Model Output Discussion - cold spell to end Autumn

[ArHu3]

3 minutes ago, warrenb said:

The deterioration has been happening progressively over the last 24 hours of runs. The -PNA has now been modelled to basically disappear and this has ramifications down the line.

It's positive and predicted to stay positive for the next few weeks 

 

[warrenb]

1 minute ago, karlos1983 said:

Disappear might be a bit strong 

372 chart from the control. Might need to try harder than that. Just look at the first 144 hours. It is like someone has popped it with a pin.

[Frosty.]

The way I see it, if the operational doesn't look so good don't despair, you get a better idea from the mean, as was the case with the Ecm op / mean last night. As far as I'm concerned anything beyond the Northerly is still up for grabs and its good to see Exeter are still going with a rather wintry outlook rather than mild zonal..Just my opinion.

[karlos1983]

3 minutes ago, warrenb said:

372 chart from the control. Might need to try harder than that. Just look at the first 144 hours. It is like someone has popped it with a pin.

Exactly..... 

i don’t need to try hard, I’ve been in model watch mode for weeks, so I won’t be making a knee jerk reaction on one operational that’s all.

Edited December 5, 2017 by karlos1983

[johnholmes]

20 minutes ago, Day 10 said:

I have placed this in the media thread also so please remove mods if you have to. I just thought it was a good read and is relevant right now

https://www.channel4.com/news/by/liam-dutton/blogs/why-you-shouldnt-believe-a-uk-snow-forecast-more-than-three-days-ahead

well worth clicking on that link for anyone unsure of who or which model to believe, well presented by Liam Dutton as one would expect from a professional

[Frosty.]

8 minutes ago, Frosty. said:

The way I see it, if the operational doesn't look so good don't despair, you get a better idea from the mean, as was the case with the Ecm op / mean last night. As far as I'm concerned anything beyond the Northerly is still up for grabs and its good to see Exeter are still going with a rather wintry outlook rather than mild zonal..Just my opinion.

So I say chin up coldies, the models  could be a lot worse..i gather there's an arctic blast on the way.. At least we are not staring down the barrel at a prolonged southwesterly mild mush fest!

Edited December 5, 2017 by Frosty.

[bluearmy]

10 minutes ago, warrenb said:

372 chart from the control. Might need to try harder than that. Just look at the first 144 hours. It is like someone has popped it with a pin.

Post mid month perhaps - this op is progressive - actually it isn't progressive at all. why do you think it goes pop after day 6 ?? it simply doesn't ????

Edited December 5, 2017 by bluearmy

[Kentish Snowman in Yorks]

16 minutes ago, sorepaw1 said:

Is this just a brief 36hr cool spell for the weekend for Northern Scotland. 

I fail to see anything else sorry

 You might need to be digging yourself out of the white stuff by the end of the weekend with your altitude if the GFS or UKMO are anywhere near correct?!

[Derecho]

24 minutes ago, ShortWaveHell said:

So reading the thread after work ... some ultra respected and knowledgeable netweather contributors suggest this month is one of the more interesting ones for many a recent year,  In terms of some signals  , then the whole December pattern has changed to zonal due to the GFS 12z run today , I’m at 6s and 7s as a novice to say the least 

Zonality is becoming a possibility a bit later but isn't set in stone yet by any means. It could still be snowy for some.

The risk with using teleconnections  is that they too are subject to uncertainties. When you have a lot of variables in the long range that are uncertain, then the overall uncertainty is huge. MJO forecasts can quickly change and how many SSW warming forecasts remain rooted to T384?

That's why reading into long term cold ramping isn't advisable and is why the Meto stay on the fence, though trends can appear. The weather can change for the better or worse at any moment, if one of the forecasts for these variables changes quickly it has big implications (the butterfly effect). The fact that we can pick up on strong signals and make forecasts in the 5-7 day range is a remarkable achievement when you consider this (with the exception of complicated scenarios like the coming weekend).

The main barrier to some good northern blocking at the moment is the cold air building over NE Canada. Despite this it may change and there is still potential to get a spell of cold. See my scenarios post a few pages back .

Edited December 5, 2017 by Quicksilver1989

[Scandinavian High.]

Heavy snow showers to come at weekend in places hard frosts to so why are folks so down beat I wouldn't take every run so seriously 384 hours out will change run after run next week is not even nailed on yet..

[Tamara]

There has been consecutive attempted, and detailed explanatory analysis to suggest (not forecast) where hiccups to a cold pattern could, and still could, arise. Such analysis suggested a possible flattening of the amplified pattern, with time, but that didn't automatically imply (and still doesn't) imply zonality, - only if signals suggest a flatter pattern change later this month.

I think that any flatter pattern, should it arise, will continue to involve the ongoing (still currently amplified) mid atlantic ridge - but would lose emphasis over time over possibilities of cold air backing west from any emerging Scandinavian ridging.

But by way of intended objective balance to the possible downsides, and because evidence of late has been evolving favourably for more upside, a latest post a few days back gave more explanatory reason why the amplified pattern might sustain further - though this doesn't automatically mean that the downside risks previously outlined have gone. The post on Friday started by citing the word "Uncertainty"

To that end:

The theme of posts since as far back as the 7th Nov has been one fully anticipating a probable crossroads to come this month in terms of the next (now current) tropical convection cycle in tandem with stratospheric developments and whether this would sustain amplification prospects beyond the shorter-medium term.

The continuity referred to above is honing in further on that crossroads - its simply been adjusted further out as the relevant factors have developed.

The WDT plots continue to echo the Global Wind Oscillation Phase 4 orbit as reflection of the large increase in AAM tendency c/o the eastward moving tropical convection

I expressed interest in this in a post late last week, but am reserving further judgement on further devlepments for a few days to gauge how much initial fall-back there will be as the tropical cycle advances towards completion.

Interesting as it is with its possibilities in terms of a break out of Nina Phase 1,2,3 orbits to the transitional more amplified phases, I would be reluctant to place too much emphasis on it as a sign that the Pacific feedbacks and atmospheric circulation are going to embrace an 05/06 type winter pattern. There is a lot of time yet for the traditional Nina phase synchronisation to return.

Many different forecaster analyses espoused in parallel theory regarding the summer pattern following a suggested analogue for that season which was 95/96. The Pacific easterly trades destroyed all immediate notion of any of that type of warm anticyclonic disconnect pattern happening.

Its my view that the seasons, with their key wavelength change cycles, have pivotal switch-over periods where the dominant signal (of signals) emerges "victorious". The La Nina, however weak, emerged as the overrider this summer as much as it did last winter (16/17). A lot has been spoken about the PDO switch helping to enable a disconnect a-typical La Nina pattern this time around, but its going to take more than the transitory augmenting of angular momentum away from the traditional La Nina low state to be persuasive that the atmosphere really wants to engage a sustained disconnect. On that basis the PDO pattern can easily comply back closer to couple the base ocean state if angular momentum falls back far enough later this month. That would see the familiar SW-NE track of the jet stream re-appear.

However weak and disorganised the polar vortex is now, the crunch time will come when AAM naturally falls back as the MJO returns to the Indian Ocean. And it will fall back to an extent that remains open to question. Where the GWO lands as a consequence in reflection of this, is going to answer all the questions as to whether (or not) the atmosphere is trying to prepare the ground for the start of a return to ocean/atmosphere neutral conditions in the New Year. A process that the ENSO modelling suggests may not happen at all till the winter is over.

I think that the crossroads when it comes will give a decisive answer one way or the other by or before the New Year. The earliest sign will be how fast the MJO returns to the inner circle - reflecting how much easterly inertia there is in the tropics and Pacific to weaken the convection band and attendant westerlies. I think even the next 10 days will begin answering that. In the meantime talk of sustained +PNA leading to late Dec/early Jan Scandinavian heights backing deeper cold west remains a possibility, but by no means assured.  The stratospheric pathway of Aleutian low and Siberian High very much depends on no return to traditional low AAM Phase 1,2,3.

Latest GEFS, ECM and GEM MJO forecasts:

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/CANM_phase_20m_small.gif

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ECMF_phase_51m_small.gif

Only one link opened to source image for some reason, but the one to watch is no further trend for the convective band to want to beat a retreat to the Indian ocean asap.

The trop/strat profile across the layers of the atmosphere are clearly in a different state heading to the close of 2017 to the colder and more stable profile that emerged at the end of 2016 and started the year and which did feature some wave activity but was still unable to penetrate a west QBO strengthened vortex.

But taking the uncertainties in the tropics and extra tropics into account, conventional belief about typical seasonal Nina progression having a final say yet again can't be put aside.

I'm not a forecaster, but from my own modest enthusiast studying stand-point I am certainly off the fence in terms of the possibilities shown in recent days, but proof of pudding and eating comes to mind as we head through the early days of the new season

Edited December 5, 2017 by Tamara

[terrier]

So this evening runs aren’t particularly or inspiring after the weekend. Yes snowfall for a few. But looks like a return to zonality as we move into middle of next week. Let’s see what the ecm has to say. 

[Man With Beard]

A little friendly bet with myself ... the ECM will have us all scratching our heads tonight and be further south!! I say this because a lot of its ensembles have been further south, and sometimes the op follows them on its next run...

[The PIT]

Living on a hill I'm not too disheartened. Sunday at the moment looks good but the chopping and changing certainly is putting the reliable time frame within T96. The trend has been to slightly less cold theme then originally shown if that theme halts we'll be okay for a while.

[Captain Shortwave]

So some good news

   

Compared to 24 hours ago the ECM has upgraded the potency of the initial cold blast. It is still a bit stingy compared to the UKMO and in particular the GFS. I guess the other good news is that the GFS has not flinched in the depth of cold it shows with the 850s between around -8C and -11C for Friday.

In terms of upstream, I am going to be honest and say it actually looks the best out of the GFS/UKMO/ECM.... now just watch day 5 show an absolutely awful chart now.  

Edited December 5, 2017 by Captain Shortwave

[Daniel*]

16 minutes ago, terrier said:

So this evening runs aren’t particularly or inspiring after the weekend. Yes snowfall for a few. But looks like a return to zonality as we move into middle of next week. Let’s see what the ecm has to say. 

Do you really think the evening output is going to determine, what happens next week?

I truly give up with some on here putting all their eggs in their basket. I’m seeing no traditional zonality jet stream is not orientated in that way, a rather fluid cold cyclonic pattern, one that is interesting.

With regards to the slider there is a large margin of error of about ~300 miles from the Wirral to English Channel IMO, a southern correction is much more likely than vice versa, simply basing this on what I have seen in the past. And do not expect any consensus until the end of the working week. 

Edited December 5, 2017 by Daniel*

[northwestsnow]

ec looks very similar to gfs at 96...

[bobbydog]

Just now, Daniel* said:

Do you really think the evening output is going to determine, what happens next week?

I truly give up with some on here putting all their eggs in their basket. I’m seeing no traditional zonality jet stream is not orientated in that way, a rather fluid cold cyclonic pattern, one that is interesting.

With regards to the slider there is a large margin of error of about ~300 miles from the Wirral to English Channel IMO, a southern correction is much more likely than vice versa, simply basing this on what I have seen in the past. And do not expect any consensus until the end of the working week. 

i think a major part of the problem is, so many people throwing in the word "zonal" when they dont actually know what it means....

[Stozzy]

Ecm looks very similar to the gfs at 96hr . Happy to be proven wrong if needed tho 

[nick sussex]

The ECM looks a bit sharper with that low to the nw than earlier outputs and is more amplified upstream. Much now depends on phasing of shortwave energy upstream to develop a more amplified low to throw up a better ridge behind the possible slider.

[Daniel*]

Liam Dutton said EC tends to overdo wind I hope so for Scotland’s sake a frightening looking chart.

[Pembroke Dangler]

4 minutes ago, Stozzy said:

Ecm looks very similar to the gfs at 96hr . Happy to be proven wrong if needed tho 

A slither more heights I would say around Iceland.

[Methuselah]

Oh dear. Oh dear. Oh dear!

[The PIT]

ECM at T120 is pretty much the same as well give or take a few miles. So I think we are good for Snow or Snow to rain event on Sunday.

[The PIT]

Just now, Ed Stone said:

Oh dear. Oh dear. Oh dear!

Lala land who cares