Model Output Discussion 18th Nov.2013-12z onwards.

[Cheshire Freeze]

 

I think the general point of Steve's post was to pick up on the point that a few people noticed the possibility of the Pacific ridging aiding a more disturbed vortex into December. Notice I said 'possibilty' there. A couple of posters 2 days ago suggested that the medium range modelling was pointing to traditional +NAO/AO conditions when in reality, (as I and other people pointed out), it was/is being modelled far from traditional zonal muck (at present).

 

A traditional zonal set up would see a circular PV with a flat jet encompassing the N hemisphere. Stick a great big Pacific ridge into the equation and you're asking for the vortex to be disturbed....(whether the ridges/troughs set up in such a way to benefit us is a different matter).

 

I do think a distinction has to be made here between someone noticing the potential for a cold pattern to develop and providing reasoning and the event actually coming to fruition.....because whether it happens or not the potential was/is there regardless of the final outcome.

Edited November 26, 2013 by Osbourne One-Nil
Because the previous post has been edited

[syed2878]

interesting the models starting to toy with the idea of a possible cold outbreak. As for some of our posters would be better off in parlerment in sted of a weather forum where they can freely have a dig at each other.

[Blake]

This may be in the wrong place, but this was GFS output for 18th Jan 2013 144 hours out and 24 hours out.

 

 

Could someone more able than myself dissect these two charts to explain what each showed at the time.

 

Where is the wind coming from in each and to what areas? Is the first showing a westerly flow for western areas and more of a NE'erly for eastern parts with showers for the east and in the second pretty much Southerly/SE'erly winds UK and a line of precipitation through Ireland down through the Bay of Biscay heading from W to E?

 

If I am on the right tracks, I am starting to understand a little more, if not, I need to go back and do some more research.

 

But if we take a look at the GFS from 20th for 26th (Today) and yesterday for today, could someone post these images and do the same for me?

 

Thanks in advance

 

(p.s. if this is in the wrong place, move it and drop me a PM to where it has been moved to?)

[Mucka]

Some good consistency regarding the pattern change to something colder and more unsettled from GFS with the cold Northwesterly now just creeping into hi res.

 

wonderful day 10 chart although again the ridge topples later

 

 

Even so that would give a wintry few days, around a 3/4 day cold snap/spell, with plentiful snow showers even penetrating South and those in the NW who enjoy snow would be in hog heaven I suspect.

All still a fair way out though and plenty of time for upgrades and downgrades, smilies and frownies.

Edited November 26, 2013 by Mucka

[TSNWK]

Short,sharp cold shock in the middle of the 00:00 topped and tailed by our friendly UK hgh.

[Mucka]

GFS ensembles.

 

http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=258&y=79

 

Still not really any signal for prolonged cold but a strong signal for a cold snap. It may be worth noting that not a single member goes for any real HLB resulting from our ridge or proper height rises over Greenland but while that is in FI there is tsill a chance of a turn around as GFS often overdoes an Atlantic influence, especially in FI.

 

I think the next positive step for me will be ECM showing something similar and its ensembles firming up on the cold.

[Ian Brown]

The ECM goes on to show what would be a brief cold snap at T240. Its about timing really and if there is a long enough gap between systems coming off the Seaboard then you get the best case scenario of the GFS run for any northerly. Still all a fair way off but the general pattern is there, and as Mucka says nothing in the models to suggest anything long lasting in the way of HLB.

[Ali1977]

GEFS Perturbation shows the colde in ten days follwed by a nice Scandy high.  That would be nice.

[Great Plum]

This mornings GFS 0Z ensembles for London shows the weather staying largely below average after the next few days...

http://www.wetterzentrale.de/pics/MT8_London_ens.png

Nothing really cold as yet, but the chance of something more exciting after 5th December perhaps?

ECM seems to think so too...

http://www.wetterzentrale.de/pics/Recm2401.gif

[IDO]

ECM seems to think so too...http://www.wetterzentrale.de/pics/Recm2401.gif

ECM D10 0z charts are significantly under performing compared to the much maligned GFS:I wouldn't go there unless you are a glutton for punishment. However this is the same time frame as the GFS toppler so we need to see subsequent charts before we start getting excited... Edited November 26, 2013 by i'm dreaming of...

[IDO]

Early days yet, but be careful what you wish for. Good support on the pressure ensembles for this toppler (D8-10):

Hopefully no downgrades on this.

However from T300-T384:

Leaving: Mean:

Looking rather uninspiring in FI (usual caveats). That sort of outcome suggest a reset back to a MLB. The amplification from the upstream development of the Pacific Ridge looks like it will only have a temporary effect on the NH, with the PV re-establishing status quo in a few days.

As Mucka's and other excellent posts attest to, early days to call the synoptics after this upcoming meridional spell but early signs are a trend back to square one.

[Severe Siberian icy blast]

IanF update shows MetO sees the W to NW and back to W air flow as likely for a while too. However I must admit I was pleasantly surprised by the contingency planning post put out by the Met that I had missed before SS posted it. I have plumped for a below average winter overall with the core of the cold from mid Jan to mid Feb - but I did not expect a 20 - 25% probability of the overall temps falling into the most severe (20%) category. I know the odds are still against it - but it smelt ever so slightly of a gentle MetO ramp moment. :-)

Iv tried to find this but can't. Can you give me a link please

[Troubleatmill]

Iv tried to find this but can't. Can you give me a link please

 

May of been looking at this mornings CFS SSIB?

Edited November 26, 2013 by tempestas

[johnholmes]

ECM D10 0z charts are significantly under performing compared to the much maligned GFS:

cor_day10_HGT_P500_G2NHX (1).png

I wouldn't go there unless you are a glutton for punishment. However this is the same time frame as the GFS toppler so we need to see subsequent charts before we start getting excited...

 

that is quite interesting as 5 and 6 day, other than fairly short spells, I have never seen GFS outperform ECMWF over several years. Can you give a link please?

[johnholmes]

Time for a quick post before sleep. Agree with assessment of polar air back in the mix once the current settled spell comes to an end but not seeing anything remarkable yet. A number of different charts pointing to a similar theme but this one from the NOAA is as good as any:

 

 

 

Mid atlantic ridge rebuilding and NW to N air flow on the horizon. However the chances of this turning into a major outbreak are small. The high is likely to be flattened again though not before the north has had a good opportunity for more snow especially at elevation. For the south its a possibility... but if so it looks transitory.

 

IanF update shows MetO sees the W to NW and back to W air flow as likely for a while too. However I must admit I was pleasantly surprised by the contingency planning post put out by the Met that I had missed before SS posted it. I have plumped for a below average winter overall with the core of the cold from mid Jan to mid Feb - but I did not expect a 20 - 25% probability of the overall temps falling into the most severe (20%) category. I know the odds are still against it - but it smelt ever so slightly of a gentle MetO ramp moment. :-)

 

 

the signs from the 3 anomaly charts I use, including NOAA, are a bit mixed. By that I mean the pattern west of mid Atlantic is not solidly meridional for anything other than a short spell of colder air from the NW-N. Still the same from ECMWF-GFS this morning. Slight indications of +ve heights developing in mid Atlantic tending to turn the 500mb flow north of west into the UK. But further upwind over N America the signal from all 3 is still, not confused but ,not sufficiently solid to suggest those slight +ve heights will be more than transitory for the moment.

Edited November 26, 2013 by johnholmes

[cobbett]

Iv tried to find this but can't. Can you give me a link please

Think this is it

http://forum.netweather.tv/topic/75389-met-office-contingency-planners-forecasts/page-3

[IDO]

that is quite interesting as 5 and 6 day, other than fairly short spells, I have never seen GFS outperform ECMWF over several years. Can you give a link please?

Here goes:http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/ Edited November 26, 2013 by i'm dreaming of...

[Yarmy]

that is quite interesting as 5 and 6 day, other than fairly short spells, I have never seen GFS outperform ECMWF over several years. Can you give a link please?

 

 

I noticed this the other day. May just be noise as it's difficult to say why a model that is worse at T144 would be better at T240. However, I suppose if the GFS takes better account of snow cover/albedo/surface temps/whatever as the run evolves you could see how it might be better later on.

Edited November 26, 2013 by Yarmy

[Tamara]

 

 

I think the general point of Steve's post was to pick up on the point that a few people noticed the possibility of the Pacific ridging aiding a more disturbed vortex into December. Notice I said 'possibilty' there. A couple of posters 2 days ago suggested that the medium range modelling was pointing to traditional +NAO/AO conditions when in reality, (as I and other people pointed out), it was/is being modelled far from traditional zonal muck (at present).

 

A traditional zonal set up would see a circular PV with a flat jet encompassing the N hemisphere. Stick a great big Pacific ridge into the equation and you're asking for the vortex to be disturbed....(whether the ridges/troughs set up in such a way to benefit us is a different matter).

 

I do think a distinction has to be made here between someone noticing the potential for a cold pattern to develop and providing reasoning and the event actually coming to fruition.....because whether it happens or not the potential was/is there regardless of the final outcome.

 

I think what was actually suggested was that the pattern didn't favour any sustained cold weather patterns besides transient polar maritime incursions and I don't think anything has changed in that respect - much as confirmed by latest official updates based on METO data and as re-iterated by Ian F on this thread

 

 "Potential" has to be weighed up on the basis of how strong the westerlies are circulating in the polar stratosphere and whether any of the associated tropospheric wave breaking from the pacific ridge can sufficiently disturb the vortex (relative to its strength).

 

Many people will want to place a more positive spin on this - which of course is a free option.

 

I think however that the amount of amplification suggested by the models has to be viewed on the basis of vortex strength vs wave breaking strength, rather than any straightforward assumption that just because wave activity is occuring, it inevitably means that the vortex is going to be disturbed sufficiently to amplify the pattern enough to advect cold air far enough south, for anything longer than a day or two before the pattern flattens out again. Yes, that is better than any traditional zonal pattern - but it is not any December 1981 re-visited either.

 

Hoping for potential to be realised, is very different to it being realised in reality. I think it is fine to positive about 'potential' - but it is also necessary to be realistic about the chances of that potential being realised.

 

As far as chances of any traditional +AO/NAO pattern is concerned then as long as the -EPO signal remains and the bulk of the vortex can be kept towards Siberia, then this scenario can be avoided - but with the peak of the vortex strength still to come in December and into January we depend on the persistence of the wave activity +also it being sufficiently strong enough to sustain the holding pattern - because any relaxation could quickly take an average pattern into something less appealing with attendant zero 'potential'.

 

That is not saying it is going to happen, but it is pointing out how it could realistically occur. 

[Paul_1978]

Is it just me or are things looking similar to Jan/Feb 1984?

 

 

Haha we've had so many comparisons the past 2 weeks, first it were November 2010 then December 1981 and now Jan/Feb 84

 

 

This period was characterised by depressions coming down from the north west over the period of a few weeks, and there were some very snowy periods in Scotland and the north of England. However I'm not sure we're far enough into the season for us to be having the same effect at the moment.

 

Looking at the models today, it just strikes me that we are seeing a similar pattern as we were then.

 

http://www.meteociel.fr/modeles/archives/archives.php?day=15&month=1&year=1984&hour=0&map=0&mode=0

 

The above is a good example of where you can have high pressure to the south/south west (a 'Bartlett' if you like), but still have memorable weather.

Edited November 26, 2013 by Osbourne One-Nil

[Summer Sun]

Latest from Gibby on the 00z models

 

All models point to a rather cloudy and less chilly spell of weather developing over the UK from later today until Friday with a lot of cloud and hill fog and drizzle all in association with very High pressure near to the SW of Britain and moist air rounding the Northern flank of the High and down across the UK. On Friday a cold front moves SE across the UK bringing clearer and much drier air with a drop in temperature. Winds will become fresh and cold from the North or NW for a time with wintry showers possible in the North and East on Saturday before milder air begins to topple back down over the UK on Sunday following a frost, all this as High pressure is very dominant to the SW.

 

GFS then shows a couple of dry and quiet days across the South to start next week before cloudy and breezy weather moves down from the NW in association with a cold front with another band of lightening rain as it moves across Southern England. Things then turn much more unsettled, colder and windy across the UK albeit briefly with spells of rain with hill snow and strong winds, moving down from the North. This is then quickly replaced by High pressure once more toppling down from the NW to settle things down into a cold and frosty period before things turn rather mild again, especially in the North and West as a SW flow takes hold.

 

UKMO today closes it's run next Monday with High pressure still positioned SW of Ireland with little change in conditions from those we have currently with a mix of cloud and clear spells but mostly dry weather allowing patchy frost and fog by night but daytime temperatures held at reasonable levels due to a maritime NW flow.

 

GEM today shows High pressure still dominant either to the South or SW during the early and middle part of next week although the far North will have a wet and windy period. This then extends further South and East to all areas by next weekend.

 

NAVGEM keeps benign and relatively mild conditions well into the middle of next week with High pressure close to Southern Britain and a moist Westerly flow over the North. Frost and fog though possible would be uncommon as cloud cover will be quite extensive.

 

ECM this morning shows very slow changes to the anticyclonic pattern early next week, taking until the end of the week to turn things much more unsettled briefly with rain, strong winds then wintry showers. It does look though this will also be very temporary as a ridge to the West has nothing to support it and would likely topple back across the UK at the following weekend.

 

The GFS Ensembles show no really cold spell on offer this morning. There is a period when most members offer some rather cold weather for a time next week with no doubt a few wintry surprises for a few but it has good support not to last as the milder Atlantic air is shown to retrieve ground by the end of the output. There will be little rain for Southern Britain until well into next week.

 

The Jet Stream remains orientated badly for UK cold as it remains well to the north of the UK for some while yet before an injection and change to a WNW to ESE flow across Britain looks possible late next week before it rises back to Iceland late in the run.

 

In Summary today there is still little to cheer for those looking for deep cold and snow across the UK as High pressure remains stubbornly anchored close to South or SW Britain for another week warding off any major attempt of colder zonal conditions to move down from the North. There is a more marked attack of unsettled and windy conditions later next week when temperatures become rather chilly and no doubt some will see some wintriness for a time in among the wind and rain but the pattern is far from conducive to bring any one place anything more than a day or two of transient cold before milder air in association with Atlantic High pressure migrating back to the SW cuts off any supply with no Northern blocking or correct Jet Stream orientation to support anything different.

 

http://www.norton-radstockweather.co.uk/Model-Analysis%282859336%29.htm

[SomeLikeItHot]

[some graphs of GFS vs ECM and other models]

 

I noticed this the other day. May just be noise as it's difficult to say why a model that is worse at T144 would be better at T240. However, I suppose if the GFS takes better account of snow cover/albedo/surface temps/whatever as the run evolves you could see how it might be better later on.

 

Or it could be the GFS pushing towards the climate mean, which hurts it in the short term but assists it in the longer term. Either way the verification of both at that range is really poor.

[UV-RAY]

Maybe I'm viewing the output incorrectly but I see the potential of another January 1984 developing from around the first week of December, maybe not the longevity of that spell which around these parts gave us over two weeks of cold and snow. 

[Summer Sun]

Friday and Saturday look unsettled before we see pressure rising once more though remaining chilly

 

[draztik]

I remember captain shortwave saying at the weekend

"I do wonder whether the models will toy with developing a deep Atlantic trough in week 2 which consequently would push the Azores/Atlantic high north east through the UK"

....and this did have support from the Korean Met, which had this evolution by mid december

Now, this has support from the ext ecm ensembles, which is showing an Atlantic trough, with heights pushing NE by day 15