Catacol

"Background Zealots"? Hmm. Is this where we are at now, where those trying to unravel the complex task of forecasting get labelled as zealots? Either you know what that word means and are therefore genuinely trying to put the boot in, or you don't know what it means and perhaps shouldn't be using it. I see in general the knives are out today. Disappointing. Let's have a go at a broad response: 1. There are 2 areas of ongoing research that interest those with a passion for this kind of stuff. First is the GSDM theory first put together about 15 years ago by Ed Berry. The second is a greater understanding of stratospheric impacts on our weather, another fledgling science that has also been around for 15-20 years approx. 2. One of the challenges of both approaches is to try and understand the inter relationship between the two. GSDM is largely anchored on developments in the Pacific alongside momentum impacts created by the big mountain ranges - Tibet and Rockies probably most importantly, Urals also. Strat modelling tries to interpret the impact of vertical wave propagation and how the column of air above the arctic is shaped/squeezed/stretched/split (or not) by these waves. Tropospheric patterns feed into the strat and vice versa - so they are definitely linked - but an understanding of the links is still in its infancy. When Amy Butler tweets that the reasons for the failed SSW in early January are not understood (given models tend to under rather than over model the likelihood of an SSW) then you know you are walking in a world of grey. And that failed SSW and what has transpired instead has had a huge hand to play in how January has developed. 3. From this, we have 2 options. Label these areas of research as a waste of time, as likely to produce accuracy as the advice of a cat (!!), or we engage with what is going on and try and unpick it. CC is not making this any easier because CC is making a mess of analogues - the atmosphere and the overall climate just isn't what it was in the 1960-90 period and adapting to the pace of change and how it impacts forecasting is a challenge. 4. Some of today's posters would clearly favour the former. Don't bother trying to unlock the door to understanding because it cannot be done. Fair enough - but not for me. I'm not a nihilist and wish to continue to try and learn. Perhaps those who see chaos theory as the only answer to our weather should have a thread all of their own, though the thread would probably make for pointless reading. 5. Finally - you might want to read posts more carefully. Only the other day I acknowledged in a post that the Xmas forecast was a bust, and that the recent cold was shorter lived than expected. Reasons for both were set out, bust was advertised. Two successes at the same time, early Dec and the snap just gone. And it looks as though next week will bust too. There you go - is that clear enough? If you want the reason laid out again, reflective strat event. Not forecast, not spotted even by those with proper qualifications in relevant climate science. But this winter is not done yet, and I still see distinct opportunity for further cold in February and again into March. As a concluding comment, we are dealing in probability forecasting. No one will ever get to the stage where we say "in 10 days' time it will snow in London and 6 inches will fall and stick." Nonsense. We look at probabilities. And when dealing in probability a 95% chance does not always land. I see some criticism of the MetO today as well. Really? Those of you happy to criticise forecasting methodology and happy also to criticise (possibly) the most advanced national Met Office in the world and its choice of language are seeking a level of absolute clarity that is unattainable. If you have something to say that adds to the debate, say away. If your words are designed to tear, rip and demolish - silence is a better alternative.

Not sure who you have been reading, but the majority of the core posters in here that tried to read the season as a whole were looking at February to be the most significant wintry zone. Im watching developments in the strat with a sinking sense of doom. Our tropospheric pathway to cold has been positive all season so far, and we have seen 2 out of 3 predicted cold snaps/spells come to pass, early December being better than expected and last week a bit disappointing. Xmas was a bust. But a fully reflective stratospheric response to the warming impacts that occurred through this month is exactly what we don’t want to see, and I have mused over the importance of the strat before as the dominant driver in most winter seasons. Early January we were so close to a major SSW - and it has now turned turtle and looks as though the strat will be above average before too long. The science of strat warming impacts is still not clear. Even the big guns such as Butler and Cohen called a SSW for early January, reflective impacts not what was expected. It is way over my head as to why in some seasons the warmth is absorbed and breaks the vortex up, and other times the warmth bounces off the vortex core and reflects zonal forcing back into the trop. One thing I do know is that CC is cooling the stratosphere and, on average, this means stronger zonal forcing for each and every winter going forward. It is our CC winter handicap that every year we are going to need to see overcome. Back to this winter. No doubt that tropospheric forcing is going to support blocking in the right places for U.K. winter starting approx next weekend. The strength of that forcing will build over the following 2 weeks. I had expected that to occur while we still had some blocking in place, but strat impacts have wiped that out in about 72 hours. So we have to build a blocking pattern from scratch. Quite doable….but not if the strat fires up and grabs control. Fine lines as ever, but I would say the odds of a cold February have now lengthened despite the confident assertions of the seasonal models and our reading of pacific led forcing. Much to watch through the coming week. All eyes on the strat, perhaps for the first time this winter. We may have been guilty of downplaying it this winter, perhaps the result of a quiet @chionomaniac, and we have to hope that reflective impacts are being overplayed and trop drivers can seize control once again. For those of a research mindset this paper is interesting. 44 reflection events identified in the modern record, and on 35 of those events an SSW was prevented. These reflective events are common. See appendix A1. Stratospheric downward wave reflection events modulate North American weather regimes and cold spells WCD.COPERNICUS.ORG Abstract. The Arctic stratospheric polar vortex is an important driver of mid-latitude winter cold spells. One proposed coupling mechanism between the stratospheric... So much still to learn. . Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5020929

Not sure who you have been reading, but the majority of the core posters in here that tried to read the season as a whole were looking at February to be the most significant wintry zone. Im watching developments in the strat with a sinking sense of doom. Our tropospheric pathway to cold has been positive all season so far, and we have seen 2 out of 3 predicted cold snaps/spells come to pass, early December being better than expected and last week a bit disappointing. Xmas was a bust. But a fully reflective stratospheric response to the warming impacts that occurred through this month is exactly what we don’t want to see, and I have mused over the importance of the strat before as the dominant driver in most winter seasons. Early January we were so close to a major SSW - and it has now turned turtle and looks as though the strat will be above average before too long. The science of strat warming impacts is still not clear. Even the big guns such as Butler and Cohen called a SSW for early January, reflective impacts not what was expected. It is way over my head as to why in some seasons the warmth is absorbed and breaks the vortex up, and other times the warmth bounces off the vortex core and reflects zonal forcing back into the trop. One thing I do know is that CC is cooling the stratosphere and, on average, this means stronger zonal forcing for each and every winter going forward. It is our CC winter handicap that every year we are going to need to see overcome. Back to this winter. No doubt that tropospheric forcing is going to support blocking in the right places for U.K. winter starting approx next weekend. The strength of that forcing will build over the following 2 weeks. I had expected that to occur while we still had some blocking in place, but strat impacts have wiped that out in about 72 hours. So we have to build a blocking pattern from scratch. Quite doable….but not if the strat fires up and grabs control. Fine lines as ever, but I would say the odds of a cold February have now lengthened despite the confident assertions of the seasonal models and our reading of pacific led forcing. Much to watch through the coming week. All eyes on the strat, perhaps for the first time this winter. We may have been guilty of downplaying it this winter, perhaps the result of a quiet @chionomaniac, and we have to hope that reflective impacts are being overplayed and trop drivers can seize control once again. For those of a research mindset this paper is interesting. 44 reflection events identified in the modern record, and on 35 of those events an SSW was prevented. These reflective events are common. See appendix A1. Stratospheric downward wave reflection events modulate North American weather regimes and cold spells WCD.COPERNICUS.ORG Abstract. The Arctic stratospheric polar vortex is an important driver of mid-latitude winter cold spells. One proposed coupling mechanism between the stratospheric... So much still to learn. .

Yep maybe. I guess I’m not really counting cold that landed before Sunday approx around here. It was chilly the week before but nothing to shout about. And further south you may have had more easterly chill whereas the midlands north were under the centre of the high. Proper cold will end up being a 4/5 day thing here. Cannon fodder out this far, but interesting pub shape tonight. The details will be off, but the general message is right. You’ll have Dorset cold again before long. Feb 1996 when I lived just outside Dorchester is one of my fondest winter memories…

And so the cold snap ends. Snap rather than a spell - 9/10 for the depth and quality of the cold (I loved the frost free dry cold and then the intense frost that broke the fuel flap on my car!) and I daresay 9/10 for many in Scotland or parts of the NW who love snow. The NW probably viewed a scandy trough dropping in with a sense of "been here before" - and then low and behold the trough developed a curious westerly and many parts cashed in. The wonderful variability of the weather. But the overall 9/10 has to lose 3 points for the shorter than expected duration, and then a further point for the failed channel runner and anything for the south. Those in the east (like me) would probably knock a further 1 off for the absence of any north sea activity. Lands as a sort of 4 or 5/10 for me. We have been unlucky with events in the strat this season, no doubt about that. First the SSW that failed at the start of the month that could have done much to cement a cold month (and was probably a key factor in suggestions from the MetO) and then a second warming that split the vortex but has turned into a reflection type of warming, where wave forcing bounces off the strat back towards the trop and helps reinforce default westerlies. Laid out nicely in Amy Butler's recent blog. And frankly a frustration....but one we have to live with. Coincides with IO MJO phases and the lagged impacts the elastic band of AAM being at the wrong end of the "ping" have ensured. Hey presto - cold out very fast, violently mobile atlantic arrives. The weather may be chaotic, but it is also broadly predictable once drivers lock in. And that broad predictability is what lends significant wintry optimism going forward. First of all, the ebb and blow of momentum that is the GWO. Look at the patterns here. Note that prior to our December snap and again prior to our January snap we saw a rising orbit take hold. This graphical representation of global windflows gives a strong indication as to whether the atmosphere is predisposed to encourage blocking, and to see the next orbit kick in we need a rising momentum profile. And here it is. This has been sluggish - I thought the gun had been fired a few days ago...but it appears now that 16 Jan was the moment we hit the starting button. Frictional torque distinctly positive Mountain torque generally positive also and this produces the awaited beginning of the next surge in momentum illustrated by a positive tendency now in play This will accelerate, not least because the MJO is coming back to where snow lovers want it - phases 6/7/8/1 broadly speaking So. We watch and wait with anticipation given GLAAM has remained positive overall and we are in a back loaded Nino context. The atlantic will fizz for the 5 days or so I have flagged before as the likely window, and then we will gradually see the effects of the forcings listed above impact on NWP. There are signs already, as expected catching the eye around 26/27/28 Jan. Note ridging towards Scandy on the EPS for the end of the week quite pronounced by the end of the weekend Someone earlier said there was little sign of such developments, and used GEFS 850s as the tool to evidence it. Worst possible source of evidence for extended forecasting possible. Don't get swayed by such stuff. Disappointing to see the intense cold depart so soon, frustrating that the strat has refused to play ball so far, but winter a long way from done and the mild I suspect will be an interlude rather than a pattern starter. I still see February as blocked and have faith in the recent Glosea, JMA, CMC and other long range models that see a -AO overall. Plenty of time still to roll those dice again and get lucky. Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5018653

And so the cold snap ends. Snap rather than a spell - 9/10 for the depth and quality of the cold (I loved the frost free dry cold and then the intense frost that broke the fuel flap on my car!) and I daresay 9/10 for many in Scotland or parts of the NW who love snow. The NW probably viewed a scandy trough dropping in with a sense of "been here before" - and then low and behold the trough developed a curious westerly and many parts cashed in. The wonderful variability of the weather. But the overall 9/10 has to lose 3 points for the shorter than expected duration, and then a further point for the failed channel runner and anything for the south. Those in the east (like me) would probably knock a further 1 off for the absence of any north sea activity. Lands as a sort of 4 or 5/10 for me. We have been unlucky with events in the strat this season, no doubt about that. First the SSW that failed at the start of the month that could have done much to cement a cold month (and was probably a key factor in suggestions from the MetO) and then a second warming that split the vortex but has turned into a reflection type of warming, where wave forcing bounces off the strat back towards the trop and helps reinforce default westerlies. Laid out nicely in Amy Butler's recent blog. And frankly a frustration....but one we have to live with. Coincides with IO MJO phases and the lagged impacts the elastic band of AAM being at the wrong end of the "ping" have ensured. Hey presto - cold out very fast, violently mobile atlantic arrives. The weather may be chaotic, but it is also broadly predictable once drivers lock in. And that broad predictability is what lends significant wintry optimism going forward. First of all, the ebb and flow of momentum that is the GWO. Look at the patterns here. Note that prior to our December snap and again prior to our January snap we saw a rising orbit take hold. This graphical representation of global windflows gives a strong indication as to whether the atmosphere is predisposed to encourage blocking, and to see the next orbit kick in we need a rising momentum profile. And here it is. This has been sluggish - I thought the gun had been fired a few days ago...but it appears now that 16 Jan was the moment we hit the starting button. Frictional torque distinctly positive Mountain torque generally positive also and this produces the awaited beginning of the next surge in momentum illustrated by a positive tendency now in play This will accelerate, not least because the MJO is coming back to where snow lovers want it - phases 6/7/8/1 broadly speaking So. We watch and wait with anticipation given GLAAM has remained positive overall and we are in a back loaded Nino context. The atlantic will fizz for the 5 days or so I have flagged before as the likely window, and then we will gradually see the effects of the forcings listed above impact on NWP. There are signs already, as expected catching the eye around 26/27/28 Jan. Note ridging towards Scandy on the EPS for the end of the week quite pronounced by the end of the weekend Someone earlier said there was little sign of such developments, and used GEFS 850s as the tool to evidence it. Worst possible source of evidence for extended forecasting possible. Don't get swayed by such stuff. Disappointing to see the intense cold depart so soon, frustrating that the strat has refused to play ball so far, but winter a long way from done and the mild I suspect will be an interlude rather than a pattern starter. I still see February as blocked and have faith in the recent Glosea, JMA, CMC and other long range models that see a -AO overall. Plenty of time still to roll those dice again and get lucky.

For those looking further out, JMA monthly published yesterday for February. UK, as usual on this one, at 10 o clock. Otherwise the current situation is not what many on here would have hoped for. This GFS for tomorrow screams all kinds of wintry wonders: but closer examination shows that much of central and southern UK is stuck in a col, neither fed by the strongest and coldest winds from the N and/or NE nor quite in line for the channel runner. There is a day or so to go for surprises to turn up, and as we speak Scotland is getting pasted....but the snow hungry majority in the south are left gasping. Feels like rolling a double 1 and damnably unfortunate. Then comes week 2. 22-29 Jan approx was always flagged as a week of greatest concern because the impacts of lowering momentum would be greatest and the need to gave got a block cemented in a good place would be highest. But that double 1 effect may be about to land again. (is that like rolling 4 x 1s?!) The strat splits tomorrow and the zonal mean is much below average, even close to a technical (if very short lived) SSW - and we could be excused for thinking that there is little better context for ongoing northerly blocking. But look how steep the recovery is, and with little to no model disagreement. Back to average in a flash, and GFS largely puts the vortex back together again by the end of the weekend. So - what's happening? Factors leaning towards a cold and blocked outlook have had to work pretty hard to get our blocking pattern in place. Even with a favourable pulse of momentum, a good GWO orbit, and lagged impacts of an amplified MFO through the west pacific we have not quite got the block in place. Meanwhile, as soon as those signals fade into a period when it was well noted that things would get less automatically "good" for winter, we get a collapse of the pattern that is on the crazy side of fast. We go from the good chart at the top of this post to this within 4 days: No obvious lag here for the flatter MJO phases!! And a reforming vortex has helped support an atlantic pattern in double quick time. It is almost as though the wax wane nature of the atmosphere has been placed on a hill. To get to a blocked phase we have to sprint up the hill on our bike, in first gear, legs pumping and burning once at the top. But then to return to the starting point it is an easy cruise downhill, hands off the handlebars, freewheeling. Maybe this is CC in action. Or maybe it is just a reflection of some very poor luck for the coming week and the one after. I don't know. I guess in the end, other than to take the learning from it, I don't really care. It has never been easy to get snow to this country and 1988 to 2008 was a 20 year run of misery punctuated by a couple of good moments. Hunting those rare major snowfalls would be no fun at all if they came every year.....but it would be good if the fates could allow us 1 in 5!! This winter is not done. I read some guff on this thread that I find annoying, folk announcing the default return of a period of westerlies as though there is something wise and significant in doing so. Saying the UK will usually have westerlies and that the best way of approaching UK winter weather forecasting is to say "westerly" each time because you will usually be correct is both lazy and daft. I don't put my money on Ronnie O'Sullivan to win the snooker each time "because he usually does." I do it because I analyse the context and decide it is the most likely outcome....and I might still put £10 on a young outsider with half a chance of making it based on analysis and form, as per Luke Littler in the Darts. If Ronnie is ill the week before Sheffield I probably don't back him at all, despite the past run of success! And this is where we are right now. January 15, half way through winter. We had a decent start, a disappointing Xmas/NY and now sit in 4 days of frigid air but without widespread snow forecast. Bugger. Westerlies to return for a while. But the analysis doesn't change, and the weighted approach to appropriate forecasting remains. The next momentum cycle is underway, signalled by rising frictional torque as of a couple of days ago. The MJO will be back in the west pacific pretty quickly looking at model forecasts, and while the vortex returns to average it doesnt appear to launch itself into an above average phase. Read Tamara's work rather than mine on this - she expresses the technical aspects of wind flow much better than anyone else on here....but in essence we are set to have more wave action return, a meridional pattern embed and poleward flux that should bring blocking back to the table quite quickly. I haven't seen a seasonal do anything other than go with a negative AO for February and the combination of high momentum and a favourable MJO in a Nino year will bring things back. I had said 3-5 days of atlantic westerlies. That was based on the cold hanging on until Sunday as I had it down as a cold week....but it appears the cold is fading faster than we might reasonably have expected....so it pushes longer. I do think by the end of week 2, that's somewhere around 26/26/28 Jan, we will have a more favourable context back on the table....or at least sitting on the hot plate waiting to be served. Winter hunting in the UK has never been easy. C'est la vie. But we continue to look, and search, and roll those dice despite the fact that 80-90% of the time they don't give us what we seek. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013243

For those looking further out, JMA monthly published yesterday for February. UK, as usual on this one, at 10 o clock. Otherwise the current situation is not what many on here would have hoped for. This GFS for tomorrow screams all kinds of wintry wonders: but closer examination shows that much of central and southern UK is stuck in a col, neither fed by the strongest and coldest winds from the N and/or NE nor quite in line for the channel runner. There is a day or so to go for surprises to turn up, and as we speak Scotland is getting pasted....but the snow hungry majority in the south are left gasping. Feels like rolling a double 1 and damnably unfortunate. Then comes week 2. 22-29 Jan approx was always flagged as a week of greatest concern because the impacts of lowering momentum would be greatest and the need to gave got a block cemented in a good place would be highest. But that double 1 effect may be about to land again. (is that like rolling 4 x 1s?!) The strat splits tomorrow and the zonal mean is much below average, even close to a technical (if very short lived) SSW - and we could be excused for thinking that there is little better context for ongoing northerly blocking. But look how steep the recovery is, and with little to no model disagreement. Back to average in a flash, and GFS largely puts the vortex back together again by the end of the weekend. So - what's happening? Factors leaning towards a cold and blocked outlook have had to work pretty hard to get our blocking pattern in place. Even with a favourable pulse of momentum, a good GWO orbit, and lagged impacts of an amplified MFO through the west pacific we have not quite got the block in place. Meanwhile, as soon as those signals fade into a period when it was well noted that things would get less automatically "good" for winter, we get a collapse of the pattern that is on the crazy side of fast. We go from the good chart at the top of this post to this within 4 days: No obvious lag here for the flatter MJO phases!! And a reforming vortex has helped support an atlantic pattern in double quick time. It is almost as though the wax wane nature of the atmosphere has been placed on a hill. To get to a blocked phase we have to sprint up the hill on our bike, in first gear, legs pumping and burning once at the top. But then to return to the starting point it is an easy cruise downhill, hands off the handlebars, freewheeling. Maybe this is CC in action. Or maybe it is just a reflection of some very poor luck for the coming week and the one after. I don't know. I guess in the end, other than to take the learning from it, I don't really care. It has never been easy to get snow to this country and 1988 to 2008 was a 20 year run of misery punctuated by a couple of good moments. Hunting those rare major snowfalls would be no fun at all if they came every year.....but it would be good if the fates could allow us 1 in 5!! This winter is not done. I read some guff on this thread that I find annoying, folk announcing the default return of a period of westerlies as though there is something wise and significant in doing so. Saying the UK will usually have westerlies and that the best way of approaching UK winter weather forecasting is to say "westerly" each time because you will usually be correct is both lazy and daft. I don't put my money on Ronnie O'Sullivan to win the snooker each time "because he usually does." I do it because I analyse the context and decide it is the most likely outcome....and I might still put £10 on a young outsider with half a chance of making it based on analysis and form, as per Luke Littler in the Darts. If Ronnie is ill the week before Sheffield I probably don't back him at all, despite the past run of success! And this is where we are right now. January 15, half way through winter. We had a decent start, a disappointing Xmas/NY and now sit in 4 days of frigid air but without widespread snow forecast. Bugger. Westerlies to return for a while. But the analysis doesn't change, and the weighted approach to appropriate forecasting remains. The next momentum cycle is underway, signalled by rising frictional torque as of a couple of days ago. The MJO will be back in the west pacific pretty quickly looking at model forecasts, and while the vortex returns to average it doesnt appear to launch itself into an above average phase. Read Tamara's work rather than mine on this - she expresses the technical aspects of wind flow much better than anyone else on here....but in essence we are set to have more wave action return, a meridional pattern embed and poleward flux that should bring blocking back to the table quite quickly. I haven't seen a seasonal do anything other than go with a negative AO for February and the combination of high momentum and a favourable MJO in a Nino year will bring things back. I had said 3-5 days of atlantic westerlies. That was based on the cold hanging on until Sunday as I had it down as a cold week....but it appears the cold is fading faster than we might reasonably have expected....so it pushes longer. I do think by the end of week 2, that's somewhere around 26/26/28 Jan, we will have a more favourable context back on the table....or at least sitting on the hot plate waiting to be served. Winter hunting in the UK has never been easy. C'est la vie. But we continue to look, and search, and roll those dice despite the fact that 80-90% of the time they don't give us what we seek.

Hmmm - that is a good question. Ultimately it will be to the NW - but there is going to be a transitionary phase that might well feature a block to the NNE first. At the moment - and the reason I have been quiet for a couple of days - is that we have nailed on 5 days of cold and then the arrival of a couple of factors that I have no confidence in the modelling’s ability to manage in any great detail and so I’d rather sit and watch and be fascinated. In the first place we have a bottom up short term vortex split that is going to end quickly and allow the vortex to reform as a whole once again, but quite how that happens and the extent to which frictional responses to this are going to impact the tropospheric pattern is very unclear. Secondly we have a solidly Nino-esque atmosphere that is sitting in a positive momentum position even as we reach the end of the inevitable ping back from the steep rise in late December, and that means (as has been stated better by others) that our baseline is already predisposed to blocking. So…when NWP wakes up to the rising momentum picture signalled by my FT screenshot earlier and enhanced soon by an imminent +EAMT and a very favourable MJO we end up with the Glosea Feb chart. The Hannibal Smith pic from a few posts back holds true still. There is nothing happening that is especially unexpected. I am quietly gutted that we did not get the forecast SSW earlier in January because I think if that had happened we would have been looking at wall to wall cold blocking for the extended, but right now the steering wheel is being grasped by tropospheric forcings that are well expressed in the GSDM…and it is a great watch. Whatever falls from the sky this week will not be winter’s final hurrah. Going back to your question - I can see NWP playing around with a more downstream wave break setting up over Scandy in the first place, so I’ll plump for a U.K./Scandy ridge first and then retrogression to Greenland. To be honest this is hardly an original view point - EC weeklies have been flagging that progression for a while. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5011560

Hmmm - that is a good question. Ultimately it will be to the NW - but there is going to be a transitionary phase that might well feature a block to the NNE first. At the moment - and the reason I have been quiet for a couple of days - is that we have nailed on 5 days of cold and then the arrival of a couple of factors that I have no confidence in the modelling’s ability to manage in any great detail and so I’d rather sit and watch and be fascinated. In the first place we have a bottom up short term vortex split that is going to end quickly and allow the vortex to reform as a whole once again, but quite how that happens and the extent to which frictional responses to this are going to impact the tropospheric pattern is very unclear. Secondly we have a solidly Nino-esque atmosphere that is sitting in a positive momentum position even as we reach the end of the inevitable ping back from the steep rise in late December, and that means (as has been stated better by others) that our baseline is already predisposed to blocking. So…when NWP wakes up to the rising momentum picture signalled by my FT screenshot earlier and enhanced soon by an imminent +EAMT and a very favourable MJO we end up with the Glosea Feb chart. The Hannibal Smith pic from a few posts back holds true still. There is nothing happening that is especially unexpected. I am quietly gutted that we did not get the forecast SSW earlier in January because I think if that had happened we would have been looking at wall to wall cold blocking for the extended, but right now the steering wheel is being grasped by tropospheric forcings that are well expressed in the GSDM…and it is a great watch. Whatever falls from the sky this week will not be winter’s final hurrah. Going back to your question - I can see NWP playing around with a more downstream wave break setting up over Scandy in the first place, so I’ll plump for a U.K./Scandy ridge first and then retrogression to Greenland. To be honest this is hardly an original view point - EC weeklies have been flagging that progression for a while.

Yes - agreed. And FT is now just positive once again. So begins the next cycle. Blocked, cold week, brief interlude (3-5 days?) and then blocking reasserted. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5011455

Yes - agreed. And FT is now just positive once again. So begins the next cycle. Blocked, cold week, brief interlude (3-5 days?) and then blocking reasserted.

This analysis nails it. It will be a very close run thing, and some average temps thrown into the mix in week 2 is an inevitability I think - but cold air will also be present and close by. These are the sorts of scenarios that, in theory, produce the snowiest conditions for the UK. It would be counter intuitive - but entirely possible - that the very cold week next week produces less of a snow impact than the milder one that follows. And then all eyes on the expected impacts of spiking AAM and MJO orbit as we hit February and that lovely Glosea chart. As for next week - well: there is a huge amount to be worked out. We are not close to knowing what might be embedded in the flow come Mon/Tues/Weds/Thurs nor what may or may not encroach from the SW. This is where the luck comes in - macro scale has done its job and it is time for the micro to sort itself out over a 5-6 day period. Once this warm ridge gets shunted to Greenland then the fun begins... Let's hope for a fair slice of that required luck because snow hunters on this island, in the best synoptics and large scale pattern in 6 years, deserve a bit! Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008507

Yes - it will indeed be that. We will learn a great deal from the current setup. That, I know, is Tamara's interest and she will continue to present the neutral picture without any of the snow obsession that dogs/inspires many of the rest of us. I have a definite snow investment so am keen to see NWP proved at least partly wrong into week 2. I cant see how the very cold uppers of next week remain in place, but marginal snow conditions I do think can be maintained as the jet stays south, before we get to the accelerating momentum picture driving that tasty looking Feb anomaly picture into week 3 and beyond. It's a win/win really. If NWP comes out on top then so be it - we have a milder 5/7 days - but with that momentum resurgence a near certainty I can suck up week 2 disappointment if we end up blocked and cold once again shortly afterwards.

Sorry MS - I've got to come back on this. The chart I posted has a moisture-laden (given its origins) system in the bay of biscay approaching on a ENE vector and a cold to very cold (-8 850s over most of the UK) trough in place that has come from Scandy to the NE. If anyone on here is frustrated at this 120h context then either they grew up in Finland, haven't been on this forum long enough to understand the usual bounds of our winter weather or are just not interpreting the pattern effectively. Maybe a combination of all 3. Deep breath. These synoptics are rare. There is no way we can have a handle on precipitation amounts at this range. If a system was forecast to hit direct from the W or SW then it becomes a snow to rain event....so we NEED it to deflect and run to the south even though it narrows the band of snowfall and involves fewer people. We would love a strong flow off the north sea for streamers, but again there is no way at this range that we can be sure quite what will occur there, and in that NE flow it is quite possible for features to become embedded that - once again - we have no chance of spotting at 120h. If what is on offer next week is not good enough then it virtually never will be. The 7 Feb 1991 style of synoptic is SO rare that, at the age of 53, I reckon I've seen no more than half a dozen of those in my lifetime and in the last 27 years only two - 2010 and 2018. Before that 1996 which locally around me was spectacular. Do we really need to go down the track of waiting for events that happen twice in 27 years to start feeling good about them? The answer has to be no. Next week is looking great. Is it looking 1991 great? No. But great nonetheless and some are going to end up very happy indeed. And bear in mind that this is just the start of a drawn out spell of cool/cold/very cold weather which I am pretty certain is going to feature more than a single bite at the cherry. The 1991 redux isn't off the table. Rant over. I hope the majority of folk on here are enjoying what is unfurling. Short range surprises will happen, next week will be properly cold and the long term prognosis is good. The models today are suddenly seeing ridges popping up in a flow that was modelled pretty flat into week 2 yesterday. Watch that trend develop. The only thing frustrating me at the moment is the wait for the MJO to get through the maritimes and for frictional torque to start climbing again. As of 9th Jan still waiting...should be soon now. But otherwise - all good!!! Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5008658

Sorry MS - I've got to come back on this. The chart I posted has a moisture-laden (given its origins) system in the bay of biscay approaching on a ENE vector and a cold to very cold (-8 850s over most of the UK) trough in place that has come from Scandy to the NE. If anyone on here is frustrated at this 120h context then either they grew up in Finland, haven't been on this forum long enough to understand the usual bounds of our winter weather or are just not interpreting the pattern effectively. Maybe a combination of all 3. Deep breath. These synoptics are rare. There is no way we can have a handle on precipitation amounts at this range. If a system was forecast to hit direct from the W or SW then it becomes a snow to rain event....so we NEED it to deflect and run to the south even though it narrows the band of snowfall and involves fewer people. We would love a strong flow off the north sea for streamers, but again there is no way at this range that we can be sure quite what will occur there, and in that NE flow it is quite possible for features to become embedded that - once again - we have no chance of spotting at 120h. If what is on offer next week is not good enough then it virtually never will be. The 7 Feb 1991 style of synoptic is SO rare that, at the age of 53, I reckon I've seen no more than half a dozen of those in my lifetime and in the last 27 years only two - 2010 and 2018. Before that 1996 which locally around me was spectacular. Do we really need to go down the track of waiting for events that happen twice in 27 years to start feeling good about them? The answer has to be no. Next week is looking great. Is it looking 1991 great? No. But great nonetheless and some are going to end up very happy indeed. And bear in mind that this is just the start of a drawn out spell of cool/cold/very cold weather which I am pretty certain is going to feature more than a single bite at the cherry. The 1991 redux isn't off the table. Rant over. I hope the majority of folk on here are enjoying what is unfurling. Short range surprises will happen, next week will be properly cold and the long term prognosis is good. The models today are suddenly seeing ridges popping up in a flow that was modelled pretty flat into week 2 yesterday. Watch that trend develop. The only thing frustrating me at the moment is the wait for the MJO to get through the maritimes and for frictional torque to start climbing again. As of 9th Jan still waiting...should be soon now. But otherwise - all good!!!

Yeah - charts like this come thick and fast in most UK winters.

This analysis nails it. It will be a very close run thing, and some average temps thrown into the mix in week 2 is an inevitability I think - but cold air will also be present and close by. These are the sorts of scenarios that, in theory, produce the snowiest conditions for the UK. It would be counter intuitive - but entirely possible - that the very cold week next week produces less of a snow impact than the milder one that follows. And then all eyes on the expected impacts of spiking AAM and MJO orbit as we hit February and that lovely Glosea chart. As for next week - well: there is a huge amount to be worked out. We are not close to knowing what might be embedded in the flow come Mon/Tues/Weds/Thurs nor what may or may not encroach from the SW. This is where the luck comes in - macro scale has done its job and it is time for the micro to sort itself out over a 5-6 day period. Once this warm ridge gets shunted to Greenland then the fun begins... Let's hope for a fair slice of that required luck because snow hunters on this island, in the best synoptics and large scale pattern in 6 years, deserve a bit!

ECM this morning showing signs of plugging into the ongoing momentum-led signal for continued amplification. Really interesting op run in the extended. I would expect the idea to be dropped and then picked up again etc etc - but we may be beginning to see a trend towards a less obviously flat pattern for week 2 and more of the battleground scenarios that have been mentioned and form part of the MetO extended. Fascinating stuff. This chart asks all kinds of questions...

Aside from staring at my lamppost our out my window on and off starting Sunday, I am fascinated how NWP forecasts develop once the cold is in town. We haven’t quite yet fired the starting pistol on the next pacific led momentum surge, though the MJO orbit looks to remain high and there is plenty of momentum sustaining within the pattern. I think the move towards less cold conditions in week 2 will be eased back. And then - for how long will a less amplified pattern sustain? Assuming we have the GSDM drivers nailed down accurately, and that starting pistol sounds soon, do we see a flatter type pattern, still potentially displaced south, for as long as 5 days? Unsure. And where will the jet sit? No certainty that it will be north of The Channel. Much murk in timing and schedule over and above micro developments in local areas next week. But one thing is for sure - there is nothing dull about what is coming, and the transition into and through February looks very good indeed.

Do my eyes - and my refresh button - deceive me? Has the MetO just put out an updated medium forecast for next week and then retracted it back to yesterday's within an hour? Hmm. Maybe my computer is broke. I'm off for an MRI shortly - my knee is definitely broke unfortunately... Meanwhile if you do nothing else today please read Tamara's surfing post and avoid being a slave to NWP output in the unusual pattern that is beginning to unfold. NWP doesn't deal with blocking patterns very well and tends to default too quickly to default westerlies when the blocks get hard to read. That's not to say that week 2 isnt going to get less cold - I think it looks likely that it will - but such phrases are relative and folk should keep in mind that Glosea Feb forecast from yesterday. I just had a team meeting and we discussed the potential impact of snowfall next week. First time I've done that since 2018. Gave me a warm, fuzzy feeling. What is it about snow that is so alluring? Best post a chart to keep the ModPolice happy. @Scott Inghamday as start of the proper cold feed now looks a nailed on certainty. Scott - early creme eggs are yours.... Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5007037

Do my eyes - and my refresh button - deceive me? Has the MetO just put out an updated medium forecast for next week and then retracted it back to yesterday's within an hour? Hmm. Maybe my computer is broke. I'm off for an MRI shortly - my knee is definitely broke unfortunately... Meanwhile if you do nothing else today please read Tamara's surfing post and avoid being a slave to NWP output in the unusual pattern that is beginning to unfold. NWP doesn't deal with blocking patterns very well and tends to default too quickly to default westerlies when the blocks get hard to read. That's not to say that week 2 isnt going to get less cold - I think it looks likely that it will - but such phrases are relative and folk should keep in mind that Glosea Feb forecast from yesterday. I just had a team meeting and we discussed the potential impact of snowfall next week. First time I've done that since 2018. Gave me a warm, fuzzy feeling. What is it about snow that is so alluring? Best post a chart to keep the ModPolice happy. @Scott Inghamday as start of the proper cold feed now looks a nailed on certainty. Scott - early creme eggs are yours....

Neither worrying, nor a trend. The up/down movement of NWP does not constitute a trend. It is mere noise. The ensemble data for the next 7 days or so has been near rock solid for a long time now - the problems come when people jump on the micro scale movements each morning and consistently emphasise any slight sense of a "downgrade" (whatever that means.) As a reminder - ensemble data for the middle of next week today: and the same day from nearly a week ago For the week after next it has been flagged by all those with knowledge of how the pattern is moving that some degree of relaxation is inevitable. Is this worrying? No. It is the direction of travel we have laid out. The exciting prospect is that NWP is likely to overestimate the speed of cold breakdown and we have potential battleground scenarios a plenty in the mix for much of that week. Personally, I think the south will miss the snow at that point but the north could do very well indeed. And then - once again flagged and evidenced and therefore not a worry - we have the shift back to a more amplified pattern. Currently NWP products are not picking this up or it is out of range, though monthly products that came out yesterday have screamed blocking through February loudly. This is going to be very interesting to watch unravel. Perhaps a routine that doesn't involve jumping into a negative interpretation of imprecise data modelling each morning might be worth considering. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5006594

Quite excellent. I was going to post something later of a similar but much less well explained and detailed nature. I won't bother now. The drivers that have lined up to produce this first amplification phase and are lined up to produce the second surge of amplification next week are going nowhere anytime soon. As I posted before, MJO progression is clear and well timed. I think week 22-29 January will be the least cold section of the next month or so but GLAAM has remained high with little damage caused by the ping back of relative AAM progression. We are shortly going to see another surge that will set us up beautifully, given lag, for the end of the month and on into February. But this is a poor summary compared to the post above. Read that and wrestle with its contents. As to next week - no change. Snow will be in the mix whether those who enjoy posting the least favourable interpretation of current signals and output like it or not. Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005117

Neither worrying, nor a trend. The up/down movement of NWP does not constitute a trend. It is mere noise. The ensemble data for the next 7 days or so has been near rock solid for a long time now - the problems come when people jump on the micro scale movements each morning and consistently emphasise any slight sense of a "downgrade" (whatever that means.) As a reminder - ensemble data for the middle of next week today: and the same day from nearly a week ago For the week after next it has been flagged by all those with knowledge of how the pattern is moving that some degree of relaxation is inevitable. Is this worrying? No. It is the direction of travel we have laid out. The exciting prospect is that NWP is likely to overestimate the speed of cold breakdown and we have potential battleground scenarios a plenty in the mix for much of that week. Personally, I think the south will miss the snow at that point but the north could do very well indeed. And then - once again flagged and evidenced and therefore not a worry - we have the shift back to a more amplified pattern. Currently NWP products are not picking this up or it is out of range, though monthly products that came out yesterday have screamed blocking through February loudly. This is going to be very interesting to watch unravel. Perhaps a routine that doesn't involve jumping into a negative interpretation of imprecise data modelling each morning might be worth considering.