Cold Winter Night

GFS, GEM and UKMO at 144h This afternoon I see a tendency to speed up the retrogression signal, with the initial High stronger and rotating that deep cold trough more rapidly towards the SW.

Close your eyes if you don't like Scandi blocking into February: Very nice EC46 on top of the already great output tonight.

Amazing to see a Day 10 mean that is nearly identical to the Operational run in the East Atlantic/European sector, in the middle of a pattern change towards a very rare setup. That only happens with strong agreement between ensemble members.

The biggest issue with GFS might be copyright issues ... with 1962/1963 Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4993598

Well, of course it's tongue in cheek to make the 1963 comparison, as we are all aware that the GFS fun and games are deep FI for now. For serious forecasts it is indeed wise to stick to charts within 120h. However, with the background signals as they right now, and with what we've seen in many ensembles over the past week, this extended GFS scenario is at least more likely, better supported than the one you showed for mid December, which was an extreme outlier in its ensemble that went against the expectation of a more mobile pattern setting up mid December.

The biggest issue with GFS might be copyright issues ... with 1962/1963

A step back in time compared to the GFS FI output, but UKMO at 168h is excellent going forward too. Not as messy as GFS was at that stage.

GFS 240h That deep cold over N-Scandinavia heading SW and the pool is growing. What a run, very clean.

Yes, it could. More CAA Southeast of the High would strengthen the High and prevent it from sinking too far into Europe initially. And lower heights and cold air farther (South)West over Europe isn't bad anyway. I don't see why any coldie would wish away short term upgrades on an Easterly at this point.

This shows that there is agreement on location and strenth of the initial High. The experience on the ground, at that time, depends on the shape of the High and the surface flow direction associated with it. That will probably keep changing over the next few days. However, a High like this would be the main course in most winters, but this time it's beginning to look like it will only be an appetiser!

No. Examples of impressive longer cold periods without a preceding SSW would be: 1963 (about 2/3 of the cold was before the late January SSW could have an impact). 1979 (SSW when winter was essentially over) 1986 (no SSW) 1987 (also about 2/3 of cold before SSW impact) 1996 (no SSW. And I will never forget the smoothest black ice I ever skated on that winter) 1997 (no SSW) 2009-2010 (most cold before SSW)

Not suggesting anything, but ECM 240h vs January 20, 1947:

GFS, GEM and UKMO side by side at 168h. UKMO easily the best, with lower heights already over Europe, a nicer angle of the Southerly tracking jet and a nicer angle for WAA SW of Greenland, and more amplification in the North Atlantic and near Greenland. Considering the true onset of amplification that GFS and GEM show following this, UKMO would probably be even better later on. In my opinion it is a really great chart.

Indeed. GFS is entering into classic cold spell territory here, with a Scandi High, Genoa Low combination - in January - It would only get colder from that point on.

About that SSW that "disappeared"/"dropped"/"was taken from us," Here's EC46 mean zonal wind at 10 hPa from one week ago, December 21: Slowest ensemble mean: +/- 5 m/s, about January 6. - Around January 3, all members are below 30m/s, the strongest reversal outliers hit -30 m/s. - Late January, the ensemble mean returns to about 15 m/s. Now the latest one, from yesterday: Slowest ensemble mean: +/- 5 m/s, about January 6. Yes, that's the same values as a week ago. What has changed is the spread that has reduced (logically at that closer date). - Around January 4, all members below 15 m/s, the strongest reversal outliers hit -25 m/s. - Again, late January, the ensemble mean returns to about 15 m/s. The output from December 20, 22, 23 and 24 is very much along the same lines. Then how about the impression that "the SSW" is now gone? Well, that's especially the 26th, the only day EC46 showed a reversal on the ensemble mean. In other words, EC46 has consistently not showed a mean reversal for more than a week, with one exception. The one off that should be rejected for that reason. Not much has changed with regards to a potential SSW. And that's ignoring the fact that a considerable number of members still go on to reverse at some point in January, and also ignoring the fact that an SSW does not equal a cold spell, nor that the absence of a SSW does not equal the impossibility of a cold spell. The current blocking signal in the extended is a trop led feature, let's watch that, and keep in mind that the stratospheric slowdown can still very much have its effect lower down. No need for nervous breakdowns at this point. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4986055

About that SSW that "disappeared"/"dropped"/"was taken from us," Here's EC46 mean zonal wind at 10 hPa from one week ago, December 21: Slowest ensemble mean: +/- 5 m/s, about January 6. - Around January 3, all members are below 30m/s, the strongest reversal outliers hit -30 m/s. - Late January, the ensemble mean returns to about 15 m/s. Now the latest one, from yesterday: Slowest ensemble mean: +/- 5 m/s, about January 6. Yes, that's the same values as a week ago. What has changed is the spread that has reduced (logically at that closer date). - Around January 4, all members below 15 m/s, the strongest reversal outliers hit -25 m/s. - Again, late January, the ensemble mean returns to about 15 m/s. The output from December 20, 22, 23 and 24 is very much along the same lines. Then how about the impression that "the SSW" is now gone? Well, that's especially the 26th, the only day EC46 showed a reversal on the ensemble mean. In other words, EC46 has consistently not showed a mean reversal for more than a week, with one exception. The one off that should be rejected for that reason. Not much has changed with regards to a potential SSW. And that's ignoring the fact that a considerable number of members still go on to reverse at some point in January, and also ignoring the fact that an SSW does not equal a cold spell, nor that the absence of a SSW does not equal the impossibility of a cold spell. The current blocking signal in the extended is a trop led feature, let's watch that, and keep in mind that the stratospheric slowdown can still very much have its effect lower down. No need for nervous breakdowns at this point.

Are you looking at output from December 2014 or something? Because the current model output doesn't show what you are describing at all. EPS days 8-15: No zonal pattern. Lots of amplification North and Northwest. The same, in panel view in the extended (336h): Certainly no "conveyor belt of zonality" in sight here. None of these show "classic" zonality, with a Northerly tracking jet; even the very few zonal members have a more Southerly track of the jet than normal for this time of the year. And "few"is the right word, as they are outnumbered by Omega blocks(!), well, usually you don't see many of those in the output. Same general story on the GEFS, although I would rate the EPS higher than GEFS. As long as the onset of potential cold is still in the extended, you will always see some milder/worse/disappointing members in the set, but the general trend is downward, and that has been going on for many days now.

EPS clusters: 120h-168h the clusters are not far apart. 192h-240h there is only one cluster, in line with ECM Operational. I think the Op is overall a good representative of the ensemble. In the extended we see the Northern blocking truly develop. Clusters 1, 3 and 4 have low heights over Europe and/or Iberia. The De Bilt plume shows the ECM as middle of the pack for 2m temps, not much spread; the extended is where interest lies.

ECM is fine IMO. Heights between Iceland and Scandinavia are steadily rising from 168h to 240h, there are low heights near Italy and a cold trough over Eastern Europe. I think that after 240h, it goes on to build a Scandi High. My guess would be an initial arrival of cold (not yet deep cold) between January 6 and 10. Some routes would be faster, others slower.

UKMO +144h slides Lows deep into Eastern Europe under a fledgling Scandi High. Interesting developments, with cold air not far away over Scandinavia and the Baltic.

Not necessarily. Averaged over multiple forecasts, higher resolution models do come out on top, but that doesn’t mean higher resolution is better on individual runs, or in specific situations. The risk with higher resolution is that there is also more opportunity for making mistakes, going off in the wrong direction, and amplifying such errors. Especially in rapid, major pattern change situations the more conservative, lower resolution models may well prove their value, so be careful not to dismiss them too easily. I’m not at all saying lower resolution is better this time though, but at this point it’s hard (or impossible) to tell which approach will handle the current changes better. Let’s await today’s EC46. “More runs needed,” is as true now as before.

EC46 has the same number of vertical levels (137) as the 15-day ensemble and Operational. The spatial resolution (longitude-latitude) of EC46 is 36 km vs 9 km for the 15-day ensemble EPS. However, above the tropopause, in the more stable stratosphere, far from topographic/orographic shenanigans lower down, for the bigger picture in 2-4 weeks for which the EC46 is designed, it is doubtful if the higher spatial resolution adds much extra (it could theoretically even insert greater error). EC46 on the other hand has the bigger ensemble with 101 vs 51 members. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4985059

EC46 has the same number of vertical levels (137) as the 15-day ensemble and Operational. The spatial resolution (longitude-latitude) of EC46 is 36 km vs 9 km for the 15-day ensemble EPS. However, above the tropopause, in the more stable stratosphere, far from topographic/orographic shenanigans lower down, for the bigger picture in 2-4 weeks for which the EC46 is designed, it is doubtful if the higher spatial resolution adds much extra (it could theoretically even insert greater error). EC46 on the other hand has the bigger ensemble with 101 vs 51 members.

The 12z EPS offered the best extended panel in a long time. Also reflected by the jump in the number of (North)Easterlies in De Bilt. Slowly growing confidence that we may see at least something that feels more like winter.

The difference with 24 hours ago is remarkable, reversal has much more support now: