sebastiaan1973

January 19

GEM same story as GFS. A anticyclone in the north west of continental Europe.

January 19

3 minutes ago, Nick F said:

None of the extended clusters showing Atlantic troughing / upper flow energy undercutting high pressure building north over Europe that would hold a Scandi high in place for a sustained enough period to bring cold air our way though, so the high would eventually collapse. My worry is the lack of low heights especially over Iberia from Atlantic troughing undercutting, as well as further east over the Mediterranean Basin from undercutting of cold air from the NE, will mean we end up with a large Scandi-Euro High of little benefit to coldies in the UK other than some surface cold perhaps.

But, we know these clusters can change, so more runs needed. But I'd feel much happier if we saw troughing extending from the Atlantic over Iberia rather than the semi-permanent Azores ridging there. Extremely dry across parts of southern and eastern Spain this winter so far, due to lack troughing extending from the Atlantic over Iberia with ridging dominating.

We can get away with cold air undercutting high pressure over Scandinavia from the NE into southern Europe to lower heights over the central Med to bring a brief cold easterly, but prefer of the Atlantic troughing undercuts too to make it more sustained.

It is clear from the Plume of the De Bilt that there is indeed no cold available.

January 19

38 minutes ago, AO- said:

The EC EPS of this morning compared to yesterday. Dry and sunny weather with probably the biggest chance of a block over our heads.

Yes, it does around day 10, later on the anticyclone moves to the west.

January 18

Windplume De Bilt this morning and evening. An significant increase memebers with easterly winds (control included). O= East. Controle = Control (blue line)

January 18

The direction of the WA is by EC the worse. (216h)

EC, GFS and GEM.

January 18

Very interesting, I share iot 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 N-A

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

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

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017833

January 18

12 minutes ago, AO- said:

It is also worthwhile to follow control after day 8.

There are some beauties in the GFS ENS.

January 18

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.

January 18

19 hours ago, Mattias said:

I actually do believe that the SSW might significantly influence the tropospheric circulation in the near future, but not in the way we usually expect. The rapid recovery of the vortex, the fast transition to NAO+, downward directed EP-flux, eastward phase tilt with height and the predicted vertical wave structure of the zonal wave number 1 component are all ingridients that together indicates that downward wave reflection from the stratosphere might be involved in the transition to NAO+ in the next couple of days. However, the time scales of downward reflection events are much shorter compared to the usual SSW-effects related to downward propagation of zonal mean zonal winds. Thus, I agree that there should be good possibilities for another regime shift in the end of January or more likely in February, related to MJO and AAM forcings.

Intresting.

This is the article Simon Lee writes about. If we have a reflective type of SSW (Judah Cohen states the same), this leads to a Pacific blocking and westerlies over the N-A

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

January 18

3 minutes ago, Mike Poole said:

Good post, the question mark for me is the highlighted bit. The ECM 46 dayer is consistently modelling the MJO to nosedive into the COD the moment it gets to phase 7. Should this happen, my concern is that any high latitude blocking available will get watered down from current expectations and it doesn’t take much of that for the UK to register a miss!

The same model has indeed watered down the signal for high latitude blocking, which probably supersedes the seasonal model updates of 1st Jan which were much more bullish, because a lot had happened since 1st Jan including in the strat, of course. I think the modelling still needs to move quite a bit to support the idea of a cold February, we will see…

How reliable is EC46 with MJO?

5 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.

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...

January 16

Just now, Scott Ingham said:

Yea typo sorry! 2 weeks earlier!

This cold of 2018 was impressive. Still at the fourth of march I was able to skate. The 28th of February had a record cold tmax. Which is in our warming world quite remarkable.

January 16

4 minutes ago, Scott Ingham said:

This is more than interesting! It’s starting to remind me of 2018. I’d take that 2 months earlier!

You mean 2 weeks?

January 16

I would say I see some similarities at these three. GFS, EC & 27th of January 1956.

January 16

4 minutes ago, Cold Winter Night said:

"Look for Scandi blocking in February."

GFS: "Like this?"

Who's quote is that?

January 16

45 minutes ago, Mike Poole said:

ECM clusters this morning show an increased signal towards something more blocked. T192-T240:

Cluster 4 shows a ridge into Scandi, hints of that on clusters 1 and 3 too at T240.

T264:

The signal is maintained on clusters 1,3 and 5, although nothing yet resembling a true Scandi high. In fact, cluster 5 shows retrogression to Greenland in the last frame - but it only has 3 members, still it is a start. Clusters 2 and 4 show any ridge at T264 flattened by the zonal train. The signal for improvement in far week 2 are getting stronger (from a low base) and it will be interesting to see how/if they develop.

I guess the support of a true Scandi high is quite low. Please see the windchart. NO/O/ZO = NE, E, SE are just a very little portion of the members.

January 13

1 minute ago, Mike Poole said:

ECM extended clusters this morning do not bode well, T264+:

Choice of zonal, zonal, zonal, zonal or zonal, take your pick!

The wind plume at De Bilt, gives the same grim picture. Z= south, NO= noordoost, ZO= zuidoost.

January 12

33 minutes ago, MJB said:

So close yet so far.......................a near miss. look at the purples across Belgium

I understand your feeling, living close to Amsterdam.

January 11

9 minutes ago, Tamara said:

Without going to into all the huge detail and nuances all over again (there isn't the time with other things to think about anyway) its worth reading exactly what is being suggested again. Not just by me but various others as well Bear in mind my own purpose is not to chase any particular weather type, but try to evaluate what is most likely to happen as to best of ability. And I do have a Portuguese head on at the same time.

The analysis also bridges heading towards and into February and does not rule out, as said earlier, milder incursions for NW Europe. However, in the round, the emphasis especially earlier and then again a little later is probability weighted for cold blocked conditions to be predominate. This too, discussed in detail how and why previously.

Also suggested was not to be reactive to each and every NWP suite and form instant conclusions - but evaluate them from day to day. One corner at a time.

A very nice evening to everyone

It is hard to say things in a way everybody understands and makes the right conclusions. Thanks for sharing your thoughts.

EC46 shows a return of a block at the northern part of the Atlantic Ocean.

January 10

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

January 10

A part of 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.

January 8

29 minutes ago, bluearmy said:

As I understand it (and @lorenzo is the go to person here in the strat), reversals in the upper strat generate several repeating waves over the following period up to a couple months. Because the current reversals are downwelling quickly, I would think it’s possible that the waves that follow will only repeat out to six weeks or so. Say two waves - three weeks from now and six weeks from now (that’s very approximate)

I'm not Lorenzo either, but I think you have to watch the work of Domeisen. In this chart you see the downwelling divided in 4 regimes. Right now we have blocking. This means there will be 2 significant downwellings after this one. This doesn't mean winter at the British Isles or at home in the Netherlands, but increased chance of negative AO.

Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002381

January 8

3 minutes ago, Scott Ingham said:

Very interesting many thanks Seb!

https://wcd.copernicus.org/preprints/wcd-2019-16/wcd-2019-16.pdf

Thank you and the others for sharing their knowledge.

January 8

1 hour ago, Met4Cast said:

In terms of where the polar boundary lies that is something that's going to shift north & south probably 100 times before we actually get to the period of interest, I wouldn't place too much focus on that.

Returning momentum in the form of the jet stream edging back northwards seems a certain bet, it will happen at some point as the MJO continues it's progression eastwards and on the back of the recent (but brief) AAM tendency dip. How this looks synoptically will depend on how much blocking we retain to the north. It could be that the jet doesn't quite get into the UK and instead we remain cold for far longer (the 00z and 06z GFS det runs played with this scenario) or it could be, like the GEM we see a widespread, high impact snow event (perhaps multiple) as lows push up into the cold air across the UK.

Current thinking is the 20th-25th for a potential Atlantic return (of sorts) and therefore increasing risk of high impact weather. Where? How? Who knows, that wont be resolved for a longgggg time.

In any case, we've already seen a return to +AAM tendency and frictional torque will soon return to +ve followed by another likely +EAMT event driving AAM tendency upwards, total GLAAM & GWO remain coupled with the El Nino base state. MJO progression likely through the Maritimes and back into phases 6 >7 around the end of January/beginning of February (MJO timing always difficult).

In essence, any waning of the block and Atlantic return will likely be temporary with renewed blocking likely into early February, perhaps Greenland/Scandinavia, more likely is we wont see the block to the north become completely eroded, cold air will never be far away.

Very, very positive moving forward away from the chopping and changing of NWP outputs and attempting to nail down precise details 10+ days away.

To me it seems, this in line with EC46 of this night.

January 8

29 minutes ago, bluearmy said:

As I understand it (and @lorenzo is the go to person here in the strat), reversals in the upper strat generate several repeating waves over the following period up to a couple months. Because the current reversals are downwelling quickly, I would think it’s possible that the waves that follow will only repeat out to six weeks or so. Say two waves - three weeks from now and six weeks from now (that’s very approximate)

I'm not Lorenzo either, but I think you have to watch the work of Domeisen. In this chart you see the downwelling divided in 4 regimes. Right now we have blocking. This means there will be 2 significant downwellings after this one. This doesn't mean winter at the British Isles or at home in the Netherlands, but increased chance of negative AO.

January 8

32 minutes ago, Mike Poole said:

UKMO excellent at T168:

Well, we all have our preferences. In my opinion the cold on the eastside of the anticlone will erode it. Probably the area of low pressure at Scandinavia will push southwest, making it harder (longer way) for cold air to reach NW-Europe.

Sign In

Forums

Blogs

Gallery

Events

Learn About Weather and Meteorology

Community guides

Posts posted by sebastiaan1973