Model Output Discussion October 2012

[Summer Sun]

A rather unsettled run tonight from GFS with plenty of rain and showers around some of these could be wintery on high ground epically in Scotland, deep FI has some very deep depressions, no need to worry yet though they'll probably be gone on the next run

This chart below more a less sums up next week, Cool and unsettled with some areas struggling to reach double figures, the south should reach mid teens at best

[phil nw.]

The blocking over our side of the Arctic having an effect on the Atlantic flow as it approaches from the west.

If we view the 12Z GFS at T72hrs it shows quite a strong jet coming off the E.Seaboard but it hits a brickwall and has to go north up towards Greenland.

The main energy is steered south and by T120hrs. we get cutoff low pressure over Scandinavia with heights over the top.

Viewing the run out right to T180hrs we can see the energy hitting that brick wall across E.Greenland and being forced south rather than going it`s usual path towards Norway.

The UKMO at T120hrs shows the same picture.

At the moment though the blocking to our NE, whilst starting to be modelled regularly, is not preventing the Atlantic lows influencing our weather with the jet stream heading across us during the next week or so.

I do find the overall pattern interesting as it `s a sign that the zonal flow has yet to show it`s usual vigour.

This can change with a cooler Stratosphere of course but for now we continue to see this buckling jet with those height anomolies to our North east.

Edited October 9, 2012 by phil n.warks.

[SMU]

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.

Cheers Stuart-

Its also worth noting the larger area that the top of your 5 day graph covers- in my eyes that shows that the rather than be concentrated at say 17M/S over 70N the jet is a lot further south within boundaries of 40N & 70N

S

[Gibby]

Hi Folks. Here's a look at the 12zs from GFS, UKMO and ECM and what they may translate to us on the ground should they verify.

All models show the current contrasting slack conditions over the UK with fine weather in the North and cloudy drizzly weather in the SW will last just a little longer before a freshening Southerly wind brings an increasingly active and complex trough system in from the West over Thursday. This moves into the North Sea on Friday with a showery westerly flow affecting the SW which lasts through saturday too.

GFS then shows Low pressure to the East on Sunday with a very unstable Northerly flow over Britain with outbreaks of rain in a chilly Northerly breeze. By Monday a ridge topples over the UK with a drier interlude before deep Low pressure areas near NW Britain steers fronts East with strong winds and rain periodically through next week. Through FI and things remain very volatile with just brief drier interludes under weak ridges. late in FI a potentially quite stormy spell is shown with deep low pressure delivering wet and windy conditions for all. Temperatures throughout the run remain close to or a little below normal.

The GFS Ensembles show a dip in 850's for the South by Friday before a recovery in values to near the seasonal normal in a very changeable and sometimes wet spell for the South. Further North 850's are also shown to remain close to the long term mean so no early taste of winter there albeit cool and unpleasant feeling at the surface at times.

The Jet Stream shows a split flow with the Southern arm sinking South and weakening over the coming days. The Northern arm ridges way up to the Arctic Circle leaving the UK in a broken and weak jet straek. Later a resurgence of the Jet moves over the Atlantic towards Southern Britain.

UKMO for midday on Monday shows Low pressure over the North sea with a slack NW flow over Britain with showers. A sliding trough will move SE over the SW half of Britain in the hours that follow bringing rain over the SW within 12 hours of the chart.

ECM looks very wet tonight in it's later stages as with High pressure blocking Northern latitudes the door is well and truly open to active and deep low pressure areas with periods of heavy ran or showers and strong winds sweeping in from the west at regular intervals.

In Summary it looks like a very unsettled period to come. Over the last few runs blocking High pressure at high Northern latitudes has served to enhance the Atlantic steam roller in bringing deep and potent depressions and rainfall to most areas of the UK with little respite shown in later stages. If some of tonight's charts verify flooding could become a serious issue in view that the ground is already at saturation point in many areas. Temperatures as a consequence would never be very cold nor with all the wind and rain would it feel very mild either.

[UV-RAY]

Hi Folks. Here's a look at the 12zs from GFS, UKMO and ECM and what they may translate to us on the ground should they verify.

All models show the current contrasting slack conditions over the UK with fine weather in the North and cloudy drizzly weather in the SW will last just a little longer before a freshening Southerly wind brings an increasingly active and complex trough system in from the West over Thursday. This moves into the North Sea on Friday with a showery westerly flow affecting the SW which lasts through saturday too.

GFS then shows Low pressure to the East on Sunday with a very unstable Northerly flow over Britain with outbreaks of rain in a chilly Northerly breeze. By Monday a ridge topples over the UK with a drier interlude before deep Low pressure areas near NW Britain steers fronts East with strong winds and rain periodically through next week. Through FI and things remain very volatile with just brief drier interludes under weak ridges. late in FI a potentially quite stormy spell is shown with deep low pressure delivering wet and windy conditions for all. Temperatures throughout the run remain close to or a little below normal.

The GFS Ensembles show a dip in 850's for the South by Friday before a recovery in values to near the seasonal normal in a very changeable and sometimes wet spell for the South. Further North 850's are also shown to remain close to the long term mean so no early taste of winter there albeit cool and unpleasant feeling at the surface at times.

The Jet Stream shows a split flow with the Southern arm sinking South and weakening over the coming days. The Northern arm ridges way up to the Arctic Circle leaving the UK in a broken and weak jet straek. Later a resurgence of the Jet moves over the Atlantic towards Southern Britain.

UKMO for midday on Monday shows Low pressure over the North sea with a slack NW flow over Britain with showers. A sliding trough will move SE over the SW half of Britain in the hours that follow bringing rain over the SW within 12 hours of the chart.

ECM looks very wet tonight in it's later stages as with High pressure blocking Northern latitudes the door is well and truly open to active and deep low pressure areas with periods of heavy ran or showers and strong winds sweeping in from the west at regular intervals.

In Summary it looks like a very unsettled period to come. Over the last few runs blocking High pressure at high Northern latitudes has served to enhance the Atlantic steam roller in bringing deep and potent depressions and rainfall to most areas of the UK with little respite shown in later stages. If some of tonight's charts verify flooding could become a serious issue in view that the ground is already at saturation point in many areas. Temperatures as a consequence would never be very cold nor with all the wind and rain would it feel very mild either.

I would say temps would be very suppressed during the daytime at least.

[ANYWEATHER]

Whatever the weather in the next few days, it looks as though high lattitude blocking will be disrupting the Jet Stream in the Northern Hemisphere in the near to medium term. Mild weather will be at a premium and expect some severe weather in the Uk from this set-up in the near future......

[Zenarcher]

Today's models are still looking good with the Northern blocking so here is my comparison between the 12z runs of the ECM, GFS, UKMO, NOGAPS, JMA and GEM.

96 hours 13th October: Things already uncertain at this point we have the GFS and UKMO showing a low pressure system just to the South East of Greenland meanwhile the rest show high pressure moving North into the Atlantic making the low pressure system move South East. It's a 4 V 2 here so UKMO and GFS may be slightly wrong.

120 hours 14th October: The models that did show the low pressure system move South East place it over England giving some wet and windy weather. However the UKMO and GFS are still very alike and show more settled weather for the UK.

144 hours 15th October: Despite all their differences they all end up looking similar here. We still have the Northern blocking in place but we have a deep low pressure system to the South of Greenland, at this range it's hard to know if the models are over reacting to the Atlantic but all six of them show it.

168 hours 16th October: Big differences here with just 4 models at this range we have the ECM and JMA looking similar with a weak low in the Atlantic and the blocking still looking good. Meanwhile the GFS and NOGAPS do keep the blocking but the Atlantic still manages to swing by some low pressure systems over the UK.

Overall - The trend continues today for a Northern blocking to occur soon and into mid October. Once again I would say the ECM shows the best run of the day because it keeps the blocking going on right up to 240 hours, so does the GFS though it's not far behind.

[Cloud 10]

Interesting times ahead for forecasters across the Northern Hemisphere!

Climate Prediction Center - 8-14 Day 500mb Outlook

Extract from CPC discussion:

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD IS: MUCH BELOW AVERAGE, 1 OUT OF 5,

DUE TO HIGH SPREAD AND UNCERTAINTY AMONG THE GFS, ECMWF, AND CANADIAN ENSEMBLE

MEMBERS COUPLED WITH POOR RUN TO RUN CONSISTENCY AMONG THE OPERATIONAL GFS

SOLUTIONS.

[legritter]

looks like totally wet ,welcome to the uk , all modells showing interesting spells of autumnal weather , and as other posters point out the flooding issue comes back after thursday . this as got to be the year with the most warnings and watches i can remember . And to add to the mix temperatures oh so depressing .all we need now is the russians to hike up the price of gas .plenty of good posts today ,im looking forward to tonights Met office Fax update for 120 hrs .

[cooling climate]

Plenty of assumptions being made in this thread this evening.Northern blocking

has happened countless times in the past during Autumn without the need of record low sea ice etc. Higher ozone levels over northern Canada may very well be playing there part in the blocking we are likely to see in the not to distant future.

Looking back through the archive charts of many Autumns that preceded cold

winters and northern blocking always showed its hand more so but not exclusively so prior to the onset of winter. Of course though there were some

that looked very promising during the Autumn months but failed to deliver during winter. Again a number of factors were probably at play not least the QBO

and stratosphere.

[johnholmes]

Two 500mb anomaly charts from NOAA 7 days apart showing the polar vortex and how a week is a very long time in meteorology?

[SMU]

Hi John I must admit I have never been a fan of the CPC charts-

Especially when the confidence is 1:5 which is the lowest level- almost makes the chart pointless-

My guess would be whatever the 500 Longwave anomalies are in week 1 will be fairly similar in week 2-

S

[damianslaw]

Models all show a disturbed atlantic dominated spell of weather for the foreseeable future, with potential for some very conditions meaning in all likelihood more flooding - indeed the charts have a de-ja-vu feeling about them i.e. very much akin to June-July... not good news, all thanks to persistant northern blocking meaning the jet will be amplified and we see slow moving frontal systems crashing into the country and remaining in situ quickly joined by further low pressure systems. All this would result in often very cool windy wet conditions for many. Temporary ridges could develop but they look very shortlived.

Longer term - GFS indicating some very deep low pressure system formation.. resulting in very wet weather with gales.. conditions that often show their hand by late October.. but with added northern blocking... interesting stuff for the time of year.

As others have stated with the ground so wet and the fact that evaporation levels at this time of year seriously decline - if such synoptics verify, flooding would be almost a dead cert.. In my autumn predictions I did say this autumn could be a very wet one indeed.

[johnholmes]

Hi John I must admit I have never been a fan of the CPC charts-

Especially when the confidence is 1:5 which is the lowest level- almost makes the chart pointless-

My guess would be whatever the 500 Longwave anomalies are in week 1 will be fairly similar in week 2-

S

You are taking a specific Steve from the current CPC discussions and much of the discussions usually ( I have not looked at that for today) refer not to the anomaly charts but to much of the operational runs from the main players.

And no the chart for week 1 is only similar let alone same as week 2 IF the pattern is shown to be consistent day after day. I never ever take one run on its own always 2-3 days to get consistency between each model and model to model on the 3 I use.

Precisely why I prefer the much less volatile anomaly charts to the 4x or 2x daily synoptic ouputs.

On the basis of my checking these over 10 months then the figures speak for themselves, at 10+ days they verify (upper air wise) on about 70% of occasions, which is a far better result than any of the synoptic models at that range, whether you choose 00, 06, 12 or 18z ouputs.

But each to their own-no issues with what you prefer.

Edited October 9, 2012 by johnholmes

[phil nw.]

The latest NAEFs`pressure anomolies from the 12z run continue to show extensive positive heights across to our north throughout the run.

http://www.meteociel...&map=1&runpara=

The low confidence expressed by the NOAA forecasters is understandable in such a setup i guess.Low zonal mean winds inducing a buckling and split jet must create great difficulties in placing the main 500 wavelengths.The added complications of stalling cut off lows muddying the waters too.

Edited October 9, 2012 by phil n.warks.

[BLAST FROM THE PAST]

A trend perhaps appearing that the HP to NE will not extend SW to us as LP dominates on this 1st occasion. Maybe its too soon and will have a second thrust back end of the month

BFTP

[Gibby]

Good morning. Here's the morning glance at the 00z output at what they mean to us on the surface.

All models show fairly slack winds over the UK as High pressure drifts away slowly East from northern Britain. An old decaying front over SW England keeps a lot of cloud here which drifts North over Western Britain through the day. A cold front then moves slowly East across Britain and on out into the North sea bringing a spell of rain then showers following behind to Southern and Western areas over Friday and Saturday.

GFS then shows a continuation of heavy showers on Sunday in a Westerly flow with low pressure near Scotland. A transient ridge then moves East in the early part of next week followed hot on it's heels with a deepand vigorous Low pressure moving into the UK from the Atlantic pushing Atlantic troughs, wind and rain through all areas midweek and beyond. The trend then through FI is for very little change with Low pressure either to the West or NW steering fronts in from off the Atlantic although Eastern parts may become less wet and slightly warmer for a while before Low pressure takes over for all areas once more.

The GFS Ensembles show a warming trend after a dip to below average uppers at the weekend in the South. They end up near normal under the Atlantic sourced wind pattern. In the North normal values are evident too with plenty of rain about. 850's do trend slightly above normal late in the run.

The Jet Stream shows the split in the flow currently taking place with the northern arm ridging high over the Arctic and fragmenting later. The Southern portion slips further south and weakens too before a new surge from the states rushes East to set up a frow near Southern England and the English channel in a week or so.

UKMO for midnight on Tuesday shows Low pressure dominating from a positions South of Greenland and the Eastern Atlantic with troughs moving into the UK from the West to bring spells of rain to the UK through Tuesday and beyond.

ECM too remains in a very volatile mood this morning with deep Low pressure South of greenland moving East towards western Britain keeping wet conditions for many and with an increasing risk of gales too.

In Summary it looks a typically unstable Autumn pattern this morning with all areas seeing wind and rain at times through the next few weeks. Temperatures will never be far from normal with an Atlantic feed over the UK for most if not all of the time. There seems little prospect of the other form of autumn conditions, namely frost and fog over the coming few weeks with Atlantic Low pressure totally dominant.

[BLAST FROM THE PAST]

Gibby

I don't see standard autumn conditions. Arctic HP to our N/NE extending down, LPs on southerly track and/or stalling. LP dominant too in my opinion because its forced on a track that impacts whole of UK rather than NW? Wouldn't standard autumn conditions be LP moving SW to NE with gales for NW and calmer conditions for SE with general SW'ly flow? I don't know, maybe its synoptically its not standard.

BFTP

Edited October 10, 2012 by BLAST FROM THE PAST

[SMU]

Chance of the first snow of the season to lower hills in Scotland...

http://www.meteociel...CM1-120.GIF?10-12

I am watching this feature above developing on the ECM at day 5 as its signal ( A lot further north on the GFS) has appeared in the last couple of runs & it presents itself with what I think a chance of seeing the first snow of the year other than being reserved for the tops of Glencoe etc-

If you look close at the 850 Charts the air touches -4C, & the thickness if around 526/527 DAM in that little circle-

So certainly a localised event in NE scotland-

I havent got a lot of the usual parameter data on this as the GFS has it a lot further North- so no Theta charts or dewpoints etc-

I would hazard a guess at 2/300 M seeing some sort of wintery mix changing to snow at higher elevation.

A small chance for a brief period that if the ZDL is brought down with any intensity MAYBE a mix getting to the surface-

It depends on the lapse rates in that coloumn as it will have travelled over the North sea...

One to track.........

S

Edited October 10, 2012 by Steve Murr

[Radiating Dendrite]

The synoptics are really weird and wonderful at the moment.

Looking at the models over the last few runs (esp the GFS) we could see a short warm spell in the 10 day timeframe with Southerly winds for a time.

Something to keep an eye on.

The blocking to the North is quite something though, as is the jet stream! It looks all confused

[chionomaniac]

Gibby

I don't see standard autumn conditions. Arctic HP to our N/NE extending down, LPs on southerly track and/or stalling. LP dominant too in my opinion because its forced on a track that impacts whole of UK rather than NW? Wouldn't standard autumn conditions be LP moving SW to NE with gales for NW and calmer conditions for SE with general SW'ly flow? I don't know, maybe its synoptically its not standard.

BFTP

For those feeling wet and cold outside it may feel like pretty ordinary standard autumnal fare on the surface!

We just know that that is not the case synoptically.

[Cloud 10]

Models all show a disturbed atlantic dominated spell of weather for the foreseeable future, with potential for some very conditions meaning in all likelihood more flooding - indeed the charts have a de-ja-vu feeling about them i.e. very much akin to June-July... not good news, all thanks to persistant northern blocking meaning the jet will be amplified and we see slow moving frontal systems crashing into the country and remaining in situ quickly joined by further low pressure systems. All this would result in often very cool windy wet conditions for many. Temporary ridges could develop but they look very shortlived.

Longer term - GFS indicating some very deep low pressure system formation.. resulting in very wet weather with gales.. conditions that often show their hand by late October.. but with added northern blocking... interesting stuff for the time of year.

As others have stated with the ground so wet and the fact that evaporation levels at this time of year seriously decline - if such synoptics verify, flooding would be almost a dead cert.. In my autumn predictions I did say this autumn could be a very wet one indeed.

A good post and highlighted by the GEM at 144hrs.

[cyclonic happiness]

Gibby

I don't see standard autumn conditions. Arctic HP to our N/NE extending down, LPs on southerly track and/or stalling. LP dominant too in my opinion because its forced on a track that impacts whole of UK rather than NW? Wouldn't standard autumn conditions be LP moving SW to NE with gales for NW and calmer conditions for SE with general SW'ly flow? I don't know, maybe its synoptically its not standard.

BFTP

and frost and fog would be in between the lows in the ridges of high pressure, so I can see Gibby's point.:-)

[Gibby]

Gibby

I don't see standard autumn conditions. Arctic HP to our N/NE extending down, LPs on southerly track and/or stalling. LP dominant too in my opinion because its forced on a track that impacts whole of UK rather than NW? Wouldn't standard autumn conditions be LP moving SW to NE with gales for NW and calmer conditions for SE with general SW'ly flow? I don't know, maybe its synoptically its not standard.

BFTP

When I do my reports I often emphasise it's what the weather feels like on the street to Joe public, most of whom don't care a toss about the synoptics. It's a case of hot wet, dry, cold or warm not what High pressure is doing 1000's of miles away that's important to most. I'm sure there are many who read these forums who become lost and confused about what the models show so I tend to fight their corner and make the model reading a bit more ABC like. I do of course take your pojnt that the synoptics are indeed not standard autumn fayre at the moment with some interesting outcomes possible in a month or so should the pattern maintain. However, there are some on here with greater scientific understanding who make great contributions to this and other forums at times and make debates about this and other weather factors even I don't fully understand very engaging and long may it continue.

[legritter]

Morning all ,A good post from Gibby ,yes i agree JOE public dont want to know anything at all technical about the weather ,just the bottom line .As for the charts ,plenty of interesting weather to come , but as always ,the 120hr and beyond charts in this type of set up could change big time .but an increasing likely hood of some deep lows turning up in next weeks charts .[will we see a mega low of 950 mbs from the GFS ] but we never know . nothing would surprise me at the moment ,certainly modell watching is full of surprises .