Cold Winter Night

It's funny how much talk there has been about a back loaded winter, seasonal models and EC46 showing a blocked February, and lo and behold, the first day February appears in the FI charts, it features a monster Scandi High Now let's get it to 0h, without tripping over all the hurdles in between...

"Look for Scandi blocking in February." GFS: "Like this?"

That discrepancy between the extended ensemble and the expectation based upon a retention and renewed increase in AAM is basically what I was wondering about in my response to Tamara's post in the afternoon. Have you read her input in this thread today? Very informative. This is what she responded: In fact, the "wedges" that we see appearing in GFS 18z are evidence of the resistance there might be in the atmosphere against the onset of a powerful Westerly flow. Models notoriously have trouble getting that right. The extended EPS tonight also contained a hint of amplification through Iberia and the UK towards Scandinavia again. So yes, ideally you would hope to see the eventual verifying outcome in the ensemble as early and as clearly as possible. If the ensembles were always wrong, they would indeed be pointless, but that is not usually the case. This however is a quite exceptional situation we appear to be in this phase of winter, so it's not strange to see the models struggle.

To me cluster 1 seems to be a slower version of clusters 2 and 3. In De Bilt it leads to milder temperatures in a Southwesterly, no doubt this would be similar in the UK. However, the building of blocking in Europe on the clusters at the last two days, January 25th and 26th, also lines up very well with the EC46 transition from that more mobile +NAO signature to a Scandi block at the end of the month, into February: IF that +NAO really comes at all, of course.

The models are really only tweaked when they get updates. The output itself doesn't get tweaked before we watch it. The output is then up for interpretation by meteorologists (professional and amateur alike, as in this thread), who are aware of the potential biases, weak points, errors and other shortcomings of each model. A real forecast as end product is always made based on all the model output information + forecaster knowledge and experience .

The ensembles are not produced by staff/people, they're "simply" model output. Some changes, originating in the Tropics or the stratosphere that are observed by people, that will very likely have a strong influence in the extra tropics (our latitude) later on, will not necessarily be handled correctly by the models, especially not at long lead times in the extended. So therefore, in some cases, people say it's not likely that the model output/ensembles will verify the way they look right now.

Thank you for your very insightful posts as always. I can imagine it must be refreshing for you for once not to be forced by the diagnostic to go against the cold preference in here... What I do wonder about is why apparently the NWP in the extended is so rudderless, as it seems to generally ignore that retention and renewed push of +AAM. With your explanation of the wind flow budget in mind I would expect a very large spread later on, but this morning's EPS had only a handful of members that retain heights in more Northerly latitudes, the ensemble even seems to converge on that +NAO outcome that is the polar opposite (quite literally) of a +AAM response. EPS even more so than GEFS, I must say. Considering all this, it seems like we might have to brace ourselves for some model output surprises over the coming week. A highly interesting battle between GSDM and NWP.

GEM has heights to our NW from start to finish and at 240h I think: "Please, can it run to 384h like GFS, just this once?" Cold over Europe, heights extending towards Scandinavia, Genoa Low in place.

Maybe, maybe not. Both teleconnections and NWP point towards a waning of heights in the North, and a somewhat less blocked period following the coming week. If this is to be followed by Scandinavian height rises end of the month/into February, then a sequence of amplification, with height rises starting near the Azores, moving through Iberia, over the UK towards Scandinavia is a logical path. Take these for example, Jan 1947, Dec 1962, Jan 1987: heights to the South, no HLB, flow from the West. Poor as standalone charts, but they're part of a sequence. (Disclaimer: No, I'm not promising 1947, 1963 or 1987 events at this point; illustration purposes only) However, if heights do manage to hold their ground in the mid term, a potential move to Scandi heights could develop in a completely different way.

Well, that's a lot of pages to plow through. Fascinating developments though, short-, mid- and long term, you don't see that very often! The GFS 6z was interesting IMO, it showed the pattern shift from Greenland heights to Scandi High that I find more plausible, because it happens the way it did many times in past cold spells. Lingering heights somewhere up North, until a new push from the Atlantic through the UK moves into Scandinavia. It would not surprise me if this run is pretty close to what will actually happen over the next two weeks.

That's not really true. For more than at least a week the EC46 ensemble mean attribution (bottom of the chart) for end of January - into February has consistently been Scandi blocking, so good signs from that corner.

GEM towards 240h is showing us the way to Scandinavia, it seems. Would be interesting if indeed we can retain heights to the Northwest until a more serious Scandi push sets in.

GFS and GEM at 180h quite similar with the rounded shape of the trough centred over Scandinavia. Both might get very interesting with the Lows coming from the Azores moving toward us, and toward the cold trough.

ICON is yet another illustration of how critical the interaction between Greenland High-Arctic High-Alaskan High is. We might remain in the dark about what will really happen there for quite a long time. The Arctic remains a problem area for the models after all, with only few observations and poor satellite coverage.

The most important thing about this EC 12z was to get it in line with the better amplified models up til 144h/168h. That is what has happened, so very good news. Watch 192h-240h of the Op for your entertainment only, but look for upgrades in that timeframe in the EPS ensemble means and clusters now.

Very good. Trough drops in further East (good for me), before the cold moves West. But this episode might leave a mark on ECM's Op reputation. It was not in shape when it should have peaked, like a world no. 1 who doesn't do well at the Olympics. I think GEM may have been most consistent so far?

A small downside of a higher resolution, compared to lower resolution is indeed that a higher resolution run can pick up an unimportant detail and make a big deal out of it than a lower resolution run that would miss the detail in the first place. It's not uncommon to see a couple of members in an ensemble go in wildly different directions, super mild or super cold, and sometimes the Operational is that member. (My undocumented speculation: I suppose in the EPS the probability for that would be close to 1 in 51. Maybe it's a bit better because of the unperturbed starting data, so let's say once a month the Op goes crazy). The upside on the other hand is that it can pick up details that do matter and rightfully make a big deal of it. This is exactly one of the reason there is an ensemble in the first place. One or two members may pick up the wrong detail and blow it up unnecessarily, 51 members won't (or rarely). This is also why it's best to follow an Op only to day 5 or 6, and to use the rest of it only for your entertainment. The ensemble mean and the clusters will be much more helpful after that. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4997751

A small downside of a higher resolution, compared to lower resolution is indeed that a higher resolution run can pick up an unimportant detail and make a big deal out of it than a lower resolution run that would miss the detail in the first place. It's not uncommon to see a couple of members in an ensemble go in wildly different directions, super mild or super cold, and sometimes the Operational is that member. (My undocumented speculation: I suppose in the EPS the probability for that would be close to 1 in 51. Maybe it's a bit better because of the unperturbed starting data, so let's say once a month the Op goes crazy). The upside on the other hand is that it can pick up details that do matter and rightfully make a big deal of it. This is exactly one of the reason there is an ensemble in the first place. One or two members may pick up the wrong detail and blow it up unnecessarily, 51 members won't (or rarely). This is also why it's best to follow an Op only to day 5 or 6, and to use the rest of it only for your entertainment. The ensemble mean and the clusters will be much more helpful after that.

This suggests we might go to Scandi blocking later on, without going through a dominant -NAO/Greenland High phase first.

You mean, because of the talk of the High moving "West"? Keep in mind that all of Greenland is not that far North. The Southern tip of Greenland is due West of the Shetlands, so the initial High that around 120-144h has its core in the Iceland-Faeroer-Shetlands area indeed moves West, not Northwest, to become a High with its core over South Greenland. This is true both for ECM 0z, and for GEM 12z, where even the final location at 240h is only slightly North of West compared to the location around 144h. Map projections can be tricky.

The increase in heights between Scandinavia and Nova Zembla could insert a whole new set of dynamics though. Exciting ones too, but this is only one run.

No complaints at all about GEM at 216h, back from its morning wobble And UKMO at 144h has that interesting extension of the High towards Svalbard, I wonder what it will do in that area at 168h.

I've added the boundary line between the end of the GFS/GEFS and EPS ensembles, and what follows on EC46. Over the next few days, watch for an increasing number of members in deepest FI that go from Greenland heights towards the development of a Scandi High.

No, it wasn't. These are yesterday's JMA runs for that same time: And two days ago: Not much different, is it? You'll still see a lot of variation on Op runs, but that's why after 120h or so, you should look at ensembles means and clusters, instead of operational output. Steadily all the elements many were excited about on Day 10+ charts over the past week have come closer. Initial amplification, instead of the zonal flow, was flagged post day 10 and is happening now. The establishment of a High near the UK, or just NW, is now at 48-72h. An Easterly flow, now at 72h-96h. The retrogression setting in is now expected 120h-168h. Little to be concerned about for now, IMO. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4995287

No, it wasn't. These are yesterday's JMA runs for that same time: And two days ago: Not much different, is it? You'll still see a lot of variation on Op runs, but that's why after 120h or so, you should look at ensembles means and clusters, instead of operational output. Steadily all the elements many were excited about on Day 10+ charts over the past week have come closer. Initial amplification, instead of the zonal flow, was flagged post day 10 and is happening now. The establishment of a High near the UK, or just NW, is now at 48-72h. An Easterly flow, now at 72h-96h. The retrogression setting in is now expected 120h-168h. Little to be concerned about for now, IMO.