Cold Winter Night

Well, we all know GFS 6z is never wrong at Day 10, right? Although GFS takes it to the extreme, it does have support from GEFS, and, contrary to what some are saying, from the EPS as well, including the EPS Control. EPS Clusters 2, 4 and 6 go along with the Scandi/Iceland amplification that GFS has shown for a number of runs in a now. Those clusters represent almost half the EPS. To illustrate this, compared to the GFS 6z above, these two EPS members are not far off height-wise in the NE Atlantic. However, the De Bilt plume does not show much in the way of cold on the surface yet, but continues with average temperatures, in contrast to this mild week. There is also that little fella dropping below -15c at 2m, stretching the y-axis. If anyone is still wondering what is meant with the word 'outlier,' well, here you go!

EPS ensemble does not support the EC HRES Operational. The EPS 0z was colder than before, with the Op as a mild outlier, now the 12z is maybe slightly less cold, but certainly not mild, with the Op once more as an outlier. London: De Bilt: Considering the GFS and GEFS trending notably colder, joined by an EPS that at that lead time should be leading the High resolution run, I’d cautiously lean towards the colder solutions.

Just a little more latitude at 264h and you have a powerful Easterly at 264h... ...that would have been followed by the Atlantic sliding under: Close to greatness. But still no sigar. To have the Scandi height rises popping up after Christmas keeps the hope alive.

Some very strange posts this morning. The outlook has improved IMO. Perhaps not for a White Christmas, which I would love to have too, but let's be realistic, maybe expecting a certain rare weather type (snow) to occur at a very precise location (your residence) in a very narrow and precise time window (24/25 December) is setting yourself up for failure. Yet, still, the further North in the UK you go, the higher the chance that this event really might occur this year, more than can be said about many a Christmas. After Christmas, the latest ensembles have been trending colder. Both EPS and GEFS. Good signs. Some are talking about the Euro heights as if they have been there forever, the opposite is true, they are just building today, and 40% of the EPS remove those Euro heights again before Day 10 on the 0z EPS. In the extended, blocking patterns are still very much prevalent. The Dutch De Bilt plume is notably colder after Christmas than it was for yesterday's 12z. Let's say I've seen worse plumes in December. The knee jerking in here is more based on emotion than on actual model output, and tbh a bit weird after an already cold first 2,5 weeks of winter, with snow and frost and ice for many. Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4772762

Some very strange posts this morning. The outlook has improved IMO. Perhaps not for a White Christmas, which I would love to have too, but let's be realistic, maybe expecting a certain rare weather type (snow) to occur at a very precise location (your residence) in a very narrow and precise time window (24/25 December) is setting yourself up for failure. Yet, still, the further North in the UK you go, the higher the chance that this event really might occur this year, more than can be said about many a Christmas. After Christmas, the latest ensembles have been trending colder. Both EPS and GEFS. Good signs. Some are talking about the Euro heights as if they have been there forever, the opposite is true, they are just building today, and 40% of the EPS remove those Euro heights again before Day 10 on the 0z EPS. In the extended, blocking patterns are still very much prevalent. The Dutch De Bilt plume is notably colder after Christmas than it was for yesterday's 12z. Let's say I've seen worse plumes in December. The knee jerking in here is more based on emotion than on actual model output, and tbh a bit weird after an already cold first 2,5 weeks of winter, with snow and frost and ice for many.

Usually in this time of the year the Tropospheric Polar Vortex (TPV) has no problems gaining speed and firing endless trains of depressions across the Atlantic, but indeed it has been very quiet on that front. If that remains so, that increases opportunities for Atlantic ridges and Greenland Highs to form and bring cold Northerlies or Northeasterlies to us. However, if such a High is placed too far Northwest, as it seems to happen next week (hence all the nervous posts in here), there could still be a Westerly flow in our area Southeast of that High. Another thing is a High over Scandinavia/Norwegian Sea/Iceland. Such a High actually fares well with a firm TPV over NE-Canada/West Greenland, because that would draw up warm air (Warm Air Advection, WAA) 'feeding' the High. So, the absence of a strong Atlantic does not necessarily equal cold weather, but it certainly keeps the hope alive for model watchers!

Already there. 38 out of 51 members build NE heights towards 360h, in very different scenarios. I can see the Thursday EC46 chart for that week verifying with these clusters. The big question will be: Will it end up with proper placement/alignment to bring us cold? We could use an old fashioned Scandi High, like the one you derived your name from!

?? Sorry Feb, but this is a bit silly. It's Friday morning. How on earth can you assume that the EPS for Day 14 (the starting point of EC46) on Monday will be much worse than Thursday's? That starting point isn't even in range yet. The extended clusters today are not all mouthwatering, but there's certainly very decent potential in them. And there is no obvious trend at that range. For all we know the extended EPS improves significantly, with 6 ensembles yet to go before that Monday EC46 takes off.

Big jump in the EPS ensemble. The ensemble mean is quite bit warmer than previous runs (0z/12z yesterday, 0z this morning), making the ensemble output questionable for the moment, so best to reserve judgment. Tomorrow's runs should give more clarity.

Compared to the 0z EPS, the Ec Operational run would have fit cluster 3 in the 120-168h range, followed by cluster 1 from 192h-240h, both with good support. Nothing new in this run therefore. The ensemble spread this morning was not as big as the past few days anymore anyway, and this afternoon the move away from cold options before Christmas is being confirmed. With cold I would mean sub zero mid day and/or serious snow chances. Next week it might still be seasonal, average or slightly colder than average though. Awaiting the 12z EPS, but IMO Christmas Eve to New Years Eve is our next chance of real cold.

GFS in FI is not that terrible. TPV apparently has no interest to set up shop in its old familiar home. Return of Atlantic ridging imminent at 264h?

Now that's a Christmas run! Removing all those Euro heights. Excellent for long term cold.

Compared to yesterday, the spread on the EPS 0z De Bilt plume has reduced quite a bit out to Christmas, with a colder mean. The good thing: It did so by removing the really mild members. The mild, above average period is now forecasted to last 3 days in Holland, Monday/Tuesday/Wednesday, followed by a return to temperatures that are average for late December, until and including Christmas. You folks in SE England will probably be in a slightly better position, and the situation will only get better (colder) the further North you go in the UK. In the extended period, the spread is still large, but with some really cold members appearing. A signal I hope will strengthen over the next runs/days. Caution is necessary as always, because the mean is still near average, mild options are also very much present. Extended clusters are more reluctant to let go of the Euro heights, but Northeastern height rises are still the theme.

1070 at the surface, and 500hPa at 576-580 dam! A beast it is. That Arctic High is also pretty much the only Day 10 thing that survived the past 24hrs comparing EC 12z yesterday 240h and today 216h!

The actual trajectory and source of packets of air is often quite different from what you would think just looking at the charts. Since you mentioned the source of 850's not being from North Africa, I ran it through the HYSPLIT trajectory calculator. Turns out that modelled GFS 6z T850 air (+/- 1500 m) is West of California at T+0h, then crosses the USA, the Atlantic and Spain, to arrive in Central Europe by December 21st! Air Resources Laboratory - HYSPLIT - Hybrid Single Particle Lagrangian Integrated Trajectory model WWW.READY.NOAA.GOV

For the bigger picture, I'd place FI at 96h right now, with models diverging on the Greenland/Arctic High evolution after that. On the ground, FI is probably a bit further out, as those changes do not influence us straight away. So, to take EC as the example, at 96h we still have a Greenland High at that time, we're still in colder conditions, but the GH influence is waning and the Atlantic Low is pushing in. That attack will very likely succeed, and the Low will sweep up milder air and precipitation, which will make Monday/Tuesday mild and probably rainy in at least SE England (and Holland). The De Bilt EPS 0z plume has little uncertainty up to and including Tuesday the 20th. HRES Operational, Control and ensemble mean are on the same page with above average temperatures to start off next week. Wednesday is when the ensemble begins to diverge. Increased spread, Control and Op are not in the same cluster anymore. So we'll have to go by the ensemble mean, which shows a gradual return to average December Temps. Christmas is still far out, but for now seems to be around average here. In the extended, the clusters reveal a range of options, a gradual increase of heights to our Northeast seems apparent, and Euro heights seem to slowly shift Eastward. There's still a lot of water to go under the bridge to make a definite call about Christmas, let alone after that. We may have to wait a bit for a return of more favourable cold conditions, but that happens in even the most severe of winters, so it's no reason for despair. We are already in a cold episode now, and we've practiced waiting for years, so we'll be fine. For those wanting to learn, I highly recommend going the archives, look up your favourite cold spells, or the coldest months/winters we've had in the past 180 years and see how those evolved. WWW.METEOCIEL.FR Archives NOAA NCEP de 1836 à maintenant You'd be surprised to see how many times there were Azores Highs, Euro Highs, mild SW days and Greenland Highs moving West in those severe winters. What divides cold winters and mild winters is how long less favourable patterns stick around. A Bartlett High (ugh, just typing it hurts...) is defined as a persistent, reloading pattern of High pressure to the SW, S and SE. Cold winters often have heights there too, but they don't linger. What this winter will bring is still shrouded in mystery, but for now, those mild patterns don't seem to settle yet. Fingers crossed. Original post: https://community.netweather.tv/topic/98087-model-output-discussion-the-cold-has-arrived/?do=findComment&comment=4767603

For the bigger picture, I'd place FI at 96h right now, with models diverging on the Greenland/Arctic High evolution after that. On the ground, FI is probably a bit further out, as those changes do not influence us straight away. So, to take EC as the example, at 96h we still have a Greenland High at that time, we're still in colder conditions, but the GH influence is waning and the Atlantic Low is pushing in. That attack will very likely succeed, and the Low will sweep up milder air and precipitation, which will make Monday/Tuesday mild and probably rainy in at least SE England (and Holland). The De Bilt EPS 0z plume has little uncertainty up to and including Tuesday the 20th. HRES Operational, Control and ensemble mean are on the same page with above average temperatures to start off next week. Wednesday is when the ensemble begins to diverge. Increased spread, Control and Op are not in the same cluster anymore. So we'll have to go by the ensemble mean, which shows a gradual return to average December Temps. Christmas is still far out, but for now seems to be around average here. In the extended, the clusters reveal a range of options, a gradual increase of heights to our Northeast seems apparent, and Euro heights seem to slowly shift Eastward. There's still a lot of water to go under the bridge to make a definite call about Christmas, let alone after that. We may have to wait a bit for a return of more favourable cold conditions, but that happens in even the most severe of winters, so it's no reason for despair. We are already in a cold episode now, and we've practiced waiting for years, so we'll be fine. For those wanting to learn, I highly recommend going the archives, look up your favourite cold spells, or the coldest months/winters we've had in the past 180 years and see how those evolved. WWW.METEOCIEL.FR Archives NOAA NCEP de 1836 à maintenant You'd be surprised to see how many times there were Azores Highs, Euro Highs, mild SW days and Greenland Highs moving West in those severe winters. What divides cold winters and mild winters is how long less favourable patterns stick around. A Bartlett High (ugh, just typing it hurts...) is defined as a persistent, reloading pattern of High pressure to the SW, S and SE. Cold winters often have heights there too, but they don't linger. What this winter will bring is still shrouded in mystery, but for now, those mild patterns don't seem to settle yet. Fingers crossed.

It shows the progression 192-216-240h of three members of the ensemble that the computer considers representative for three separate clusters of solutions. Sometimes the other members in a cluster are actually better than the one shown, though. In this case two of them seem poor, cluster 3 could be worse. Considering the De Bilt box plot I posted earlier, the ensemble is generally milder on the ground up to day 10, especially the further South and East you go, with indeed Euro heights fading again in the extended. Well, there have been times when we were stuck with them for many a month. Glas half full!

EPS clusters show that the Euro high anomaly is as good as unavoidable. 192-240h all clusters have that, with resulting Westerly flow, despite massive HLB over the North Pole. After that, 264-360h, we see blocking return in more favourable locations, mainly Northeast, or Northwest. Euro high anomalies are fading again, which has to be good news. So, based on this EPS, a return to colder conditions around, or just after Christmas is more likely than before. We remain very much in the game though, no tendecy to install the TPV near Greenland/Iceland.

EPS 2m box-and-whiskers for De Bilt show milder than 0z middle next week, slightly colder at the very end of the 15 day extended. Not (yet?) the EPS shift we hoped for. A warm-up before Christmas is a classic though, a singularity which in Germany they call "Weihnachtstauwetter" (Christmas thaw weather). And then going cold towards the New Year? Well, that would be classic too.

We're on a complicated, risky path with ravines on all sides. We should not be surprised to have some operational runs fall off, especially at their unreliable later lead times, but tbh I'm more interested in the EPS output tonight. Does the European model introduce colder clusters like several recent Ops and GEFS have done?

EC around 144h-192h seems closer to GEM than to UKMO tonight, and even more progressive.

We have often seen a Battle of the Models, where EC and UKMO take on GFS and GEM, or something like that, but it seems to become a Battle of Operationals vs Ensembles at the moment. This morning's runs have been very promising, rapidly moving towards an amplified setup and cold returning to NW Europe. But the ensembles, particularly the EPS is indeed still reluctant to go along in the festive mood. The De Bilt 2m plume is (beyond the weekend) not particularly inspiring for coldies. First a big jump to above average after the weekend, then a return to 'just average.' The cold whoppers are lacking completely ATM. In the past we've seen (in)famous swings in the ensemble though. There have been many updates since, but they haven't truly been put to the test by the real atmosphere for many years. Could we see a swing like that again? This makes for highly interesting model watching this afternoon and the next few days. I almost can't remember it being this exciting, I'd have to go back to January 2012, Nov/Dec 2010.

So of the models going beyond a week, GFS, GEM and EC all come up with different solutions, but they also agree on two things in FI territory: Scandi height rises and an Arctic High (always a wildcard). We could be in a worse position, methinks.

GFS in FI just refuses to really let go of heights building somewhere North. This, in my opinion, is encouraging. The Atlantic remains weak and opportunities for Greenland and Scandi Highs keep coming back. I am also of the opinion that having some of the TPV back in the Western Hemisphere would be a good thing, if you wish for a 1947/1963 style winter. As long as it stays far enough West, it is a necessary component to build a really strong High.