Model Output Discussion October 2012

[Frosty.]

How typical, it's the Ecm 00z ens mean which is now showing an anticyclonic further outlook with a major scandi block of high pressure extending as far southwest as the uk and now it's the Gfs which is showing the more atlantic low pressure dominated outlook, the latest 6z mean is looking pretty unsettled all the way to T+384 hours with low pressure to the nw of the uk for much of the time and occasionally the pressure looks a bit higher to the south but nothing significant, the major blocking is much further away from the uk to have no influence on our weather at all. The week ahead is showing the best weather north of the midlands in the next few days as areas to the south have occasional rain but by thursday it looks like a lot of rain will be spreading across the uk followed by an unsettled fr/sat/sun but then the ecm ens mean shows a steady improvement whereas the gfs continues the unsettled westerly flow, sometimes backing south of west so temps generally around average or a little above and coolest in nw britain.

Edited October 8, 2012 by Frosty039

[phil nw.]

Whichever run we look at we can see on the hemisphere view how the fledgling polar vortex is far from organised.This is the GFS006Z run at T96hrs.

We can see the core of the vortex pushed away from Greenland towards Canada/Alaska allowing those heights to rise in the Arctic regions to our North as we go into the next week.The height anomolies forecast by day 8 from both ECM/GFS show this clearly

The trough modelled to move across from the North west towards the end of the week sinking lower(blue heights)pressure into Europe.

I think at the moment those heights to our NE are too far away to influence surface conditions here, with the core more towards Siberia, but i must say we are in a different pattern than what we would normally see in mid Autumn.

The jet is very broken and weaker than usual and with those height anomolies over the Arctic it would be easy to visualise a complete switch to a pronounced -NAO pattern-alluded to earlier by GP and Chiono.

We have seen a very quiet period for Pacific scourced tropical convection recently and consequently little influence from the MJO on the hemispheric patterns.Latest forecasts do show this now on the move eastwards and this willl have to be monitored to see if it does trend towards phase 7 -favourable for Greenland/Scandavian blocking down the line.

Whilst the weather is nothing unusual at present i find there`s plenty of interest in current modelling.

[SMU]

A perfect wedge of high pressure.

S

[Snowstorm1]

http://modeles.meteo...nh-0-168.png?12

A perfect wedge of high pressure.

S

If this was one month later be close to meltdown on here ... get this pattern in and lock it then oooo....

[Summer Sun]

Northern Blocking is showing to affect our weather into next week on tonight's GFS sending the UK into a cooler and unsettled period don't expect lots of snow though its too early away from high ground

Firstly UKMO's take on things for the end of its run

GFS

After a few unsettled days high pressure sweeps back in sending low pressure further north

Edited October 8, 2012 by Summer Sun

[Cheese Rice]

Too bad we are in October...

Although synoptically not perfect it has the attributes to form a decent easterly providing the cold pool is in place.

[Zenarcher]

Going to do a comparison between the models at the moment as they seem to show a Northern blocking becoming more likely. I'll be comparing the ECM, UKMO, GFS, JMA, GEM and NOGAPS.

96 hours 12th October: Most of them agreeing with each other but I would say GEM and NOGAPS show things to be slightly different out in the Atlantic with the low pressure system near Canada is placed slightly more South East.

120 hours 13th October: We have a 3 V 3 situation here, the ECM, GFS and GEM show high pressure moving up in the Atlantic allowing a low pressure system to move South East. The rest of the models show the same low pressure system to be further North and not being pushed South East.

144 hours 14th October: Despite their differences at 120 hours all the models do show the blocking continuing at 144 hours. Pretty much all of them show something similar at this range apart from NOGAPS which seems to have a bit more energy going into the Atlantic.

168 hours 15th October: For those new to model watching we are now down to just 4 models at this range the ECM, GFS, JMA and NOGAPS. The ECM is showing a good strong solid block at this point meanwhile the other ones do show it continuing but not as great compared to the ECM.

Overall - All the models continue to show a Northern blocking pattern starting later this week, one good notable change is in the ECM it's 00z run this morning was poor with the Atlantic taking charge however this evening it has changed things around completely going with a very blocked weather pattern into mid October.

Edited October 8, 2012 by weathermaster

[Frosty.]

one good notable change is in the ECM it's 00z run this morning was poor with the Atlantic taking charge however this evening it has changed things around completely going with a very blocked weather pattern into mid October.

That is not surprising since the Ecm 00z ens mean was looking mega blocked (scandi high) towards the end of it's run, a complete turnaround since yesterday when it showed atlantic domination, wonder if the gfs ens mean will be jumping onboard again by the 00z.

[Gibby]

Good evening. here is the latest look at the 12z output from GFS, UKMO and ECM.

All models continue the pattern of a ridge across Central Britain with the remains of a warm front straddled over SW England delivering occasional rain and drizzle over the next 48hrs. By Thursday a cold front deepens and extends Eastwards over the UK on Thursday bringing rain and increasing Southerly winds to all areas . By Friday the trough lies down eastern Britain with a closed centre area of Low pressure developing over Northern Britain.

GFS then shows the weather being distinctly unsettled and at times very wet as Low pressure is steered directly over the UK bringing wind and rain in abundance for all areas. Very late in the run High pressure is pumped up towards the UK in response to an intense Autumn Storm moving NE through the Atlantic and away to the North. Fine and milder weather would develop with mist and fog overnight as winds fall light.

The GFS Ensembles show typical Autumn conditions under an Atlantic influence. The fine weather breaks in the North over Friday with unsettled weather with rain at times universally over the UK thereafter. 850's look very average for the foreseeable with no unwelcome cold or welcome mild spells to speak of.

The Jet Stream continues to split with the Northern half of the flow ridging North as the Southern slice slips South and weakens. As we move into the beginning and middle of next week a renewed surge piles eastwards across the Atlantic towards the UK.

UKMO for noon on Sunday shows Low pressure over Europe with a cloudy and chilly NE flow over Britain. Some rain is likely chiefly towards the Se while Northern and Western areas become dry and brighter with time.

ECM looks very disturbed in it's later stages tonight with High pressure establishing near Scandinavia with SE moving Low pressure slipping across the SW with periods of copious rainfall here while the best of the drier and brighter spells remain favoured for the NE of the UK. Temperatures will feel quite cool in the strong ESE winds and cloud cover.

In Summary there is a growing trend from the Euro's of a High pressure build over Scandinavia with some very unsavoury charts for SW Britain as Low pressure troughs become slow moving with heavy rain at times here. GFS though keeps things more unsettled for all with Low pressure crossing the UK with rain at times for all. Temperatures will be near to or a little below normal accentuated by the breeze if the ECM run verifies.

[Cloud 10]

Excessive rainfall may become a problem as we go into the weekend and next week

if charts like the one below from the 12z gfs verified,with low pressure systems

tracking directly across the UK as the jet-stream heads south in response to

northern blocking.

[TonyH]

Probably a case of GFS over dramatising things though..actual patterns usually turn out much more moderate.

[Geordiesnow]

Probably a case of GFS over dramatising things though..actual patterns usually turn out much more moderate.

I tend to find the GFS over complicate things when these patterns occur with more shortwaves on the charts than anything else and it looks like the GFS 12Z run is an example of that.

Again, the output is interesting on a pressure pattern POV rather than the actual weather for us, unfortunately if anyone want an proper early cold shot, it has to be from the North rather than the East so the trend for blocking does seem a bit of a waste but interesting nonetheless.

[Cloud 10]

Probably a case of GFS over dramatising things though..actual patterns usually turn out much more moderate.

Possibly,but the same sort of charts are showing up on many of the models now

so potentially another very wet spell of weather coming up especially for England

and Wales

ECMWF/GFS DAY 8-10 MEAN 500MB HEIGHT COMPARISON

Climate Prediction Center - 8-14 Day 500mb Outlook

[chionomaniac]

Latest 18Z GFS looks to be very similar to ECM at around T+120.

Now will that block head west?

Also could be pretty miserable next weekend.

Edited October 8, 2012 by chionomaniac

[IDO]

We have an Op (0z) run from GFS that is close to the mean so a more persuasive forecast. October, on this run looks like "Autumnal", troughs and ridges crossing the country giving us a nice spectrum of seasonal weather. Temp mean over the period is average, with cooler and milder interludes. No obvious sign of anything remotely wintry.

This weekend appears to bring a wet period for the south and the clusters are 100% sure of this, though intensity and timing remain the variables:

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cpre&HH=132&ZOOM=0&ARCHIV=0&RES=0&WMO=&PERIOD=

From then changeable, though at the end of FI the op tries a HP scenario (no real support amongst members).

The GFS Ens has low close to the UK for FI (T120 onwards), but this appears to be a relative outlier compared to most members:

http://cdn.nwstatic.co.uk/ensimages/ens.20121009/00/prmslAberdeenshire.png

Still plenty of scatter amongst members from the weekend so other possibilities, though the current op run looks a strong favorite for a trend.

[Gibby]

Good morning. Here's a look at the 00z output from GFS, UKMO and ECM this morning.

All models show a slack airflow across the UK currently . A frontal trough lies across SW England remaining slow moving over the following 36hrs. Another trough lies close to Northern Scotland with some rain here while all central areas stay fine and dry under a ridge of High pressure. On Thursday a deepening trough and Low pressure moves East over Britain with a spell of wind and rain for all before clearer and fresher conditions move East to all as the Low moves out into the North sea over the start of the weekend.

GFS then shows another Low pressure piling in from the West towards Southern Britain with spells of rain here through the day. This moves us towards a very changeable pattern through FI as low pressure troughs cross the UK in association with parent Lows close to the NW. The situation though looks blocked with High pressure over Scandinavia or close to the SE at times allowing some dry and brighter spells between the rain bands as they cross and decay. By the end of the run High pressure develops near the South with some fine but foggy conditions developing if it verifies.

The GFS Ensembles show a short cooler snap after the cold front passes on Thursday before uppers recover towards the seasonal average thereafter. A very changeable outlook is shown by the members with rain possible at most times in an Atlantic feed. Conditions for Scottish locations look equally changeable once the next few days are passed in uppers close to normal throughout.

The Jet Stream profile has changed this morning. The current split in the flow North and South of Britain continues for a few days before a strong surge from the States brings a strong jet towards Southern Britain in a week or so.

UKMO shows a cool Northerly flow in association with a Low centred over Germany. There could be rain at times on Monday in the East with a chilly wind blowing from the North.

ECM keeps a low pressure complex close to Southern Britain and continues it there for the remainder of its operational run with periods of rain and showers for all. High pressure remains in its blocked position to the North of the UK .

In Summary Northern blocking is giving repeated signals to the UK's weather over the coming couple of weeks. It looks like positioning over Scandinavia or between Iceland and Norway, too far away to help the weather from being anything other than wet and unsettled over Southern Britain as Low pressure is steered in from the Atlantic across the South. Northern areas may see some drier spells or in terms of GFS SE areas too later.

[johnholmes]

yes thanks Gibby I suspect you summary is about right.

All 3 anomaly models increasingly show northern blocking but also a mainly westerly feed of air at 500mb suggesting an unsettled theme. Some slight indication that the block MAY edge a shade further south with perhaps the main emphasis on ridging being east of Iceland towards Scandinavia but that part is far from clear at the moment.

[SMU]

Morning All-

Is this for the winter area or model discussion- hey ho I will paste into both-

I think the ECM evolution is the most likely with retrograde into Greenland.

However that aside for one moment look at the ECM -

http://www.meteociel...ype=0&archive=0

Load up every map in Meteociel & run your cursor over the times - watch the area of 504 DAM heights ( purple ) which starts over North West Greenland & gets reversed around the pole to be on course for central Russia at day 12-

For that to happen the zonal flow has to be well below the mean to such an extent that the blocking is predisposed in the northern part of the NH pattern- especially in the 2 key quadrants that effect the UK ( greenland & Scandi)

Its the chicken & the egg, but we should be falling back to the net thermal gradient outputs from the latter part of summer-

Taking that into the equation & what it means for autumn is that the MEAN location of the NH polar front will be several degrees further south than the NH MEAN average-

This in itself isnt the guarentour of the UK being below average on CET, what it does mean is the colder air is in closer proximity to the UK,- On average I would say the PF runs across 50N- 60N

Perhaps on AVERAGE its running NET around 45N-55N

For the UK though we are actually seeing the result of the SSTA around Greenland effecting the jet even further-

So even though the net of the whole PF is further south we are getting varying degrees of disruption around 50 W & 50 N-

You then end up with either a weak jet that dives north up towards western greenland & then returns south angled towards France.

The other scenario is even more severe where the jet splits ( NOTE ECM DAY 10) where we get an arm forced around the pole & an even weaker southern arm heading towards france.

There is also something else that I dont thing any single person has mentioned- so I will put it forward now-

The southern tip of greenland is always a point of reference I use to see what effects its going to have on any low pressure exiting the NE States-

Traditionally the low pressure systems creep under the tip of greenland on course for iceland- & of course that positive NAO pattern that we normally see-

NOW the jet is displaced further north & at a greater angle its actually sending these low pressures towards or up to the left of that greenland tip-

If a system crashes into Southern greenland you will see a large loss of energy ( a bit like a hurricane hitting land) - & soon over and the systems fall apart-

whats the net of this- LESS easterly progression towards europe-

Whats there more of- More lows splitting energy across the west coast of greenland with energy going south & North-

Remember these 2 key charts that demonstrate this PERFECT-

http://modeles.meteo...2-12-26-0-0.png

http://www.meteociel...=0&map=5&mode=0

its all about Western Greenland-

What does this mean in terms of October- well its important to recognise that where the MEAN jet for october is & the fact that even with a Greenland high the trough that sets up on the SE side could still sit towards western Norway or Northern Scotland leaving the UK mild-

Thats the warmest scenario^

The coldest scenario is the trough is forced south & east of the UK & we are in the early season polar air.

even the middle ground is cold & unsettled with the heaviest of the PPN in the south of the UK with a string of runners along the channel.

Taking that back to the CET we are odds on 80/20 to be below average, where the trough sets up is probably the difference between the catagory of cold / below ave we fall into-

will it be 9-10 CET or even 8-9 CET. with a rank outsider sub 8c-

Naturally we are already turning towards November, & if we return the status quo then the only difference to October would be the expansion of the polar cell & how suddenly we go to North & east for cold air instead of the North in October.

So you 'could' forecast a below ave November already with one footnote-

Week 2 of November will see the stratsphere show its hand in terms of cooling temps V the norm- if we get VERY cold then the net anomaly of the jet could be wiped out & the signal for an erratic jet over southern greenland will be muted.

Exciting times ahead- watch out for a big renewed cold push of air into NORTHERN Europe at day 12 & the possibility of it pushing towards the UK day 12-14-- it depends on the trough....

regards

Steve

[lorenzo]

All about the Western Greenland indeed.

A comparison of where the anomalies lie in respect of SSTs looking at 2010 due to it's pre-disposition to deliver monster blocking anomalies compared to where we are now.

This year has similarities with SSTs around Greenland, further North the anomalies are greater.

July - each year sees extensive warmth West Greenland and a significant anomaly in Beaufort Sea, nearly off the grid.

August - sees warmth on southern tip of Greenland in 2010 this year pretty similar for this area.

September - 2012 core warmth still in the Beaufort Seas, in 2010 core of warmth further west in Chukchi Seas. Shape of ENSO showing it's hand over Japan for 2012, as the warmer SST's creep eastward to Central Pacific.

July / August / September -

That PV is going to have a job setting up home..

[chionomaniac]

Further more, height rises around Greenland can cause local wave breaking back into the stratosphere - the type we saw at the start of winter 2 and 3 years back. This agian breaks up the lower stratospheric vortex allowing further wave breaks better chances of succeeding, especially early in the season before the upper vortex can override the lower vortex.

[Glacier Point]

Morning All-

Week 2 of November will see the stratsphere show its hand in terms of cooling temps V the norm- if we get VERY cold then the net anomaly of the jet could be wiped out & the signal for an erratic jet over southern greenland will be muted.

Exciting times ahead- watch out for a big renewed cold push of air into NORTHERN Europe at day 12 & the possibility of it pushing towards the UK day 12-14-- it depends on the trough....

regards

Steve

We can already get some idea of where we sit in terms of stratospheric jet profiles heading towards that mid November phase.

For similar years (we need an east phase QBO persisting throughout the first winter and subsequent summer), here's how the first 5 days have shaped up..

That's a mean westerly fow of 10m/s at 70N. Not significantly strong.

For our nearest comparable year, 1968, we are actually running 'light' as for the same period there was a mean westerly flow at 70N of 12 m/s.

During last year (different stratospheric profile), the mean zonal winds at 70N ramped up significantly during the second half of October, reaching 18 m/s by the 20th. That's 11 days from now and almost doubled wind flow.

very latest 30mb zonal flows as below.

.. still very weak. You can monitor this daily at http://ds.data.jma.g...lat_u30_nh.html

The longer this goes on without significant cranking up at 70N, the better we will sit in terms of pre New Year polar vortex and the increasing likelihood that lowering of heights to the north will be unstable and vulnerable to large scale amplifications in the longwave pattern as without the co-operation of a well defined stratospheric vortex, the whole thing becomes liable to jacknife.

Allowing for lag times for any stratospheric / tropospheric coupling, I would say we have at least 3 weeks 'in the bank' with light upper level flow allowing for the sort of (MJO/GWO induced) tropospheric amplification. That takes us to early November and I would suggest mid to late November on the basis that a rapid increase of upper level flow seems unlikely at this time. By which time, big blocking anticyclones around the periphery of the Arctic rim set up feedback loops for Rossby Wave trains directed poleward and upward into the stratosphere giving rise to the prospect for deccelaration of the polar night jet and warming of the stratosphere.

Edited October 9, 2012 by Glacier Point

[legritter]

looking very interesting across northern hemisphere over coming two weeks or so . it will be interesting to see where any high pressure cells eventually finish up . also i will be taking a look at temperatures in these northern latitudes to see what [Could ] be on offer .exciting times at the moment but i must point out to new members ,its only one part of the puzzle .the other part is what happens to our far south and s/west , MR Big fat Azores comes to mind , but remember anything severe could be 12 weeks or more away ,or Just around the [Next corner ].onto the model output ,remaining very autumnal , some very wet periods and with the possibility of a block setting up shop to our n/east or east always the possibility of low pressure becoming bogged down over us or very close by .cheers gang

[minus 9]

some great posts on here today.

[Frosty.]

The latest Ecm 00z ens mean seems keener to introduce high pressure from the north during the course of next week with the weather becoming gradually more settled from the north but taking some time for the low pressure influence to subside in southern britain, the Gfs 06z ens mean is showing low pressure being much more stubborn and covers the whole of the uk in unsettled weather throughout next week but further on, there are signs of a probable nw/se split with higher pressure to the south and east but remaining low to the northwest. The ecm mean tends to become more anticyclonic in the mid range but then low pressure returns more widely later. As for the rest of this week, the main change arrives on thursday with wet and windy weather slowly pushing east and maybe lingering in the far northeast on friday but probably becoming brighter elsewhere but with some showers, then the weekend is looking cooler and continuing unsettled with ene'ly winds off the north sea, then the main question next week is how far south will the high pressure to the north of the uk extend or will low pressure remain slow moving over the uk.

[BLAST FROM THE PAST]

very latest 30mb zonal flows as below.

.. still very weak.

.

So we want to see blue between 50-80?

BFTP