a relatively quiet (and safe!) Christmas period is most likely with the polar front kept well to the north. After recent weather here, I would settle for that. 

On the other hand, though we might be losing out on the chance of colder weather through Christmas itself, the eastward movement of the PV looks to be becoming more consolidated - 

 

here at day 15 on the 0z GEFS, the core PV returned very much to the Siberian side of the Arctic - this might well open the door to some very different patterns. 

That little hook of core low heights westward through the north of Greenland might well be representing a particular cluster that keeps the core PV more on the Greenland side.

I’ll be looking out for that getting flushed out from the models for the last week of the year over the next few days, which would allow a cleaner alignment of the PV through Svalbard into the Norwegian Sea, and allow some meaningful retrogression of the Azores high and a more definite drawing of low heights south into Europe at the second bite of the cherry in the days after Christmas, as what is currently shown will not cut it for any meaningfully cold air getting into Western Europe.

The obvious caveat to all this speculation is the extended time range, so I’m going to enjoy keeping a keen eye on the models as well as looking forward to making the most of the drier and brighter spells for some good walks with family during this most precious time of the year. All the best.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185086

[jonboy]

All this gnashing of teeth. When I was growing up in the it's we never considered winter to start until the winter solstice the 21st of December. 

All memorable wi ters start after this date. I still considered 2010 to be a late autumn event. 

I will start looking at the models properly next week. 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185135

[blizzard81]

When there are huge differences like this between runs at day 8, it's still unwise to make any predictions for the run up to and including Christmas.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185106

[summer blizzard]

 nick sussex It's been stuck in phase 5 because we've seen a (temporary I suspect) Nina standing wave since since late November. So the models have been forecasting progression that never arrives. 

It looks like we may see a relaxation in the trades for January (Euro agrees with this) which will allow progression to phases 5-6-7-8-1 (though models may overdo this).

 

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185336

[WYorksWeather]

Let's see if we can pick anything out of the clusters.

Days 3-4

Massive ridge to the SE setting up an exceptionally mild Wednesday.

Days 5-7

Cluster 1 (31%) has high pressure centred to the west. Wind direction is slightly north of west, so perhaps near average temperatures.

Cluster 2 (20%) has high pressure slightly further south in the Atlantic and closer to the UK. A flatter westerly, dry in the south and mild.

Cluster 3 (20%) has winds from just north of west at day 5 and 6, but quickly flattening off to a milder westerly at day 7.

Cluster 4 (18%) is westerly throughout. Relatively dry though with high pressure never far from the UK, but also mild.

Cluster 5 (12%) makes slightly more of the mid-Atlantic ridge around day 6 with the chance of a brief north-westerly accompanied by stormy conditions in the far north of the UK, before quickly flattening off at day 7.

The OP was in Cluster 1.

Days 8-10

Cluster 1 (41%) is westerly, dry and mild from days 8-10.

Cluster 2 (31%) is also westerly, but low pressure further south at day 9 and 10, making for a very wet and/or stormy Christmas Eve and Christmas Day, and slightly cooler than Cluster 1.

Cluster 3 (27%) has a very brief cooler interlude at day 8, before the ridge to the west topples into the UK, leaving us with a dry and mild Christmas with high pressure linking back to Iberia.

The OP was in Cluster 2.

Days 11-15

Cluster 1 (43%) has a large ridge from Europe through the UK up to Greenland. Still mild, with the Euro heights likely to feed mild air into the UK regardless of the Greenland heights.

Cluster 2 (33%) is mild and dry at days 11 and 13 with a large area of high pressure linking back to Iberia. By day 15, the mild feed is cut off, so possibly a more seasonal UK high by that point.

Cluster 3 (24%) keeps high pressure in control over the UK, but a continued link back to southern Europe keeps mild air feeding into the high. Likely mild but gloomy.

Summary

Absolutely horrendous update from a cold perspective - it remind me of some of the updates I was doing in late Spring earlier this year looking for warm and settled weather.

You can try to pick the bones of it - an odd transient north-westerly here, a brief cooler anticyclonic spell there, but even with all these clusters there's absolutely nothing there that looks even close to interesting I can find in here.

Probably the only consolation is that it will at least be fairly dry, so perhaps usable for those Christmas to New Year walks. It won't feel like winter if this update is right though - much more typical of perhaps late October or early November.

Still time for things to change before the end of the year, which does bear repeating, but a few more days of this and it'll be time to throw December in the bin from a cold perspective.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185435

[WYorksWeather]

Just had a look at EC46 for the next few weeks to compare with the dreadful CFSv2 for cold from yesterday. Hardly worth the bother, but here you go.

I've rarely seen the 3-6C above average dark red colour for week 2 on a UK chart, which shows how confidence the model is, even that far ahead.

Weeks 3-4 look solidly above average as well, though of course much more scope for those to change.

To be clear this is not a winter is over post - I'm never that pessimistic about the output as things can and do crop up at short notice all the time. My point about a 7-10 day memorable cold spell still being possible in an otherwise mild winter still stands - that sort of thing will never be picked up by seasonal models or background drivers alone.

But what I would say, is that expectations from me have now hit absolute rock bottom. I already predicted in the long range winter thread that all three months will finish above the 1991-2020 average, and absolutely nothing I have seen so far suggests a reason to change that prediction.

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185496

[Cambrian]

With just over a week to go, weyhey, I’m looking forward to Christmas. It’s a great time. 

The prospect of a white Christmas for Britain and Ireland is an enjoyable, romantic notion, but that’s all. For our interests on here, if we remove the statistically (largely) unfounded association of snow with Christmas from our expectations and enjoy the exploration of the model outputs for what they are, we’ll probably enjoy this a lot more too. 

And what we do have is a fascinating battle going on over the Arctic currently staged for between Christmas and the New Year. 

0z EPS and GEFS at day 10, end of Christmas Day heading into St. Stephen’s / Boxing Day, stuffed full of food and at least mildly inebriated, rather like these charts. An impressive build of heights to the south of the UK and Ireland, but the ridge is keener to move through than in recent days. An upper trough has formed down through the west Atlantic. 

  

This could be important because though it’s probably going to fail to fully establish there, the Arctic underpinning of it draws off low heights from the Canadian lobe of the PV. This hands the supremacy to the Bering Sea lobe and further weakens the Atlantic. It also helps kill off the eastern seaboard trough, so no snow there either, much of the US and Canada looking mild too under a westerly upper flow. Bing will be doing his nut!

The primacy of the Bering Sea lobe allows the whole body of the PV to swing east, so that by day 15, it’s very much on the Eurasian side of the Arctic, feeding a tentative Scandinavian trough, but importantly we’re getting marked retrogression of the Atlantic heights, consolidating with those over Canada. 

   

The 0z GEFS and EPS (12z Sunday) both show this and the trend is a growing one - for comparison, yesterday’s 0z from GEFS at day 16 the last one above.

These charts aren’t intimating at anything that exciting for the interest in a cold spell yet, but there are some reasonable signs here that while we’re at a bit of a sluggish juncture right now, better charts will begin to emerge in the coming days.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185649

[WYorksWeather]

 Cheshire Freeze

Looking further ahead, I'm struggling to find any seasonal output within the next four weeks that shows much sign of change. Here is the latest EC46 for the next four weeks.

The week 2 chart is one of the mildest I've ever seen over the UK for week 2, when certainty is usually quite a bit lower than week 1. That is 3-6C above average, across virtually the entire UK. Weeks 3 and 4 see a slight relaxation in that mild signal, but still widely 1-3C above average.

To compare, the CFSv2 is on the same page. Ranging 2-4C above average for the next two weeks, then 1-3C above average for the two weeks after that.

There is of course a chance that the model output is overly persistent with the high pressure to the south - something shorter-term could come up to shift the inflated Azores High. But the fact that this sort of outcome is even plausible just shows how close to rock bottom we are.

About the only things I can really say to inject some optimism are the usual platitudes - the output can't really get worse from here (though maybe the GFS 18z will try to prove me wrong on that ), and there's still plenty of time left for things to change for the rest of the winter.

Whilst we wait for a change, I do take an interest in record-breaking weather, so I for one won't be switching off from the models.

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5185978

[Ladyofthestorm]

A wee update on the teleconnections.  Forecasting a weak phase 6, but much stronger  phase 7 and interestingly this is being picked up on the NAO and AO as a negative phase on the ensembles. 

 

 

Also watch out for significant changes. More runs on the ECM are picking up on a reversal compared to a few days ago. 

Saturdays runs 

 

Mondays 

 

Watch this space, the trend is your friend.   

Whilst Christmas is green , thank goodness as peeps need to travel to be honest . I still think end of December and into January looks very promising for wintry weather.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186046

[Premiere Neige]

 northwestsnow I believe there was a Canadian warming in December 1962...

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186101

[Blessed Weather]

 LRD This chart - posted by the Met Office's Marco Petagna on X some weeks back - is worth keeping in the back pocket. Broad-brush impacts of each MJO phase:

 

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186113

[Blessed Weather]

Latest weekly blog from Dr Cohen at AER suggests the sPV and tPV are in a period of alternating coupling and uncoupling. A strong sPV coupling with the tPV normally means a positive Arctic Oscillation and a strong Jet Stream with zonal (westerly wind dominated) weather for us; not what coldies would want to see.

"The latest plot of the polar cap geopotential height anomalies (PCHs) currently shows normal to warm/positive PCHs in the troposphere, albeit very weak with cold/negative PCHs in the stratosphere (Figure 11). The cold/negative PCHs from the stratosphere are predicted to descend all the way to the surface next week but only briefly.  For now, this suggests that the stratosphere and troposphere are mostly uncoupled but does look like the strong PV is increasingly coupling to the troposphere. Still waiting to see if the cold/negative PCHs in the stratosphere could couple to the surface for a longer duration or whether the warm/positive PCHs in the troposphere could force a larger polar vortex disruption. But over the past week, the cold/negative PCHs are starting to dominate."

Other useful info in the blog:

"The atmosphere still seems to on the “lather, rinse, repeat” cycle of stretched polar vortex (PV) followed by a snap back to a strong circular PV and then repeat the whole thing over again. The interval between each stretched PV seems to be about a week or so."

Not mentioned by Dr Cohen but I would venture the ongoing strong pulses of Wave 1 into the stratosphere bringing about the rinse/repeat stretching is also helping prevent a strong coupling with the tPV.

Wave 1 forecast:

Source: http://weatheriscool.com/page8.html

One to watch according to Dr Cohen is the hint from both ECM and GFS in the far reaches of FI of a possible Canadian Stratospheric Warming. A CW often leads on to a further disruption of the sPV and potentially also Greenland blocking.

Full blog: https://www.aer.com/science-research/climate-weather/arctic-oscillation/

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186082

[TEITS]

Looking at the 0Z and I couldn't give a monkeys if Christmas day reaches 20C as long as the rest of the run verifies. The latter part of the 0Z run isn't surprising to me as we have seen hints of this from previous runs. The transition from Xmas Day to New Years eve does make sense and is something I have seen before.

I shall also add that the Xmas period will not be as mild as some are saying with the exception being Xmas day. Obviously cloud cover will play a significant part but ground frosts are possible followed by possible stubborn fog patches reducing max temps.

Finally writing off Jan, Feb already is just foolish and is only based on your emotions of our current weather.  

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186084

[Cold Winter Night]

Obviously the interesting synoptics currently aren't found in the nearest future.
The De Bilt T 2m plume keeps temperatures away from anything wintry for the rest of this year, with a spread too tight to offer any relief.

However, this graph hides what the ensemble sees happening with Northern Hemisphere synoptics, something others have noted as well.

Extended EPS clusters are shown as one cluster. This means it shows the member that best represents the mean when the algorhythm cannot partition the ensemble into meaningful clusters.

Clearly the mean has the TPV moving from the Western into the Eastern hemisphere, which opens up opportunities for high anomalies over Eastern canada and Greenland.

A look at the panel with all members of the ensemble gives more insight, and it reveals how broad the support for this move is.

Although it's not all 51 members that shift the main section of the TPV East, it's close. The support is for it is surprisingly strong.
While at 360h most of them still have winds coming in from the West/ Northwest in our part of the world, many are at the doorstep of turning that North or Northeast.
The two members below show a bit of the range of options on offer.

The first one, p10, is more similar to what GFS 6z did in deep FI, the second one, p13, is not unlike the GFS 0z, so EC/EPS and GFS/GEFS do not even disagree that much.

So although it is deep FI, with any tangible good at ground level even further away than 15 days, the broad support for these developments is interesting and it does give hope that January might not have to be as zonal, mild, grey and wet as feared by many.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186139

[phil nw.]

Some positive signs that we will see a pattern change-eventually.

Latest discussions on the MJO confirm what many of us know already that it has become slow moving over the Maritimes(phases 4/5) for many days but they believe that in weeks 3/4 it will move into the Pacific(phase 6/7- colder phases) and reamplify.

CPC - Climate Weather Linkage: Madden - Julian Oscillation

WWW.CPC.NCEP.NOAA.GOV

Up above, signs of a dramatic slow down in the Strat filtering down in week 2

   

These are taken from the later gefs and are outside the ECM 10 day strat..charts currently so i can't compare yet but good signs.

I speculated a few days ago that we were at a crossroads for January's prospects.We have been stuck in this warmer pattern with the MJO slow to move but finally the experts are expecting this to move into the west Pacific and continue eastwards phases 6/7.

Phase 7 is the pathway to the weakening of the vortex and consequent increased chances of higher latitude blocking from a slower jet. If these latest forecasts verify then allowing for the lag of 10/12 days after it hits the W.Pacific then prospects for January will look much better for cold.

 

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186155

[nick sussex]

 northwestsnow

You should factor the ECM bias in terms of the signal and the Rossby wave doesn’t dissipate till later in December .

I’d not take too much notice of the longer term forecast at this stage until that’s happened .

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186204

[nick sussex]

Interestingly the biggest trop response to the MJO in terms of impact on the NAO comes from phase 6 .

This in some research is the pre-cursor to a negative NAO.

And it’s in a way quite logical as phase 7 and 8 could already be coming from that negative NAO .

This chart shows the impact of the MJO and its phases .

 

North Atlantic Oscillation (NAO) response to the Madden–Julian Oscillation (MJO). The bars represent the percentage change in the probability of observing a particular NAO state, at a given lag after observing a particular MJO phase, in the HadGEM3-GC3.1-MM model. Bars that are coloured in red represent a change that is statistically significant at the 95% level. The NAO response to the MJO in the observed data is plotted as the black line, with circular markers to indicate significance.

From:
North Atlantic Oscillation response to the Madden–Julian Oscillation in a coupled climate model

Skinner , Matthew’s and Stevens.

Original post: https://community.netweather.tv/topic/101008-winter-season-forecast-and-model-discussion-commentary/?do=findComment&comment=5186201