Catacol

Not really understanding this one. The only trend I see here is for winds to decrease on each run 24-26 Dec before seeing a slight increase on the 27th. And the bottom of each curve sits at around the 14 day mark, a point which is well documented as being the outer limit of model skill for strat reversal. It may well be that this event ends up less strong than we hope but this particular dataset is of no concern to me. If ECM starts to reverse inside the 12 day mark then I’ll start chewing my lip. Meanwhile from yesterday

Ha - your kids are going back later than most in that case! But yes, things continue to line up. Top priority today will be to see the ECM strat forecast to see whether the less impressive forecast yesterday was a blip or a new pathway. Relevant to the back end of January. In terms of the more near term pattern let’s just ponder this ECM from overnight. Hehe - ummmm - yes ok. That’s clear then. . Model confusion as the pattern starts to change due to developments already flagged upstream. Same NWP chaos as yesterday. Going to be a fun watch.

Ah - missed that one so thanks. She is great. Very knowledgeable and passionate about the stratosphere. We have all the big guns posting with confidence about what is about to transpire despite the earlier Huffman tweet. From my very amateur perspective the flux she discusses here, which I also put into a post last night, is not well modelled by NWP. It is an area that is perhaps open to human interpretation more than others. When one factors in the consistency of the Ural/Aleutian pattern in recent weeks and then the magnitude of the jet extension happening now as a result of a huge +EAMT event I think we can be confident that the strat is about to hit very hard indeed, and perhaps harder than modelling is projecting still. Given that NWP underestimates flux impacts on the strat at long lead times we have a modelling context in situations like this where output is constantly playing catch up. I remember the same in 2018...at least I think I do! GFS modelling on 24/12 and 25/12 was better for a strat split than today. If we get a return of the split profile tomorrow, making 3 out of the 4 most recent op runs seeing a split, then I will start to breathe a little easier. If we end up with a reinforcement of today's less bullish runs then it will be nail biting time. But even without a split we are looking at a context very favourable for cold down the line. However, I'm greedy. I want that split because I want to see chances of something akin to 2018 but 4-5 weeks earlier happen if at all possible! Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984618

Agreed. Average crap is getting crappier and we are getting more of it too.....but extremes are the order of the day and cold extremes remain on the table alongside all the others. To bed now, but for the NWP junkies yet more cold news from the GEFS 18z. Still rolling out but this is pretty decent as cold things go...

Ah - missed that one so thanks. She is great. Very knowledgeable and passionate about the stratosphere. We have all the big guns posting with confidence about what is about to transpire despite the earlier Huffman tweet. From my very amateur perspective the flux she discusses here, which I also put into a post last night, is not well modelled by NWP. It is an area that is perhaps open to human interpretation more than others. When one factors in the consistency of the Ural/Aleutian pattern in recent weeks and then the magnitude of the jet extension happening now as a result of a huge +EAMT event I think we can be confident that the strat is about to hit very hard indeed, and perhaps harder than modelling is projecting still. Given that NWP underestimates flux impacts on the strat at long lead times we have a modelling context in situations like this where output is constantly playing catch up. I remember the same in 2018...at least I think I do! GFS modelling on 24/12 and 25/12 was better for a strat split than today. If we get a return of the split profile tomorrow, making 3 out of the 4 most recent op runs seeing a split, then I will start to breathe a little easier. If we end up with a reinforcement of today's less bullish runs then it will be nail biting time. But even without a split we are looking at a context very favourable for cold down the line. However, I'm greedy. I want that split because I want to see chances of something akin to 2018 but 4-5 weeks earlier happen if at all possible!

Yes - things are only moving in one direction at the moment. Cold hunters in here deserve a bit of luck - let's hope the trend in both trop and strat continues to firm up.

Jittery in here tonight - even X is causing some angst! For what it is worth the 4 people on X I follow with some genuine respect are Simon Lee, Anthony Masiello, Eric Webb and Amy Butler. Amy has gone quiet this season and I think Anthony has abandoned X for now, but both Simon and Eric are very active and worth following. Those questioning - will it, won't it....and it hasn't happened yet might perhaps reflect on the much wider context. I put out a post last night that gave a pretty full analysis of what is going on - but to reiterate in brief: NWP output is not produced in a vacuum. There are processes and trends going on that are still identifiable from a human perspective in a way that computer modelling doesn't see, and the context at the moment is strong for northern blocking in the medium term. Momentum is high, the pacific jet is extended, the MJO is in a good place right now. These don't guarantee a cold block because twists and turns happen but I think estimates of 10-20% chance of cold/snow are miserly. We probably had that kind of % over the Xmas period once the MJO began to falter, remembering that the longer term drivers were not anywhere near as well aligned in mid December as they are now. I think chances of cold given the current context must come in at better than 50% and I'd be tempted to go with 70%. And this is without an SSW. If we get it, and the odds are in favour, then we have a split driven through the north atlantic sector that must - as Eric Webb has posted today - increase the chances of extended Greenland blocking. And if we get that 2018 style shard from the split dropping down into Russia then we can expect frictional forcing to support frigid easterlies. This will be further down the track and we must watch closely what happens in the strat in the next 7-10 days, but the trends are looking rather good I'd say. For those who feel NWP is the only way to go and are not sold on the stuff above, let's just go with the EPS for now. The trend towards northern heights before we get to the end of week 1 January is bedding in. If you don't value the drivers that make things happen, then let the computers provide some confidence. By Jan 10 the signal is strengthened further. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4984601

Jittery in here tonight - even X is causing some angst! For what it is worth the 4 people on X I follow with some genuine respect are Simon Lee, Anthony Masiello, Eric Webb and Amy Butler. Amy has gone quiet this season and I think Anthony has abandoned X for now, but both Simon and Eric are very active and worth following. Those questioning - will it, won't it....and it hasn't happened yet might perhaps reflect on the much wider context. I put out a post last night that gave a pretty full analysis of what is going on - but to reiterate in brief: NWP output is not produced in a vacuum. There are processes and trends going on that are still identifiable from a human perspective in a way that computer modelling doesn't see, and the context at the moment is strong for northern blocking in the medium term. Momentum is high, the pacific jet is extended, the MJO is in a good place right now. These don't guarantee a cold block because twists and turns happen but I think estimates of 10-20% chance of cold/snow are miserly. We probably had that kind of % over the Xmas period once the MJO began to falter, remembering that the longer term drivers were not anywhere near as well aligned in mid December as they are now. I think chances of cold given the current context must come in at better than 50% and I'd be tempted to go with 70%. And this is without an SSW. If we get it, and the odds are in favour, then we have a split driven through the north atlantic sector that must - as Eric Webb has posted today - increase the chances of extended Greenland blocking. And if we get that 2018 style shard from the split dropping down into Russia then we can expect frictional forcing to support frigid easterlies. This will be further down the track and we must watch closely what happens in the strat in the next 7-10 days, but the trends are looking rather good I'd say. For those who feel NWP is the only way to go and are not sold on the stuff above, let's just go with the EPS for now. The trend towards northern heights before we get to the end of week 1 January is bedding in. If you don't value the drivers that make things happen, then let the computers provide some confidence. By Jan 10 the signal is strengthened further.

Read the tweet replies. He was basing it on the wrong dataset. Simon Lee challenged it and then 2 hours ago posted his own tweet. I'd read that one instead....

I love it when the models struggle for coherence. ECM toward the end of the run is a mess - doesn’t know if it is coming or going. Sure sign that things are becoming more than a little interesting…

Not SSW - driven by tropospheric factors already in play.

Well - here we go. Time to forget the Xmas chase entirely and focus on the path into January that always looked a more likely landing zone for extended cold given the ENSO signature. And the signals are lining up. First of all we have the expected firing up of mountain torque, sending the pacific jet into overdrive and prompting eddy patterns in the atlantic Don’t underestimate the likely impact on the vortex as well further down the line of such a massive spike off the Tibetan plateau. GLAAM now very strongly positive …and this now means we are firmly in coupled Nino territory. GWO orbit consequently climbing fast, and this means high lat blocking and probably split flow potential too Supportive of this very positive overall picture is the MJO which has not fallen into COD territory as EC and GFS had it doing - instead we have a decent amplitude phase through 8/1 until we get to the end of the calendar year and the wave resets in the IO. All of this means we have an extremely positive envelope for blocking potential to work within as we move through New Year and into the first week of January. NWP beginning to play catch up. And running parallel to this, the vortex looks set to be shredded. Strong poleward heat flux in week 1 of 2024 likely to provide a killer blow A savage warm air assault on the vortex illustrated here - mostly wave 1 but with some wave 2 impacts also. Currently the likely angle of this split (which is what we look to be heading towards) puts the U.K. in a good place for further impacts with one vortex shard breaking towards Scrussia and the other into Canada, allowing further blocking potential over Griceland - just in case the very positive tropospheric drivers aren’t enough! Beyond this? Best to wait and see. All I will say at this early stage is that a 2018 style event is possible which, given we are 6 weeks earlier in winter, would be brutal. But there is still much to unravel yet and best not expecting the kind of downwelling response we got 6 years ago quite yet. Need to see how blocking emerges, how the vortex actually splits - if it splits. This is going to make for some fabulous watching. NWP is going to upgrade steadily. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4983959

Well - here we go. Time to forget the Xmas chase entirely and focus on the path into January that always looked a more likely landing zone for extended cold given the ENSO signature. And the signals are lining up. First of all we have the expected firing up of mountain torque, sending the pacific jet into overdrive and prompting eddy patterns in the atlantic Don’t underestimate the likely impact on the vortex as well further down the line of such a massive spike off the Tibetan plateau. GLAAM now very strongly positive …and this now means we are firmly in coupled Nino territory. GWO orbit consequently climbing fast, and this means high lat blocking and probably split flow potential too Supportive of this very positive overall picture is the MJO which has not fallen into COD territory as EC and GFS had it doing - instead we have a decent amplitude phase through 8/1 until we get to the end of the calendar year and the wave resets in the IO. All of this means we have an extremely positive envelope for blocking potential to work within as we move through New Year and into the first week of January. NWP beginning to play catch up. And running parallel to this, the vortex looks set to be shredded. Strong poleward heat flux in week 1 of 2024 likely to provide a killer blow A savage warm air assault on the vortex illustrated here - mostly wave 1 but with some wave 2 impacts also. Currently the likely angle of this split (which is what we look to be heading towards) puts the U.K. in a good place for further impacts with one vortex shard breaking towards Scrussia and the other into Canada, allowing further blocking potential over Griceland - just in case the very positive tropospheric drivers aren’t enough! Beyond this? Best to wait and see. All I will say at this early stage is that a 2018 style event is possible which, given we are 6 weeks earlier in winter, would be brutal. But there is still much to unravel yet and best not expecting the kind of downwelling response we got 6 years ago quite yet. Need to see how blocking emerges, how the vortex actually splits - if it splits. This is going to make for some fabulous watching. NWP is going to upgrade steadily.

Has to be flushed out before the impacts of the reversal can be felt. Standard stuff - hence the lagged nature of SSW impacts. How lagged? There lies the conundrum. I notice on X today that EC chances of an SSW are now at 88%. Before we get there though we have chances of tropospheric led cold. Double whammy!

A downwelling response to a vortex split changes the board completely. No vortex energy means heights to the south are free - indeed encouraged - to migrate poleward. There is no guarantee that things will align for U.K. cold as they did so well back in 2018, but the idea that the Azores High is destined to remain fixed over or close to Iberia in the aftermath of a major split SSW (if it downwells) is not the case. Lots of water to flow under the bridge over the next few weeks, and plenty that can go wrong - but if we get the 2018 kind of setup then a limpet Iberian ridge will not be a concern.

Merry Xmas everyone! Trop split quickly followed by Strat split Roll on The New Year…. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4983518

Merry Xmas everyone! Trop split quickly followed by Strat split Roll on The New Year….

Starting to look more than likely…

I think you are right. We are experiencing a rising tide of GLAAM with GWO now firmly in the Nino phases - and these are supportive of high lat blocking. The MJO currently also in the beneficial phases. We have the strat vortex looking as though it will be begging for its life by the New Year. We did not quite get the Pacific kick we needed to force a cold block for Xmas and prior to that the predictable IO transition alongside a Nina-like momentum profile meant we had a dour middle to the month, but there is every reason to be optimistic that things will turn. From here things will hinge on: - GLAAM remaining high for a decent length of time because any downwelling impacts from a SSW will take time. I’m greedy. I want a block between NY and mid month with longevity and then we will see what a SSW might bring on top… - MJO staying in as high a 7/8/1 orbit as possible. We are seeing a compromise solution between what the EC and BOM was showing 10 days ago and we need the CPC prediction of a reamplifying signal in the western pacific to come true. - Warmth making a mess of the Strat vortex. This is key. If it is bumped but not broken then chances of cold weather later in January and on into February take a hit in my opinion. At the very least we need a displacement and reversal centred largely over Siberia…but the pot of gold scenario is a split and fast downwell. We had very good tropospheric precursor patterns earlier in December, in particular an ongoing deep Aleutian trough that it looks as though fired plenty of toasty air vertically upwards and with sufficient poleward direction to create the current forecasts. The best NWP output is not good at reading strat developments regarding an SSW so it is a watch and wait style brief. As you say - given we are moving out of the barren lands of mid Dec we should be seeing some good charts before long. The failed Xmas cold that centred on the MJO passage can soon be forgotten if a combination of factors clicks over the next 2-3 weeks.

Hard to be certain…but one of the artefacts of CC is the northerly shunt of the sub tropical high pressure belt. When we combine this with a generally stronger stratospheric polar vortex (another consequence of CC caused by a cooling stratosphere) we have a more difficult envelope for high latitude ridges in winter. Pressure from the north in terms of the vortex and from the south in terms of a more obvious and intrusive Azores/Euro High suggests to me that we get less cold blocking and tropospheric forcing from the pacific is less reliable and dominant in shaping patterns. This is why I continue to think that we need the removal of one of these factors in order to achieve cold…and there is little sign of the Hadley Cell retreating….so that leaves the vortex. I have a totally unevidenced sense that CC might provide more frequent setups for SSWs to occur though we will need a much longer tale of the tape to be sure. So…in winters without a SSW we are really up against it to see a properly cold spell but when we get a SSW we are in the game…though admittedly an SSW is not a guarantee of anything and the 2018 style setup is unlikely to become common. Our grandchildren may reflect on a U.K. context which sees properly cold spells in winter becoming a 1 in 10 year event. Sadly I’m not sure the direction of travel suggests anything other than this. I grew up in the 80s when cold spells were common. Those days - until something significant changes in the climate - are gone for now. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4981762

Hard to be certain…but one of the artefacts of CC is the northerly shunt of the sub tropical high pressure belt. When we combine this with a generally stronger stratospheric polar vortex (another consequence of CC caused by a cooling stratosphere) we have a more difficult envelope for high latitude ridges in winter. Pressure from the north in terms of the vortex and from the south in terms of a more obvious and intrusive Azores/Euro High suggests to me that we get less cold blocking and tropospheric forcing from the pacific is less reliable and dominant in shaping patterns. This is why I continue to think that we need the removal of one of these factors in order to achieve cold…and there is little sign of the Hadley Cell retreating….so that leaves the vortex. I have a totally unevidenced sense that CC might provide more frequent setups for SSWs to occur though we will need a much longer tale of the tape to be sure. So…in winters without a SSW we are really up against it to see a properly cold spell but when we get a SSW we are in the game…though admittedly an SSW is not a guarantee of anything and the 2018 style setup is unlikely to become common. Our grandchildren may reflect on a U.K. context which sees properly cold spells in winter becoming a 1 in 10 year event. Sadly I’m not sure the direction of travel suggests anything other than this. I grew up in the 80s when cold spells were common. Those days - until something significant changes in the climate - are gone for now.

Thanks Feb - but still no joy. If you set the date to 4 Dec are you able to make those load?

Anyone know what's happened to the archive charts? Mine on NetW and also Meteociel won't load. I'm wanting to go back and look at SSW precursor patterns around 3-4 weeks ago....

The more drivers that align the better. Quantity is good. Your question is an interesting Pub Quiz style approach though. I quite like the idea of coming up with the theoretical "best mix" combo for an upcoming cold spell. For me I'd go: 1. Weak to moderate El Nino. Allows a positive momentum context without too much to scupper things... 2. eQBO for sure. This is key for enhancing blocking scenarios. 3. Low solar. Evidence suggests this weakens the jet. 4. QBO orbiting phases 5-8. Nino phases, so atmosphere in harmony with the ENSO backdrop. 5. Then - once this is all in place, I'd look for a high amplitude MJO progression through 7/8/1 combined with the right pressure differential over China to extend the pacific jet. This creates the right kind of Rossby wave setup along with a momentum burst for wave eddy opportunity. Get this at a time of points 1-4 and you have a pretty damned good chance of a cold shot. The other method would be the potent Ural/Aleutian Combo. There is the perfect blueprint for this. Go and look at hemispheric charts for 14 Jan 2018. That synoptic pattern set the vortex up for a shattering and a top down frictional setup that made all tropospheric drivers irrelevant such was the force of this occurrence. The vortex split, the negative winds dropped down through the layers and we had that vortex shard work from E to W across Siberia and towards Eastern Europe that led to the unbelievable chart showing winds blowing from Siberia to Canada the wrong way. I'm not sure if such a stratospheric event will ever happen like this again in my lifetime - I live in hope, and in hope that it can happen a few weeks earlier/faster - but it showed an alternative route to cold that may end up being, in the fullness of time, the best hope for sustained UK cold. The problem with points 1-5 at the top of this post is that CC is messing around with the ENSO context, the Hadley Cell has shifted north and overall the reliability of these factors to provide a sustained NE flow in winter when the vortex is present is reducing. Remember too that CC is creating a warming troposphere but a cooling stratosphere. We see this most years now with temps in the stratosphere noticeably below climatological average most of the time. This whips up the stratospheric vortex, and that alone makes winter high lat blocks harder to achieve. This year we have a ropey 1 (Nino is a bit strong), 2 and chances at 4 + 5. We don't have 3. It isn't a perfect setup....but its better than many other years we have had recently. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4980203

The more drivers that align the better. Quantity is good. Your question is an interesting Pub Quiz style approach though. I quite like the idea of coming up with the theoretical "best mix" combo for an upcoming cold spell. For me I'd go: 1. Weak to moderate El Nino. Allows a positive momentum context without too much to scupper things... 2. eQBO for sure. This is key for enhancing blocking scenarios. 3. Low solar. Evidence suggests this weakens the jet. 4. QBO orbiting phases 5-8. Nino phases, so atmosphere in harmony with the ENSO backdrop. 5. Then - once this is all in place, I'd look for a high amplitude MJO progression through 7/8/1 combined with the right pressure differential over China to extend the pacific jet. This creates the right kind of Rossby wave setup along with a momentum burst for wave eddy opportunity. Get this at a time of points 1-4 and you have a pretty damned good chance of a cold shot. The other method would be the potent Ural/Aleutian Combo. There is the perfect blueprint for this. Go and look at hemispheric charts for 14 Jan 2018. That synoptic pattern set the vortex up for a shattering and a top down frictional setup that made all tropospheric drivers irrelevant such was the force of this occurrence. The vortex split, the negative winds dropped down through the layers and we had that vortex shard work from E to W across Siberia and towards Eastern Europe that led to the unbelievable chart showing winds blowing from Siberia to Canada the wrong way. I'm not sure if such a stratospheric event will ever happen like this again in my lifetime - I live in hope, and in hope that it can happen a few weeks earlier/faster - but it showed an alternative route to cold that may end up being, in the fullness of time, the best hope for sustained UK cold. The problem with points 1-5 at the top of this post is that CC is messing around with the ENSO context, the Hadley Cell has shifted north and overall the reliability of these factors to provide a sustained NE flow in winter when the vortex is present is reducing. Remember too that CC is creating a warming troposphere but a cooling stratosphere. We see this most years now with temps in the stratosphere noticeably below climatological average most of the time. This whips up the stratospheric vortex, and that alone makes winter high lat blocks harder to achieve. This year we have a ropey 1 (Nino is a bit strong), 2 and chances at 4 + 5. We don't have 3. It isn't a perfect setup....but its better than many other years we have had recently.