Catacol

Talking +EAMT and jet extension here is the current EPS for the days before Xmas, backing up the GEFS same period as per Webb yesterday. That is the by product of low pressure dropping down the eastward edge of the Siberian high and engaging with high pressure east of Tibet. Trigger here Until by the 16th the low pressure is exiting east of the plateau Interesting to get a time lag calculation on this - looks like around a week. Whatever else is happening in our sector of the atlantic at around this same time, we are looking at a significant momentum burst into a pattern already sympathetic towards an MJO induced high lat block over Greenland. Timing, as ever, difficult - but from Xmas to New Year we do look to have great context to look forward to. Now then....what year featured a Canadian Warming in November that then produced a surging blocking pattern on Boxing Day? Hmmmm. Running the NOAA archive for that year it is interesting to see that December also started blocked, and then turned mobile in the middle. Just saying. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4972136

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.

Talking +EAMT and jet extension here is the current EPS for the days before Xmas, backing up the GEFS same period as per Webb yesterday. That is the by product of low pressure dropping down the eastward edge of the Siberian high and engaging with high pressure east of Tibet. Trigger here Until by the 16th the low pressure is exiting east of the plateau Interesting to get a time lag calculation on this - looks like around a week. Whatever else is happening in our sector of the atlantic at around this same time, we are looking at a significant momentum burst into a pattern already sympathetic towards an MJO induced high lat block over Greenland. Timing, as ever, difficult - but from Xmas to New Year we do look to have great context to look forward to. Now then....what year featured a Canadian Warming in November that then produced a surging blocking pattern on Boxing Day? Hmmmm. Running the NOAA archive for that year it is interesting to see that December also started blocked, and then turned mobile in the middle. Just saying.

Spotted, courtesy of Eric Webb. How’s this for a jet streak at FI range from an ensemble mean? Bring on the wave breaking….

I'm still jealous of your foot of snow comment from the other day! Agree that GFS can accelerate things and that Xmas to New Year week might be better for all. Chaos on the roads on Xmas Eve or Boxing Day is actually not what anyone wants. I'm trying to get my head around timings. We had a good trend towards a Nino coupled ocean/atmosphere in November that helped bring about the cold we got, but we did see a big fall back in total GLAAM. Now the recovery is underway. How fast will it recover? Will we see proper coupling between ocean and atmosphere in the coming weeks? The commentary I am reading around the decline of the +IOD suggests yes, and we can look forward to Nino-esque GWO phases towards the end of this month and on into January. That is all good news. But what, meanwhile, about the vortex and its shape/influence? Already it is below climatological average and forecast to decline further. This chart makes me think a SSW has to happen - lead times for SSW forecasts are normally sub 14 days for any accuracy, but the sheer weight of long term indicators for a SSW cannot help but force the forecast. That decline sets us up beautifully for later in January and on into February....but what about December? Currently the vortex has shifted away from the Siberian sector as the impact of the early Canadian Warming that helped enhance our cold spell fades. As the UK block emerges next week we have the centre of the lower strat vortex over Greenland and I wonder to what extent this will work against that mid lat high pushing up to high latitude prior to Xmas. Hard to know. With it being weak, or weaker than average at least for this time of year, it is possible we can overemphasise its impact...but then again it may work to suppress heights a bit. Which will hold the whip hand? The sensible line would be to go with the slow burn analysis I put out yesterday. Trop led enhancement of high lat blocking potential from 16/17 Dec onwards, but only slowly coming to fruition as the vortex shifts away from Greenland once again (GFS has it heading back east by 22/12) and hopefully an extended period of MJO phase 8 emerges. So. Mid lat block. Slow evolution towards the phase 8 composite as temperatures drop. Deep cold around 27/28 December onwards courtesy of a NE blast. Cold to be sustained by AAM-linked factors through the New Year and then.....bang. Vortex pops. At that point the sensible position is to halt the forecast because an SSW would possibly pass the whip from the pacific to the vortex in terms of driving our weather. And that could either make things even colder and have winter dig in....or we could get unlucky and have a shifted vortex or vortex shard set up shop over the north atlantic and enhance a westerly regime in our sector. Way too far ahead that. Fun and games. I don't know what I'd do in my winter time lunch breaks without the weather to absorb me.... Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4971604

I'm still jealous of your foot of snow comment from the other day! Agree that GFS can accelerate things and that Xmas to New Year week might be better for all. Chaos on the roads on Xmas Eve or Boxing Day is actually not what anyone wants. I'm trying to get my head around timings. We had a good trend towards a Nino coupled ocean/atmosphere in November that helped bring about the cold we got, but we did see a big fall back in total GLAAM. Now the recovery is underway. How fast will it recover? Will we see proper coupling between ocean and atmosphere in the coming weeks? The commentary I am reading around the decline of the +IOD suggests yes, and we can look forward to Nino-esque GWO phases towards the end of this month and on into January. That is all good news. But what, meanwhile, about the vortex and its shape/influence? Already it is below climatological average and forecast to decline further. This chart makes me think a SSW has to happen - lead times for SSW forecasts are normally sub 14 days for any accuracy, but the sheer weight of long term indicators for a SSW cannot help but force the forecast. That decline sets us up beautifully for later in January and on into February....but what about December? Currently the vortex has shifted away from the Siberian sector as the impact of the early Canadian Warming that helped enhance our cold spell fades. As the UK block emerges next week we have the centre of the lower strat vortex over Greenland and I wonder to what extent this will work against that mid lat high pushing up to high latitude prior to Xmas. Hard to know. With it being weak, or weaker than average at least for this time of year, it is possible we can overemphasise its impact...but then again it may work to suppress heights a bit. Which will hold the whip hand? The sensible line would be to go with the slow burn analysis I put out yesterday. Trop led enhancement of high lat blocking potential from 16/17 Dec onwards, but only slowly coming to fruition as the vortex shifts away from Greenland once again (GFS has it heading back east by 22/12) and hopefully an extended period of MJO phase 8 emerges. So. Mid lat block. Slow evolution towards the phase 8 composite as temperatures drop. Deep cold around 27/28 December onwards courtesy of a NE blast. Cold to be sustained by AAM-linked factors through the New Year and then.....bang. Vortex pops. At that point the sensible position is to halt the forecast because an SSW would possibly pass the whip from the pacific to the vortex in terms of driving our weather. And that could either make things even colder and have winter dig in....or we could get unlucky and have a shifted vortex or vortex shard set up shop over the north atlantic and enhance a westerly regime in our sector. Way too far ahead that. Fun and games. I don't know what I'd do in my winter time lunch breaks without the weather to absorb me....

It's going to be hard not to become obsessed with chances for cold/snow on Xmas Day.... it would be fantastic to see a proper nationwide snow event on the 25th but even with a favourable pattern such as we have seen evolve over the last few weeks (and is continuing to evolve positively) it is an outside bet. Anyway. The value of reading drivers and then using a point in time to reference a potential development and benchmark against op runs has been shown to be positive. At a rough count over the last several days about 75% of op runs have had a UK high in place for next weekend as pacific impacts begin to work through, and we have an EPS now for Sat 16 that is about as close to nailed on medium range forecast as we can get. Again - note the Russian High and Aleutian Low combo. Note also a pattern that is quite meridional across the hemisphere. This is anything but a flat picture, and the trick in our sector is to get this strong azores ridge to kick higher. That kick doesn't just "happen." It will be the product of drivers that have been well referenced over the last few weeks, drivers that we are confident are being under represented by NWP at the moment. @Met4Cast referenced torques earlier which is one...and the MJO is another. We continue to see BOM going high amplitude - and as one of the top 3 MJO models it has credence - but ECM not following suit. At least - not yet. Others have posted these charts this morning - I won't duplicate. If we put some weight on composites then these are worth considering. Phase 7 Dec looks like this = significant similarity for the end of next week when compared to ENS and direction of Op runs. Phase 8 then goes here: Even without a great degree of amplitude in the GFS/ECM MJO forecasts we are seeing a move in this direction in the GFS extended. See Sat 23rd: The question would be - if GFS is picking up on this now with a low amplitude pacific forecast and one we actually hit phase 7/8 the amplitude is much higher, what occurs? In a nutshell greater meridionality. So - punch that high further north, drop that low further south. Both GFS and ECM bias corrected MJO models have phase 8 being each around 19/20 December. To me the lag of this impact will be longer - so the models are over accelerating the changes that are coming. Deep cold by Xmas? Might be more a case of deep cold by New Year. A little snip from the CPC assessment on Monday: All good. White Xmas might be a stretch in terms of timing but not an outrageous possibility. But no bumps in the road for the overall progression - not yet anyway. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4971584

It's going to be hard not to become obsessed with chances for cold/snow on Xmas Day.... it would be fantastic to see a proper nationwide snow event on the 25th but even with a favourable pattern such as we have seen evolve over the last few weeks (and is continuing to evolve positively) it is an outside bet. Anyway. The value of reading drivers and then using a point in time to reference a potential development and benchmark against op runs has been shown to be positive. At a rough count over the last several days about 75% of op runs have had a UK high in place for next weekend as pacific impacts begin to work through, and we have an EPS now for Sat 16 that is about as close to nailed on medium range forecast as we can get. Again - note the Russian High and Aleutian Low combo. Note also a pattern that is quite meridional across the hemisphere. This is anything but a flat picture, and the trick in our sector is to get this strong azores ridge to kick higher. That kick doesn't just "happen." It will be the product of drivers that have been well referenced over the last few weeks, drivers that we are confident are being under represented by NWP at the moment. @Met4Cast referenced torques earlier which is one...and the MJO is another. We continue to see BOM going high amplitude - and as one of the top 3 MJO models it has credence - but ECM not following suit. At least - not yet. Others have posted these charts this morning - I won't duplicate. If we put some weight on composites then these are worth considering. Phase 7 Dec looks like this = significant similarity for the end of next week when compared to ENS and direction of Op runs. Phase 8 then goes here: Even without a great degree of amplitude in the GFS/ECM MJO forecasts we are seeing a move in this direction in the GFS extended. See Sat 23rd: The question would be - if GFS is picking up on this now with a low amplitude pacific forecast and when we actually hit phase 7/8 the amplitude is much higher, what occurs? In a nutshell greater meridionality. So - punch that high further north, drop that low further south. Both GFS and ECM bias corrected MJO models have phase 8 being each around 19/20 December. To me the lag of this impact will be longer - so the models are over accelerating the changes that are coming. Deep cold by Xmas? Might be more a case of deep cold by New Year. A little snip from the CPC assessment on Monday: All good. White Xmas might be a stretch in terms of timing but not an outrageous possibility. But no bumps in the road for the overall progression - not yet anyway.

A little addendum to my earlier post, and then time to move on to other areas associated with the hunt. Since the 2018 paper I referenced and quoted from there have been further papers examining MJO skill. Many of the same points come up, particularly around modelling of moisture as a core problem and related to that cloudiness. One other recurring conclusion in each of the 3 papers I have just fast-read is around the transition through the Maritime Continent. So - from phase 6 to phase 7 approx. This quote sums it up from a paper posted with NASA in 2021: We can argue round and round about whether we are going to see an MJO progress as forecast....but whichever model we look at this issue with the MC holds true. And as this same paper concludes, winter time forecasting of the MJO as it passes through the MC into the 7/8/1 orbit is still affected by a tendency to under model amplification. All fine and dandy. End point of this issue = expect to see the MJO progress more strongly than most of the models (bar the BOM) are showing and therefore expect current NWP modelling of the atlantic pattern for the final third of the month to be off target and playing catch up. Once the MJO gets fully into phase 5 - several days away yet - then I continue to expect to see higher lat blocking appear in the runs. (Anyone any idea the last time the BOM was tweaked as a model? I'm wondering, since the 2018 paper, whether it has undergone a rejig. Can't find any really up to date verification stats....but its higher amplification than ECM bias corrected is noteworthy. An interesting piece of observational research we can do here perhaps.) Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4971035

Yes. And I think this one will be more sustained in terms of time line and will hopefully feature bigger impacts. Once the pattern switch beds in we then need some luck. But - baby steps. Let's get a blocked pattern back and then see whether we can source cold from the E and NE. The only negative for me at the moment is that it appears the deep Scandy cold will be pushed back as the Russian High loses some traction over the next week or so. Can rebuild extremely quickly of course but I had expected it to hold on a bit better. Never mind.

Date watch continuing to bear fruit. High pressure in place by next weekend and then signs now emerging consistently for ridging further north. Wont be long now before we get ECM op runs joining in the transitionary fun.

Hmmm. Its right at the outer edges of NWP and therefore an attempt to scan the horizon with only one eye half open - but today's 360h EPS is worth a mention Definite sign of a ridge there pushing up south of Greenland. Signs of troughing pushing south into Scandy. And I'm going to say it again - feels as though it has been a constant for eons - we have a Kara/Russian High and Aleutian Low. Poor old vortex... Vortex suffering. IOD fading. MJO coming around to 7/8/1 in a week or so. eQBO context. Nino context. Decent atlantic SST profile. Likely shift of global wind flows via increased GLAAM into a constructive Nino pattern conducive to atlantic blocking. This is a Calcutta Cup game at Murrayfield, England down to 13 players, Scotland 10 points up, only a quarter of the match to play. Can't guarantee George Ford wont drop 4 goals to win the game....but fans of a blue/cold victory have to be optimistic.....

Taking a look at other drivers while we wait for NWP to get itself sorted - the IOD would appear to have peaked. Again from BOM: "The positive Indian Ocean Dipole (IOD) event continues. IOD index values have eased from their highest values in October and are unlikely to re-strengthen, meaning the positive IOD event is likely past its peak. All international climate models surveyed by the Bureau suggest the positive IOD is likely to ease in December." Nothing to fear there - what we want to see if UK cold floats your boat.

A little addendum to my earlier post, and then time to move on to other areas associated with the hunt. Since the 2018 paper I referenced and quoted from there have been further papers examining MJO skill. Many of the same points come up, particularly around modelling of moisture as a core problem and related to that cloudiness. One other recurring conclusion in each of the 3 papers I have just fast-read is around the transition through the Maritime Continent. So - from phase 6 to phase 7 approx. This quote sums it up from a paper posted with NASA in 2021: We can argue round and round about whether we are going to see an MJO progress as forecast....but whichever model we look at this issue with the MC holds true. And as this same paper concludes, winter time forecasting of the MJO as it passes through the MC into the 7/8/1 orbit is still affected by a tendency to under model amplification. All fine and dandy. End point of this issue = expect to see the MJO progress more strongly than most of the models (bar the BOM) are showing and therefore expect current NWP modelling of the atlantic pattern for the final third of the month to be off target and playing catch up. Once the MJO gets fully into phase 5 - several days away yet - then I continue to expect to see higher lat blocking appear in the runs. (Anyone any idea the last time the BOM was tweaked as a model? I'm wondering, since the 2018 paper, whether it has undergone a rejig. Can't find any really up to date verification stats....but its higher amplification than ECM bias corrected is noteworthy. An interesting piece of observational research we can do here perhaps.)

A few thoughts in relation to this given the publication of a peer-reviewed paper on MJO modelling skill back in 2018. A few years old now, but likely still relevant: 1. Initial starting phase is important. This quote: We have seen this ourselves now. The forecast for the MJO while it was sitting in real time in 2/3 was low amplitude. This is now being revised up as we get close to entering phase 4. 2. An overall assessment of skill is reflected in this summary table. BOM comes out 2nd - ECMWF is top. 3. BOM has a significantly larger ensemble size and reforecast period. I would argue that this is because it matters to the Australian Met that they get Pacific conditions as accurate as possible. Locality does matter. 4. Further snippets on skill include: and this substantive table for starting phase of the forecast. This table for lead times given amplitude. My take away would be that ECM, BOM and UKMO are ahead of the pack. 5. And from the paper's conclusions some relevant statements:

Quite right. The previous final sentence had been there for days. They have simply rewritten the same long term prognosis using different words and added a standard disclaimer about likelihood of westerly dominance. I was surprised it wasn’t there in the weekend wording. EPS for mid month sticking to the script. High pressure rebuilding. From here we await signs that the GWO orbit is rising and responding to increased momentum - this should force the block higher. Specific timeline uncertain as always but my watching brief on Sat 16th is confirming likelihood of a U.K. block to start. MetO have identified the same today. Both ECM and GFS I think are underestimating the amplitude of the next wave. MJO plots remain weak for both models and those tracking these charts will note they have consistently underestimated the amplitude of the IO transition happening now. As soon as they get a handle on the MJO as it passes through the maritimes I expect NWP forecasts to shift. Dec 10 approx for entry into phase 7. Assuming there isn’t an enormous let down with the progress of the MJO, and assuming this aligns with an uptick in torques that will help drive the GWO into Nino phases, NWP is going to end up playing catch up here. Worth also stating the following. I’m pretty confident in this transition and continue to see enormous potential for Jan and Feb. The fact that seasonals have broadly been positive too is encouraging. But the weather doesn’t always follow the script. Look at the summer just gone. Dec 12 is still sharp in the memory. There have been plenty of others. We are playing a game of probabilities here and at the start of the season I made the point that a 5% v 95% setup doesn’t always fall the way of the 95. If this goes t*ts up it will be a blow and I for one will be left looking a bit daft….but forecasting involves risk. We either go with what we see or play it safe and don’t bother saying anything. I’ll stick with the former and accept the risk. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4970847

Quite right. The previous final sentence had been there for days. They have simply rewritten the same long term prognosis using different words and added a standard disclaimer about likelihood of westerly dominance. I was surprised it wasn’t there in the weekend wording. EPS for mid month sticking to the script. High pressure rebuilding. From here we await signs that the GWO orbit is rising and responding to increased momentum - this should force the block higher. Specific timeline uncertain as always but my watching brief on Sat 16th is confirming likelihood of a U.K. block to start. MetO have identified the same today. Both ECM and GFS I think are underestimating the amplitude of the next wave. MJO plots remain weak for both models and those tracking these charts will note they have consistently underestimated the amplitude of the IO transition happening now. As soon as they get a handle on the MJO as it passes through the maritimes I expect NWP forecasts to shift. Dec 10 approx for entry into phase 7. Assuming there isn’t an enormous let down with the progress of the MJO, and assuming this aligns with an uptick in torques that will help drive the GWO into Nino phases, NWP is going to end up playing catch up here. Worth also stating the following. I’m pretty confident in this transition and continue to see enormous potential for Jan and Feb. The fact that seasonals have broadly been positive too is encouraging. But the weather doesn’t always follow the script. Look at the summer just gone. Dec 12 is still sharp in the memory. There have been plenty of others. We are playing a game of probabilities here and at the start of the season I made the point that a 5% v 95% setup doesn’t always fall the way of the 95. If this goes t*ts up it will be a blow and I for one will be left looking a bit daft….but forecasting involves risk. We either go with what we see or play it safe and don’t bother saying anything. I’ll stick with the former and accept the risk.

BOM has the MJO stalling in phase 8 for a fortnight. Can't ask for much more than that from the perspective of encouraging a high lat blocking pattern. 10hpa strat forcing on the way down in the run up to Xmas with a large hatful of members going for a reversal in early January Very good looking EPS for the middle of next week in terms of mountain torque - note high pressure anomalies moving downstream of both the Rockies and the Tibetan Plateau You could pull data points from multiple sources at the moment and they are all leading in a single direction for the final third of the month and on into January. Given the slow burn nature of potential frictional vortex impacts and the lag implicit in MJO passage and torque effects (and as has been stated elsewhere this will impact alongside other factors on the anticipated rising GWO orbit that we hope will reflect strongly an atmosphere coupled to Nino forcings) it is important probably to emphasise that the pattern shift is likely to be gradual and then steadily intensify. The MetO text might be suggesting as much with their maintained "longer" "cold" spell. Any negatives? Tamara mentioned the caveat of a pacific wave pattern derailed by less than expected added momentum. Today's GFS hovmoller is the least impressive of the last few days. MJO passage still obvious but not as strong on this forecast as the one from November. I'm banking on the opposite being the case....time will well. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4970583

Date watch - UK high once again appears on the GFS for Sat 16 Genoa low in play...just needs that secondary shunt to force the ridge NW and drop that lovely deep trough straight down through the UK...but probably a reach from this setup. Maybe the next pulse.

BOM has the MJO stalling in phase 8 for a fortnight. Can't ask for much more than that from the perspective of encouraging a high lat blocking pattern. 10hpa strat forcing on the way down in the run up to Xmas with a large hatful of members going for a reversal in early January Very good looking EPS for the middle of next week in terms of mountain torque - note high pressure anomalies moving downstream of both the Rockies and the Tibetan Plateau You could pull data points from multiple sources at the moment and they are all leading in a single direction for the final third of the month and on into January. Given the slow burn nature of potential frictional vortex impacts and the lag implicit in MJO passage and torque effects (and as has been stated elsewhere this will impact alongside other factors on the anticipated rising GWO orbit that we hope will reflect strongly an atmosphere coupled to Nino forcings) it is important probably to emphasise that the pattern shift is likely to be gradual and then steadily intensify. The MetO text might be suggesting as much with their maintained "longer" "cold" spell. Any negatives? Tamara mentioned the caveat of a pacific wave pattern derailed by less than expected added momentum. Today's GFS hovmoller is the least impressive of the last few days. MJO passage still obvious but not as strong on this forecast as the one from November. I'm banking on the opposite being the case....time will well.

It would be quite hard to paint a better anomaly picture than that for snow potential. If folks hoping for wintry conditions aren't happy with this run they never will be.

Agreed. The cold block discussed was over Scandy. Historically this is typical. Hard to get a deeply cold and dense block over the warm waters surrounding the U.K.

Into phase 7 on or around the 10th. This begins to apply conditions favourable for Atlantic wave breaking. Lag? Let’s say a week. So I’d expect to begin to see a shift in the pattern around 17 Dec though the lag may push that back a few days. And then the pattern needs to evolve. That takes more days. I’m thinking the Xmas period might be the sweet spot. Models will begin to pick this up in a few more days. I reckon there are signs already in the GFS outer reaches….blocking signature showing it’s hand weekend 16/17 as a theme in op runs. Big U.K. block on the 18z tonight for that weekend.

Yep. We wait with bated breath for events in that final third. Might be signs of it by weekend 16/17 Dec at the absolute earliest but probably a week later. Working out lag timing is a pig and seemingly impossible to pin down.

And additional to my reply in the model thread, this presentation is probably an easier way into the murky and complex world of the GWO... GWO.pdf