Cold Winter Night

I would go as far as saying that some form of a Greenland High or pronounced Atlantic Ridge is already near certain. It is hard to argue against that from current output. For now, looking at the EPS 0z, the regime chart shows a move through BLO+ (the Scandi High) towards –NAO (Greenland height rises). On the Z500 diagram for Western Iceland, there clearly is ensemble agreement on height rises in that area until Day 8, up to a mean of about 563 dam on March 2. However, there is also a marked drop in heights over Iceland right after those height rises, supporting the idea that the High might quickly move too far West for us to profit. We all know a Greenland High/Atlantic Ridge is not at all guaranteed to bring cold and snow. It will be a while before we know the exact placement, alignment and duration of the High, let alone the temperatures and precipitation types that will be the result. Almost a week of impatient waiting is ahead of us until we get some clarity about the early March events, although short term upgrades on the budding Scandi High are still very well possible too. The ensemble has been tiptoeing towards a slightly colder Easterly influence to end February. Expectations are high in here anyway, so I think “March 2023” /”The 2023 SSW” will be remembered and referred to in future winters one way or another, either as an infamous failure or as an example of what an SSW can do to a winter. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4809447

I would go as far as saying that some form of a Greenland High or pronounced Atlantic Ridge is already near certain. It is hard to argue against that from current output. For now, looking at the EPS 0z, the regime chart shows a move through BLO+ (the Scandi High) towards –NAO (Greenland height rises). On the Z500 diagram for Western Iceland, there clearly is ensemble agreement on height rises in that area until Day 8, up to a mean of about 563 dam on March 2. However, there is also a marked drop in heights over Iceland right after those height rises, supporting the idea that the High might quickly move too far West for us to profit. We all know a Greenland High/Atlantic Ridge is not at all guaranteed to bring cold and snow. It will be a while before we know the exact placement, alignment and duration of the High, let alone the temperatures and precipitation types that will be the result. Almost a week of impatient waiting is ahead of us until we get some clarity about the early March events, although short term upgrades on the budding Scandi High are still very well possible too. The ensemble has been tiptoeing towards a slightly colder Easterly influence to end February. Expectations are high in here anyway, so I think “March 2023” /”The 2023 SSW” will be remembered and referred to in future winters one way or another, either as an infamous failure or as an example of what an SSW can do to a winter.

Yes, EC seems to keep the core of the High more East for longer, which is better if we want to avoid a Greenland High that is setting up too far West. Let's see if the ensemble agrees with that. As a rule of thumb for GH's I usually look at Iceland. It's best if Iceland remains under 560 dam heights or higher (yellows to reds on the meteociel charts) for as long as possible, to steer the cold our way instead of the Central Atlantic. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4808628

Yes, EC seems to keep the core of the High more East for longer, which is better if we want to avoid a Greenland High that is setting up too far West. Let's see if the ensemble agrees with that. As a rule of thumb for GH's I usually look at Iceland. It's best if Iceland remains under 560 dam heights or higher (yellows to reds on the meteociel charts) for as long as possible, to steer the cold our way instead of the Central Atlantic.

As it stands, we can be quite confident that during Day 4-9 we will see a Scandi High getting established, building from the Atlantic through the UK (classic development). The EPS ensemble regime chart shows the move towards a Positive Blocking episode with good amplitude. This will bring in Easterlies from Day 6 to Day 10 at least, ending February -and also the meteorological winter- on a colder note. After that, I see much agreement on the general, big picture developments in the extended, and longer term deep into March, with heights somewhere near Greenland and the tPV setting up in the Eastern hemisphere. Those are good looking synoptics from a distance, but the details up close might be more stubborn. I’m still very much on the fence when it comes to our lived experience on the ground. As others have alluded to, the ensembles suggest that there is a serious risk of the Greenland heights setting up a bit far West. Right on the edge perhaps, reminiscent of last December, or a genuine West based Neg. NAO. The EPS 0z wind direction chart for De Bilt this shows a return of SW/W/NW winds within 15 days, which is associated with heights over West Greenland, and an outflow of cold further to our Northwest. Coldies in Scotland, Northern England and Northern Ireland could very well be in a better, more lucky position than those of us further South and East. To be honest, I expected wilder ensemble swings after the SSW than we’ve seen so far; the spread in the extended isn’t that huge. But it’s still deep FI and there is plenty of time and uncertainty left for corrections East. The effects of the probable second stratospheric warming could hit us well beyond the reach of today's regular ensemble as well. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4808430

As it stands, we can be quite confident that during Day 4-9 we will see a Scandi High getting established, building from the Atlantic through the UK (classic development). The EPS ensemble regime chart shows the move towards a Positive Blocking episode with good amplitude. This will bring in Easterlies from Day 6 to Day 10 at least, ending February -and also the meteorological winter- on a colder note. After that, I see much agreement on the general, big picture developments in the extended, and longer term deep into March, with heights somewhere near Greenland and the tPV setting up in the Eastern hemisphere. Those are good looking synoptics from a distance, but the details up close might be more stubborn. I’m still very much on the fence when it comes to our lived experience on the ground. As others have alluded to, the ensembles suggest that there is a serious risk of the Greenland heights setting up a bit far West. Right on the edge perhaps, reminiscent of last December, or a genuine West based Neg. NAO. The EPS 0z wind direction chart for De Bilt this shows a return of SW/W/NW winds within 15 days, which is associated with heights over West Greenland, and an outflow of cold further to our Northwest. Coldies in Scotland, Northern England and Northern Ireland could very well be in a better, more lucky position than those of us further South and East. To be honest, I expected wilder ensemble swings after the SSW than we’ve seen so far; the spread in the extended isn’t that huge. But it’s still deep FI and there is plenty of time and uncertainty left for corrections East. The effects of the probable second stratospheric warming could hit us well beyond the reach of today's regular ensemble as well.

I wouldn't say that March 2013 was the "main event" following that January 6th SSW. Mid January 2013 was very cold. Here in Holland, De Bilt counted no less than 12 ice days in a row from the 14th to the 25th, several with snow falling as well. I had a 9 cm snow cover on the 21st. If indeed that was the result of a QTR impact, that would have been the main event, in my opinion. Like @feb1991blizzard mentioned, then there were more impact waves. After a late Jan milder phase, early mid february onwards was colder again, but not as cold and snowy as January, and after another milder phase early March, that mid-late March cold arrived, mostly very dry, windy cold here. But the further out, the weaker the response of SSW impact waves, so can the remarkable cold even late March still be fully attributed to the early January SSW? This chart from a Domeisen article (2018, 2019, I think? I lost the link to the original article) shows for an SSW during European blocking a series of downwellings, gradually weakening, and the chart is cut off at Day 60 post-SSW. The current output suggests that we don't have to wait that long to see the impact from this SSW though. It's probably too late for ice to skate on, so I personally hope to see more Greenland blocking with big snow events, instead of a Scandi High with bone dry Easterlies like 2013 and 2018.

At Day 8 GFS 12 z is already more amplified than the 6z, both on the Pacific and the Atlantic side.

We have the MJO that entered phases favourable for amplification to our Northwest yesterday. With a typical 10 day lag that takes us to the 23rd/24th of February for a response. Now we see EC, GFS and GEM, and several ensemble members/clusters amplifying right around those dates. The SSW is also happening right about now. A typical response in the troposhere takes 15-20 days, so we'd expect to see something happening in the first week of March. However, the sample size for SSW's is very small, especially when subdivided into ENSO phases, so a faster descent of the effects can not be ruled out, and Quick Troposheric Responses are also a known phenomenon. QTR's typically take 9-10 days. That would, again, take us to somewhere around the 24th of February for a QTR to become visible at 500 hPa. Now, overnight, across models we see a move to that Atlantic amplification, all of a sudden. The MJO cycle has been moving along for a while now, but the only sudden thing is, well the Sudden Stratopheric Warming. My take is that the MJO may struggle to amplify, not strong enough by itself, but with the help of a QTR forcing the same effect (amplification) at the same time, they really start working together, instead of following each other. The next few runs may begin to show quite extreme solutions, I think, visible in the Ops first, followed by the ensembles. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4805757

We have the MJO that entered phases favourable for amplification to our Northwest yesterday. With a typical 10 day lag that takes us to the 23rd/24th of February for a response. Now we see EC, GFS and GEM, and several ensemble members/clusters amplifying right around those dates. The SSW is also happening right about now. A typical response in the troposhere takes 15-20 days, so we'd expect to see something happening in the first week of March. However, the sample size for SSW's is very small, especially when subdivided into ENSO phases, so a faster descent of the effects can not be ruled out, and Quick Troposheric Responses are also a known phenomenon. QTR's typically take 9-10 days. That would, again, take us to somewhere around the 24th of February for a QTR to become visible at 500 hPa. Now, overnight, across models we see a move to that Atlantic amplification, all of a sudden. The MJO cycle has been moving along for a while now, but the only sudden thing is, well the Sudden Stratopheric Warming. My take is that the MJO may struggle to amplify, not strong enough by itself, but with the help of a QTR forcing the same effect (amplification) at the same time, they really start working together, instead of following each other. The next few runs may begin to show quite extreme solutions, I think, visible in the Ops first, followed by the ensembles.

Exactly. Over the last week, there seemed to be broad agreement that next week we would have to endure a phase of fairly mobile NW-SE flow deep into Europe, before MJO/SSW forcings might change the picture end of the month into March. However, especially EC, but also the latest GEM and GFS runs, are moving away from that, shortening that phase more and more. Hints of heights extending NW from Europe, over the British isles into the NE-Atlantic. So, more High pressure influence near us, followed by increasing probabilities of Northerlies/Northeasterlies?

Those profiles show that the reversal is descending slowly, not making it anywhere near 500hPa yet. Considering the lead time, that Euro and Atlantic High amplification that GFS, GEFS, and to a degree, EPS, are showing could IMO very well be more of a response to the phase 5 to 6 MJO progression. With the MJO moving from 5 to 6 around February 12, and a 10 day delay, that would fit amplification starting around February 22/23. Apart from a possible, but rare QTR, I think the first SSW effects may land at 500 hPa in the first week of March, some 15-20 days after the event. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804447

Those profiles show that the reversal is descending slowly, not making it anywhere near 500hPa yet. Considering the lead time, that Euro and Atlantic High amplification that GFS, GEFS, and to a degree, EPS, are showing could IMO very well be more of a response to the phase 5 to 6 MJO progression. With the MJO moving from 5 to 6 around February 12, and a 10 day delay, that would fit amplification starting around February 22/23. Apart from a possible, but rare QTR, I think the first SSW effects may land at 500 hPa in the first week of March, some 15-20 days after the event.

No, there wasn't. 2004/2005 was even the only winter from 1999-2010 without an official SSW. But nevertheless, that pattern brought a memorable snow event to Holland early March.

It remains difficult to attribute cold spells to SSW's with certainty. Take for example the one in late January 1963. That winter had already earned a place in the hall of fame as the SSW hit, but more cold was produced in February. We can speculate, was that Feb 63 cold the result of the SSW? Or would it have followed anyway, since it was a cold one already? Or did the SSW perhaps prevent an even colder month? Some SSW's were followed by cold spells, some were not. It is far from 1+1=2, if you consider that, for example, SSW's can be both the result and the cause of blocking events. That's why in many cases a serious cold spell preceded the SSW. If you subdivide SSW's according to ENSO state and seasonal timing, you are left with very small sample sizes that do not show homogeneous outcomes. The complexity increases even more if you include MJO phases. It is a subject that still needs a lot of research, that's for sure. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4803160

It remains difficult to attribute cold spells to SSW's with certainty. Take for example the one in late January 1963. That winter had already earned a place in the hall of fame as the SSW hit, but more cold was produced in February. We can speculate, was that Feb 63 cold the result of the SSW? Or would it have followed anyway, since it was a cold one already? Or did the SSW perhaps prevent an even colder month? Some SSW's were followed by cold spells, some were not. It is far from 1+1=2, if you consider that, for example, SSW's can be both the result and the cause of blocking events. That's why in many cases a serious cold spell preceded the SSW. If you subdivide SSW's according to ENSO state and seasonal timing, you are left with very small sample sizes that do not show homogeneous outcomes. The complexity increases even more if you include MJO phases. It is a subject that still needs a lot of research, that's for sure.

No, they're not. There are records of SSW's since the late 50s. SSW's were quite common in the 60s, 70s and 80s and then "disappeared" between 1989 and 1998. Then they happened regularly again (almost yearly) during the 2000s, but over the last 10 years not as frequent. They get discussed a lot more, but that has everything to do with forums such as this, social media and increased access to data and model output.

There is enough snow in the Alps for skiing already, and the next few days much of the Austrian Alps will get a lot of fresh snow, as @carinthian mentioned earlier today. Only the Western Alps won't get anything of note. Next week looks to be a very sunny week for most of Europe, but with low dewpoints, far below zero in the Alps, so that's not a problem at all. It might be close to perfect conditions there. The only thing that might make things awful in ski resorts is the avalanche risk. Next Thursday's dewpoints:

GEM moves the tPV convincingly East, and UKMO at 168h seems to be doing the same. Interesting Atlantic pattern as well.

The GFS bashing is getting a bit ridiculous in here. The GFS option with a High further North over Scandinavia, and CAA pulling cold Southwest has been present in more or less all the ensembles, so the GFS Op has never been alone in showing it. And let’s go back in history, all the way to Monday, January 30, 2023. Yup, that’s just three days ago, everyone should be old enough to remember it. What did the Supermodels ECM and GEM show for –then Day 10- Thursday the 9th? EC: Massive High over Scandinavia/Russia, Low Mediterranean heights. GEM: Massive Scandi High, Low Low SE European/Mediterranean heights. And what did the "Rubbish/Cannon Fodder/Only fools look at it/Let’s ignore it" –model GFS show? GFS: Mid latitude Euro Heights, with only moderately low heights to the South. Well, this is awkward, I spy the middle ground solution! On GFS. Yes, GFS at Day 10 was closest to what is now considered the most likely outcome (which has not yet happened btw). So, are EC and GEM cannon fodder too? Of course not, and neither is GFS. I think a big problem in here is that 60% or 85% probabilities are casually rounded off to 100% and 40% or 15% probabilities are rounded off to 0%. It annoys me when operationals or ensembles show unusual synoptics, especially at short lead times (like GFS just did) that some posters dismiss it as “0% chance of that happening.” Well, if it was 0% it would not be shown. Just be accurate and fair. It’s not as black-and-white as we would like. And, @MATT TATTOO just mentioned it too, let’s not evaluate before the thing has even happened. Verification stats can be useful, but not to evaluate the likelihood of single model runs verifying. Just because a model has slightly worse stats on average does not mean you can dismiss the present forecast. The most recent run might be a model’s peak performance or its worst show, and that goes for EC just as much as for GFS. You don’t know in advance, only in hindsight. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800929

The GFS bashing is getting a bit ridiculous in here. The GFS option with a High further North over Scandinavia, and CAA pulling cold Southwest has been present in more or less all the ensembles, so the GFS Op has never been alone in showing it. And let’s go back in history, all the way to Monday, January 30, 2023. Yup, that’s just three days ago, everyone should be old enough to remember it. What did the Supermodels ECM and GEM show for –then Day 10- Thursday the 9th? EC: Massive High over Scandinavia/Russia, Low Mediterranean heights. GEM: Massive Scandi High, Low Low SE European/Mediterranean heights. And what did the "Rubbish/Cannon Fodder/Only fools look at it/Let’s ignore it" –model GFS show? GFS: Mid latitude Euro Heights, with only moderately low heights to the South. Well, this is awkward, I spy the middle ground solution! On GFS. Yes, GFS at Day 10 was closest to what is now considered the most likely outcome (which has not yet happened btw). So, are EC and GEM cannon fodder too? Of course not, and neither is GFS. I think a big problem in here is that 60% or 85% probabilities are casually rounded off to 100% and 40% or 15% probabilities are rounded off to 0%. It annoys me when operationals or ensembles show unusual synoptics, especially at short lead times (like GFS just did) that some posters dismiss it as “0% chance of that happening.” Well, if it was 0% it would not be shown. Just be accurate and fair. It’s not as black-and-white as we would like. And, @MATT TATTOO just mentioned it too, let’s not evaluate before the thing has even happened. Verification stats can be useful, but not to evaluate the likelihood of single model runs verifying. Just because a model has slightly worse stats on average does not mean you can dismiss the present forecast. The most recent run might be a model’s peak performance or its worst show, and that goes for EC just as much as for GFS. You don’t know in advance, only in hindsight.

EC 240h, new attempt at NE height rises... They do it on purpose, to tease us, that must be it.

It's different, but not necessarily better. Stronger High over Central Europe, yes, but it doesn't extend as far North of Scandinavia (even more so compared to yesterday's 12z for the same time), and it also removes the SE European/Central Mediterranean Low heights, which are critical to get the Easterly going. So that's not good for a Scandi High/Easterly setup, although ironically, it might very well be colder on the surface, under that mid latitude High without Easterly.

Looks like the EPS 12z has moved towards the GFS/GEFS with the HRES Op on the milder side. Not bad. For De Bilt winds are shifting towards East Day 6-9, compared to the 0z. Colder ensemble Days 6-11.

GFS is easily the best run this winter from my perspective. I love snow, and there is none of that in Holland in this run, but I love cold without snow just as much, as long as it gives me ice to skate on. And GFS does that, it keeps giving, ice day after ice day. Nearby lakes would soon look like my profile pic again. About UKMO, it's obviously not as good, but at 168h it could still lead to something good (better than expected) later on. I could see a new WAA push in the Atlantic, and it holds on to heights North of Norway (more than GEM) and the low heights in SE Europe. It's a pity we don't have 192h-240h charts for UKMO. A couple of EPS members this morning were actually similar and started building Euro/Scandi heights a bit later. Nevertheless, GFS is preferred!