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Model Output Discussion 18th Nov.2013-12z onwards.


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From a mildie point of view overall I'm quite pleased with the next week or so, sure there will be some frost around in the mornings but with much lighter winds than recently and if we get some unbroken sunshine it won't feel all that cold from late morning.

 

6z ensembles ---------->

 

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A number of posts have been removed - as much as the opinions in them were put forward in a reasonable and calm way, they weren't model discussion and that's what this thread is for - no-one is going to learn anything about the models in this thread if we allow it to fly off on tangents talking about other members posting styles. 

 

For what it's worth - three tips for posting in here:

 

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Quick summary of today's output from me. 

 

I don't see anything to be overly negative or positive about from a coldies perspective at the moment with MLB close to the UK likely to be in control of our weather until early December at least, so what has changed if anything?

 

I would say the models have firmed up on the signal for some king of mid Atlantic ridge to build in early December and moved away from the idea of building a Scandinavian high for now. 

Currently it looks as though the any ridge (if that is how things pan out) may be too far East and not amplified enough to bring a cold blast but it is a window of opportunity and there is no way the models will have a handle on the energy distribution upstream yet.

 

The period we are looking at is now just creeping into ECM's range which gives us extra data to go off but unfortunately thus far ECM is not showing enough amplification but it wouldn't take big changes to bring a wintry spell to the UK from the day 9 chart

 

Posted Image

 

We need to see the high further West and less energy around SW Greenland here and the 240 chart would of been quite different.

 

GFS operational's are flatter today although they still show a similar pattern developing a few days later. For now we can't take much from single operational runs as they will have a lot of natural variation and as I have said previously, signals this far out tend to wax and wane so it is just a case of keeping a watching brief.

Still, it is always nice to see a wintry signal for the UK grow stronger as this obviously builds more confidence, we are not currently seeing that though.

No sign of anything zonal for the period though and I would say the form horse is for a continuation of high pressure close to or over the UK continuing the current theme with a small but not insignificant chance of a wintry blast from the NE and very low probability of unsettled westerly type regime as we go through the first week of December based on current output.

 

No good news from the strat thread yet and I can't help wondering what type of weather we would of seen with some warming promoting HLB, given we have been swimming against the tide with the current MLB - so to speak.

 

If we are to see a decent pattern develop as we head into December then it should start showing its hand over the next few days so fingers crossed for a little more eye candy to start appearing the output over the period.

Edited by Mucka
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I think at the moment anything after D5 is not going to tell us specifics; maybe a possible solution, but one of many. The ECM temp for London (0z):

post-14819-0-54334000-1385042065_thumb.g

That tells us this morning's GFS op was a massive outlier compared to the ECM ensembles. Even the ECM op was near the top of possible temps from the ensembles.

I would not be calling anything from next Tuesday onwards though HP close to the UK is still the call if the rainfall mean is the narrative:

post-14819-0-50736100-1385042272_thumb.g

I suspect the position of the high maybe the story behind the temp range. Still more time needed before we explore zonality.

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There seems to be good model agreement at the moment for the pattern to stay set with a continued High pressure anomaly over the Gulf of Alaska (much as has been the case for most of November) and the NAO and AO positive, (bulk of the polar vortex moving in the short to medium term over to Siberia).

 

With Atmosphere and Angular Momentum (AAM) building over the sub tropics then logically the atmosphere is correspondingly losing angular momentum to the ground at mid latitudes and westerly momentum is poised to be transported to mid latitudes to compensate for this. This is manifested through a clear +NAO signal in the models and the enhanced ridging shown across the atlantic (following our current colder interlude) and the flatter jet we see running eastwards across the top of the High at our mid latitudes as this burst of westerlies moves polewards from the sub tropics

 

Its a case of what can be squeezed out of this pattern and I think that prospects in this respect don't look as good now as in recent days. Any further amplification of the jet stream to bring colder air south is only really open as long as the bulk of the PV remains towards Siberia and in tandem with the negative EPO ridge over the Pacific. However with the strength of the upper vortex overall, then expectations need to be kept quite low for the time being. As Nick S suggested earlier toppling polar maritime incursions look the best opportunities at presentPosted Image

 

Its easy to now become rather more cautious of continued model suggestions of re-amplification based on the evidence of the last day or two. The concern, potentially, is that *if* wave activity in the stratosphere either diminishes completely or continues to not live up to model forecasts and suggestions, then the polar vortex could quite readily re-organise more significantly back towards Canada and Greenland with the result that the jet stream re-orientates itself SW-NE, and it becomes even harder to get cold air southwards.

 

But this does not obviously mean winter is over - and is for another day only if and when it happens.

Great post Tamara, regarding the PV movement I wonder how much behind the scenes variability this might cause in the modelling. In terms of any toppler the window opens around the 144 to 192hrs timeframe on the ECM. At this stage I feel for coldies this opportunity has to be taken in case the GFS lower resolution trend in terms of reforming this to the north is on the money.

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I think this chart from the GEM 00z is interesting since it suggests a spell of cold zonality with nw'ly incursions of polar maritime air through early december, zonality doesn't have to be mild, nor do I think it will, worst case scenario is a mixture of mild and cold zonal as we go further into next month and bearing in mind that winds from north of west or even due west can be cold enough for snow if the air is sourced from the arctic. The Ecm 00z ensemble mean T+240 chart is also hinting at a cold zonal pattern further upstream.

post-4783-0-65319200-1385043205_thumb.gi

post-4783-0-15029800-1385043422_thumb.gi

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Great post Tamara, regarding the PV movement I wonder how much behind the scenes variability this might cause in the modelling. In terms of any toppler the window opens around the 144 to 192hrs timeframe on the ECM. At this stage I feel for coldies this opportunity has to be taken in case the GFS lower resolution trend in terms of reforming this to the north is on the money.

Hi nick - putting aside what may or may not happen afterwards I agree with you regarding the toppler. The GFS suggestions can't be ignored for the longer term and I think the reasoning as above at least explains how this *may* come about. Whether things pan out like that however, then obviously time will tell as uncertainties abound and so no reason to worry yetPosted Image .

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I think this chart from the GEM 00z is interesting since it suggests a spell of cold zonality with nw'ly incursions of polar maritime air through early december, zonality doesn't have to be mild, nor do I think it will, worst case scenario is a mixture of mild and cold zonal as we go further into next month and bearing in mind that winds from north of west or even due west can be cold enough for snow if the air is sourced from the arctic. The Ecm 00z ensemble mean T+240 chart is also hinting at a cold zonal pattern further upstream.

Unfortunately Frosty with the PV stuck to the north this will eventually lead to the jet axis more sw/ne. The modelling bias also has to be taken into account with that kind of set up, generally the models in FI will place the jet further south but nearer the time this gets edged further north, also shortwaves around Iceland won't be picked up till nearer the time.It's very difficult to sustain cooler zonality with the PV stuck to the north of the UK, in terms of colder zonality that really needs some ridging to the north or ne to push the jet further south. I admire your optimism Frosty but if the PV ends up as shown in the early stages of the lower resolution GFS then I'll be needing to order in extra supplies of Prozac for traumatized net weather members.

 

The issue isn't so much the PV having a brief love-in with Greenland, its how long this will last. Anyway that's well into the future, lets hope for some upstream changes , can we order a more amplified negatively tilted low around 144hrs to take advantage of a window of opportunity? go on models you know it makes sense!!!

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weve seen before what happens if energy is transferred between the vortex segments over siberia and canada - it normally results in a crank up of the atlantic jet. unless we can get a split in the trop vortex, i fear we will continue to see the jet scupper any attempts at sustained atlantic amplification. the period around 6/7th dec looks prime for a ridge but without a split, it will probably be transient as per this week.

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There seems to be good model agreement at the moment for the pattern to stay set with a continued High pressure anomaly over the Gulf of Alaska (much as has been the case for most of November) and the NAO and AO positive, (bulk of the polar vortex moving in the short to medium term over to Siberia).

 

With Atmosphere and Angular Momentum (AAM) building over the sub tropics then logically the atmosphere is correspondingly losing angular momentum to the ground at mid latitudes and westerly momentum is poised to be transported to mid latitudes to compensate for this. This is manifested through a clear +NAO signal in the models and the enhanced ridging shown across the atlantic (following our current colder interlude) and the flatter jet we see running eastwards across the top of the High at our mid latitudes as this burst of westerlies moves polewards from the sub tropics

 

Its a case of what can be squeezed out of this pattern and I think that prospects in this respect don't look as good now as in recent days. Any further amplification of the jet stream to bring colder air south is only really open as long as the bulk of the PV remains towards Siberia and in tandem with the negative EPO ridge over the Pacific. However with the strength of the upper vortex overall, then expectations need to be kept quite low for the time being. As Nick S suggested earlier toppling polar maritime incursions look the best opportunities at presentPosted Image

 

Its easy to now become rather more cautious of continued model suggestions of re-amplification based on the evidence of the last day or two. The concern, potentially, is that *if* wave activity in the stratosphere either diminishes completely or continues to not live up to model forecasts and suggestions, then the polar vortex could quite readily re-organise more significantly back towards Canada and Greenland with the result that the jet stream re-orientates itself SW-NE, and it becomes even harder to get cold air southwards.

 

But this does not obviously mean winter is over - and is for another day only if and when it happens.

OK - I'm pleased as punch because my knowledge has got to a state whereby I can fully understand this. :-)

 

But a follow up question. A spike in AAM at the tropics is therefore not something we want to see for blocking - as GP showed in a graph I reposted yesterday, it tends to force the GWO through phases 1 - 4 when we want it ideally in 5 - 8. But how do we go about trying to forecast conditions at the equator in the first place? Is it simply looking through the pacific at the weather patterns along the equator and spotting any potent convection? And if so then what factors help control the pattern of tropical convection?

 

In other words in the same way as we trawl through the Berlin site looking at data on wave 1 or wave 2 warmings that might affect the strat, is there a place somewhere that contains background signals and trends for what might occur over the next few weeks in the tropical pacific?

 

I'm trying to get as close to the source of global forecasting as I can...

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There seems to be good model agreement at the moment for the pattern to stay set with a continued High pressure anomaly over the Gulf of Alaska (much as has been the case for most of November) and the NAO and AO positive, (bulk of the polar vortex moving in the short to medium term over to Siberia).

 

With Atmosphere and Angular Momentum (AAM) building over the sub tropics then logically the atmosphere is correspondingly losing angular momentum to the ground at mid latitudes and westerly momentum is poised to be transported to mid latitudes to compensate for this. This is manifested through a clear +NAO signal in the models and the enhanced ridging shown across the atlantic (following our current colder interlude) and the flatter jet we see running eastwards across the top of the High at our mid latitudes as this burst of westerlies moves polewards from the sub tropics

 

Its a case of what can be squeezed out of this pattern and I think that prospects in this respect don't look as good now as in recent days. Any further amplification of the jet stream to bring colder air south is only really open as long as the bulk of the PV remains towards Siberia and in tandem with the negative EPO ridge over the Pacific. However with the strength of the upper vortex overall, then expectations need to be kept quite low for the time being. As Nick S suggested earlier toppling polar maritime incursions look the best opportunities at presentPosted Image

 

Its easy to now become rather more cautious of continued model suggestions of re-amplification based on the evidence of the last day or two. The concern, potentially, is that *if* wave activity in the stratosphere either diminishes completely or continues to not live up to model forecasts and suggestions, then the polar vortex could quite readily re-organise more significantly back towards Canada and Greenland with the result that the jet stream re-orientates itself SW-NE, and it becomes even harder to get cold air southwards.

 

But this does not obviously mean winter is over - and is for another day only if and when it happens.

OK - I'm pleased as punch because my knowledge has got to a state whereby I can fully understand this. :-)

 

But a follow up question. A spike in AAM at the tropics is therefore not something we want to see for blocking - as GP showed in a graph I reposted yesterday, it tends to force the GWO through phases 1 - 4 when we want it ideally in 5 - 8. But how do we go about trying to forecast conditions at the equator in the first place? Is it simply looking through the pacific at the weather patterns along the equator and spotting any potent convection? And if so then what factors help control the pattern of tropical convection?

 

In other words in the same way as we trawl through the Berlin site looking at data on wave 1 or wave 2 warmings that might affect the strat, is there a place somewhere that contains background signals and trends for what might occur over the next few weeks in the tropical pacific?

 

I'm trying to get as close to the source of global forecasting as I can...

 

Yes that is right what you say about the spike in AAM at the tropics but that was posted to simply illustrate one factor as to why we are not getting quite the positive boost that has been envisaged in modelling in previous days. That is, in tandem with the strength of the polar vortex which is not going to do us any favours into December. On the subject of tropical convection, the MJO is stuck in Phase 4 at low amplitude and atm shows little sign of changing much and that will keep the status quo of the current model suggestions. This is creating further uncertainty to the pattern ahead as we start winter proper - especially if the signal stays weak.

 

This link is available to get MAP room info from: http://www.esrl.noaa.gov/psd/map/clim/gsdm.composites.shtml

Edited by Tamara תָּמָר
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It's also true to say if you flick through the archives that the latter part of november and much of december 62 was characterised by high pressure hanging around the UK with occasional drifting south and allowing cold zonality in over the top. The HP then migrated to Scandy as Xmas approached... and the rest is history. The point is that at this time of year having HP around the uk is no bad thing... and as has been suggested by some observers we are actually in a rather interesting global pattern where ridging is occuring despite the strong vortex, and the pattern is meridional from the pacific round to the atlantic. This too isnt a bad thing at all if cold is what you want. If HP continues to show its hand north of Europe then we are potentially in business. IB is right - we need it at high latitude to get the really cold temps across us - and the november we have had so far would suggest that this is very possible as the season goes on. Another 62/63? Yes please. I wasnt alive then - but now that Examination modules have disappeared from January (hooray!!) I would not be unhappy to have some snow inspired disruption. Sorry for an IMBY perspective there - I am aware that for many such disruption is bad news....

I agree on this day in 62post-21257-0-24789900-1385048799_thumb.jThen late Novemberpost-21257-0-56379800-1385049061_thumb.jThen dec 10th 62post-21257-0-09527300-1385049121_thumb.jSo having a high floating around like around on charts at the moment carn't be a bad thing at all. Like said few post ago better than zonal .Never know dec 62 might just make a visit lolpost-21257-0-80950800-1385049364_thumb.j
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Hmm if you have nothing else to look forward to in recent outputs then have a look at this...

 

http://modeles.meteociel.fr/modeles/gfs/runs/2013112106/gfsnh-10-384.png?6

 

Obviously its in the VERY FAR reaches of FI but its something to look forward to if you have nothing else to look at.

not quite sure what its showing tbh?Posted Imagesorry just looked to the bottom left.cold strat conditions???

Edited by swfc
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Hmm if you have nothing else to look forward to in recent outputs then have a look at this...

 

http://modeles.meteociel.fr/modeles/gfs/runs/2013112106/gfsnh-10-384.png?6

 

Obviously its in the VERY FAR reaches of FI but its something to look forward to if you have nothing else to look at.

I am confused, why would cold strat temps be interesting to look at?

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Hmm if you have nothing else to look forward to in recent outputs then have a look at this...

 

http://modeles.meteociel.fr/modeles/gfs/runs/2013112106/gfsnh-10-384.png?6

 

Obviously its in the VERY FAR reaches of FI but its something to look forward to if you have nothing else to look at.

 

I think if that came off would be snowmageddon if i am reading the chart right

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I am confused, why would cold strat temps be interesting to look at?

What is coming up around Siberia.

 

If it was to develop and push inwards it could lead to something more interesting down the line, its nothing at this stage but could be later on.

 

 

GFS around T156 not big changes apart from pressure lower in Eastern Europe.

 

Posted Image

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Not much change on the GFS, temperatures by day seem to lie between about 4-9C, though next Monday looks cold as areas further East of the UK get a proper cold plunge,  temperatures in the UK for many struggling to get out of low single figures

Posted Image

On the other hand when the Azores high fully establishes itself, from Wednesday onwards it turns much milder

Posted Image

High pressure pretty much wants to be in charge to be honest no real signs of it clearing out of the way by any real method.

Edited by Captain shortwave
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I am confused, why would cold strat temps be interesting to look at?

 

It is a forecast of a bit of warming in the strat - a long way out but if you remember, this chart (at +384) from last year was the harbinger of great things further down the line.

 

Posted Image

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High pressure pretty much wants to be in charge to be honest no real signs of it clearing out of the way by any real method.

 

I would not say high pressure will be in charge in all honesty, especially into next week as there is an warm front toppling in from the NW which will bring Northern areas some moderate bursts of rain and then much milder air behind that so the trend does appear to be that as we head into Next week, it will turn more cloudier on a widespread scale and frost should become less of issue due to the milder airmass and a lot of cloud it will bring. 

 

Not a good outlook for snow lovers but so what, any changes will lead to big changes, we have seen that from the model output many times before and will again. At least it should be frosty for some this weekend so its not totally a mildfest but it more than likely it will turn significantly milder as we head into next week. 

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