Cold Winter Night

I'm not saying I'm right either , but what I'm talking about is developing better after 240h, and it's also better visible on NH charts. Here's the 336h NH views, and it's not immediately boom charts, but we've got to start somewhere....

Well, you can't ignore the considerable and slowly growing number of members in GEFS that are not successful anymore in flattening the Atlantic ridge, even develop Scandi Highs or that inject low heights into Europe, where they remain. This morning's EPS had support for those scenarios too, so let's see what it comes up with tonight.

It's encouraging at this moment that the initial developments over N-America and the Atlantic (amplification, height rises to the North) are happening well within the 10 day period. They are actually getting closer, instead of remaining distant promises in the extended. And there is decent enough agreement between models (and ensembles). ECM, GFS and GEM at 240h:

After I wrote this in the afternoon, it's nice to see variations of the same theme from the ensemble reflected in the later frames of the GFS and ECM Operationals. GFS is slower, with the "East Atlantic" ridge over Scandinavia: ECM sets it up sooner, with the ridge much further West over Iceland: But the direction of a Ridge-Trough pattern over Canada, with the next ridge in the East Atlantic sector is the same. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4979638

After I wrote this in the afternoon, it's nice to see variations of the same theme from the ensemble reflected in the later frames of the GFS and ECM Operationals. GFS is slower, with the "East Atlantic" ridge over Scandinavia: ECM sets it up sooner, with the ridge much further West over Iceland: But the direction of a Ridge-Trough pattern over Canada, with the next ridge in the East Atlantic sector is the same.

I would agree with that. There is MJO influence at our latitudes, but its effect is far from straightforward (which is also reflected in the article I referred to in my post above). Consider it as distributing some of the weight on probabilities. It's still very much possible that "good" MJO-ENSO-QBO combinations can fail to deliver "good" results for us, and vice versa, those good results cannot be ruled out definitively with a poor background, with the history books as witnesses. It's interesting, but IMO sometimes the tropical processes are given a bit too much emphasis, ignoring all the extratropical, local and regional, processes that also influence what is going on at our latitudes. It's definitely a subject that still needs a lot of research.

Keep in mind that the MJO as a described phenomenon dates from the 70's. In terms of historic MJO activity since 1979, NOAA-PSL has this: https://psl.noaa.gov/mjo/mjoindex/ The data are there, but working with that requires a bit of homework, I suppose. You'd have to make your own RMM graphs. And on links between MJO phases and European weather regimes, there's this Lee et al. article from 2020: The links between the Madden-Julian Oscillation and European weather regimes LINK.SPRINGER.COM Skillful weather forecasting on sub-seasonal timescales is important to enable users to make cost-effective decisions. Forecast skill can be expected to be mediated by the prediction of atmospheric flow patterns...

The output for Christmas remains interesting. It’s precisely around Christmas Eve and Christmas that the ensembles show a bifurcation: milder or colder. Visible on the latest GEFS 6z (London): And also visible on EPS 0z: The problem with the colder options could be a lack of precipitation. After Christmas, the extended ensemble output is now more convincingly pointing at the combination of a Pacific Coast Ridge-Labrador Trough-East Atlantic Ridge pattern I mentioned in earlier posts. This pattern is now well reflected in the extended clusters: The panel at 336h shows many variations on this same theme, some very clean and promising, like p32: Some are messier, some very unfortunate, for example these two: It’s a setup that initially always brings milder SW-lies to our shores, that’s why the interest is visible on NH charts and not yet on temperature graphs. However, it’s also one that takes just a nudge of amplification to develop into the output most of us would like to see, with the risk that this amplification never comes. Oh well, we'll see. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4979230

The output for Christmas remains interesting. It’s precisely around Christmas Eve and Christmas that the ensembles show a bifurcation: milder or colder. Visible on the latest GEFS 6z (London): And also visible on EPS 0z: The problem with the colder options could be a lack of precipitation. After Christmas, the extended ensemble output is now more convincingly pointing at the combination of a Pacific Coast Ridge-Labrador Trough-East Atlantic Ridge pattern I mentioned in earlier posts. This pattern is now well reflected in the extended clusters: The panel at 336h shows many variations on this same theme, some very clean and promising, like p32: Some are messier, some very unfortunate, for example these two: It’s a setup that initially always brings milder SW-lies to our shores, that’s why the interest is visible on NH charts and not yet on temperature graphs. However, it’s also one that takes just a nudge of amplification to develop into the output most of us would like to see, with the risk that this amplification never comes. Oh well, we'll see.

Beyond the mid term details, looking deep into the extended EPS at the panel of individual members, I still notice a tendency to move a segment of the tPV back West to the North American side, with ridging near the Pacific coast, and that trough over Eastern Canada, West of Greenland. In my opinion this is poorly reflected in the clusters that show a positive height anomaly in the latter area, but we must keep in mind that at this time of the year this is usually the deep purple home of the main tPV, so it doesn't take much to cause a positive height anomaly there, compared to long term averages. Anyway, this setup is now resulting (in the output) in a growing number of members that allow height rises in the Greenland-Scandinavia-British isles triangle. Some very tasty patterns are beginning to appear. Let me shamelessly pick these three cherries that previous ensembles didn't have at all: It's far into FI, and on the ground many don't bring cold to our shores yet (with some exceptions, see the back end of the De Bilt plume below), but the number of Northerlies/Easterlies is on the increase again, and taking the members at face value, more would follow later on. Good for longer cold patterns into the new year.

The EPS 0z today has only one cluster in the extended, the familiar “we-just-don’t-know-cluster,” but inspection of the whole panel of individual members reveals some interesting hints. After the initial move of the tPV East, nearly half of members indicate renewed ridging near the American Pacific coast/Rockies, generally pulling a trough away from the main vortex towards Canada, SW of Greenland. This American amplification in turn increases opportunities for ridging near the British isles. To pick one as an example, p5: Keep this in mind: In spite of the bad name they have, a solid tPV (or segment) West of Greenland and an Azores/Iberian High are actually essential starting points for serious cold spells (longer than 2 day affairs). If you don’t believe me, look up the most severe cold spells in NW-Europe, then check the NH setup 5, 10, 15 days before, and you’ll see what I mean. What it needs is amplification though, and that usually starts in the Pacific, so it’s good to see some hints of that deep in the fog of the extended. It could be something that disappears again, but worth to keep an eye on IMO. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4976326

The EPS 0z today has only one cluster in the extended, the familiar “we-just-don’t-know-cluster,” but inspection of the whole panel of individual members reveals some interesting hints. After the initial move of the tPV East, nearly half of members indicate renewed ridging near the American Pacific coast/Rockies, generally pulling a trough away from the main vortex towards Canada, SW of Greenland. This American amplification in turn increases opportunities for ridging near the British isles. To pick one as an example, p5: Keep this in mind: In spite of the bad name they have, a solid tPV (or segment) West of Greenland and an Azores/Iberian High are actually essential starting points for serious cold spells (longer than 2 day affairs). If you don’t believe me, look up the most severe cold spells in NW-Europe, then check the NH setup 5, 10, 15 days before, and you’ll see what I mean. What it needs is amplification though, and that usually starts in the Pacific, so it’s good to see some hints of that deep in the fog of the extended. It could be something that disappears again, but worth to keep an eye on IMO.

Was about to say the same thing. ECM is potentially better for longevity than GFS. Perhaps it would fail, perhaps it could just about make it, with a decent angle and the trough descended deep into Europe.

ECM definitely moved toward the GFS solution, but there may be difficult times ahead for outdoor Christmas trees... At 216h it has lower heights over Europe than GFS. Now what will happen near Greenland?

It's a pity that UKMO ends at 168h. With a better NW-SE alignment than GFS at that time and heights already lower over NW Europe, the next push on the trough might very well dive further South towards Italy than GFS does, developing faster. Interesting runs from multiple models.

And they're reasonably similar too, considering the FI time range. Strange, but welcome, just as the mood in here was about to hit rock bottom.

GFS 12z Op seems to go nicely along with GEFS/EPS anomalies in the days leading up to Christmas, posted earlier this afternoon. Excellent run in deep FI.

EC 240h, with that TPV lobe moving over towards Scandinavia/Russia and the Arctic High getting closer to Greenland, there is definitely room for the High to expand Northward. That's what GFS did after 240h, and EC is better, with more heights near Iceland and lower heights over Scandinavia and Western Russia.

It has to be said, a few juicy outliers aside, the De Bilt plume is a firm downgrade for wintry cold compared to this morning and yesterday, from mid-term to the end. Slowly moving to average December temperatures. But with -3C on the thermometer and ice forming on the garden pond, I can live with that for now.

Mildies better enjoy that "mild" weather next week while it lasts...

That's because, since the ensemble update earlier this year, they are the same. Only some minor differences because of built-in chaos in the model and minor technical differences between the Operational run and the Ensemble. But resolution and starting data are identical nowadays. So that means that essentially the control shows where the operational would have gone post 240h.

Like I said I suspected, the EC control will be quite a sight to behold . It slides us into deep winter. Later on it's alone in its severity though. 12z EPS De Bilt plume: But the ensemble is definitely colder as a whole Day 10-15.

That huge High that ECM had just North of Kazakhstan on the 0z and previous runs, has shifted some 2000 km West. A good illustration of the difference that makes for us, because instead of a being a wall keeping Siberian cold out of Europe, it becomes a conveyor belt rapidly transporting that cold West. At 240h the very deep cold has made it to eastern Poland already. The control run will be interesting viewing, I think after 240h it could very well be a boom run.

There we go again... GFS 300h,m but still, it's hinting at Scandi + Atlantic ridge support later on.

Here's a list that includes Canadian Warmings (CW) From here: https://www.atmosp.physics.utoronto.ca/SPARC/News15/15_Labitzke.html And then there's the original source of the whole idea of Canadian Warmings, the 1977 Labitzke article "Interannual Variability of the Winter Stratosphere in the Northern Hemisphere." That one does not have a list, nor mentions 1962, but it does describe the nature of the phenomenon an the distinction between it and major and minor warmings. Interannual Variability of the Winter Stratosphere in the Northern Hemisphere JOURNALS.AMETSOC.ORG Abstract The interannual variability of the stratosphere in the northern winter is discussed, mainly on the basis of zonal harmonic wave analyses of the daily height and temperature fields in the middle stratosphere. Comparing...