WInter Model Output Discussion 12z- 28/01/2013

[Nick F]

New poster on this thread here. I think this clearly highlights how we need to be careful about taking individual runs as the truth - if they can't manage to agree on what will happen in 90 hours time, how can they possibly be expected to give a conclusive answer on the chances of cold in 10 days time?

I tend to look at model trends at the 500mb level, i.e. the flow at the mid-levels of the troposphere - which tends not to have such drastic changes with each run, when looking out as far as 10 days. Because at the surface, areas of low pressure can often change track with each run - even as close as 3-4 days out!

But a track of an individual surface low won't necessarily change the overall pattern thereafter. Signal still from the ens means for the 500mb pattern into the 8-10 day range consisting of a large Azores ridge slightly displaced north, while a deep trough digs south over Europe - which indicates northerly topplers. Perhaps may lead on to something more sustained cold-wise in Feb, if we see the PV to our NW retreat west to allow the Azores high to ridge north and northeast, but no definite signs yet.

Edited January 29, 2013 by Nick F

[bluearmy]

Yes you do make a very good point about the low at the weekend. However, I would say that given that the strength of any low pressure systems has an effect on the formation of high pressure (I think it's called WAA or something like that?) small features can make a big difference. On the 6z all low pressure systems seem to be much stronger in my eyes at least and consequently the high in south-western Greenland is at 1025mb at 156hrs as opposed to 1015mb from the previous run.

T156 is a rather different place than T84 ! of course we can see differences run to run at that timescale that can have bigger consequences thereafter and cause a movement in the longwave pattern.

[Joe Levy]

T156 is a rather different place than T84 ! of course we can see differences run to run at that timescale that can have bigger consequences thereafter and cause a movement in the longwave pattern.

Yes that is true! Mind you, given experience from recent model output, FI can change position so much that t84 and t156 have been equally uncertain at times! I think it will be very difficult to gauge the chances of sustained cold until much closer to the time, possibly only a couple of days away, especially since slight changes in the positioning of the Azores high and the strength of the Canadian vortex can have extensive repercussions.

[TEITS]

T165 come on Scandi low....start falling down the North Sea!

Won't happen.

Whats going to happen next is another LP will move E and bring another NW/N,ly attack around +240

[Nick F]

Yes you do make a very good point about the low at the weekend. However, I would say that given that the strength of any low pressure systems has an effect on the formation of high pressure (I think it's called WAA or something like that?) small features can make a big difference. On the 6z all low pressure systems seem to be much stronger in my eyes at least and consequently the high in south-western Greenland is at 1025mb at 156hrs as opposed to 1015mb from the previous run.

The surface highs over Greenland are not really a direct consequence of WAA, there tend to be strong surfaces highs there due to the dense cold air at the surface over the ice fields. To get a proper strong Greenland high which creates blocking, you need high pressure not just at the surface but through all levels of the troposphere - this is created by WAA aloft rather than at the surface - hence why we see the higher heights on 500mb charts wherever there's a block.

The strength of an individual surface low won't have a huge consequence on the upper pattern, as it's the strength of the upper flow that determines the depth of the low at the surface.

[Joe Levy]

The surface highs over Greenland are not really a direct consequence of WAA, there tend to be strong surfaces highs there due to the dense cold air at the surface over the ice fields. To get a proper strong Greenland high which creates blocking, you need high pressure not just at the surface but through all levels of the troposphere - this is created by WAA aloft rather than at the surface - hence why we see the higher heights on 500mb charts wherever there's a block.

The strength of an individual surface low won't have a huge consequence on the upper pattern, as it's the strength of the upper flow that determines the depth of the low at the surface.

Oh I understand. Thanks for clearing that one up well I still maintain that there is too much uncertainty for people to be giving up hope on chances of cold or to be affirming that there will be cold!

[TEITS]

Like I said last night this is a very easy pattern to predict.

http://modeles.meteo...gfs-0-252.png?6

The only uncertainity is the details of these NW,ly outbreaks i.e how cold but the outlook becomes more difficult beyond +240. The real pain is that lobe of PV despite weakening refuses to leave the area which we wish to see blocking develop.

http://modeles.meteo...snh-0-300.png?6

If you compare to the 0Z a massive difference in the modelling of the PV.

Look what happens when we see this lobe of PV weaken and vacate Greenland.

Edited January 29, 2013 by THE EYE IN THE SKY

[Nick F]

Oh I understand. Thanks for clearing that one up well I still maintain that there is too much uncertainty for people to be giving up hope on chances of cold or to be affirming that there will be cold!

Of course, the track of lows will have an impact on the microscale to who sees the coldest air and chance of snow in our small little island. So certainly agree of uncertainty over chances of cold and snow for individual areas. But on the broaderscale of things, there seems to more certainty out to 10 days and perhaps beyond that we will see a chilly polar maritime flow from the west or northwest generally with perhaps turning northerly for short periods, bringing down colder arctic air.

Edited January 29, 2013 by Nick F

[Severe Siberian icy blast]

In deep fi the vortex shows signs of complete disintegration , with big heights forming over the polar regions , including greenland , this is the set up we hoped to see around the 120 time fame , we can hope that this becomes a trend and repeats over the coming runs.

Lets see

[Matty M]

The 6z represents my believe on the coming patter, increased weak northwesterly topplers but eventually draining the PV out of Greenland towards mid-late Feb for a a real cold spell from the 2nd half of Feb. March is anticipated to be well below average.

[TEITS]

Last post until the 12Zs.

If you look at the GFS 0Z&06 then to be honest those who are saying no chance of real cold i.e Steve M are correct if you base this on the 0Z GFS run. However those like BFTP, Crewecold etc are correct if you base this on the 06Z.

The cold NW,ly outbreaks look likely and we could see 2 of them excluding the LP at +96. The uncertainity is with regards to the PV beyond this and whether we see this weaken and back W. If it does so like the 06Z then every chance of real cold with decent HLB blocking. If the PV doesn't like the 0Z then very little chance of this occurring.

[Tom Montalbano]

Like I said last night this is a very easy pattern to predict.

http://modeles.meteo...gfs-0-252.png?6

The only uncertainity is the details of these NW,ly outbreaks i.e how cold but the outlook becomes more difficult beyond +240. The real pain is that lobe of PV despite weakening refuses to leave the area which we wish to see blocking develop.

http://modeles.meteo...snh-0-300.png?6

If you compare to the 0Z a massive difference in the modelling of the PV.

Dave, what I really find interesting, and I'll probably get shot down for mentioning this, how similar the pattern developing in a few days time is to how the synoptics developed in mid-Feb 2005. Of course I realise that the archives are littered with benign northerly topplers, that we never see posted.

Anyone nailing their colours to any definitive conclusion, a week/10 days time, could be a very premature call.

http://www.wetterzen...s/Rtavn1861.png

http://www.wetterzen...00120050214.gif

http://www.wetterzen...s/Rtavn2881.png

http://www.wetterzen...00120050217.gif

Regards,

Tom

Edited January 29, 2013 by TomSE20

[SMU]

http://modeles.meteociel.fr/modeles/gfs/runs/2013012906/gfsnh-0-384.png?6

GFS gets there in the end with the hallowed vertical advection over greenland- sadly its the 06z & ever worse its the 384 hour chart.

S

[snowking]

Look what happens when we see this lobe of PV weaken and vacate Greenland.

http://modeles.meteo...snh-0-372.png?6

Stratospherically this scenario has support from the ECMWF too at the 100mb level. Here we are at day 2, with the main emphasis of the vortex Greenland/North Atlantic Based, with separate lobes towards the Siberian sector (with a decent warming of the Canadian sector helping to weaken the energy here somewhat over time):

By day 7, we start to see this energy transferring more and more towards the Siberian sector, with a small ridge around the UK/Atlantic:

By day 10, we see more ridging towards the Greenland sector, with most of the energy having vacated:

And increasingly moving further towards the Siberian sector.

Notice through this period the Pacific ridge wanes as the Atlantic one begins to build. We know all too well that the stratospheric forecasts are not infallible, but this transfer of energy has been a repeated suggestion at 10 and 30mb, and is now beginning to downwell to the 100mb level.....and as TEITS shows from the 6z, increasingly suggestion that this downwells to the troposphere too

SK

[Matty M]

http://modeles.meteo...snh-0-384.png?6

GFS gets there in the end with the hallowed vertical advection over greenland- sadly its the 06z & ever worse its the 384 hour chart.

S

It will happen but probably late Feb/ March, better than nothing

[Severe Siberian icy blast]

Stratospherically this scenario has support from the ECMWF too at the 100mb level. Here we are at day 2, with the main emphasis of the vortex Greenland/North Atlantic Based, with separate lobes towards the Siberian sector (with a decent warming of the Canadian sector helping to weaken the energy here somewhat over time):

By day 7, we start to see this energy transferring more and more towards the Siberian sector, with a small ridge around the UK/Atlantic:

By day 10, we see more ridging towards the Greenland sector, with most of the energy having vacated:

And increasingly moving further towards the Siberian sector.

Notice through this period the Pacific ridge wanes as the Atlantic one begins to build. We know all too well that the stratospheric forecasts are not infallible, but this transfer of energy has been a repeated suggestion at 10 and 30mb, and is now beginning to downwell to the 100mb level.....and as TEITS shows from the 6z, increasingly suggestion that this downwells to the troposphere too

SK

I hope your right , if you are then it will be good to finally see the back of this Canadian vortex that's been the dominate player all winter.

[AWD]

Lets not overlook what could be a nasty winter storm for much of the UK at the end of the week;

Both the GFS and ECM bring in troubling amounts of rainfall for many;

And equally problematic Windspeeds which, if verify, will cause transport and structural damage;

And both bring down colder uppers and the prospect of back edge snowfall as the low clears to the SE;

The chart below taken from an excellent netweather extra package shows the potential gusts around some southern areas of Britian;

This could be a notable event and one that, IMO, needs watching closely.

Edited January 29, 2013 by AWD

[bluearmy]

the london ecm ens show the slight uptick in mean temps towards mid month as the scatter from cold to mild widens.

not really interested in the 06z gfs low res. the 00z run showed why there is little point in looking at it as a predicitve tool without run to run consistency.

thats the glass half empty post. from a glass half full perspective, temps this saturday in london look like being around 3c max with a stiff noreaster. looking at the models a few days ago, you would have been carted off in a straightjacket for predicting that. the point being that within the atlantic ridge/scuero trough set up, there is much that can happen at fairly short notice to make a big difference to surface conditions across large parts of the uk.

EDIT: the 06z GEFS at day 11 have a big spread just se of greenland and a less sig one over france. the clusters will be far more informative than the mean.

Edited January 29, 2013 by bluearmy

[EML Network]

I've been watching the various charts, runs, ensembles for the past week and have been keeping quiet about the possibility of another cold spell..until now.

I just can't see another sustained cold spell developing at least in the first week of February that High Pressure over the Azores seems reluctant to link to Greenland, instead we're seeing a series of short lived topplers leading to milder, cooler, milder, cooler.

Until things settle down upstream it'll be some time yet before we start seeing anything in the charts that the Met Office 15-30 day outlook is hinting at.

Some of thing mornings runs are hinting toward High pressure flattening out with the lows riding over the top, leading us back toward to path of zonality, I'm hoping this isn't a trend that starts to become followed by the other models, but sadly the UKMO at 144 is already showing it's hand at this.

There's plenty of time left for things to get colder and more entrenched, but if we don't start to see the signs for a Greeny or a Scandi high developing in FI in the next weeks runs, then I fear that time will start to run out.

An important weeks model watching looms but at least with Friday's potential Bomb we have got plenty to keep us busy until then

[Frosty.]

The Gfs 06z op run saves the best until last simply because we have a strong looking Greenland High by then and the arctic blast looks more sustainable which would allow enough time for embedded troughs to swing south across the uk in the icy flow, there are a number of polar maritime incursions before then with variable degrees of potency but T+384 is the real deal, since the jet is tilted nw/se for most of the run, I see no reason why the strongest arctic blast won't occur after earlier slightly less successful cold incursions.

Edited January 29, 2013 by Frosty039

[Man With Beard]

Oh I understand. Thanks for clearing that one up well I still maintain that there is too much uncertainty for people to be giving up hope on chances of cold or to be affirming that there will be cold!

I think what both posts highlight is that there is a big picture and a small picture in the models at present. In the big picture, early Feb will most certainly see attempts at blocking through mid-Atlantic up into Greenland which may it may not be successful - as shown by 500mb charts. Small picture though - being late January, it only takes a very small rise in heights to the west or north and a southerly tracking low to put us a risk of snow, especially as you go further north. But the small detail is subject to changes at very short notice which will affect what we actually see on the ground.

[seabreeze86]

Hi guys just a question for the more knowlegable in here.

Is there a reason why threwout winter we have seen forecasts from various modles for heights to rise around Greenland and also the backround signals pointing in that directions at times. There seems to always to much energy around the iceland area to allow heights to build. Even though the AO has been neutral the NAO has not followed must of the time.

I thought that these two followed each over and a dissconnect was not a regular occurence or am i wrong?

[Barking_Mad]

Lets not overlook what could be a nasty winter storm for much of the UK at the end of the week;

Both the GFS and ECM bring in troubling amounts of rainfall for many;

And equally problematic Windspeeds which, if verify, will cause transport and structural damage;

And both bring down colder uppers and the prospect of back edge snowfall as the low clears to the SE;

The chart below taken from an excellent netweather extra package shows the potential gusts around some southern areas of Britian;

This could be a notable event and one that, IMO, needs watching closely.

Thanks, nice to see some solid detail

[Summer Sun]

Does anyone know what the latest EC 32 dayer is showing?

Lots of scatter from the ensembles this morning

The trend to drier weather seems fairly consistent at the moment

[TEITS]

http://modeles.meteo...snh-0-384.png?6

sadly its the 06z & ever worse its the 384 hour chart.

S

Yes the negative side is as you say its the 06Z run. Highlighting the +384 chart is a bit pointless though because its what happens much earlier with regards to the PV that allows the blocking at +384 to appear.

Still the 06Z does show what is still possible. At the moment opinion is divided whether we see a GH and I think its fair to say neither camp has enough evidence to suggest either way at the moment.

Clearly we have alot of disagreement within the Greenland/Iceland region which is why the Iceland ensembles keeping flip, flopping all the time. I know you said its pointless looking at the Iceland SLP mean but to be honest you're wrong. The 0Z/06 GFS runs clearly show the difference in the modelling of the PV and this will have an impact on the SLP across Iceland.