Zakos

Much better anomaly to my eye Retrogression is nearing the reliable timeframe!

Just to highlight the model uncertainty. Change in the forecast over the last 4 days. Look to me like the models are getting the overall pattern fairly well, but they are clearly they handling the retrogression poorly. The forecast shown from 4 days ago show that the retrogression is getting pushed back. However, aslong as the ECM and GFS mean indicate retrogression will occur, there remains hope for a cold spell in the near future IMO. As others have highlighted, the block may not be in the perfect position for UK cold, and it may be difficult to attain deep cold just yet. Still, aslong as this block remains, at the very least it will block the PV from setting up over Greenland, and its presence should maintain a weak jet stream, and, potentially, block the Atlantic from encroaching into the UK. Im astounded with the negativity here considering it is 10 days until winter actually starts. plenty of pleasant anticyclonic conditions to experience in the coming days - no sign of south westerlies. Thereafter? who knows... The models being "wrong" on one occasion does not affect the probability of them being"correct" on any given day in any way. beyond day 5, they should only really be used to gain general pattern changes and synoptics over the hemisphere, certainly they cannot pin down specific details for the UK beyond this timeframe. The models are computer programs - nothing more. Our understanding of Meteorology is too limited to accurately predict the weather beyond this time and there are simply too many unknown variables that the models do not take into account. Use them as a guide, not as gospel!

Fully agree! Im quite happy with any weather in winter that doesnt involve mild and wet south westerlies, though i must say i do have a preference for falling snow. Still, Im enjoying the continuation of this remarkably blocked autumn to be honest. As you said, I doubt at any point in early winter last year we had ensemble means with anywhere near as much potential as the above charts. Yes they are at day 10, but in my opinion they've been getting progressively more conducive for cold spell for days now. Also,the next attempt at retrogression appears to be slowly creeping in to the reliable timeframe, hopefully it does not get pushed back this time. At the very least,the jet stream looks to remain weakened and southerly tracking, and in my opinion a noteable cold spell as we head into winter remains a plausible possibility. Hopefully the block, if sets up in a favourable position, will be as stubborn to decay as it was to retrogress!

Some runs had it occurring by the 23rd to be fair. However yes most runs forecast it for the end of November. The event still looks set to occur IMO, but I do think the retrogression itself has been slightly pushed back. No real cause for concern unless the ensemble means swing away from the event. To my mind, the ensembles from both ECM and GFS have strengthened the blocking signal.

The retrogression has been always been forecast to be a slow and arduous process,the modelling is starting to frustrate me as it always seems to get pushed back. The ensemble means from GFS and ECM now both strongly indicate retrogression by 216+. The ECM was always reluctant to build heights around Greenland, however clearly it is now on onboard. Consistency from both models, however we need to get these within the 192+ timeframe as the event seems to be getting pushed back. GFS 6z looks like an outlier at 216 + The above chart is from 6 days ago. The consistency from the GFS is remarkable and encouraging, its the retrogression process itself which is being modelled poorly. It seems this is the most likely pattern change to me. Can we finally see these charts creep into the reliable timeframe?

GFS 18Z mean shows further improvement, ECM mean at day 10 also now strongly hints towards retrogression Worryingly, the GFS mean at the very end of the run appears to show a breakdown of the block However, looking at the anomalies, it looks to me as if there is large spread in the ensembles, however still with a weak indication of a continuation of a negative AO and low heights over europe.

Agreed. Both the 12Z and 18Z GFS shows the block effectively breaking down towards the end of the run. Neither run seem to have much support from the 12z GFS mean which has been improving over the last day or so. hopefully the 18z mean shows further improvement GFS 12z mean anomaly shows strong signal for blocking to the NW until day 12, where it slightly weakens however the signal is effectively maintained until day 15, slightly weakening at the very end of the run.

06z is a stunning run IMO

Superb anomalies at day 10 from, GFS and ECM ensemble mean. intersting mean chart at +312 from GFS Fantastic chart at +384, looking at the anomaly chart, really looks like the UK could be in the sweet spot for snow in this setup.

. . Blocking signal remaining right out until day 14, where yes I agree the signal clearly starts to fade. Something to watch I think, but nowhere near as disappointing as the operational

Too busy to post charts, but l think the GFS ensemble mean still indicates blocking to the NW

We are approaching December now, really don't understand all this worry about the cold uppers. If we get a sustained flow from the N/NE/E...it WILL turn cold enough for slow regardless of the temperature of the air over Europe... Provided the flow is sustained of course

Deep cold continuing to edge closer! GFS ensemble mean showing blocking remaining solid in this area right through into December, also now indicating the atlantic will remain blocked. Surely this cold pool will move west with time aslong as the atlantic remains blocked?

Theres plenty of brutal cold around, we just arent getting the favourable airflow just yet. GFS somehow manages to keep the cold air away from the UK on this run, will all change next run, but there is certainly plenty of cold to tap into now

Not sure if this has been posted ECM ensemble mean anomaly finally shows retrogression to Greenland occurring before day 10. GFS and ECM both now agree on retrogression of the block to greenland, with a cold/very cold airmass approaching from the North East

Im amazed at the continuity of the blocking in the atlantic. 3 day snapshots of the 18z run show positive height anomalies in the atlantic for the entire run. By far the best NAO forecast this season.

Arctic High has been beefed up a fair bit on the 18z, aswell as blocking over Canada

. GFS has been hinting at retrogression to Greenland/Hudson consistently for 4 days now. . It first picked up on the signal over a week ago. I personally also think the ECM is wrong, retrogression of the block to this area is most likely scenario IMO.Question is, will there be enough blocking in the Atlantic to maintain a cold air flow for the UK?

GFS at 384. Its been hinting at this pattern change for a number of days now. Comparing the start of December from the last 5 years to todays forecast, looks pretty clear to me that, if it verifies, it will be the best start to winter since 2010 in terms of the state of the PV. This of course being the coldest December in over 100 years. The only year that even comes close is 2012 2012 still had much deeper cold over Canada. GFS mean anomaly has been hinting at this pattern change for a number of days now... all we need is for these charts to make it within the 10 day timeframe.

On the ECM at 240+ looks to me like that altantic ridge is going to attempt to link up with the Arctic High, looks very promising to me. The problem with the 06z GFS is that there isnt enough bocking in the atlantic, leaving the atlantic door open. Both GFS and ECM ensemble means agree the atlantic will be effectively dead as we head into the Start of winter. ECM still a little reluctant to build heights over Greenland.

Todays ECM at 240+ compared to what we had on that date last year. Arctic high, no raging vortex, weak jet stream, low heights to our south. We may find out tommorow that the GFS was wrong. In the grand scheme of things thats irrelevant,in my opinion. Should never get your hopes up over cold that shows on the models unless it is hitting the UK consistently within the 144+ timeframe. The bigger picture as we head into December is fantastic. Not saying we shouldn't be cautious, but the pessimism on here is too prevalent IMO, not surprising really after the dire winter we had last year! we just are not seeing the same synoptics as that winter, every reason to be optimistic as we head into December IMO.

Still no closer to a firm resolution really. All models agree at 96 hours there will be an attempt at ridging into Greenland. Ive seen dramatic changes in the ouput occur at 72+ hours before, would have thought at 120+ hours there is fair chance the GFS could be correct. Surely by tommorow morning we will know if the ridging into Greenland will be successful.

Looking at the 12z GFS mean, looks as if the Russian High is causing us to be stuck in a continental, but warm airflow. As soon as the Russian High decays and heads east, we start to draw in an easterly feed from the continent.The block backs west and low heights start to deepen over europe, puting the uk into a cold airflow - a consistent theme from GFS. Not a bad looking mean at all at 288+... lets hope the ECM leans this way tonight.

In my opinion, yes I think we will end up with a cold N/NE/E flow at some point in the next 2 weeks. Potentially very cold, but its too far out to tell really at this stage. As for a Greenland high, the GFS has trended towards this pattern over the last 3 days. The ECM is still not on board at the moment, everything should become clearer in the next few days, hopefully!

I think this is certainly something we cannot exclude from the output because a number of runs are showing the high backing too far west, e.g 00z and 06z GFS. This leaves us prone to atlantic attack, however, even in this scenario, with such a weak and southerly tracking jet stream we actually maintain the easterly flow right into December and until the end of the run. on yesterday's 12z and 18z, the high also backed west, but with enough blocking remaining in the atlantic to give us a cold airflow from the N/NE. Several possibilities on the horizon, nothing set in stone, however the trend currently remains towards better long term cold potential as November draws to a close. ECM not really on board yet, plenty of time for change.