Catacol

I think this is accurate as of today. We remain in the holding zone between the cold earlier in the month and anticipated conditions conducive for cold towards the end. NWP is see-sawing around as you might expect, and it looks to me as though the timeline for the landing zone of any substantial cold has certainly shifted to after Xmas. It looks as though we have entered MJO phase 7 now - a very swift progression through phases 2-6 - and we await a concrete sense of what is going to happen as the wave pushes further into the west pacific. We have a strong pacific jet streak on the cards following a likely substantial +EAMT event. But again we await an understanding of just how big that streak will be, how high AAM will climb, and what the downstream response will be. And - will we see a SSW? All part of a waiting game, and it is hard to wait when what we really want is knowledge NOW as to when these predicted impacts will kick in, and the extent of their effects. We have seen some better charts for cold - though that 00z storm from hell chart on GFS last night can certainly take a running jump because....snow or not....we don't want our roofs blown off. But we have yet to see charts showing proper high lat blocking even in the extended. A bit surprising maybe, but part of the waiting game. A degree of faith required. Playing our forecasting probability game, the chances of a high lat block in mid December looked extremely slim to anyone with a grasp of drivers when looking at the picture in mid to late November. But we will soon be entering a phase when those chances increase. We need to get a decent dice roll as we move towards Xmas and beyond.

Last 3 GFS Op strat runs have renewed warming on the US side shunting the vortex east. Connectivity through the layers suggested In the end this is a forecast like all others, reflective of one element of a big 3D global picture, but there is a sustained op signal for the strat vortex to shift in this direction. With strength failing, and a profile like this, it will take less trop forcing in order to create a block in the right place to pull colder air in. If we get to the end of the current MJO cycle and there is no shift in NWP - and if the vortex doesn't end up as battered as forecast data is suggesting will be the case, then (and only then!) will I declare the first half of winter bust.

We will see - I'm not sold on that yet. The CPC report this week declares that "extended range solutions favor some reorganization of the MJO signal over the Western Hemisphere with continued eastward propagation towards the end of December and into early January" and that is phase 8/1. Good winter phases. The amplitude of the current wave is greater than it was in November at the same point, and if the GWO manages to get a higher orbit as a result of forecast momentum injection - and the vortex relocates as extended forecasts are suggesting over to the Scandy side, then I still see significant cold potential. 13 December is still in the holding zone. We have gone from a fairly confident forecast of cold in the latter third, to the naysayers declaring all is bust....and now to the possibility of a cold trough arriving after all. Once the signals shout bust then we can shout bust, but right now there is plenty still to be optimistic about. I went into the winter thinking it would be back loaded, and nothing has changed that view, but a wintry spell in late Dec and on into the New Year is still a distinct possibility. Following that, all eyes on a SSW with benefits synched to the next pacific wave in late Jan/early Feb.

I'd probably stick to this chart. ECM bias corrected is now broadly in line with the BOM. The difference they have is around amplitude. We wait to see.

Yep - I’m happy with the update. Decline of factors associated with the +IOD flagged, and more than one reference to westerlies injected in the pacific. My interpretation of the report is that they do not see the MJO stalling and are still convinced it will progress, albeit more slowly. And we are going to get a decent spike in torques I think in any case which will enhance momentum needed for wave breaking. It’s still game in as far as I am concerned, even if the clock has slowed….

Given the content of your earlier article, and some of the stuff I dug out a week or so ago, there is a fairly key potential turning point here, especially given the admitted reality of a lack of understanding as to the physics of what happens when the MJO traverses the MC. We could see a decent sized shift in the medium range forecast one way or another. I had known a while - and had noticed through observation - that the phase 5-8 transition was a problematic one, a wave development generally poorly modelled, but reading into it recently has furthered my grasp of the complexity and potential variation. The BOM amplitude is a head scratcher given the way other models are reading it. Given ECM and BOM according to my research are the top 2 available (UKM seems to be unattainable now?) there is a reckoning coming. I am learning the words to "Waltzing Matilda" as I type.... Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4974370

Given the content of your earlier article, and some of the stuff I dug out a week or so ago, there is a fairly key potential turning point here, especially given the admitted reality of a lack of understanding as to the physics of what happens when the MJO traverses the MC. We could see a decent sized shift in the medium range forecast one way or another. I had known a while - and had noticed through observation - that the phase 5-8 transition was a problematic one, a wave development generally poorly modelled, but reading into it recently has furthered my grasp of the complexity and potential variation. The BOM amplitude is a head scratcher given the way other models are reading it. Given ECM and BOM according to my research are the top 2 available (UKM seems to be unattainable now?) there is a reckoning coming. I am learning the words to "Waltzing Matilda" as I type....

Battleground scenarios. Strong southerly jet running up against block to the north that prevents the trough flying through. If I still lived in the SW I would be grinning from ear to ear at this. And definite potential from the scandy trough of incursions from the NE too. There's a bit for everyone from this monthly average.

Fair point, enhanced by the seasonals. Were it not for hopes being raised by the more wintry end product to the spell at the very start of December I think there would be less impatience now. Expectations have increased! The Dec 500hpa anomaly charts were nothing to write home about when we looked at them in mid November.

Yes - agreed. I'm a strat junkie because I think in the world of CC and the statistical reality - completely impossible to refute - that our seasonal snow levels in the UK have nosedived over the last 40 years means that our best chance of sustained and brutal cold lies in top down frictional impacts of a SSW, and really I mean a split SSW more often than not. But right now, as is pretty much standard stuff, our weather is definitely being led by trop drivers. Still waiting for the CPC MJO report which will come out later today....and if we are going to bag a cold spell at the end of the month we will need that wave to pass through the maritimes and not hit the buffers as referenced by Blessed Weather earlier! I watch the MJO every December keenly....I think a west pacific phase is still likely. It certainly managed it in November. Once we get through that wave then we will have a month to wait for the next, and strat impacts really come into their own....

Not got a huge amount of time right now - but as the accountability brigade are out in force I'll put a quick analysis together. Note that the kind of stuff put onto this thread in the last couple of days is exactly why there are knowledgeable folk who choose not to post forecasts. As I have said more than once, we are playing a game of probabilities and not certainties. If people on here want an attempt at reasoned analysis then responses to changes/adjustments need to be balanced. Given - as I showed over the weekend - the MetO adjust their text forecast regularly to fit a changing situation, it might be worth considering the relative toolset of the amateur enthusiast on here and the super computer power down in Exeter that still struggles! The answer as to why the forecast is changing at range is timing. It isn't about the signals themselves necessarily because the patterns discussed are still in place, but as I have also said more than once the bugger of an issue we can have on all this is timing. A couple of examples. MJO forecast first: The pacific wave which is so crucial to our understanding and forecasting of the hemispheric wave pattern has slowed down. It is still going to get through phases 7 and 8 but BOM now has the phase 8 transition as post Xmas. This is quite a significant alteration in speed, and I will be interested to read the update later today from the CPC to get their take on it. This means the forcing towards a high lat block is delayed, and hence our mid lat block in the ensembles is not getting the shunt we expected it to get around Xmas time. Given lag, if the speed of MJO passage is getting closer to reality then that phase 7/8 kick is more likely now to be around New Year. Note also the context of GLAAM and the elastic nature of momentum. Here is the current relative chart You'll note the cyclical nature of momentum, and we are awaiting the next positive surge. A major +EAMT event is on the horizon caused by the pressure patterns around Tibet that I have posted previously, and given the lag of this it was already looking as though peak impacts would be post Xmas. Note what is happening at present with these important mountain-led processes: Both East Asia and North America falling into negative territory....but a rebound is coming - the bigger the better. So - to conclude. Pacific wave appears to be slowing, momentum surge likely to chime with this post Xmas....so pattern development is delayed. And this is before we factor in any top down influence from the strat vortex. I'm out of time to address this right now. It's only December 11th. Let's keep some perspective. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4974237

Not got a huge amount of time right now - but as the accountability brigade are out in force I'll put a quick analysis together. Note that the kind of stuff put onto this thread in the last couple of days is exactly why there are knowledgeable folk who choose not to post forecasts. As I have said more than once, we are playing a game of probabilities and not certainties. If people on here want an attempt at reasoned analysis then responses to changes/adjustments need to be balanced. Given - as I showed over the weekend - the MetO adjust their text forecast regularly to fit a changing situation, it might be worth considering the relative toolset of the amateur enthusiast on here and the super computer power down in Exeter that still struggles! The answer as to why the forecast is changing at range is timing. It isn't about the signals themselves necessarily because the patterns discussed are still in place, but as I have also said more than once the bugger of an issue we can have on all this is timing. A couple of examples. MJO forecast first: The pacific wave which is so crucial to our understanding and forecasting of the hemispheric wave pattern has slowed down. It is still going to get through phases 7 and 8 but BOM now has the phase 8 transition as post Xmas. This is quite a significant alteration in speed, and I will be interested to read the update later today from the CPC to get their take on it. This means the forcing towards a high lat block is delayed, and hence our mid lat block in the ensembles is not getting the shunt we expected it to get around Xmas time. Given lag, if the speed of MJO passage is getting closer to reality then that phase 7/8 kick is more likely now to be around New Year. Note also the context of GLAAM and the elastic nature of momentum. Here is the current relative chart You'll note the cyclical nature of momentum, and we are awaiting the next positive surge. A major +EAMT event is on the horizon caused by the pressure patterns around Tibet that I have posted previously, and given the lag of this it was already looking as though peak impacts would be post Xmas. Note what is happening at present with these important mountain-led processes: Both East Asia and North America falling into negative territory....but a rebound is coming - the bigger the better. So - to conclude. Pacific wave appears to be slowing, momentum surge likely to chime with this post Xmas....so pattern development is delayed. And this is before we factor in any top down influence from the strat vortex. I'm out of time to address this right now. It's only December 11th. Let's keep some perspective.

Cracking update from the JMA monthlies this morning. Significantly better in January and the very good looking February from the November run has been maintained. (Note the UK is at 10 o clock on these maps) Meanwhile the hunt for December cold is beginning to look a little elusive - I'll delve a bit more into this later.

In the context of everything that has been said over the last few days I don't understand the pervasive gloom. Let's hit the data. EPS for 20 Dec (when it was flagged we would have interest returning) is pretty good as far as I am concerned. That strong high pressure is easing north....the slow burn scenario. And - as repeated over and over - this is a good setup hemispherically for strat disruption especially with that deep low pressure just upstream from the Rockies. GLAAM is steadily rebuilding. This is 2 days old, but shows we may cross into positive territory soon This is the result of increased tendency once again, after that crash in November which was a bit of a surprise in its depth. What this will do - if it continues (and the peak/trough pattern hemispherically suggests to me more torque events approaching) - is reduce the Nina-style predisposition for a mid atlantic ridge and increase the chances of a block gaining higher latitude. Where is the kick to do this? The MJO has taken a battering today in posts but I have no idea why. BOM ECM CFS The BOM has been consistent. ECM now has a more coherent track - amplitude to come I think. CFS has amplitude now through phase 7. Remember the CPC report from earlier in the week - experts (and we have to trust them occasionally!) stating in a confident tone that amplitude would be retained. Articles have been posted recently showing that research demonstrates all models have a tendency to under represent amplitude when forecasting west pacific progress from the IO - exactly what we have seen already with progress through 4/5 which was not modelled to be so strong. This - we hope - continues. I had thought that, by now, we would have had one or two stellar FI GFS op runs. We have had some decent ones but not yet a stellar one. And ECM is out of range - though, once again, the EPS for 20 Dec is a pretty decent launch point. Maybe tonight. And those fretting over the MetO text forecast - dont. A fortnight before the change to the mid lat pattern this was their take for 13 - 27 Dec - - - "Conditions are most likely to be changeable through this period. Wetter and windier than average conditions are slightly more likely than normal, especially in the west and northwest." Well - that's not going to happen. Things are going to settle down quite considerably. For all their computer power and experts the MetO are as apt to get it wrong as the rest of us once range is out at 336h, even with ensemble tools. And if the MetO cant get it right using their kit and the ensembles at 336h why would we place much credence in op runs at the same range now? I'm happy. It is only 9 Dec. I have seen 3cm of snow for about half a day and more frosts in the last 2 weeks than in many winters gone by in total. The long toothed members here can recall weeks and weeks of mild dross and no frosts. Not so this year. And we have a big high about to set up shop, gradually ease its way north, and drivers in the background aligning for something more substantial. Only timing is the bugger - but frankly I wont care if it delays a week and takes until New Year for this to click. Goodnight all. Fingers crossed for more general optimism tomorrow. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4973256

In the context of everything that has been said over the last few days I don't understand the pervasive gloom. Let's hit the data. EPS for 20 Dec (when it was flagged we would have interest returning) is pretty good as far as I am concerned. That strong high pressure is easing north....the slow burn scenario. And - as repeated over and over - this is a good setup hemispherically for strat disruption especially with that deep low pressure just upstream from the Rockies. GLAAM is steadily rebuilding. This is 2 days old, but shows we may cross into positive territory soon This is the result of increased tendency once again, after that crash in November which was a bit of a surprise in its depth. What this will do - if it continues (and the peak/trough pattern hemispherically suggests to me more torque events approaching) - is reduce the Nina-style predisposition for a mid atlantic ridge and increase the chances of a block gaining higher latitude. Where is the kick to do this? The MJO has taken a battering today in posts but I have no idea why. BOM ECM CFS The BOM has been consistent. ECM now has a more coherent track - amplitude to come I think. CFS has amplitude now through phase 7. Remember the CPC report from earlier in the week - experts (and we have to trust them occasionally!) stating in a confident tone that amplitude would be retained. Articles have been posted recently showing that research demonstrates all models have a tendency to under represent amplitude when forecasting west pacific progress from the IO - exactly what we have seen already with progress through 4/5 which was not modelled to be so strong. This - we hope - continues. I had thought that, by now, we would have had one or two stellar FI GFS op runs. We have had some decent ones but not yet a stellar one. And ECM is out of range - though, once again, the EPS for 20 Dec is a pretty decent launch point. Maybe tonight. And those fretting over the MetO text forecast - dont. A fortnight before the change to the mid lat pattern this was their take for 13 - 27 Dec - - - "Conditions are most likely to be changeable through this period. Wetter and windier than average conditions are slightly more likely than normal, especially in the west and northwest." Well - that's not going to happen. Things are going to settle down quite considerably. For all their computer power and experts the MetO are as apt to get it wrong as the rest of us once range is out at 336h, even with ensemble tools. And if the MetO cant get it right using their kit and the ensembles at 336h why would we place much credence in op runs at the same range now? I'm happy. It is only 9 Dec. I have seen 3cm of snow for about half a day and more frosts in the last 2 weeks than in many winters gone by in total. The long toothed members here can recall weeks and weeks of mild dross and no frosts. Not so this year. And we have a big high about to set up shop, gradually ease its way north, and drivers in the background aligning for something more substantial. Only timing is the bugger - but frankly I wont care if it delays a week and takes until New Year for this to click. Goodnight all. Fingers crossed for more general optimism tomorrow.

I haven’t read anyone suggesting it is, nor are many people on here interested much in the next 10 days. That general pattern is set. What comes after is of significant interest, timescales uncertain, because of what is lining up in the wings. It feels as though you are spoiling for an argument, but over what I’m not sure.

Lots of jitters in here today. Eyes seem to have gone freely to the FI zone - and folks are getting frustrated because op runs at 300h (22 Dec) aren’t showing Siberia knocking on our door. Similarly now with the MJO - because there isn’t a high amplitude phase 8 signal on the EC or GFS out at 10-14 days it is a disaster. There is never a guarantee of anything. But to be fraught over the accuracy of NWP at this kind of range is not sensible. Instead look for patterns. There is no doubt that the MJO is going to run into phase 7/8 territory soon. There is little to no doubt that in a week’s time there will be a mid lat block - and a strong one - in place over the U.K. Similarly, little to no doubt that the strat vortex is going to come under significant pressure as this month progresses. Ensemble runs are showing a very strong North Pacific trough consistently and that will keep the US mild as well as promote the ridging potential in our sector. So….nothing has changed. We are going to be in a holding pattern now for several more days, until we see the block emerge, find out just how much amplitude the MJO will have as it hits phase 7/8, assess the impact of what looks to me a very likely chain of positive torque events, first East Asia courtesy of a trough descending towards China and that North Pacific trough running up against the Rockies. A combination of these is still highly likely to promote Nino phases within the GWO orbit, and that means more blocking potential. By all means pull up op runs at 300h and look for trends. Focus more on ensembles. But be clear that NWP is going to struggle to resolve the Xmas period and beyond until a particularly uncertain phase in the development of key drivers is resolved. It might all go belly up, but we certainly aren’t going to know one way or another for a while yet. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4972994

Lots of jitters in here today. Eyes seem to have gone freely to the FI zone - and folks are getting frustrated because op runs at 300h (22 Dec) aren’t showing Siberia knocking on our door. Similarly now with the MJO - because there isn’t a high amplitude phase 8 signal on the EC or GFS out at 10-14 days it is a disaster. There is never a guarantee of anything. But to be fraught over the accuracy of NWP at this kind of range is not sensible. Instead look for patterns. There is no doubt that the MJO is going to run into phase 7/8 territory soon. There is little to no doubt that in a week’s time there will be a mid lat block - and a strong one - in place over the U.K. Similarly, little to no doubt that the strat vortex is going to come under significant pressure as this month progresses. Ensemble runs are showing a very strong North Pacific trough consistently and that will keep the US mild as well as promote the ridging potential in our sector. So….nothing has changed. We are going to be in a holding pattern now for several more days, until we see the block emerge, find out just how much amplitude the MJO will have as it hits phase 7/8, assess the impact of what looks to me a very likely chain of positive torque events, first East Asia courtesy of a trough descending towards China and that North Pacific trough running up against the Rockies. A combination of these is still highly likely to promote Nino phases within the GWO orbit, and that means more blocking potential. By all means pull up op runs at 300h and look for trends. Focus more on ensembles. But be clear that NWP is going to struggle to resolve the Xmas period and beyond until a particularly uncertain phase in the development of key drivers is resolved. It might all go belly up, but we certainly aren’t going to know one way or another for a while yet.

There's no change in the signals this morning - a few of our US weather passionate cousins are wailing and gnashing their teeth over a very mild and flat forecast pattern for them - but this is gravy on the turkey for us. Once we get into the interesting final third of the month we can chalk off concerns over cold US air helping locally to enhance low pressure development. And in that old simple minded maxim - if arctic air isnt flooding the US then the same air is up for grabs to flood somewhere else! For a few more days - unless the signals change - the best thing to do is stick to ensemble runs in the extended. Here is GEFS for a few days before Xmas. Nothing here to concern UK snow hunters - and this is the position before we get the knock on impacts of developments upstream. Look at the size and depth of that north pacific trough signal. Wow. HP downstream of the Rockies too. Expect to see some major US torque and warm air firing up into the strat. SSW for early January has to be considered as more than just a possibility now. We want a split if we are to stand a chance of something more than the Blankety Blank Chequebook and Pen.... Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4972594

There's no change in the signals this morning - a few of our US weather passionate cousins are wailing and gnashing their teeth over a very mild and flat forecast pattern for them - but this is gravy on the turkey for us. Once we get into the interesting final third of the month we can chalk off concerns over cold US air helping locally to enhance low pressure development. And in that old simple minded maxim - if arctic air isnt flooding the US then the same air is up for grabs to flood somewhere else! For a few more days - unless the signals change - the best thing to do is stick to ensemble runs in the extended. Here is GEFS for a few days before Xmas. Nothing here to concern UK snow hunters - and this is the position before we get the knock on impacts of developments upstream. Look at the size and depth of that north pacific trough signal. Wow. HP downstream of the Rockies too. Expect to see some major US torque and warm air firing up into the strat. SSW for early January has to be considered as more than just a possibility now. We want a split if we are to stand a chance of something more than the Blankety Blank Chequebook and Pen....

In other news - oh looky looky Separation at 30hpa on GFS. It's an extended GFS op run - we all know what that means - but the weight of data pointing in the same direction is beginning to be more than a little noteworthy. Can we get a trop induced high lat blocking pattern then reinforced by top down vortex impacts over time? I would like to live through a winter season that gets a BBC documentary all of its own that my grandchildren and great grandchildren will watch with interest one day. "Daddy - what were you doing during the Great Winter of 2023/24?" Putting feet back on Planet Earth - fun times ahead I think with multiple outcomes possible over the season, but a return of cold at the end of the month looks increasingly likely to me. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4972141

US and Canada looking increasingly warm through later December. About time that North Pacific ridge that has been semi permanent for years goes into retreat and stops promoting the Atlantic train…

Because if we get it wrong the world keeps spinning. If the MetO gets a big call wrong it has reputational and consequently business impact. They will never ever go all in on a cold spell at extended range. These spells are rare in the UK first of all, and cold calls therefore carry much greater risk (and substantial media attention.) I'm betting their teams are watching all the same drivers as we are and they will be very aware of the potential for a cold spell on the horizon, but until it comes into semi-reliable NWP range they will stick to fence sitting. The do also have some high res tools that I think give them a distinct edge when we get to around 240h or so. But out at 300h plus NWP forecasting is fraught with unreliability. Look at modelling of the MJO, notoriously hard to get right. No way certainty can follow if big drivers like this retain mystery. FI GEFS mirroring EPS. All good.

It feels a fair call. MJO high amplitude phase 7 somewhere between 14-16 Dec (as often happens the timeline has slipped a bit) and that means phase 8 transition somewhere around 20 Dec. Remember recent posts about peak impacts of +EAMT not until 21 Dec and lagged impacts of the MJO progression probably not until 21 Dec and after also. So - until we get to the week of Xmas itself the chances of deep cold are low (though better than during the current westerly wet hammering phase!). We will start to see and feel the gradual transition from roughly 16/17 Dec as the UK block emerges but it is going to take 10 days or so for the kick we need to push it to high latitude. Every mile of northerly progress will be key in getting some frost and cold in place, something which will help enormously if we then get a trough dropping in from the north. MetO text leaves us hanging for that late phase post Xmas. Whichever way the weather goes they have their bases covered. Don't be surprised if the timeline slips a bit further. In many years of hunting and watching for cold spells things seem to evolve slower, and rarely faster, than early signs suggest.

Here we go - outer limits EPS beginning to smell the coffee.