Jump to content
Holidays
Local
Radar
Snow?
Paul

Model output discussion - winter proper underway

Paul

Please only post model discussion in this thread. 

For more general chat and banter, or moans and ramps loosely around the models, please head to the banter thread:
https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

For general weather chat including about the snow/cold chances around the country, please go to the regional threads:
https://www.netweather.tv/forum/forum/142-regional-discussions/

Thank you!

Message added by Paul

Recommended Posts

As my post got removed, not too surprised as it was borderline MOD related, so apologies there. But was hoping an attempted explanation of the why it didn't snow IMBY or elsewhere for others would help the learning curve of many in here. Many of us put too much emphasis on the models, follow them religiously and expect them to deliver. As it is one of the weirdest days of snow watching I've ever experienced (as mentioned in my removed post). Perhaps Nick F, Phil nw or someone with plenty of knowhow could daft something in the near future, it WILL aid the learning curves of a number in here and will perhaps stip too many of those posts the MODS don't want to see. Including this post, lol. Apologies again.

  • Like 5
  • Thanks 1

Share this post


Link to post
Share on other sites
2 hours ago, Borei said:

Yes, but the question is whether those atmospheric drivers are still present.

Today's output is about as flat and vile as we've seen for a couple of years, going back to December 15's horror show.

They are mainly oceanic drivers - and yes: as of 6th Dec my data says they are still present. Awaiting the next update, but no change of emphasis yet.

  • Like 3
  • Thanks 1

Share this post


Link to post
Share on other sites
2 hours ago, Nicholas B said:

I have total respect for GP and Tamara. Im not sure they have said there will be a Scandi high only it is a distinct possibility given what is expected in the pacific and subsequent PV movement west. There also has to be the possibilty on what we see in the 06z Op and have a strong PV to our North. If GP or Tamara could forcast that far out for our little corner and nail it everytime they would both be very rich people. Saying this i hope this is of the ones they Nail as the 06z op is total pants!

Re the Scandi HP, there is definitely signals for a strong Scandi block, several methods suggest it.  What isn’t clear is the infkuence it will have on us.  Wrong orientation or too far east and nothing, then the other option. I too am not buying the brutal flat outlook in FI charts, I think we’ll lose a touch of amplification along the way but next weekend’s Atlantic Ridge still very much on in my books. Beyond .....it is FI.

 

BFTP

Edited by BLAST FROM THE PAST
  • Like 6

Share this post


Link to post
Share on other sites
Guest

WINTER 2017/18 REPORT No. 4a WITH DECEMBER 10th INPUT

PART 1: With my main weekly reports tending to be quite long, I shall continue to split them into at least 2 parts probably posted several days apart. This one will be in 3 parts. As they can take many hours to prepare, this will enable me to draw more on the most recent model runs rather than earlier ones. Part 2 will include an update of my European indicators and analysis and part 3 will focus on my Arctic indicators.

A REVIEW OF THE MODEL OUTPUT OVER THE LAST FEW DAYS AND A LOOK FURTHER AHEAD

I am writing this from a rainy and very windy Exmouth (currently 8 am) but I am keeping one eye on the radar and following the areas receiving the snow. Good luck to those that get (or have already had) a decent fall and enjoy it while it lasts. At least it gives me an opportunity to concentrate on this report! With the snow occupying so many regular posters with many of them on the specialist regional threads, there has been a real lack of activity on this thread with little analysis of the model output going beyond the next few days. So, I thought that I would spend a little more time today looking at this compared to my usual approach

Well that was another extraordinary and very exciting week for model watching.  Having struggled to nail down the detail regarding the northerly that arrived during Thursday behind storm Caroline the models then encountered the complex pattern concerning the slider low. There was reasonable agreement on the timing and the formation zone but variations in the trajectory. Although on a macro scale these were very small differences, they were highly significant in terms of our tiny island. The track varied from model to model and run to run right up until 12 hours out but they all showed a generally east-south-easterly to south-easterly direction. Around 5 days out, the range of tracks were mostly between north Northern Ireland exiting around the Humber estuary and central Ireland exiting around the Thames estuary or north Kent. A few varied north and south of these limits. Then the trend was slightly further south and back again. All this fluffing about would not normally get so much attention but the final track would determine who gets snow (and how much), who gets rain and who gets nothing out of the ordinary. With so many snow starved members on this forum, emotions began to run very high. If computer models were given an emotion chip they would probably laugh at our behaviour!

Turning to the broader picture and looking ahead we are in the middle of some very interesting pattern changes and the models have been struggling with the next week and beyond.  It looks like most of the next 7 to10 days will be rather cold to cold but not quite as cold as the last couple of days. The milder wedge that encroached into the south-west overnight and today is being squeezed out and moving away south-eastwards. Most models now show another slightly less potent northerly later this week and, yet again, more or less coinciding with another weekend. There will be some sharp frosts wherever it clears overnight, particularly over the snowfields. Some more wintry precipitation looks quite likely but also some snow melt as well. The day to day detail will vary and really needs to be studied in the T+24 toT+60 range.

This is not meant to be an attempt at a detailed medium range weather forecast, I’m just setting the scene for the following week where there is once again some considerable uncertainty with the models showing some diverse evolutions. Broadly, the background signals suggest (as explained in several excellent posts by the  likes of @Tamara, @Glacier Point and several others) that we “may” briefly see the PNA turning negative with somewhat reduced amplification over the Atlantic with a flatter pattern for a few days(or slightly longer) and the PV reasserting itself to some extent. Then, the indications are that we shall see the PNA going strongly positive again with renewed strong amplification in the mid-Atlantic and into the Arctic with the PV thoroughly disrupted again and unable to take up its usual position and strength for this time of the year.  There are also signs that the MJO may come to life again later this month just as it’s moving towards its important phases 7, 8 and 1 which often assist with HLB patterns.

“Should” these changes transpire, we are likely to see some very blocked patterns again with the jet stream buckling, meandering, possibly splitting with the southern arm quite likely to be stronger and more dominant and probably taking a route well south of the UK. If we stay on the cold side of the jet, this might lead to further northerlies but there are some tentative but strengthening indications that we might see a strong build of pressure to our north-east. This might lead to a Scandinavian HP and even a build of pressure from Siberia and Russia pushing westwards. If this set up really takes hold, then a true “cut-off” Greenland HP is not out of the question at times and even linking up with the Scandinavian HP at times. There are also signs of stratospheric warmings later this month – not a full scale SSW shown yet but this may assist in prolonging the cold spell well into January.

Remember that GP and Tamara both said that the models are highly likely to struggle with this possible pattern change and the timing of the changes is particularly uncertain. Some of the output has been quite progressive by hinting at a build of pressure towards our north-east from as early as day 10. Other runs have shown the changes around or just after Christmas (including yesterday’s MetO 15 to 30 day outlook) and this would be right at the end of the GFS and GEFS runs.

So we must be really patient and not be overly concerned with any run showing a 10 day period of much milder and more zonal weather in the run up to the Christmas holidays (I know that as the model output changes from run to run so will the mood with some posters producing their usual agony to ecstasy and back again comments!).  It’s extremely rare to see a prolonged cold spell lasting for weeks on end and even most of our severest winters had at least one milder interlude with December 2010 and December 1981/ January 1982 being prime examples. In fact during my lifetime (1953 vintage) only 1962/63 saw very longs periods of ice days with just the briefest of slightly less cold weather (although the south-west did see a few short-lived milder periods).

CAUTION:  Before anyone gets too excited about this, the renewed blocking is by no means certain and a flatter more zonal pattern with a much stronger PV may still prevail later on. The temporary change to a flatter pattern next week might gather momentum and last for an extended period. There is no point in me or anyone else having hunches about the forthcoming broad scale pattern changes and we need to take stock and follow the updates from our teleconnection specialists. Remember it’s these signals that drive the models NOT the other way around. Let’s just say that there seems to be some great “potential” for something much more memorable in terms of cold spells for this winter. We’ve got off to an excellent start and there are still 80 days of meteorological winter remaining!

We can begin by having a closer look at some of the longer term output.  I rarely comment on the model runs much beyond the 7 to 10 day period. What I want to show here is the range of possible evolutions.  I will not do one of my cross model analysis in this report (perhaps I’ll do that comparison in a week’s time). I will not show the jet stream or temperatures and I will not even use the usually slightly more reliable model(s). I will use the GEFS and look at some of the perturbations and examine some of the outcomes shown. The 6z output has been rolling out for a while (it’s now 1200).

GEFS 6z RUN ANALYSIS FROM DECEMBER 10TH:

           The current chart T+0

      gensnh-0-1-0.png

Moving on I have selected the T+144 and T+384 charts as well as the halfway point at T+240.

a) The control run:

                        T+144                                                 T+240                                                 T+384

      gensnh-0-1-144.png           gensnh-0-1-240.png           gensnh-0-1-384.png

I really do not understand all the worry.  The control run is one of the warmest towards the end and finishes with HP just to our south and a fairly week westerly flow.  The most important feature is the PNA returning towards neutral and showing signs of going positive. Out of the 20 perturbations there are none which are really negative and only 5 which are close to neutral with the other 15 either positive or very positive again. Many show HP somewhere over the Arctic with some maintaining it right over the pole. About 6 have HP over or close to the UK. Some have LP close to the UK but often to our north or north-west (not dissimilar to the patterns we have seen recently with quite frequent northerlies).  The most  common feature is that the vast majority of perturbations show HP somewhere over Europe, Scandinavia of Russia, with some showing some very strong cells and ridges.

b) The Mean:

                         T+144                                                T+240                                                T+384

        gensnh-21-1-144.png             gensnh-21-1-240.png              gensnh-21-1-384.png 

The mean chart can be a little misleading as it averages out some of the more extreme variants. The main thing to notice is the PNA going positive again with higher pressure extending across the pole from Alaska to Siberia. The weakish looking LP centred around Greenland masks a few perturbations showing much deeper LP in that region and many showing higher pressure near there.

 

b) Perturbation 4:

                         T+144                                               T+240                                                T+384

       gensnh-4-1-144.png              gensnh-4-1-240.png             gensnh-4-1-384.png

 

b) Perturbation 7:

                         T+144                                              T+240                                                 T+384

      gensnh-7-1-144.png              gensnh-7-1-240.png              gensnh-7-1-384.png 

 

b) Perturbation 8:

                        T+144                                               T+240                                                 T+384

      gensnh-8-1-144.png              gensnh-8-1-240.png              gensnh-8-1-384.png   

 

b) Perturbation 12:

                     T+144                                                  T+240                                                 T+384

    gensnh-12-1-144.png           gensnh-12-1-240.png           gensnh-12-1-384.png

So if you run through all these charts, you'll see that I deliberately selected those which show quite a variation in the final outcome but my main point stands and even the charts which show LP close to the UK still show "mostly" colder than average patterns. Currently, following the milder period in week 2 (possible lasting from 7 to 10 days or so), the longer term indications are very encouraging for "coldies" and very much in line to what GP and Tamara have hinted at.

Finally, I'll be back within a day or two with part 2 of this report with a close look at European temperatures and what we might expect from a possible easterly later on.    

Edited by Guest
Correct typos and check charts

Share this post


Link to post
Share on other sites

Growing signals from GFS ens for a spell of milder air in the run up to Christmas for the main day its self it looks like we might see a fall again

gefsens850London0.thumb.png.912186bd02c23fae983ac52ed77dec4a.png

Around the 18th looks to be the transition period from cold to mild

  • Like 2

Share this post


Link to post
Share on other sites

I think the issue the modelling has is resolving what happens with all the energy in the Atlantic after the relaxation in the pos PNA allows the Canadian vortex to push west

during week 2 an big renewal of the pos PNA will encourage the Canadian trough to pull back and dig south to potentially allow an amplification in the Atlantic. However, with the strong Atlantic jet in place I think the models are struggling to work out where that amplification can occur. As I mused a couple of days ago, the fi op gfs (and the eps control) could be the ones to sniff this out ahead of the ens

  • Like 5

Share this post


Link to post
Share on other sites
4 minutes ago, Summer Sun said:

Could you explain what is 'interesting' to some new members that chart just looks like a kid has drawn on it with crayons

Heights towards the NE and a trough to the SE

Edited by Hocus Pocus
  • Like 1
  • Haha 1

Share this post


Link to post
Share on other sites
22 minutes ago, Dennis said:

interesting

854.gif

Spirograph working wee😀😀

  • Like 1
  • Haha 4

Share this post


Link to post
Share on other sites

I note cmc charts tend to get posted if favourable so I feel obliged to include the 00 5 day anomalies as an addendum to my earlier post

cmc_z500a_5d_nh_61.thumb.png.98beee5ffd16aa1e7a26d6d525f5e0a3.pngcmc_z500a_5d_nh_41.thumb.png.c2276f5b0aff6bbefddf0bf8bd37133d.png

  • Like 1
  • Thanks 1
  • Sad 2

Share this post


Link to post
Share on other sites
24 minutes ago, Summer Sun said:

Could you explain what is 'interesting' to some new members that chart just looks like a kid has drawn on it with crayons

these are the High's and Low's on the NorthernHemisphere (Redlines are High's and Blue's are Lows) isobar

 

  • Haha 4
  • Thanks 1

Share this post


Link to post
Share on other sites
31 minutes ago, Summer Sun said:

Could you explain what is 'interesting' to some new members that chart just looks like a kid has drawn on it with crayons

Well said

No offence to technical posters on here and others of us who claim to have a little amateur knowledge, but there's a technical model thread for the cognoscenti. No excuse for making things obtuse elsewhere.

I'll butt out there.

No more snow here in Woking. Just a bit of snizzle.

  • Like 3
  • Thanks 1

Share this post


Link to post
Share on other sites
43 minutes ago, Dennis said:

these are the High's and Low's on the NorthernHemisphere (Redlines are High's and Blue's are Lows) isobar

 

The pedant in me is forced to state that this isn't a SLP chart but a heights one. (And it's the Canadian ens which as knocker says gets little exposure in here and its for day 8 which isn't currently really an unknown scenario ) 

Share this post


Link to post
Share on other sites

I'm dreaming (for yet another year?) of a White Christmas...:cold-emoji:

h850t850eu.png

  • Like 4
  • Haha 2

Share this post


Link to post
Share on other sites

Storm Ana looks pretty serious for Spain, Portugal and France this storm could also bring some heavy rain and temporary heavy snow to southern parts of England if it tracks further north than shown

GFSOPFR12_24_1.thumb.png.98f0ed567570e9b4039415e77f76735d.png

  • Like 4
  • Thanks 1

Share this post


Link to post
Share on other sites
47 minutes ago, Ed Stone said:

I'm dreaming (for yet another year?) of a White Christmas...:cold-emoji:

h850t850eu.png

i'm sure 2 weeks ago, we were shown to in raging South Westerlies? :-P

  • Like 1
  • Haha 2

Share this post


Link to post
Share on other sites

Right - That's the snow out of the way lets get back to looking out into the mid-term with lust and hope. 

The models are hinting towards height rises over Scandinavia and have been doing so for a few days now.

Scandi.thumb.png.8dc6bb57297c2b289ba145a5fafaa373.png

Azores High ridging North-East towards developing heights over Scandi. No model has gone full scale with it yet because the GFS as usual revs up the Polar Vortex and pushes it all away. But, as long as continue to see the trend towards heights over Scandi as per the GFS 12z above, we've got something to look forward to. 

In the meantime, less cold towards the end of the week but certainly not what I'd call "mild".

  • Like 7

Share this post


Link to post
Share on other sites

Well after the frenzy eyes cast towards the models...

Not sure im as optimistic as others...growing signs of a resurgent jet stream ..this time much flatter and less emphasis on Atlantic ridging.

Ukmo looks flat at 144 and gfs-

Added to that fergies latest tweet/ musings do not inspire...

Hoping for some positives from the strat..do not want to see zonal winds increasing..!

  • Like 2

Share this post


Link to post
Share on other sites

Interesting scatter again on the ensembles, from a relatively short way out too. A lot of milder members from T +7 days but then most are colder than the operational further out beyond T +10 days and into Christmas:

5a2d8338a53a7_ScreenShot2017-12-10at18_55_04.thumb.png.12dda44b4b3414c52cd733d5ad3c3c0f.png

  • Like 5

Share this post


Link to post
Share on other sites

Chart of the evening for coldies is JMA day 8. 

Incidentally, ecm runs that little system along s England Thursday night which has some snowfall on its n edge 

not quite getting the concern for the outlook being flatter. Even if it verifies, we live in the UK, not Canada! 

  • Like 5

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...