Mucka

Decent Icon and GFS this morning but UKMO not as good as 12z although it would get some cold air across for Christmas

It has never been there though has it? Been all about the timing of the phasing and trough action. Maybe toward the New year?

Another soul crushing ECM, it really is Xmas Grinch this year

It has been moving the mean trough back and forth W to E, hard to make any judgements on one run though obviously it would be nicer if the Op was an optimum run for cold

GFS still on track, UKMO isn't great but we will need to see 168 chart to see the trough can drop

Some run to run improvement on Icon 06z, every little helps. Icon 06z V 00z

It is good to see the ensemble mean trending colder again, especially over Christmas. As you say, ECM ensembles clearly aren't on a par with GFS but they do have some colder members again, The Op continues to be stubbornly on the mild side but has moved a little closer to a better solution. UKMO is a pretty decent Northerly, just a little further W would be even better, It would be great to see all 3 main models show a GFS type solution this evening,

Rather chill under that ridge.

GEM potential white Christmas some up N

UMO 168 V GFS 168

MO watch Synopsis Quite a few "hindcast" posts today, but even though some make perfectly reasonable points those dismissing any cold snap maybe guilty of doing exactly what they say others are guilty of for getting to attached to FI charts. That said, there is no way to put a positive spin on this mornings output, indeed the output has in general been moving away from any decent cold snaps in the run up to Christmas and ECM and GEM have always been the most reluctant t show any Arctic plunge. Counter to that, they have shown the trough digging down as with earlier GFS runs previously and the discussion back then was generally whether upper air temps would support snow and how far S cold air would get and not that the Azores would ridge across the UK as a spoiler although it was noted that upstream phasing could shunt the pattern E. At that time it wasn't a massive worry to me or others expecting a cold snap because the trough was being programmed too far W if anything and it looked like we would still get a cold snap, just delayed and with shortened prospects. But I did mention it on the 12th and again when highlighting a post by Nick Sussex on the matter. So what has gone wrong and why is the AH playing spoiler? As noted above it is all about the upstream pattern and given GFS was giving the most wintry output I will use the 00z as a guide and contrast it with a previous 00z run that was bringing the trough S. GFS 00z (Dec 13th) for Dec 18th. The red eclipse shows the upstream area of concern for potential phasing. Green arrow shows movement of low with no phasing (not pulled W). Red arrows and X show movement of shortwave and low we do not want. GFS 00z (Dec 13th) for Dec 20th Red Eclipse shows area where phasing was avoided. .Top green tick shows how shortwave held back and low not pulled W. Lower Green arrow shows movement of low. Lower green tick shows AH not forced SW by phasing to NW. The above shows how a cold NW flow was all but certain so long as we avoided upstream phasing. Now below today's 00z showing the phasing and resulting consequence of a much flatter pattern. GFS 00z (Dec 15th) For Dec 18th Red eclipse shows area of phasing. Red Arrow shows forcing of the high E due to phasing. Green arrow show movement of low now forced more E GFS 00z (Dec 15th) for Dec 20th We can see how the trough has not pushed cleanly through to the E with the phasing upstream and the forcing of the low to the W flattening the pattern and the main trough being deflected more E by the AH rather than pushing SE. Obviously there are many more complications in the detail but essentially the reason the AH is further E and S than previously modelled is because of the upstream phasing and the trough not pushing through cleanly with low pressure developing in the phasing area. So where do we go from here? "There's life Jim, but not as we know it." Assuming that phasing is now nailed down, then the chances of cold will need the low that was phased to now phase again with the main trough to the E in such a way that we still get a delayed but briefer cold snap as mentioned previously. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4976988

MO watch Synopsis Quite a few "hindcast" posts today, but even though some make perfectly reasonable points those dismissing any cold snap maybe guilty of doing exactly what they say others are guilty of for getting to attached to FI charts. That said, there is no way to put a positive spin on this mornings output, indeed the output has in general been moving away from any decent cold snaps in the run up to Christmas and ECM and GEM have always been the most reluctant t show any Arctic plunge. Counter to that, they have shown the trough digging down as with earlier GFS runs previously and the discussion back then was generally whether upper air temps would support snow and how far S cold air would get and not that the Azores would ridge across the UK as a spoiler although it was noted that upstream phasing could shunt the pattern E. At that time it wasn't a massive worry to me or others expecting a cold snap because the trough was being programmed too far W if anything and it looked like we would still get a cold snap, just delayed and with shortened prospects. But I did mention it on the 12th and again when highlighting a post by Nick Sussex on the matter. So what has gone wrong and why is the AH playing spoiler? As noted above it is all about the upstream pattern and given GFS was giving the most wintry output I will use the 00z as a guide and contrast it with a previous 00z run that was bringing the trough S. GFS 00z (Dec 13th) for Dec 18th. The red eclipse shows the upstream area of concern for potential phasing. Green arrow shows movement of low with no phasing (not pulled W). Red arrows and X show movement of shortwave and low we do not want. GFS 00z (Dec 13th) for Dec 20th Red Eclipse shows area where phasing was avoided. .Top green tick shows how shortwave held back and low not pulled W. Lower Green arrow shows movement of low. Lower green tick shows AH not forced SW by phasing to NW. The above shows how a cold NW flow was all but certain so long as we avoided upstream phasing. Now below today's 00z showing the phasing and resulting consequence of a much flatter pattern. GFS 00z (Dec 15th) For Dec 18th Red eclipse shows area of phasing. Red Arrow shows forcing of the high E due to phasing. Green arrow show movement of low now forced more E GFS 00z (Dec 15th) for Dec 20th We can see how the trough has not pushed cleanly through to the E with the phasing upstream and the forcing of the low to the W flattening the pattern and the main trough being deflected more E by the AH rather than pushing SE. Obviously there are many more complications in the detail but essentially the reason the AH is further E and S than previously modelled is because of the upstream phasing and the trough not pushing through cleanly with low pressure developing in the phasing area. So where do we go from here? "There's life Jim, but not as we know it." Assuming that phasing is now nailed down, then the chances of cold will need the low that was phased to now phase again with the main trough to the E in such a way that we still get a delayed but briefer cold snap as mentioned previously.

Football, meteorology, they are the practically the same thing. VAR (Very Average Run) Lines Person, (fax chart compiler) Goalkeeper (Atlantic block) High press (Anti Cyclone) And so on

I marked your post "insightful" I misread it as "inciteful"

Where is @nick sussex with his NCEP report and US shortwave commentary? We need to avoid any nastiness like this.

UKMO avoids the GEM US phasing tribulations but not by much. UKMO/GEM 144 Cracking UKMO chart by 168.

You were right about it not being firmed up though. Still plenty of variation run to run and within the ensembles so while it is enjoyable and fun to see runs like this it is not indicative as yet as to what weather we will actually get beyond a spell of NW/N flow

Ice day for the N on the 23rd with lying snow, such are Christmas fantasies for our island.

Cheshire gap snow showers, likely prolonged and heavy at times on this run. A long way to go though...

As explained earlier, you do if you want a more polar and less maritime air in the flow. But it is all relative to earlier GFS runs pushing the trough further W, this is better for colder flow. 12z V 06z

I think this is spot on and worthy of consideration. All the models, but GFS especially, will simplify the trough and any polar maritime flow 6/7 days+ out and the further W the flow comes from the more likely embedded lows not yet modelled will appear and cut off the colder arctic air getting in the mix. If the trough is further E with a more Northerly flow then the risk of embedded lows is diminished and further S the better chance any embedded lows will be far enough S not to mix in too much Atlantic air for our Island which could mean a dumping of snow instead of rain. In these situations the N is much better placed than the S, at least initially, but as the trough moves E then S comes more into play, especially if embedded lows run across the base of the trough but it would be a marginal setup. If the current modelling is about right then it will another 2/3 days at least before we can even begin to guess at snow chances beyond the vagaries and then it will take a few more days to start trying to pin them down so we are still in the broader forecast phase for a while yet. We could get anything from a damp squib to a white Xmas, but most years we don't have any colder Arctic air in the mix at all over the Christmas period so may as well be positive for now.

Some GFS ensembles blow up the low I talked about last night a la ECM 12z and the mean trough is a little further W so maybe ECM won't back down this morning. We could do with mean trough position edging E not W in the ensembles though. If we can get some kind of consensus on this evenings runs for 168 having the trough digging down through the UK and N Europe/Scandinavia then we should at least good for some wintriness in the run up to Xmas. 00z mean V 18z mean

UKMO pretty much on board, certainly no ECM 12z

It is a little too far W for perfection but this sort of setup can be epic for the NW

IIt will be at least decent for sure and the high is further N than the 18z, all about the upstream post 240