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

[Summer Sun]

GFS 06z ensemble highlighting the potential for something colder next weekend

 

 

After this pressure slowly starts to push back over the UK

 

 

For now we are just looking at some short cold snaps last a few days, there is nothing of any great length showing on the models at the moment

 

For any new members here don't be fooled by why you read in certain newspapers

[Chess01]

This period of the next 7 days was always going to be boring and an increase temperature the models showed this 3 days ago so people talking short term that it's turning mild and there's not much chance of cold are being over the top with this as the models predicted this . It's what happens after this period that's interesting yesterday's models were garbage but today they show some nice charts for December hopefully by next Saturday we should start seeing some outputs that show how things are going to pan out for the first few weeks of December . Plenty of positives for cold don't let these mundane postsers fool you

[snowmadchrisuk]

Also at +192 ECM and GFS are pretty close as they both attempt the Northerly , just Ecm fails as it is slightly to far East ....It's all going to be about the placement and strength of the P/V over the top ... If the P/V moves to Siberia has has been hinted at so much lately , then I expect we will see a much better NH profile and HLB becoming much more West based with time . It may well take it's time but I expect we will have some sort of pressure build over Greenland by the second week in December. 

[TwisterGirl81]

Yes, some good chances for some very chilly air reaching E Britain on those runs. Plus once Europe gets cold it tends to be harder to shift and could be interesting further down the line...the roller coaster continues...

 

I tried posting the Air Pressure Height hpa 500 + APL but I don't know how so I appologise....

 

If the run on 06z at 300hrs came off it would be the whole country in the cold and snow firing line I hope, please don't let it miss Costa Del Devon & Cornwall as per bloody usual....

 

I don't mind this chilly sunny weather as it will keep the ground cold so better chance of any snow sticking....

 

I've read on one of the threads here that this is starting off much like 1962/63 winter in the UK and North America, I went onto Wikipedia and that winter the first proper snow cold came in the south of UK early part of the second week of December so this is interesting....could they be really on to something?

Edited November 22, 2013 by TwisterGirl81

[Frosty.]

There is a short / medium range upgrade for the chances of a cold blast by the end of next week and into early december according to the latest 6z mean, even by T+168 hours, the high is being forced to retreat southwestwards as lows swing down from the northwest along with progressively colder air  which could then be followed by an arctic blast, the question then will be whether the high tries to muscle it's way back into the uk as the latest GEFS 06z mean shows or whether the high will continue centred well to the southwest with the nw / se jet axis continuing to enable wintry reloads further into next month.

Edited November 22, 2013 by Frosty.

[snowice]

Have to say alot on here where writing off the cold spell even if it was in FI,however i think on the 12z later we may see something better for cold lovers!

 

can`t get too excited as the last few runs have shown how quick things can change, but having seen last nights ECM and now gfs hinting at a possible cold

 

blast later in the run !(caution needed) but i think that High pressure will merge with the one shown on ecm?so mild return may be some time off.

[snowice]

• Have to say alot on here where writing off the cold spell even if it was in FI,however i think on the 12z later we may see something better for cold lovers!

   

  can`t get too excited as the last few runs have shown how quick things can change, but having seen last nights ECM and now gfs hinting at a 

• possible cold blast later in the run !(caution needed) but i think that High pressure will merge with the one shown on ecm?so mild return may be some time off.

   

Edited November 22, 2013 by snowice

[shedhead]

Regrettably MPG it's a fact of life that post 144hrs SW'erlies are more likely to verify as depicted than straight N'erlies. Clearly I'm talking from a statistical standpoint here, so there is nothing to say next weekends plunge will not deliver as shown by GFS, indeed it could even upgrade. However at the kind of range currently involved and particularly in view of the wider hemispheric pattern, a shift east over the coming days is more likely than not...that's if any potential N'erly doesn't get completely dropped of course.

Edited November 22, 2013 by shedhead

[chionomaniac]

Regrettably MPG it's a fact of life that post 144hrs SW'erlies are more likely to verify as depicted than straight N'erlies. Clearly I'm talking from a statistical standpoint here, so there is nothing to say next weekends plunge will not deliver as shown by GFS, indeed it could even upgrade. However at the kind of range currently involved, a shift east over the coming days is more likely than not...that's if any potential N'erly doesn't get completely dropped of course.

Over the last few years, Shed, westerlies have been continually been programmed to return following easterlies, south easterlies, northerlies etc and have been delayed and not verified at all. Please show me the statistic that shows the number of westerlies forecast, compared to the verification of said westerlies for the UK in FI, to back up your standpoint.

[Boro Snow]

More of same blandness on todays runs.. H pressure dominating but at least it will be dry  A slider low by the end of Nov down the North sea before H pressure returms BUT just the hints of a change on todays 06Z by abt Dec 3rd on as a block establishes to the west and possibility we might see the first really cold plunge of winter with 507DAM thicknesses into Scotland. But a very long way to run on this!,

 

dont usually post in here, keep up the good work

[Frosty.]

There is good support for some type of cold blast from the 6z mean around the T+192 hours mark on the GEFS 06z perturbations, some look more substantial than others and could lead to further reloads down the line while others (not shown here) are flimsy topplers with the high too close to the west. I think if the models can build on this trend and tilt the alignment further to the northeast, it would bring a better chance of a sustained wintry outbreak rather than a 24-48 hour N'ly toppler, it's work in progress but at least it is progress for all us coldies and snow lovers.

Edited November 22, 2013 by Frosty.

[shedhead]

Over the last few years, Shed, westerlies have been continually been programmed to return following easterlies, south easterlies, northerlies etc and have been delayed and not verified at all. Please show me the statistic that shows the number of westerlies forecast, compared to the verification of said westerlies for the UK in FI, to back up your standpoint.

That isn't what I said Chiono, as you can clearly see. My point was at T+144hrs and beyond, SW'erly winds are more likely to verify as progged than N'erlies.  Put another way, at T+144hrs and beyond winds from between 230-250deg are more likely to verify as progged than winds from between 350-010deg.

[chionomaniac]

That isn't what I said Chiono, as you can clearly see. My point was at T+144hrs and beyond, SW'erly winds are more likely to verify as progged than N'erlies.  Put another way, at T+144hrs and beyond winds from between 230-250deg are more likely to verify as progged than winds from between 350-010deg.

No, winds are more likely to occur from a westerly direction, not necessarily verify from a forecast on a computer model- there is a subtle difference - unless you can show me statistical evidence showing otherwise.

[shedhead]

I think you know what I mean C...

[Captain Shortwave]

So after watching a video which has analysed some of the longer range models, they all seem to agree on this pacific block being a big player in the northern hemisphere patterns over the coming winter. They also want to build heights to the north east during week 2 which has not been shown at all really on the shorter range models, so really no agreement again over our part of the world. This coming month could be a real pain to forecast.

[Catacol]

Over the last few years, Shed, westerlies have been continually been programmed to return following easterlies, south easterlies, northerlies etc and have been delayed and not verified at all. Please show me the statistic that shows the number of westerlies forecast, compared to the verification of said westerlies for the UK in FI, to back up your standpoint.

 

Agreed. In another thread I posted an anomaly comparison of NH patterns before and since 2007. Prior to 2007 I suspect you would be right that SW tended to verify more accurately... but since then we have positive anomalies to our north and negative ones to our south and as a result I rather suspect model accuracy has struggled. Indeed there was a post from someone a couple of weeks ago that presented an image of the models actually verifying less well now than used to be the case.

 

Steve would say it is an overall westerly bias to their programming. I am an observer rather than a programmer... but I would agree with him.

[legritter]

Some very interesting posts and thanks for all the input from posters .the modells are Hinting at a change in later output and perhaps the next couple of days will show some firming up of this .going to try my hand at posting some charts soon but still trying to master my new windows 8 .It realy is a Minefield trying to compare historical charts with present synoptic situation but i suppose History does repeat itself occasionally .roll on GFS sometimes this run can pull off a big change past 216 hrs ,but concistancy is what we should be looking at with back up from other models ,so the hunt is on yet again with winter proper starting soon .

[Mucka]

Nice to see the signal for for increased amplification strengthen today and our Mid Atlantic ridge is very much back in play for early December. If it comes off that will be twice that GFS has picked out a pattern in deep FI so those much maligned FI charts can be of use if you understand all the pitfalls and can sort the wheat from the chaff among the ensembles.

Still, a way to go before we can celebrate.

 

It looks to me that the first attempt is doomed to fail and will likely be a toppler although upgrades are always possible at that range - I think upgrades are more likely than downgrades of this first ridge. Still after the initial toppler (if that is what transpires) we may get some deep trough into Europe which will help amplify the pattern behind and hopefully give us a better chance of some HLB around Greenland as the next low comes in. 

No way to know yet if this signal will get stronger or the models will begin to flatten things out again but it will  beof renewed interest among many a coldy.

 

Despite what some have had said about ECM being flat, it is showing much the same signal only a little weaker and we would see WAA toward Greenland beyond this day 10 chart as the trough sank into Europe but it would be better if things were further West and more amplified. (again toppler followed by stronger ridge)

 

 

Let's hope this becomes a trend in this evenings output.

 

(If so, Murr incoming!  )

Edited November 22, 2013 by Mucka

[bluearmy]

 

So after watching a video which has analysed some of the longer range models, they all seem to agree on this pacific block being a big player in the northern hemisphere patterns over the coming winter. They also want to build heights to the north east during week 2 which has not been shown at all really on the shorter range models, so really no agreement again over our part of the world. This coming month could be a real pain to forecast.

 high heights to our ne week 2 dec ? that would be a big surprise looking at the current extended ens output. more likely a trough

[chionomaniac]

I think you know what I mean C...

Err No. I thought that you meant that westerlies are more likely to verify on computer models than other wind directions - but hadn't shown the statistical evidence to back this up. So is that not what you meant?

[DAVID SNOW]

The 30_hPa Temp over the pole may have 'bottomed out' and we now have a slight warming, I have no idea if this will continue but if it does maybe some favourable HLB down the line?

 

Sorry cant post the chart

[Cecil Hogmanay Melchett]

The 30_hPa Temp over the pole may have 'bottomed out' and we now have a slight warming, I have no idea if this will continue but if it does maybe some favourable HLB down the line?

 

Sorry cant post the chart

The only was is uuuuuuuuuuuuuuup!

Whilst a mid Atlantic high is posible down the line i can't see for the life of me anything meaningful.

Keep telling myself its 22nd of November though i honestly think Nov 2010 has clouded my judgement and we must remember some of the best winters in the UK haven't actually started until after Christmas.

[Mucka]

Err No. I thought that you meant that westerlies are more likely to verify on computer models than other wind directions - but hadn't shown the statistical evidence to back this up. So is that not what you meant?

 

I don't know Chino, I see what you are saying but is it not also self evident what Shed is getting at?

If a westerly flow is more common then is it not logical to assume Westerly based charts are more likely to verify than Easterly ones once we are out of the reliable range without looking at statistics? (no matter how slightly)

That said, if there is statistical confirmation of this it is undoubtedly too insignificant to warrant dismissing Easterlies on such a basis or even worth considering at all - how's that for a compromise?

 

GFS 12z at 132h is flatter than any previous output today including ECM and MetO for the same period. Not sure what difference this will make later just an observation.

Edited November 22, 2013 by Mucka

[Snowman.]

CFS is also going for something similar.

 

 

Uppers are good as well.

 

Now lets just sit and wait to see what happens down the line.

[Catacol]

I don't know Chino, I see what you are saying but is it not also self evident what Shed is getting at?

If a westerly flow is more common then is it not logical to assume Westerly based charts are more likely to verify than Easterly ones once we are out of the reliable range without looking at statistics? (no matter how slightly)

That said, if there is statistical confirmation of this it is undoubtedly too insignificant to warrant dismissing Easterlies on such a basis or even worth considering at all - how's that for a compromise?

 

No - just because one weather type is more common does not mean that charts of that type are more likely to verify. There will be a greater number of westerly predictions but if the models have common accuracy for all weather types then the chances of each prediction coming true should be the same. My suggestion is that actually the models do have a westerly bias... but because global pressure patterns have changed in recent years it possibly means the opposite: that westerly predictions - numerous though they continue to be - may actually be less likely to verify than those of a more meridional type. 

 

It would be interesting, but probably practically impossible, to do a data analysis of this. Perhaps a stat monkey out there might take it on...

Edited November 22, 2013 by Catacol_Highlander