Model Output Discussion - The Start Of Winter

[nick sussex]

Looking at the ECM ensembles for De Bilt it looks like the control run holds a nw flow for three days from the 19th to 21st, this suggests more ridging north of that high pressure cell out of Canada.

 

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

 

For the north of the UK looking at those De Bilt temps for that period I think it would likely be a bit colder so perhaps a little interest, overall though theres no sign of a stronger cluster of colder solutions towards Christmas.

 

We have to hope that events in the strat deliver a change, of course the Christmas period is still two weeks away and alot can change but its a case of a race against time now to salvage the festive period, personally if its not going to be cold I'd rather it was dry and mild.

 

Anyway lets hope  something colder pops up in the coming days.

[Ali1977]

The GFS is a warm outlier for the entire run, I think the 06z might be quite different in FI. 

[Nick F]

Some dreadful charts on GFS and ECM leading up to Christmas which if verified would be very mild indeed, who invited Uncle Barty to the Christmas party!

I think also that the AH ridging into Europe route to cold is extremely dangerous and we are more likely to be left with a New Year long fetch south westerly than easterly.

 

 

00z ECM EPS mean/anomaly at day 10 thinks Uncle Barty may struggle to form, with troughing digging SE into eastern Europe:

 

 

Alternating milder westerly flow and colder northwesterly flows after Saturday (which is looking chilly nationwide) - perhaps lasting through into Xmas week too. Perhaps becoming increasingly dry across the south, as the Azores high extends its influence.

 

MJO in the circle of death, though some uncertainty where it may re-emerge, but that driver seems to be done and dusted for now. We await to see what a weak El Nino and possible Strat warming can deliver ahead, though we may have to wait until the New Year for a big pattern change from these drivers.

Edited December 12, 2014 by Nick F

[winterof79]

So let us have a quick look at the three most negative OPI years.Then lets see if there was a turn of the year NH pattern change.....

62 / 63  12th Dec. http://modeles.meteociel.fr/modeles/reana/1962/archivesnh-1962-12-12-0-0.png

End Dec   http://modeles.meteociel.fr/modeles/reana/1962/archivesnh-1962-12-31-0-0.png

76 / 77  2nd Dec. http://modeles.meteociel.fr/modeles/reana/1976/archivesnh-1976-12-2-0-0.png

http://modeles.meteociel.fr/modeles/reana/1976/archivesnh-1976-12-31-0-0.png

Eventually massive - AO http://modeles.meteociel.fr/modeles/reana/1977/archivesnh-1977-1-12-0-0.png

09 / 10  A little different evolution with S Murrs EPO   http://modeles.meteociel.fr/modeles/reana/2009/archivesnh-2009-12-2-0-0.png

 http://modeles.meteociel.fr/modeles/reana/2009/archivesnh-2009-12-12-0-0.png

Eventually leading to this at the turn of the year

http://modeles.meteociel.fr/modeles/reana/2009/archivesnh-2009-12-31-0-0.png

 

I certainly expect something to change before long.Hang in there.I do not recall OPI value for 78/79 perhaps somebody can enlighten me.The pattern change was earlier but the turn of the year was when the NH action began

 http://modeles.meteociel.fr/modeles/reana/1978/archivesnh-1978-12-30-0-0.png

Edited December 12, 2014 by winterof79

[fergieweather]

Agreed Nick. Noteworthy (as some others here have also spotted through different output) are the increasing EC and MOGREPS members offering ridged solutions towards latter stages of 10-15d trend period, which, in words of UKMO Dep. Chief, "...may be the first signs of a general change of type across northern Europe, with a slow-down in the predominantly W/WNW’ly jet – this in response to some signs from global teleconnectors of a move toward a negative NAO." There's no sign of meaningful change/cold pre-Christmas, but the period afterwards *might* offer broadscale change.

[Nick F]

Agreed Nick. Noteworthy (as some others here have also spotted through different output) are the increasing EC and MOGREPS members offering ridged solutions towards latter stages of 10-15d trend period, which, in words of UKMO Dep. Chief, "...may be the first signs of a general change of type across northern Europe, with a slow-down in the predominantly W/WNW’ly jet – this in response to some signs from global teleconnectors of a move toward a negative NAO." There's no sign of meaningful change/cold pre-Christmas, but the period afterwards *might* offer broadscale change.

 Interesting insight from UKMO chief as usual.

 

FWIW 00z GFS going for a -ve east-based NAO later this month after the 24th, well above before then:

 

You can see on the 00z op troughing digging SE towards Portugal from 24th and higher pressure over Iceland. Normally one run of the GFS op that far out I wouldn't normally bother to raise an eyebrow, but now you mention the cluster of EC/MOGREPS and chief forecasters view ... it may have some creedence. Though if the Azores high is held out west as per ECM - it won't occur so easily.

Edited December 12, 2014 by Nick F

[winterof79]

 An interesting  graphic on the AO: For the newbies this graphic on the right is what we would much prefer.A displaced or weak Polar Vortex and a warmer strat.High level Blocking is prevelant.

http://modeles.meteociel.fr/modeles/reana/1987/archivesnh-1987-1-13-0-0.png  A Noreaster for the US and nervana for us

 

It also illustrates why many,over the years,believe we follow the Eastern states for cold during winter months.(Mods feel free to move if not suitable)

[mushymanrob]

hmmm...



the gfs is a pretty mild run from day 4 onwards, and even suggests a bartlett type scenario, and this is plausible, however...



these charts suggest that high pressure somewhere to our south /southwest in the near time regresses and allows a more mean northwesterly flow days 10-14 , so dont support the current gfs's bartlett type high to our south... if im interpreting the 10-14day anomaly correctly it appears to put us back into a pattern we are seeing now with frequent polar maritime incursions and quite cold.

of course this is one run, is it picking up on a future pattern shift, or is it its own outlier?..

 

or are the coloured dotted lines confusing me?

Edited December 12, 2014 by mushymanrob

[Recretos]

Perhaps JMA is onto something.

 

  

[joggs]

Great input guys,thanks also Fergieweather for the insight from chief at mo.Much appreciated as it helps some of us amateurs wiat maybe to start looking for longer term even though the models not playing ball yet.

Regards.

[damianslaw]

When it comes to longer range forecasting, it pays well to look at broad possible trends, rather than becoming too focused on each model run - as these will always chop and change at such a timeframe.

 

My earlier post was a reflection on hints in the models of a possible gradual change from unsettled to more settled thanks to stronger influence of heights from the azores high - how this may manifest itself remains uncertain, but there is every reason for heights to ridge into a position favourable for a colder outlook as we move through the Christmas period, perhaps shifting north and east to cover mid atlantic and southern England, allowing lower heights to filter into Iberia - all eyes then would be on how the jet behaves - a split jet with more energy in the southern arm, would be a scenario that would allow sufficient heights to build northwards in the direction of Iceland and a classic scandi trough formation, dare I say it heights would then be sucked into Greenland.

 

I'm just suggesting this is a plausible scenario - and an evolution that could possibly occur, indeed I would expect some of the models to play around with such a scenario over the coming days.

[Recretos]

Before I go into more details, I wonder how many of you are familiar with NCEPs GEFS Reforecast 2 project/model?

 

To quote ESRL:
"The ESRL/PSD 2nd-generation Reforecast Project has produced a dataset of historical weather forecasts generated with a fixed numerical model, using the 2012 version of NCEP's Global Ensemble Forecasting System (GEFS). This Reforecast V2 dataset consists of an 11-member ensemble of forecasts, produced every day from 00 UTC initial conditions from Dec 1984 to present. The horizontal resolution of GEFS is T254 (about 50 km) out to 8 days, and T190 (about 70 km) from 8-16 days. Real-time forecasts are ongoing.

Among the advantages associated with this long reforecast dataset is that model forecast errors can be diagnosed from the past forecasts and corrected, thereby dramatically increasing the forecast skill. Past results have shown that the improvements may be particularly large for medium-range forecasts and for forecasts of relatively uncommon events such as heavy precipitation."

Edited December 12, 2014 by Recretos

[terrier]

Intresting that the far reaches of the gfs 6z run are showing real cold in scandi. Let's see if the models start to show some hlb in future output.

[chionomaniac]

To demonstrate what Steve has been describing in what to look out for upstream, it is worth looking at the jet stream pattern. Currently we have no chance of a Greenland block whilst the upstream Pacific pattern remains the same. The jet stream is breaking and fragmenting over Alaska slighty sending energy over the top of Canada which is then rejoining the Atlantic jet stream over the southern tip of Greenland. This will only set to reinforce the polar vortex over Greenland and the best we can hope for is an amplified Azores ridge dragging down colder northwesterlies - pretty much as has been occurring (not a bad trend to have in position for later!)

 

See here:

 

 

We need to lose any jet stream energy crossing north of Canada and rejoining the Atlantic jet at the southern tip of Greenalnd before any height rises will even begin to grow to our northwest and this is dependent on the flow in the NE Pacific.

 

Once we have signs that the jet stream can become amplified and split and travel north at the southern tip of Greenland, then we can start to think that we have a fighting chance of NW height rises.

 

OK so this chart is for Boxing Day but forget that, it is what we need to see more of in the change of jet stream pattern to improve the chance of a -ve NAO developing.

 

 

The signs are there that the pattern is changing upstream (around Xmas)......

Edited December 12, 2014 by chionomaniac
lousy spelling

[Ali1977]

p2,5,6,10,12,13,17,19 are all full of potential in FI

[Alexis]

00z ECM EPS mean/anomaly at day 10 thinks Uncle Barty may struggle to form, with troughing digging SE into eastern Europe:

 

ecmwf-ens_z500a_nhem_11.png

 

Alternating milder westerly flow and colder northwesterly flows after Saturday (which is looking chilly nationwide) - perhaps lasting through into Xmas week too. Perhaps becoming increasingly dry across the south, as the Azores high extends its influence.

 

MJO in the circle of death, though some uncertainty where it may re-emerge, but that driver seems to be done and dusted for now. We await to see what a weak El Nino and possible Strat warming can deliver ahead, though we may have to wait until the New Year for a big pattern change from these drivers.

The heights in the north don't look too over the top, so any high may not sink too far south. A UK high might be a likely option, with nothing particularly cold, but some frost and fog for us.

[bluearmy]

Finally we have a mean upper ridge beginning to show in the greenland area on the 06z gefs by the end of the run. At such a range, you are not going to see greens and yellows but from acorns.....

The anomolys look ok

[mountain shadow]

Complete agreement on the NAO forecasts to start declining towards neutral, another few days though to see whether a -NAO is likely or not..

 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.sprd2.gif

 

Things are beginning to firm up on a New Year pattern change.

[offerman]

Hi, I will be brief because we are veering off topic and there are other threads people will be able to point you to that are more appropriate.

Essentially the Azores high is a semi permanent anticyclone (high pressure) so called because it is located around the Azores region. It tends to exist at around 30 degrees North latitude in Winter (just to our South) and move north in summer.

It is part of a belt of high pressure systems that dictate Northern latitude weather patterns.

 

On the charts I posted or on any chart a part of the PV naturally exists around the Greenland area which spawns low pressure systems which run across the belt of high pressure West to East (typical zonal winter pattern) this series of low pressure systems prevents high pressure ridging North.

When the jet is more southerly it can force low pressure further South "amplifying" the pattern and high pressure can be displaced from its usual home.

In such circumstances we can get a cold zonal flow such as we have now with the Azores high displaced West of its usual home.

If we can also get the PV weakened or moved from Western Greenland then we have the prospect of a ridge of high pressure building in the Atlantic but this also requires low pressure to dig into the Azores highs Western flank and push WAA polewards. When this occurs we can get high pressure into Greenland as low pressure undercuts the Atlantic ridge and forms a "cut off" high in that region. This not a typical pattern but such HLB can be very beneficial in dragging in very cold polar air from the NE.

 

When the jet is flatter the Azores high will ridge into Southern UK and Western Europe giving us milder unsettled weather (typical zonal). Where the PV is weak and low pressure system slow and weak to travel East to West then Azores high can build across the UK and form  a UK high.

There are many more variations too numerous to mention here.

 

At present there is no sign that we will build a strong Atlantic ridge within the next 10 to 12 days but looking at GFS 00z we can foresee how modification to that pattern might allow for it.

 

Hope that helps.

Hi Mukka, 

 

That`s great, Many Thanks for taking the time to post in details.

 

Much Appreciated.

[karyo]

Complete agreement on the NAO forecasts to start declining towards neutral, another few days though to see whether a -NAO is likely or not..

 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.sprd2.gif

 

Things are beginning to firm up on a New Year pattern change.

You can try this link for a look further ahead: http://www.atmos.albany.edu/student/macritch/naoindex.png

 

It is reasonably reliable for up to 4 weeks ahead and then it varies considerably from run to run.

[mountain shadow]

You can try this link for a look further ahead: http://www.atmos.albany.edu/student/macritch/naoindex.png

 

It is reasonably reliable for up to 4 weeks ahead and then it varies considerably from run to run.

Thanks Karyo, as you say though, the run to run differences are quite marked. The blue dotted ensembles run from yesterday, must have been a cracker.

 

The link would seem to indicate no decent -NAO until mid to late January.

[bluearmy]

They look to be derived from the CFS enesmbles. i guess it depends how much faith you have in the CFS model ........................... 

Edited December 12, 2014 by bluearmy

[karlos1983]

They look to be derived from the CFS enesmbles. i guess it depends how much faith you have in the CFS model ........................... 

I have more faith in Arsene Wenger, and that says a lot really for the CFS..... none of it good

[Polar Maritime]

The CFS is actually pretty good at picking up long term signals/trends if used correctly, Obviously looking at every run and picking out detail its useless.

Edited December 12, 2014 by Polar Maritime

[bluearmy]

Watching the various gefs members over the past few days, you would expect one of the next four runs today (ops and para) to deliver a cold latter week 2.