Model Output Discussion 4th Dec.2013-12z onwards.

[TSNWK]

06z appears to have ditched the Xmas day storm - thats the good news, bad news for coldies is that it looks like it will be a much milder run.

[stodge]

Morning all

 

A rare opportunity to comment on the morning's output and there's not a lot to be said which hasn't already been said by those who frequent the early hours.

 

My observation is less related to wind (so to speak) than rain - seems very hard to tell but could we see secondary features developing along the cold fronts which would bring more in the way of rain (rather than the wind) to southern counties ?

 

The current set up looks to offer plenty of potential for the rapid eastward clearance of frontal systems but a much slower southward progression - very hard as they might develop at short notice, but I do see the possibility of rainfall to the south from these not so much secondary LPs but "wave" formations along the cold front.

[legritter]

Im taking orders gang for a low pressure system running across northern france come later next week ,and for a premium little extra charge some cold air in place over the continent ,Just a dream ,well anything at this range is possible but certainly looking at the current Models alot of weather to come ,enough to keep us interested ,Stellas all round after tonights runs .

[gottolovethisweather]

If you think ECM is bad enough for Christmas day take a look at GFS

 

 

A closer look shows a 935mb low just north of Scotland

 

 

The GFS ensemble has a 940mb low

 

 

On the other hand we have GEM which has backed away from a Christmas day storm this morning

 

 

Instead it looks like boxing day could see some stormy weather

 

 

Notice as well GEM has pressure building to our east

 

Not that I confess to being a psychic but having now seen some of the outputs above, the potential is seemingly there for my long-range prospects to at least partially verify.

 

As an example, I firmly believe the latter part of next week's runs will be much more revealing for colder prospects given the start signals and its quite probable a switch over in the Jet position may occur around Boxing Day to something at least more wintry. This last comment is based on a hunch more than anything but all it will take is one of Nick's undercutting Shortwaves to dive South and voila.

 

Please bear in mind we are however talking about the deep realms of FI at t+240 hours or thereabouts.

Edited December 16, 2013 by gottolovethisweather

[Summer Sun]

The Christmas day low is still there on the 06z but not to the extreme of the 00z's 935mb low

 

 

00z

 

Edited December 16, 2013 by Summer Sun

[gottolovethisweather]

The Christmas day low is still there on the 06z but not to the extreme of the 00z's 935mb low

 

 

 

00z

 

 

 

Indeed Gavin, if we can just move the superlow a few hundred miles South and buckle the Jet to move in a NW to SE positioning and maybe, just maybe...   On that basis, I'd bank the GEM for now thankyou kindly.

 

Speaking of the Jet, here is the current projection from the GFS 6z at t+204 hours, i.e. 1800 hours on Christmas Eve.

 

 

Only to be replaced by this flow right over the UK some 24 hours later, at t+228 hours on the big day itself.

 

 

I'm not sure exactly what causes this buckling of the Jet to change to its more usual UK positioning (SW to NE) but I imagine its that big stubborn vortex placement.

Edited December 16, 2013 by gottolovethisweather

[Summer Sun]

Yesterday's NAO update continues to show it remaining positive for the rest of this month

 

[Frosty.]

The Gfs 06z op run shows huge potential for a major new year cold blast, even before then, there is a lot of cold zonality, at least across the north of the uk but occasionally the colder air digs further south to bring the risk of wintry ppn, especially over high ground, due to probable timing changes, christmas day could end up looking like boxing day.,i.e. ..wintry across the uk rather than just the north but I get the sense that something more substantially wintry could be unleashed on the uk into the new year, there is only a weak surface high across greenland in low res but it doesn't stop very wintry synoptics from evolving. It does look as though the jet will be forced further south as time goes on which opens up more wintry possibilities.

[Newberryone]

big changes on the 6z ie the deep low has vanished at 192 hrs?pv looks to be weakening to a certain extent.Not sure if its a dodgy run but its a huge change

Yes, it certainly appears to be a downgrade on the previous run but so long as it doesn't start to go down the route it had us on yesterdays 12 z for Christmas Day I shall remain upbeat.

Edited December 16, 2013 by Newberryone

[nick sussex]

Morning all

 

I see lots of discussion re a possible Xmas storm, sadly with his type of set up , strong jet and PV located where it is you're always likely to find the models developing these fast moving intense depressions. But certainly I wouldn't be hanging my hat on detail re solutions well into FI.

 

The ECM is awful for Xmas Day I sincerely hope that doesn't verify. These systems that develop on the southern flank of the main trough are always the worst type to forecast because the models will chop and change frequently, dropping them and then bringing them back between outputs.

 

In terms of the overall pattern theres not much change, its very mobile, a mix of milder and colder interludes, a little snow for the north but nothing troublesome in terms of that, its more the rain and wind that's an issue.

 

From a cold perspective theres a suggestion that the jet may sink further south but I wouldn't bank on this just yet until the models have this within T168hrs, perhaps of more note is that we are now seeing some different solutions between the ensembles at the nearer timeframe, there are some mixed messages there with some wanting to move the main PV east.

 

Looking at the De Bilt ensembles no real sign there of troughing getting far enough east/se to develop a nw flow behind that for that region although of course in this type of set up, the UK especially the nw could be in that flow and would likely be colder than Holland:

 

http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

 

The main wind clustering is still between south and west, a few solutions towards the nw but overall very much in the minority.

 

In terms of the ECM ensemble spread the interest there is with a clustering taking low pressure further to the east and also a suggestion of some weakish pressure rises near Svalbard:

 

 

The zonal strat winds still show a weakening towards the pole, indeed a reversal here before they pick up again later on:

 

 

The reversal is only at the higher level but still could help develop some weakish pressure rises in that region, or at least helping that ridge from the Siberian side extend a little further towards the pole.

 

Overall the outlook is really dependent on whether we do indeed see that southwards jet adjustment verify, still unsettled but whether theres more cold air to tap into, it won't however be a cold spell even with that, more that the milder interludes will be more likely followed by colder rather than cooler snaps. 

Edited December 16, 2013 by nick sussex

[Frosty.]

The GEFS 06z mean has a very unsettled look about it throughout with lots of wet & windy weather and generally cold zonality across the north of the uk, occasionally extending into southern britain, probably more so in the run up to the new year, it's very disturbed and northern hills / mountains look like being wintry for most of the time with sleet and wet snow either in the form of showers or more persistent ppn with a rather cold and strong westerly airflow of polar origins with the PFJ to the south of the uk, sometimes digging further south as disturbances clear to the east.

Edited December 16, 2013 by Frosty.

[shedhead]

Morning all

 

I see lots of discussion re a possible Xmas storm, sadly with his type of set up , strong jet and PV located where it is you're always likely to find the models developing these fast moving intense depressions. But certainly I wouldn't be hanging my hat on detail re solutions well into FI.

 

The ECM is awful for Xmas Day I sincerely hope that doesn't verify. These systems that develop on the southern flank of the main trough are always the worst type to forecast because the models will chop and change frequently, dropping them and then bringing them back between outputs.

 

In terms of the overall pattern theres not much change, its very mobile, a mix of milder and colder interludes, a little snow for the north but nothing troublesome in terms of that, its more the rain and wind that's an issue.

 

From a cold perspective theres a suggestion that the jet may sink further south but I wouldn't bank on this just yet until the models have this within T168hrs, perhaps of more note is that we are now seeing some different solutions between the ensembles at the nearer timeframe, there are some mixed messages there with some wanting to move the main PV east.

 

Looking at the De Bilt ensembles no real sign there of troughing getting far enough east/se to develop a nw flow behind that for that region although of course in this type of set up, the UK especially the nw could be in that flow and would likely be colder than Holland:

 

http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

 

The main wind clustering is still between south and west, a few solutions towards the nw but overall very much in the minority.

 

In terms of the ECM ensemble spread the interest there is with a clustering taking low pressure further to the east and also a suggestion of some weakish pressure rises near Svalbard:

 

EEH1-240.gif

 

The zonal strat winds still show a weakening towards the pole, indeed a reversal here before they pick up again later on:

 

ecmwfzm_u_f168.gif

 

The reversal is only at the higher level but still could help develop some weakish pressure rises in that region, or at least helping that ridge from the Siberian side extend a little further towards the pole.

 

Overall the outlook is really dependent on whether we do indeed see that southwards jet adjustment verify, still unsettled but whether theres more cold air to tap into, it won't however be a cold spell even with that, more that the milder interludes will be more likely followed by colder rather than cooler snaps. 

Excellent post overall Nick, but the most telling sentance for me is the one highlighted.  It's seems to be taken as a given now (born primarily out of desire) that the Jet will sink south towards Xmas and in turn dislodge the limpet Euro high, but those of us who have seen many similar set ups over the years will be very wary of making this assumption.  It's no coincidence that this pattern started to emerge 4 or 5 days ago in the outlook period and that is effectively where it still remains.  As we get closer to Xmas there is still a very real danger that the models will start to pick up spoiler features and that the Jet alignment become far less favourable. I have no evidence to support this claim, but I think widespread cold zonality progged to develop post +T168hrs fails to verify on far more occasions than it does, in fact cold zonality is a relatively rare feature...without some sig changes at higher latitudes, this still has all the hallmarks of another such occasion imho. 

Edited December 16, 2013 by shedhead

[bluearmy]

still no convincing evidence that the jet will sustain its southward placement after it gets there beyond xmas. would say that the scots should just about stay north of the pfj but over the remainder of the uk meandering north and south. as nick f posted earlier, that allows for some snowfall in the north but pinning that down will be a forlorn task until a couple of days beforehand. (maybe less)note the GEM again showing the general NWP propensity to throw that WAA if the chance is there. that would appear to be the only curve ball in the modeeling for the time being.

[BLAST FROM THE PAST]

big changes on the 6z ie the deep low has vanished at 192 hrs?pv looks to be weakening to a certain extent.Not sure if its a dodgy run but its a huge change

Indeed hence my comment re 'now time' watch.  These southern flank features as Nick S has said are very difficult to nail down. Wednesday and Thurs looks absolutely terrible particularly for W/NW, that is a heck of a deep system

 

 

My eyes keep getting drawn to NY period.

[nick sussex]

Excellent post overall Nick, but the most telling sentance for me is the one highlighted.  It's seems to be taken as a given now (born primarily out of desire) that the Jet will sink south towards Xmas and in turn dislodge the limpet Euro high, but those of us who have seen many similar set ups over the years will be very wary of making this assumption.  It's no coincidence that this pattern started to emerge 4 or 5 days ago in the outlook period and that is effectively where it still remains.  As we get closer to Xmas there is still a very real danger that the models will start to pick up spoiler features and that the Jet alignment become far less favourable. I have no evidence to support this claim, but I think widespread cold zonality progged to develop post +T168hrs fails to verify on far more occasions than it does, in fact cold zonality is a relatively rare feature...without some sig changes at higher latitudes, this still has all the hallmarks of another such occasion imho. 

Thanks Shed, in terms of cold zonality this is often as misused as Bartlett high scenarios in terms of peoples expectations, cold zonality IMO is a set up of lows moving either west/east or nw/se but the the jet is so far south that generally any milder interludes are very shortlived, often the north will stay cold throughout, snow often on the northern flank of these lows and generally snow falling to lower levels even in the south between lows. Now we can see differing scenarios in terms of where any higher pressure is located, a few years back I think we saw a scenario with some pressure rises to the ne and a jet axis nw/se so this could still count as low pressure headed in from the Atlantic and got diverted se, the clear distinction IMO is the type of air following the lows so, not PM air but Arctic origin from the north not backdoor from the west/nw, this is often too modified IMO.

 

The key component of cold zonality is blocking to the north or ne that acts as a trigger to force the jet southwards, we have some suggestions of that horseshoe type low heights with a lifting out of low heights in the northern chunk of Greenland but no strong block, indeed you don't always need a strong block but in that case you need a more favourable placement of the PV and a weaker jet.

 

Realistically its a case of making the best out of the current pattern for coldies, I don't suddenly see ice days and severe frosts within the next two weeks, some snow possible to the north, perhaps a bit more interest further south if enough cold is embedded before a low runs in but its hard to make a case for a cold spell, given the state of the stratosphere I'd class it as a success if there is at least some interest even if its more snaplike than spell.

[Summer Sun]

Today's NAO update maintains the positive them for the rest of December

 

[shedhead]

Thanks Shed, in terms of cold zonality this is often as misused as Bartlett high scenarios in terms of peoples expectations, cold zonality IMO is a set up of lows moving either west/east or nw/se but the the jet is so far south that generally any milder interludes are very shortlived, often the north will stay cold throughout, snow often on the northern flank of these lows and generally snow falling to lower levels even in the south between lows. Now we can see differing scenarios in terms of where any higher pressure is located, a few years back I think we saw a scenario with some pressure rises to the ne and a jet axis nw/se so this could still count as low pressure headed in from the Atlantic and got diverted se, the clear distinction IMO is the type of air following the lows so, not PM air but Arctic origin from the north not backdoor from the west/nw, this is often too modified IMO.

 

The key component of cold zonality is blocking to the north or ne that acts as a trigger to force the jet southwards, we have some suggestions of that horseshoe type low heights with a lifting out of low heights in the northern chunk of Greenland but no strong block, indeed you don't always need a strong block but in that case you need a more favourable placement of the PV and a weaker jet.

 

Realistically its a case of making the best out of the current pattern for coldies, I don't suddenly see ice days and severe frosts within the next two weeks, some snow possible to the north, perhaps a bit more interest further south if enough cold is embedded before a low runs in but its hard to make a case for a cold spell, given the state of the stratosphere I'd class it as a success if there is at least some interest even if its more snaplike than spell.

Agree completely Nick.  I think we can and probably will prise the colder door open at times and that could well result in at least some of the white stuff, especially across the higher ground in the north, but as you say making the case for a 'cold spell' remains very difficult. That said, last nights overnight mins of 11-13c in many places do look like being a thing of the past, so I suppose you could argue that given those sort of values the only possible way is up.....or down if talking about temps rather than expectations.

 

PS: Seeing winter wonderland scenes in the media from Jordan and Israel this weekend is hardly going to lighten the mood in here either...

Edited December 16, 2013 by shedhead

[TwisterGirl81]

I thought the GFS charts start updating at 15:30, it's still showing this mornings model 06z?

[Nick L]

I thought the GFS charts start updating at 15:30, it's still showing this mornings model 06z?

 

Yeah it seems NW is having problems updating the charts, Wetterzentrale is updating though:

 

http://www.wetterzentrale.de/topkarten/fsavneur.html

[Barry12]

 

Cold enough for snow over higher ground?

[shedhead]

Interesting developments over the US just before Xmas according to GFS, with the core of cold getting lifted well north and +15c 850Hpa air affecting some parts of the NE that have seen recent blizzards.

 

[Summer Sun]

I thought the GFS charts start updating at 15:30, it's still showing this mornings model 06z?

 

meteociel always updates the quickest click Map Hemi. North to get a better view

 

http://translate.google.co.uk/translate?sl=auto&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.meteociel.fr%2Fmodeles%2Fgfse_cartes.php&act=url

Edited December 16, 2013 by Summer Sun

[gottolovethisweather]

 

Cold enough for snow over higher ground?

 

Yep, see my posts from yesterday, I expect this trend to continue but perhaps with a lessening of the wintry impact down in any parts of England.

 

http://forum.netweather.tv/topic/78671-model-output-discussion-4th-dec2013-12z-onwards/?p=2862368

 

and

 

http://forum.netweather.tv/topic/78671-model-output-discussion-4th-dec2013-12z-onwards/?p=2862485

 

Thanks for posting those updates Barry as some will not have seen them. The next watch period will be Friday into Saturday.

Edited December 16, 2013 by gottolovethisweather

[Panayiotis]

The NASA model has been consistently showing a minimum of -6C uppers for parts of the west on the 19th:

Where as the GFS only wants to bring in a minimum of -4C/-5C uppers:

Edited December 16, 2013 by Panayiotis

[alexisj9]

The NASA model has been consistently showing a minimum of -6C uppers for parts of the west on the 19th:

Where as the GFS only wants to bring in a minimum of -4C/-5C uppers:

That little wave might bring some gusts down here.