Model Output Discussion - 31/10/2014 and Beyond

[knocker]

The ECM monthly update. There would appear to be no significant deviation from a mobile low pressure Atlantic, depressions centred rather to the north, so continuation of unsettled weather and average temps. No development of the PV or any suggestion of Arctic air pooling south or retrogression.

 

In N. America, after the initial cold spell has above average temps, especially in the north. The above average temps also applies to the Arctic, particularly at the beginning of the month although it's as well to remember these are 850mb anomalies not the surface.

Edited November 4, 2014 by knocker

[SMU]

Morning all -

With reference to my last post in my preliminary winter forecast thread, I am expecting a drop in the AO index to significant negative levels spanning the next 10-12 days.

Despite some of the modelling ( mostly the GFS ENS ) the signal has started to manifest stronger & stronger with the CPC discussion picking up on it as well.

The very cold wave into the US & far east is the first step which eventually supports the retrogression of everything west in 10-12 days time -

Expect this thread to become very busy in the next few days & maybe just maybe those T 336 ensembles may pick up the signal

The ECM monthly looks pretty spot on barring perhaps a little more positive height anomaly SW of greenland which changes the pattern for us.....

Watch out for todays NOAA AO ensemble update - will we see a mean trend below -4

S

S

[IDO]

Certainly the repercussions of Nuri has meant the first chance of an early taste of Winter. But this shows even when we get a good HLB you still need the luck. This time again its the USA that will get the cold and the UK the mild (ECM):

 

 

+10 850s for the UK and -16 for parts of the US. Hopefully its not going to be another year where these cold shots are bias towards US (for the coldies on here that is).

 

My worries yesterday was that this was a one off disruption and was it enough for long term changes to the PV or will it just delay the PV's inevitable organisation. Its difficult to know as ECM continues to shred the PV to a much greater extent than the only current  LR guide, the GFS. The latter does try to reform the PV in FI, but it is a slow process, though a definite trend for the main PV lobe to be nearer Siberia. Though still not organised. At D16 the op, control & Parallel:

 

  

 

From the GFS op run the next 16 days look very ordinary (for London), average temps (excluding next 2 days) and average rainfall as we head into the last third of the November forecasting period:

 

 

 

 

Edited November 4, 2014 by i'm dreaming of...

[mushymanrob]

sorry, im not being obtuse here, but why is a block ne america - western greenland good for the uk getting cold? surely thats too far west to produce a polar northerly, wouldnt it just allow low pressure to sit in the mid atlantic and thus leaving the uk in a mild southwesterly? (hopes).

[garbagebags]

Over the past few days now I've noticed FI on the GFS trying to build heights over greenland. Yes its FI and yes its different every run. But its the fact that it keeps trying is making my ears prick up just a bit more than normal. Ill post a chart, and on its own its pointless because its FI. But its a growing trend (in my eyes).

[johnholmes]

sorry, im not being obtuse here, but why is a block ne america - western greenland good for the uk getting cold? surely thats too far west to produce a polar northerly, wouldnt it just allow low pressure to sit in the mid atlantic and thus leaving the uk in a mild southwesterly? (hopes).

 

It can give the correct wave length across the northern hemisphere to put the UK on to the cold side of a ridge downwind from N America, but it does not always work, the wavelength is critical.

The current output from the anomaly charts shows the pattern I refer to, nearly but not quite for a deep cold incursion if it was mid winter

the EC-GFS version below with NOAA 6-10 and 8-14 along very similar lines. Thus showing the other idea of slow moving wave patterns. This one looks to last 5-10 days possibly longer.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

Edited November 4, 2014 by johnholmes

[bluearmy]

sorry, im not being obtuse here, but why is a block ne america - western greenland good for the uk getting cold? surely thats too far west to produce a polar northerly, wouldnt it just allow low pressure to sit in the mid atlantic and thus leaving the uk in a mild southwesterly? (hopes).

I suspect rob, that if some of those who have predicted a cold n American winter are right, that we could well be worrying about west based -NAO's quite a bit. howevwr, seeing as its early November and not February, I'm just going to enjoy the ride as Im sure there will plenty more opportunities ahead.

[garbagebags]

sorry, im not being obtuse here, but why is a block ne america - western greenland good for the uk getting cold? surely thats too far west to produce a polar northerly, wouldnt it just allow low pressure to sit in the mid atlantic and thus leaving the uk in a mild southwesterly? (hopes).

 

I believe positioning is critical. Ive seen ridges and blocks where a couple of hundred miles east and west of the ridge you've got +10's and the -10's. 

 

[Gibby]

Some interesting synoptic patterns this morning and while not supporting deep cold and snow at the moment some building blocks are beginning to take shape but will it hold firm for Winter 2014-15. My daily thoughts can be found below.

 

HERE IS MY LATEST ANALYSIS FROM THE OUTPUTS OF THE WEATHER COMPUTER PREDICTION MODELS FOR TWO WEEKS FROM 8AM TODAY TUESDAY NOVEMBER 4TH 2014.

NEXT UPDATE WEDNESDAY NOVEMBER 5TH 08:00

 

THE CURRENT GENERAL SITUATION. A complex Low pressure area over the British Isles will fill and move away to the East over the next 24 hours.

 

MODELS-2 WEEK HEADLINE  Generally unsettled and rather windy at times with rain or showers. Temperatures look like staying generally quite close to average though it will feel rather chilly at times. Perhaps becoming drier from the North later.

 

THE JET STREAM ENSEMBLE FORECAST The GFS Jet Stream Ensemble forecast indicates that the flow keeps the UK under a Low pressure trough with the flow crossing the Atlantic and to the South of the UK before returning North over Europe. This structure remains in place through the reliable timeframe before the flow lifts North through the British Isles in a weakened and ill defined form in the less reliably correct second week.

 

GFS Today's operational run shows Week 1 governed by several deep Low pressure areas moving SE from the NW Atlantic down over the UK with attendant rain and showers in tow. As they fill in situ next weekend It will feel chilly with some frost and fog possible at night. Through week 2 the operational indicates a rise of pressure displacing the Low with brighter and drier weather with mist and fog issues night and morning along with patchy frosts. Low pressure areas to the NW continue to deliver some rain at times to NW areas though and daytime temperatures would not be far from average if the pattern evolves as shown.

 

THE GFS ENSEMBLES.  The GFS Ensembles show very similar evolutions through Week 1 and the start of week 2 with pressure becoming higher to the North or NE and lower to the SW at the start of Week 2. Throughout this period rain and showers along with rather cool conditions will remain in situ under UK based low pressure. Later in Week 2 the Atlantic winds up somewhat with a Low to the NW likely to maintain unsettled and breezy weather then with rain at times and it could become rather milder under more of a SW flow UK wide.

 

UKMO. UKMO today shows a deep depression close to or over NW Britain filling up over the weekend and leaving a showery trough under slack winds at the start of next week. So a lot of squally showers to begin the weekend will be followed by winds falling light and showers becoming more coastal under temperatures probably a shade below average. The unsettled pattern at Day 6 still looks to hold sway as Low pressure to the NW looks like it could become more dominant later next week.

 

THE FAX CHARTS  The Fax Charts shows our current UK based Low pressure filling up but being replaced by complex Low pressure and trough structures through the latter part of the week and weekend with temperatures close to or a little below average in variable winds.

 

GEM  GEM shows Low pressure the dominant factor in the UK weather as successive centres drift down from the NW to become slow moving close to western and NW Britain with fresh to strong winds from the SW or west maintaining a mix of rain and showers at times through to the end of the period covered by this morning's output at least.

 

NAVGEM NAVGEM shows the basic pattern of the other models too gradually raising pressure to the North in a weeks time and sending Low pressure down to be SW of the UK and bringing a chilly and rather cloudy ESE flow across the UK to end the run. 

 

ECM. ECM shows Low pressure areas feeding in from the NW over the UK with rain and showers at times in often rather cool conditions. It too raises pressure to the North of the UK as we move towards the end of it's run and with Low pressure by then to the South a chilly easterly flow develops with quite cloudy skies but by then not a lot of rain away from the far South and SW.

THE ECM ENSEMBLES  The ECM Ensembles show strong support at Day 10 for a Low pressure belt to stretch from Greenland to the UK with pressure High to the North and NE. This would indicate rain at times in the South and West while the North and East sees the driest and brightest conditions. It could be quite chilly in the SE or East flow over parts of the UK, especially the North.

 

NOTABLE TREND CHANGES FROM PREVIOUS RUNS There seems strong agreement between the models that shows a lot of Low pressure close to the UK slipping SE from the NW over or just to the West of the UK over the period with a slow pressure build to the North later.

 

MY THOUGHTS  The theme of Low pressure areas moving down towards and over the UK from the NW has strong support from all output this morning which if verifies will maintain a mix of sunshine and showers mixed with some longer spells of rain when it could become briefly milder. Amounts of rain look like being quite variable mostly dependant on how quickly rain bearing troughs clear East out of the UK but all areas look like they could see a fair amount at times. Longer term there seems a desire to rise pressure to the North of the UK with Low pressure becoming cut off either to the SW or South of the UK. This would dry things out for many but a chill East wind could take hold and while no cold weather as such is likely to develop from this so early in the season under quite a lot of cloud it could well feel chilly. Longer term still and it appears that the Atlantic could push such a block away into Europe to bring more wind and rain and slightly higher temperatures but at such a range in time this is purely speculative. Looking deep into upper air patterns at the moment and it does appear that a shift in patterning could suggest that a straightforward and mild Westerly flow through the early part of our Winter season is unlikely and the net result of such could bring about some cold snaps at times this side of Christmas and while predictions for the latter and main event part of Winter are still an ocean away patterns that set up early in the season can often be hard to shift as we well know from the long term blocking patterns that have ensued over all seasons in recent years. If I am right then it would be unlikely that large scale flooding such as witnessed in parts of the UK seen last Winter would occur but it could be that parts of the UK could see some snow quite early this Winter. However, I stress this is not a forecast but a mere observation of how upstream air pressure patterns could evolve if the current setup is maintained.

 

[Polar Maritime]

This mornings runs continue to show a cool/wet N/W flow in the reliable time-frame, Further out +144hr and the signals are still very mixed with the Models continuing to struggle with the disorganised PV. The interest continues..

 

Edited November 4, 2014 by Polar Maritime

[Chris K]

Joe B has just put this on twitter

 

Joe laminate floori â€@BigJoelaminate floori  14 mins14 minutes agoState College, PA

SST analog model continues to support http://Weatherbell.com  idea of nasty US winter with major blocking again!

 

B1jXKJWIAAE7s13dfj.jpg

 

That is one heck of a long fetch easterly... surely it cant be right !!  or can it ?  an OPI of -2.12 puts us in a good stead providing blocking favours our neck of the woods. 

 

looks too good to be true TBH , but if something like that came off.....WOw 

 

Unless I am reading that wrong, it is not really suggesting a long fetch Eastery as it is not a surface pressure chart. To me that shoes a forecasted anomaly of higher heights over E. Canada  to W Greenland and lower heights stretching across the Atlantic towards the UK.

 

There is a less-strong higher pressure anomaly N of the UK and Scandi so you couldn't really say from this alone whether this would result in mild, wet weather pushing in from our West, or if troughs would undercut any high and form some sort of battleground over the UK.

 

If that chart verified, I would imagine it would be quite a mixed bag at the surface in reality. Depends on the positionings of pressure patterns...which others with better knowledge than me have already explained

Edited November 4, 2014 by Chris K

[knocker]

Little change with the D10 GEFS and ECM anomalies this morning. Still running with a meridional jet south of the UK and tending above average temps/

 

 

[garbagebags]

Little change with the D10 GEFS and ECM anomalies this morning. Still running with a meridional jet south of the UK and tending above average temps/

 

Your going to have to help me get my head rounds this one. How does the Jet dipping down below the UK in the third pic equate to the above average temps in the last pic, im confused, Surely such a JS would be pulling in cold air from the north?

[Severe Siberian icy blast]

It can give the correct wave length across the northern hemisphere to put the UK on to the cold side of a ridge downwind from N America, but it does not always work, the wavelength is critical.

The current output from the anomaly charts shows the pattern I refer to, nearly but not quite for a deep cold incursion if it was mid winter

the EC-GFS version below with NOAA 6-10 and 8-14 along very similar lines. Thus showing the other idea of slow moving wave patterns. This one looks to last 5-10 days possibly longer.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

Hi John. Like you say it looks close. From what I can see the ecm looks like the jet although dipping well south of the UK may come back over us taking us just the wrong side of the jet where as on the gfs the wave dips under the UK keeping us on the polar side therefore dragging the low pressures in a southerly track which would leave us open to attacks from the north and east ? Please feel free to correct me I'm reading this wrong ? Thanks ☺

[Nick F]

Your going to have to help me get my head rounds this one. How does the Jet dipping down below the UK in the third pic equate to the above average temps in the last pic, im confused, Surely such a JS would be pulling in cold air from the north?

 

The upper flow coming across the Atlantic going into the amplified trough across western Europe isn't particularly cold and, as the charts suggest much of the UK (not EIRE and N Ireland) is just on the eastern edge of the trough, it only takes a southerly or southeasterly flow at the surface to draw in mild air (above average temps) present over the near continent.

 

Really we need to see a robust Atlantic ridge build north into Greenland and the long wave trough to move east of the UK to get cold air south across us. Really the upper flow patterns or waves really aren't showing signs of playing ball to pull any significant cold air south from the arctic for now.

 

At least there are no signs of a Polar Vortex organising over Greenland/Iceland area, with HLB keeping upper lows displaced south across this side of the northern hemisphere, though signs of vortex organising over eastern Canada - which needs keeping an eye on. As although it will bring a cold start to November across eastern N America, it may also power up a strong jet downstream across the Atlantic, which may prevent N Atlantic pressure ridging, if the cold pooling spreads east out of NE Canada.

 

Still, it's too early to worry about lack of cold air to tap into. But really we need to look to the north rather than towards the E or NE for a cold source this early in the cold season. Ern/NE Europe and W Russia looks like warming up rather than cooling down atm.

Edited November 4, 2014 by Nick F

[SMU]

The lowley 06z out to 144, showing a better shape to the polar blocking, we could start to carve out some troughing down through scandi at day 9-12

S

[Polar Maritime]

Yes S, Much stronger Heights over the Pole/Greenland on the 6z. Parallel first.. 

 

Edited November 4, 2014 by Polar Maritime

[shaky]

Anyone seen the gfs 06z!!amazing blocking in the Arctic at only t144 hours!!!big upgrade already!!!even the parallel run has stronger blocking up north at only t126 hours!!

[Yarmy]

The parallel not quite so keen (yet):

 

Edited November 4, 2014 by Yarmy

[IDO]

Morning all -

With reference to my last post in my preliminary winter forecast thread, I am expecting a drop in the AO index to significant negative levels spanning the next 10-12 days.

Despite some of the modelling ( mostly the GFS ENS ) the signal has started to manifest stronger & stronger with the CPC discussion picking up on it as well.

The very cold wave into the US & far east is the first step which eventually supports the retrogression of everything west in 10-12 days time -

Expect this thread to become very busy in the next few days & maybe just maybe those T 336 ensembles may pick up the signal

The ECM monthly looks pretty spot on barring perhaps a little more positive height anomaly SW of greenland which changes the pattern for us.....

Watch out for todays NOAA AO ensemble update - will we see a mean trend below -4

S

S

 

 

The AO is going strongly negative in line with the strong amplification due to Nuri but the index only suggests that it is a temporary feature:

 

 

It dips to around -4 before trending towards zero. Do you think there will be another trigger to maintain the PV disruption? I am not sure this punch will be enough to change the upcoming early Winter pattern, as at this time of year the PV default is to build and organise itself. My worry is that this delay in the normal PV life cycle will just mean that as December starts we will head into a period of normal Atlantic service till the (if) stratospheric warming kicks in and we get another shot at cold. Its now trending that this transient opportunity of cold will pass us by and the upper air flow doesn't look conducive for a cold flow even beyond FI as it is a westerly flow; as you said retrogression will be needed and with the core PV over Siberia I am unsure what trigger will bring that about assuming the forecast neutral AO. Thanks.

[garbagebags]

Can someone tell me please, is the PV in general always "the enemy"? Like, would it be better if just never was there all winter (for cold and snow). Or do we need it to form but in the right places, or form and burst? how exactly does it work. Because im not sure if I want to be looking for no signs of PV or a ruined one, or do we need those dark purples but just not over greenland etc?

[knocker]

I notice on the GFS 06z the meridional jet has pepped up (130kts) around the mid Atlantic ridge and south of the upper low to the west of the UK.and into Portugal. Surface - complex low pressure area Ireland down to Spain.

[damianslaw]

Quick one from me - won't be able to post now until weekend. The northern hemisphere has a Nov 96 esque feel to it, which as many will  remember produced a deep low pressure from the NW mid month producing localised snowfalls and cold conditions thereafter..

 

The theme for November could well be an increasingly cold one with the jet aligned NW-SE, enabling some wintry conditions second half, nothing exceptional,  but very seasonal will frost, fog and some snow in the north at times - generally a wet one as well. 

[Polar Maritime]

Very much my thoughts to Damian looking at the N/H profile, Especially the last few days.. The continuation of N/W flows building towards Months end.

Edited November 4, 2014 by Polar Maritime

[Summer Sun]

The majority of the UK sees below normal 2m temperatures over the next 8 days

 

8 day anomaly

 

 

Normal 2m temps

 

 

Expected 2m temps