Model Output Discussion - Cold spell ending - what next?

[Severe Siberian icy blast]

14 minutes ago, Met4Cast said:

The state of the stratosphere needs to be taken into account. An unstable profile (such as we have now) often favours higher latitude blocking. If the strat had been in a strong position we'd likely have seen the current blocking fail. 

SSW's cannot be predicted with any real accuracy at longer ranges so it's always a wildcard. Unfortunately on this occasion instead of amplifying the blocking signal, it's flattened it with a displacement event. You win some, you lose some..

Well we've had two warmings over Canada now, ironically the recent spike in strat temps have had the effect we didnt want.

I've only Just caught up i lost pages when it went mad and needed to understand because i was under the impression this last warming ongoing the last few days would infiltrate itself into the modeling over the coming 10 days but you're saying we had a quick response and next WK is the response?! 

[Mike Poole]

13 minutes ago, sebastiaan1973 said:

How reliable is EC46 with MJO? 

 

Additional note. Amy Butler suggests the Greenland anticyclone was reinforced by the minor warming. 

But what makes the stratosphere’s current behavior unexpected and somewhat rare is that the polar vortex seems to be more disrupted at the lower levels, closer to the stratosphere-troposphere boundary. For more than a week, high pressure has been sitting in the troposphere over Greenland . It’s possible that the recent minor stratosphere warming reinforced this Greenland high pressure, which then drove a wedge into the stretched-out polar vortex in the lowest part of the stratosphere, splitting it into two lobes.  

The polar vortex is acting up | NOAA Climate.gov

WWW.CLIMATE.GOV

---

The latest forecast says a major disruption of the polar vortex is on its way, but the stratosphere has been acting up for a while. Our bloggers explain what it might mean...

 

Difficult to know yet how reliable the 46 dayer is with anything since it is a new approach with 100 low resolution runs since last year.  But as @Met4Cast posted above, other models are showing the same MJO trend.

It has been a very unusual winter in the stratosphere, starting with that Canadian warming (the first for 30 odd years).  But that left the strat vortex weak, and allowed the trop to lead the dance since.  What effect the latest warming will have into February is not clear, but provided the strat vortex doesn’t end up in the wrong place, it may at least allow the upcoming trop drivers for amplification to unfold unfettered.

[Gary L]

24 minutes ago, Met4Cast said:

Comments like this confuse me and I think it's down to a lack of understanding of "background signals" that trigger it. The teleconnections are what drive our weather and create the weather patterns that we see, NWP modelling is based entirely upon these signals. Understanding teleconnections allows you to view NWP modelling in a much broader context. "Too much emphasis" absolutely cannot be placed on the things that literally drive our weather. If anything, not enough emphasis is placed upon them. 

I think where people get caught up is that they expected certain drivers to produce specific weather conditions outside their front door & unfortunately, that's not how it works. You can use these drivers to get a flavour of the broader, global scale weather patterns but the micro scale, i.e outside your front door is so local & isolated compared to the northern hemisphere that x + y does not necessarily = a snow day. 

This current cold period & blocking spell we're in the middle of was well advertised weeks in advance. The MJO cycling through phase 1/2 and slowly through 3 helped to generate a Rossby wave packet within the Pacific which led to wavebreaking in the Atlantic & the Greenland high that has brought about the current cold weather. This, in conjunction with a high total AAM state (increased westerly momentum within the atmosphere) led to a perturbed and amplified jet stream capable of generating the HLB we've seen. 

A strong +EAMT (East Asian Mountain Torque) event created the Pacific jet extension which developed a downstream trough, causing a jet streak which then created a downstream trough, follow this all the way into the Atlantic with each "wave" amplifying the next. We've got a Greenland high, we've got cold weather across the UK, broadscale pattern? Check. The next step is the micro, i.e small-scale weather systems that may or may not bring about snowfall in specific areas, that's something background/teleconnective signals can never help you predict. 

Ironically, the "downfall" to this cold pattern & the reason for next weeks milder & stormy weather isn't because of a sudden change in background tropospheric forcing but down to the recent SSW. The SSW has helped to displace the Canadian vortex eastwards towards Siberia which has flattened the pattern.  A case of bad timing, again, something teleconnections can never help you predict. 

This is the thing I have doubts about - If it were so simple we'd have the forecast broadly nailed down weeks in advance, which simply isn't the case. My comments come from a place where there absolutely is a lack of understanding - but I've not seen much to convince me that these indicators produce much certainty in any forecast weeks in advance. It seems to me they tip the balance, but are not definitive?

[Met4Cast]

2 minutes ago, Gary L said:

This is the thing I have doubts about - If it were so simple we'd have the forecast broadly nailed down weeks in advance, which simply isn't the case. My comments come from a place where there absolutely is a lack of understanding - but I've not seen much to convince me that these indicators produce much certainty in any forecast weeks in advance. It seems to me they tip the balance, but are not definitive?

Nothing is ever definite in weather, the atmosphere is chaotic, complicated and unless you can model every single molecule of air you'll never have 100% accuracy. However; as described above teleconnections have led the way in terms of the broader forecasts but of course that's never 100%. Unexpected things crop up (such as the SSW impacts) that you just can't account for. 

Long-range forecasting is essentially a "best guess", but I don't think teleconnections/background signals are too over stated or relied upon, you just can't expect 1+2 to always = 3, sometimes you end up with 2+2 unexpectedly.

[jules216]

41 minutes ago, Met4Cast said:

I know some are downbeat about this current colder period due to the lack of snowfall (in southern areas, anyway) but the teleconnections advertised this period very well. 

This current cold spell isn't over yet but already it seems a return to blocked/colder conditions is the broad direction of travel into February. The mechanism and drivers for this to occur are already in motion. 

The MJO looks to progress through the Maritimes into the western Pacific, with this frictional torque has risen with +MT following on behind. MT always follows FT. Westerly momentum is transferred from the earths rotation into the atmosphere and the response is AAM tendency goes up, driving total AAM upwards. Indeed, AAM tendency has recently turned positive once again in response to the MJO progression eastwards.

As the MJO continues into phase 6 (and possibly 7, this is more uncertain) we see a configuration favourable for high latitude blocking. It seems probable we'll see a period of mild (perhaps exceptionally so) weather as high pressure builds northwards through the UK but there is an increased likelihood of Scandinavian blocking & thus, colder easterly winds 6th - 15th February as a broad timeframe.

The starting pistol, to borrow a phrase from Tamara has been fired. NWP modelling isn't quite in range of this period yet however we're already seeing signs of pressure rising to the NE via a route through the UK, I suspect these runs are a little progressive in terms of timing but do advertise the broader direction of travel. 

Eyes down.. the next chase is about to begin.

To be talking about specifics. With using tools like GSDM it often does good in diagnostics of current or past events but as a predictor is still quite a broad prone to be too general in specific microscale areas, maybe as a global diagnostics is okay. Lets count today is 18.1 and the "supposed" pattern change to something "maybe" colder is not advocated to arrive not much earlier then 3 weeks from now. That is awful long time in a season, this similar even longer hiatus here lasted over 3 weeks from mid December until 8th January which was onset of a dry cooler week or 2. So overall this is very much the same as winters 2021/22 and 2022/23, and beyond every winter since 2016/17. So despite all the fun and games of predictions its well  on the way to be a very very mild overall and not diverging at all from what is  recent trend. This should not be overlooked. As too much attention is being given to those hanfull cold snaps and not the overall net results of - T2m anomalies, snow cover days, total snow fallen in cm etc. Taking the Scandinavia away which is been cold since October everywhere else its another typical winter of last decades and there is only really few weeks left which would need to be almost historic to make this winter something else then any of last 8-9. 

[Met4Cast]

1 minute ago, jules216 said:

To be talking about specifics. With using tools like GSDM it often does good in diagnostics of current or past events but as a predictor is still quite a broad prone to be too general in specific microscale areas, maybe as a global diagnostics is okay. Lets count today is 18.1 and the "supposed" pattern change to something "maybe" colder is not advocated to arrive not much earlier then 3 weeks from now. That is awful long time in a season, this similar even longer hiatus here lasted over 3 weeks from mid December until 8th January which was onset of a dry cooler week or 2. So overall this is very much the same as winters 2021/22 and 2022/23, and beyond every winter since 2016/17. So despite all the fun and games of predictions its well  on the way to be a very very mild overall and not diverging at all from what is  recent trend. This should not be overlooked. As too much attention is being given to those hanfull cold snaps and not the overall net results of - T2m anomalies, snow cover days, total snow fallen in cm etc. Taking the Scandinavia away which is been cold since October everywhere else its another typical winter of last decades and there is only really few weeks left which would need to be almost historic to make this winter something else then any of last 8-9. 

Yes.. 

Although many in this thread are chasing the cold & snow patterns rather than the “typical winter” patterns. 

What you’ve said fits well with broader climatic trends of course, but that’s not really where this thread tends to focus on! I don’t think anybody is expecting historic cold spells, just a bit of snow would be nice

[feb1991blizzard]

Here comes the GEM 0z redux.

[Bricriu]

2 hours ago, Troubleatmill said:

Meanwhile on our door step, Sunday in to Monday is still looking very wild , our friends over in Ireland/n Ireland could be in for a shocking time, sure if it carries on being modelled like this, the met will be out with the warnings

Aperge overdid the last storm here. So its probably  doing the same again. ECM has downgraded it  to a windy day for us on Sunday.  The GFS still  has it as a storm. Plenty of time for it to downgrade  on all models yet 

[bluearmy]

1 hour ago, Mike Poole said:

Does actually, need to see the next few frames really, here it is at T360:

Yes - Running the frames up to day 15 shows that if it is retrogressive, it will probably take another cycle upstream to force it 

second week feb is beginning to crop up a bit 

regarding the current spell of cold and it’s flagging up via various methods

the two week cross model ens were rock solid counting down (give ot take a couple of gefs runs that lost the ridging into Greenland )

the ec46 saw the pattern well in advance  - four weeks away at least but it had it a week too early to begin with 

im still intrigued as to what would have evolved if we hadn’t suffered the shortwave system running across the country from Iceland  and cutting off the cold flow for at 25/36 hours and indeed, encouraging it to head broadly southwest which brought the lowest heights closer to the Canadian  trough.  The Azores low would have tracked east at a lower latitude and dragged the troughing way down into France.  someone will make the case that we would have seen a strong wedge left griceland that could have disrupted the Atlantic trough on a much further southerly  track …..

the macro cannot see the micro such as these shortwaves and how they then manifest themselves. They can have big consequences 

 

[jules216]

14 minutes ago, Met4Cast said:

Yes.. 

Although many in this thread are chasing the cold & snow patterns rather than the “typical winter” patterns. 

What you’ve said fits well with broader climatic trends of course, but that’s not really where this thread tends to focus on! I don’t think anybody is expecting historic cold spells, just a bit of snow would be nice

Yes I agree, the line of messages I want to put across touches on models thread/next weeks expected mild bonanza, the idea/message I am putting across is more a general re-analysis of how this winter evolves. The chasing of some snow at least has been the main theme of models forever with 90% forum viewers I agree and they don't want/need to read the more climatological/analytical remarks I make. A lot of times the reality check in weather is very hard to look at and to stay positive upbeat even  I often revert to chasing the pattern change that can produce snow and frost, not that we dont have them here every winter but this has to be taken contextually where is your location as having maybe 2-3 weeks of 3-5cm lying snow and absolute Tmin of -11C in central Europe IMBY is like 0 days of snow in London and -4C abs Tmin. Which is like you said a broad climatic trend - less snow days, less cold overall, higher abs. Tmin etc. 

[TillyS]

3 hours ago, Nick2373 said:

At ten days out that's FI The pattern can change over two to three days even by next Wednesday the temps are around the 9c-10c mark not exactly mild considering the wind is from a WSW direction.    

 

Yes the pattern can change but there’s no real evidence for it at the moment and the problem with heights to our south, or Europe, is that they don’t tend to shift swiftly. The main models show a run of mild west to south-westerlies. Here are some sample temps through the week from the latest GFS. Some of these are night time minima  

The models point to a mild or very mild week:

Edited January 18 by TillyS

[tight isobar]

8 minutes ago, TillyS said:

 

Yes the pattern can change but there’s no real evidence for it at the moment and the problem with heights to our south, or Europe, is that they don’t tend to shift swiftly. The main models show a run of mild west to south-westerlies. Here are some sample temps through the week from the latest GFS. Some of these are night time minima  

The models point to a mild or very mild week:

Nxt week pretty much set in stone @ mobility.. and unseasonably mild!.. but the question is .. is this the by point for transition to a different outcome!! I’d say so.

[Nick2373]

16 minutes ago, tight isobar said:

Nxt week pretty much set in stone @ mobility.. and unseasonably mild!.. but the question is .. is this the by point for transition to a different outcome!! I’d say so.

Spot on was just about to type that thank you. 

[Gowon]

17 minutes ago, bluearmy said:

Yes - Running the frames up to day 15 shows that if it is retrogressive, it will probably take another cycle upstream to force it 

second week feb is beginning to crop up a bit 

regarding the current spell of cold and it’s flagging up via various methods

the two week cross model ens were rock solid counting down (give ot take a couple of gefs runs that lost the ridging into Greenland )

the ec46 saw the pattern well in advance  - four weeks away at least but it had it a week too early to begin with 

im still intrigued as to what would have evolved if we hadn’t suffered the shortwave system running across the country from Iceland  and cutting off the cold flow for at 25/36 hours and indeed, encouraging it to head broadly southwest which brought the lowest heights closer to the Canadian  trough.  The Azores low would have tracked east at a lower latitude and dragged the troughing way down into France.  someone will make the case that we would have seen a strong wedge left griceland that could have disrupted the Atlantic trough on a much further southerly  track …..

the macro cannot see the micro such as these shortwaves and how they then manifest themselves. They can have big consequences 

 

This is so difficult to accept but an important message for everyone to take on board and not to get too carried away until a pattern is in the reliable timeframe. 

I will still enjoy looking at cold synoptics evolve and learning how they manifest as that is part of the fun for me.

[AO-]

Quite a potent chart at day 8 in the GFS06. With the shortwave potentially sliding into Germany/Poland we could be in the game. Nice evolution if it comes to fruition in this way.

Edited January 18 by AO-

[Anthony Burden]

The way the polar vortex is with all the uncertainty I’m not sure the chart’s even in the short/medium have got this nailed on surprises could be on the agenda.

[AO-]

I present to you P01 of GFS06. Still potential. 

[sebastiaan1973]

Very interesting, I share it here too, because it is important for understanding the models.   

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JD023359

 Simon Lee writes in a tweet about this article. If we have a reflective type of SSW (Judah Cohen states the same), this leads to a Pacific blocking and westerlies over the North Atlantic Ocean

Abstract

Sudden stratospheric warming (SSW) events have received increased attention since their impacts on the troposphere became evident recently. Studies of SSW usually focus on polar stratospheric conditions; however, understanding the global impact of these events requires studying them from a wider perspective. Case studies are used to clarify the characteristics of the stratosphere-troposphere dynamical coupling, and the meridional extent of the phenomena associated with SSW. Results show that differences in the recovery phase can be used to classify SSW events into two types. The first is the absorbing type of SSW, which has a longer timescale as well as a larger meridional extent due to the persistent incoming planetary waves from the troposphere. The absorbing type of SSW is related to the annular mode on the surface through poleward and downward migration of the deceleration region of the polar night jet. The other is the reflecting type. This is characterized by a quick termination of the warming episode due to the reflection of planetary waves in the stratosphere, which leads to an amplification of tropospheric planetary waves inducing strong westerlies over the North Atlantic and blocking over the North Pacific sector. Differences in the tropospheric impact of the absorbing and reflecting SSWs are also confirmed with composite analysis of 22 major SSWs.

Key Points

New classification of sudden stratospheric warming during the recovery phase

Absorbing type warming events induce Arctic Oscillation on the surface

Reflecting-type warming events produce a Pacific blocking

For the reflecting type (the SSWs in February 1979, December 1998, February 2007, and February 2008.), the deceleration of stratospheric zonal winds is confined mainly to the polar region. Warming is rapidly terminated by reflection of planetary waves, which induces downward propagation of the wave packets. Fluctuations, including intermittent warming periods, precede or follow the major warming. The tropospheric response of this type of SSW appears as an amplification of the tropospheric planetary wave in the recovery phase of the SSW. In particular, a deepening trough over the North Atlantic and an enhancing ridge in the North Pacific sector are evident. The latter enhancement provides a favorable condition for a blocking formation over the North Pacific.

Edit. I place the tropospheric setting after Absorbing & Reflecting. 

 

 

Edited January 18 by sebastiaan1973

[Severe Siberian icy blast]

1 hour ago, Mike Poole said:

Difficult to know yet how reliable the 46 dayer is with anything since it is a new approach with 100 low resolution runs since last year.  But as @Met4Cast posted above, other models are showing the same MJO trend.

It has been a very unusual winter in the stratosphere, starting with that Canadian warming (the first for 30 odd years).  But that left the strat vortex weak, and allowed the trop to lead the dance since.  What effect the latest warming will have into February is not clear, but provided the strat vortex doesn’t end up in the wrong place, it may at least allow the upcoming trop drivers for amplification to unfold unfettered.

Again im catching up now, so what gets me with the warming that's undergoing this week why are people so quick to write the next wk or two off when a fast response may happen and change the entire game 

[Daniel*]

2 hours ago, TEITS said:

Brilliant post as you have summed this up perfectly.

On a different topic I note some are being a little OTT with regards to next weeks mild weather. Just using the GFS only one day does my location reach a max temp of 13C. The other days for next week is around 8/9C. So just above average and nothing exceptional. What is noticeable next week is just how wet and windy it shall be although thankfully the low pressure on Wednesday should be the last one for a considerable time.

In summary after the wild weather this sunday and early next week the next destination is fairly clear to me. However the route it takes and how long the journey will be is up for debate. If members thought the recent chase was stressful they ain't seen anything yet.

Hi TEITS, nice to see you’re still around   I agree with you, using Birmingham based on ECM 00z fairly representative of CET zone yes notably mild this Sunday into early next week, but afterwards not especially so, perhaps frost and fog could become a feature in the second half of the week. I think there are too many who see oranges and the southerly flows from continent and assume it’s mild/v mild the thing is it’s midwinter, definitely later in February you can see that as seen in 2019, but we’re still in that core part of winter. 

[AO-]

It is also worthwhile to follow control after day 8. 

The rapid evolution from something seemingly hopeless to something potentially cold.

Edited January 18 by AO-

[northwestsnow]

What an absolutely fabulous read this morning...

I'm not posting much, I'd only moan and with age I've realised thats  just an annoyance to others when all said and done !!

A truly old school freezing week up here ,temps haven't really got much above freezing since Sunday night and still snow cover  ,one last cold shot in Feb would be grand ...

 

Edited January 18 by northwestsnow

[sebastiaan1973]

12 minutes ago, AO- said:

It is also worthwhile to follow control after day 8. 

There are some beauties in the GFS ENS.

[Duane S.]

Whether people like it or not, the next chase has been signed off, and is about to get underway. Feb ought to produce another cold spell.

When/where/for how long (and of course, still 'if') TBD

P1 definately over progressive on bringing in the cold I'd say (we will probably need that secondary bout of WAA) but it is fine margins, the tipping point to early cold is definately clear and present. Some other great members are emerging and several other members that just missed this evolution.

 

[bluearmy]

13 minutes ago, Severe Siberian icy blast said:

Again im catching up now, so what gets me with the warming that's undergoing this week why are people so quick to write the next wk or two off when a fast response may happen and change the entire game 

You’d expect any response likely within the next two weeks to now be picked up by the models (especially eps ) as the warmings of the past three weeks are pretty much done 

nothing solid showing yet although the scandi ridge solution is the most common departure from the norm that we are seeing play out 

@jules216 - I think you’re in a decent  location for weeks 2 and 3. Either a cold trough or a good chance of a hit from a deep cold pool