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Model Output Discussion - 30th November onwards


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A very wintry Gfs 06z op run throughout the high res with the cold weather persisting for much of the following week and this is just a glancing blow from the icy blast, imagine what a direct hit could doPosted Image

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Edited by Frosty.
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Indeed, as I think has been said before, far too much emphasis put on the strat, it isn't the be all and end all, merely part of a very complex puzzle. To say we can't and won't get anything sustained is not in my view correct. Sure it helps, and we have seen plenty of evidence of that in the not too distant past. But I don't think it's as simple as 'strat says no'. Anyway, I'll get my coat...

I wholeheartedly agree, it's nonsense saying you can't get a prolonged cold spell if the Strat doesn't play ball, of course it helps no end if it is but we can and have done many times before managed to be on the right side of any cold block with a strong PV in its favorite location. Sorry for being off topic by the way mods. Edited by Sceptical Inquirer
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So the theme of a brief Northerly at the weekend looks consistent but what follows is open

 

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Uppers decently cold for the northern hills

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This type of setup doesn't produce much wintry interest for the south other than a few flurries and some reasonable frosts for a few days.

We need the cold from the NE or E and that looks very tenuous with 06z going for full blown super mild uppers crossing the UK but with luck the surfacee conditions should be cold / average despite the horrendous synoptics

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As usual, GFS wants to shove us all into a zonal nightmare at the far end of FI.

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This is where surface temps get really hopeless

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At least there is some eye candy about but it will probably remain as such as the cold blip gets downgraded nearer the time. Posted Image

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I wholeheartedly agree, it's nonsense saying you can't get a prolonged cold spell if the Strat doesn't play ball, of course it helps no end if it is but we can and have done many times before managed to be on the right side of any cold block with a strong PV in its favorite location. Sorry for being off topic by the way mods.

Spot on SI, even with a strong warming strat event, you still require a lot of luck regarding where the block sets up, in the uk we need all the luck in the world.

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Nice explanation Tamara, so basically... after next weekend get the barbecue out and the sun-cream  :):):)

 

Copied from previous thread as it closed when I postedPosted Image

 

I think it is true that the pattern, at least for the present time and first part of winter, does favour short cold snaps and in essence that is what CH is saying. As we know, there have been several instances of tropospheric and lower stratospheric interactivity through this year - and this has continued this autumn (albeit weakly). However it is all about equating how much forcing is required from this trop/lower strat activity to disrupt the net energy of the upper vortex and the signals are that it is going to take a lot more than we have seen in previous times to disrupt the vortex.

 

Without going into acronym land, there are reasons as detailed previously on here and ongoing in the technical threads why this winter looks less favourable for lower atmosphere activity to be successful on the upper vortex than we have seen in recent winters

 

The recent attempted downstream amplification the other week as triggered by wave activity from the continued presence of the Alaskan ridge was insufficient to disturb the vortex and amplify the atlantic ridge as much as suggested at one stage by the models - and the jury is still out as we know on the upcoming northerly as to how much amplification may be present and how the jet energy is handled upstream.

 

The jet stream is favourable in terms of a split flow being present to allow the possibility for the northerly - and we have the -EPO (Aleutian ridge) to thank for that - but the complicated upstream pattern is making the model calculations on degree of eastward moving energy and amplification of the atlantic ridge tricky and hence the erratic disagreements amongst the models - but, all that said, what we do know is that without background support for upper blocking, whether we get a more amplified and colder arctic incursion or not - the vortex is too strong, and wave activitity likely too insufficient, to make next weekends cold shot nothing more than a transitory affair.

 

There are continuing consistent signals in the modelling, post northerly, for the vortex to return towards Canada through Greenland and it is quite conceivable that the upcoming polar incursion presents the 'best' opportunity at wintriness before the pattern flattens out somewhat and the ridging de-amplifies and potential for northerlies reduces - at least for a while.

 

Both the GFS and ECM do agree on this even if they disagree on the northerly strength and duration itself.

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The reason I worry is purely because of the UKMO. Im always consistent and that is until the UKMO is pn board its not happening...Also the other week when ECM saw polar ridging the UKMO didnt.... The UKMO was correctS

A very sensible approach Steve; of course UK could be wrong, ECMWF could be wrong, GFS could be wrong. The clever bit is finding which one will actually deliver nearest to what the actual ends up being. To reserve judgement at shorter time scales, that is within UK outputs we see is the sensible option.

One or two salivating over precipitation charts as well. Forget it until it is not more than 24 hours out, even then it is probably wrong on about 50% of occasions. Not believe me? Cast you memories back to the summer period when the only variable is will it rain. Now you have will it precipitate, when/where/how much as in the summer but another 7 or so variables to get correct before your back garden gets the whote stuff. It really is best to be realistic, lots of fun to hope but don't let that turn sour if the actual weather is not what you had hoped for.

Most model outputs do give the general idea of a short, sharp cold spell from about Friday to maybe Wednesday at the most. It will be a really fascinating period to then for cold lovers to see how the various models all eventually end up with very similar looking charts, perhaps by 96h but more like 24-48h. By then the Fax chart will be as good a guide as anything any of us can suggest, probably, and they should be, rather better.

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Nice explanation Tamara, so basically... after next weekend get the barbecue out and the sun-cream  Posted ImagePosted ImagePosted Image

 

Probably High pressure close enough by once more so reasonable chance of inversions to keep temperatures seasonalPosted Image Not what is hoped for on here by many - but just what seems most likely. Maybe more unsettled to the North West though as lows track across to the north of the mid latitude ridges

 

Those that think that the stratosphere is not the be all and end all - well, it is a pre-requisite to have favourable conditions, or at least condusive conditions for tropospheric influence into at least the lower stratosphere, to be able to assist any more significant cold weather than most who inhabit this thread hope for. I think this subject comes up most every winter these daysPosted Image  For sure, we can get an average to maybe slightly below average pattern if the jet stream patterns are placed such as they track more NW-SE. At present it is the Aleutian Ridge that has been allowing this as repeated so often.  Yes, a two day northerly incursion is better than nothing - and it is possible to also get a Scandinavian ridge and an easterly in the absence of a definitive -AO stratospheric profile - but without upper blocking in place these will be much harder to achieve and to sustain.

Edited by Tamara תָּמָר
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As much as the GFS is perhaps catching up with the ECM its also catching up (finally) with the increased polar heights-

 

Much more emphasis on the cross polar flow!

 

S

(Cheers John)

 

 

Looking forward to the 06z Ensemble watch- keep up the good work!!

Edited by Steve Murr
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A comparison of the 00z ECM and GFS 06z ensemble mean at 96 hrs.

 

gfs..  ecm..

 

 

Ensemble mean verification at 120 hrs.

 

 

 

 

Which model is more likely to move towards the other?

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A comparison of the 00z ECM and GFS 06z ensemble mean at 96 hrs.

 

gfs..Posted Imagegens-21-1-96.png  ecm..Posted ImageEDM1-96.gif

 

 

Ensemble mean verification at 120 hrs.

 

Posted Imagecor_day5_HGT_P500_G2NHX.png

 

 

 

Which model is more likely to move towards the other?

 

Good post Cloud- I didn't know there was a Ensemble mean stat!!!

 

So then No model painting a Scandi high to develop-

 

As Long as the UKMO moves to the ECM I would say the Scandi high evolution is the short odds favourite,with the UK easterly at Evens, as the scandi high amplitude could just be a bit low & we get a SE flow.

 

Zonal- against.

 

 

Anyway- lets resolve this feature @ 120 first-

 

S

 

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A comparison of the 00z ECM and GFS 06z ensemble mean at 96 hrs.

 

gfs..Posted Imagegens-21-1-96.png  ecm..Posted ImageEDM1-96.gif

 

 

Ensemble mean verification at 120 hrs.

 

Posted Imagecor_day5_HGT_P500_G2NHX.png

 

 

 

Which model is more likely to move towards the other?

 

that is a pretty good run over the last week or so for ECMWF especially, well over 0.9 verification showing in that period. So IF that continues one would go with ECMWF at 120h. Of course it is for the northern hemisphere and variations on regional scales can show different biases. Nevertheless it does suggest that ECMWF is the one to take note of at 120h.

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just a quick comparison of the 850hpa at 144hr from the big 3.

 

 

Gfs ...post-18134-0-64133900-1385811641_thumb.p

 

ECM....post-18134-0-89267200-1385811679_thumb.g

 

UKMO...post-18134-0-16421900-1385811704_thumb.g

 

Clearly the Gfs has got quite a bit of catching up to do......in fact in not so sure the ukmo image has the cold uppers digging as far as the windflow forcast on the bbc morning post here http://www.bbc.co.uk/weather/. the northerly makes it all the way into spain.

 

Also if you look over the presenters shoulder, at the eastern seaboard, the low exiting is more akin to the ecm as well,

 

Basically , expect upgrades from the gfs

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http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=187&y=178 (South West England)

http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=234&y=1 (Northern England)

A bit more agreement on next weekend amongst the ens, trending colder than the 0z. There is considerable scatter after that point, however there is not much in the way of prolonged cold until much further into FI. In spite of this, it is worth remembering that all of this is still quite some time away meteorologically speaking, so there is a lot of time for change.

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that is a pretty good run over the last week or so for ECMWF especially, well over 0.9 verification showing in that period. So IF that continues one would go with ECMWF at 120h. Of course it is for the northern hemisphere and variations on regional scales can show different biases. Nevertheless it does suggest that ECMWF is the one to take note of at 120h.

 

It seems the ECM ensemble mean is the tool of choice for day 5,even when compared with the operational runs.

 

operational runs..  ens..

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not much doubt the arctic air will make it across the uk - but its the duration and intensity thats the question. the beeb dont have to worry themselves with that yet.

 

just a comment on the extended ens from ecm and naefs this morning. remembering that both models set the agenda on this pattern two weeks ago, it should be noted that both todays runs have grown euro high anomolys in a fortnights time. this isnt in line with nearly all recent runs so i would be waiting to see some consistency before making a judgement.

 

and smiler, the weather has dried up - i dont need to !!  (mine was a serious question? there is currently no gfs solution.  just wide variations on a broad theme)

 

last year when  i looked at the stats, the ens (in general) edged ahead of the ops around T102. ecm op and ens have had upgrades since then so might be interesting to revisit this in a month or so.

Edited by bluearmy
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Beeb weather forecast already pointed to next weeks Arctic air on the air mass chart they display for longer range hints, so that's good enough for me. Posted Image

 

The latest met office update from the 5th to 14th suggests snow later next week even in some wintery stuff in some southern parts before milder air returns

 

Showers may turn wintry in the south later on Thursday and during Friday but the south and southwest should see the driest weather. Temperatures are likely to be below normal and feel colder still in the wind. Little change is expected during the weekend, with unsettled and cold weather continuing, and snow for northern Britain in particular. Thereafter, milder conditions are likely to spread from the west across much of the UK, with some more settled weather over the south.

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