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Model output discussion - late November

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5 minutes ago, Decemberof2010 said:

Hi Steve. Look forward to your inputs as always. Just one small matter. On the image we can’t see the date or what GEFS member it is sometimes. If you long hold the image and save, then upload we can see the full image. Apologies if you already know this. I think Ali sometimes posts the same as you. Not a big deal but hey ho

No worries I always resize them but will include the image

remember the colour of the dots determines the run though 🙂 

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4 minutes ago, johnholmes said:

To my untutored eye using these charts I would suggest anything could happen beyond 6-7 December, or am I posting rubbish?

 

It would suggest that coldest day between now and the 17th is today and tomorrow, for that area.

Edited by That ECM

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6 minutes ago, johnholmes said:

To my untutored eye using these charts I would suggest anything could happen beyond 6-7 December, or am I posting rubbish?

 

Indeed John, anything can happen...As in, 'Potential it seems, is a very moveable feast!':santa-emoji:

h500slp.png   h850t850eu.png😱

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10 hours ago, CreweCold said:

Think I've fooked up once in 5 years- last year when I called a very cold January due to the SSW.

17/18 I said we'd need a SSW to break the vortex down before we saw cold- much to the disdain of people in this forum. Yet what happened. Pretty sure @feb1991blizzard can vouch for me...

Then there was 16/17 when the Metoffice were going cold and I refuted it. 

I HATE hubris, but if you're going to push me to it...

Agree in the main but do still believe December can deliver something (luck required) of note regarding snow, very unlikely proper blocking and a long severe cold spell via a Greenland or Scandi high until end December, where i do think you might be going a little over the top (nothing in your recent posts though - just what you have said previously to me) is you seem to be very pessimistic further into winter, although even then i agree with you that we may need a 'good' SSW, i am scratching my head because it looks to me like the strat vortex will go at some point in the mid season, but the best LR strat modelling tools don't, i am going winter to come out around average but with some very cold spells becoming more frequent from Jan onwards, difficult to pinpoint exact timeframes.

Edited by feb1991blizzard

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More GFS ENS 'trending' to the ECM - of course not all - so essentially this is why we compare the Mean V Mean timestamps because compare say 162 06z V 168 00z > If you see a slight bit more amplification then net the ENS are trending in a direction.

06Z compared with 00z shows a weakened westerly flow

05A0EC83-134C-4172-A48F-CDD622649BE8.thumb.png.f2b06940b135ce9520faab44763b9436.png7EB7FE97-2B64-4BDD-90D3-ABA03BD6EAE3.thumb.png.60f0f2534d38b4e6f3e44955b66249fe.png

 

 

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3 hours ago, bluearmy said:

 and current direction of travel is that trough retrogressing into the Atlantic which is not what coldies want to hear

Sums up the Gfs 6z operational longer term perfectly!👍

06_372_mslp500.thumb.png.2cce94f01a7517234b48e3f0ca88b46a.png06_384_mslp850.thumb.png.4166288d0722f67abf582ec22889ac29.png

Edited by JON SNOW

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What a fine example of chaos (both in terms of unstable equations and the chaotic nature of the weather itself) the GFS 06Z ensemble-suite is: okay, out to around Day 9, and then simply decohering into...well, chaos!:oldgrin:

t850Leicestershire.png   prmslLeicestershire.png

t2mLeicestershire.png   prcpLeicestershire.png

Are we really soon going to see ensembles going out to 35 days?😱

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17 hours ago, Mike Poole said:

Yes, I think so, and weirdly was just editing my previous post to suggest similar to GFS 0z, when you posted that!  So it is definitely a solution that is in the mix, but so too are others given the uncertainty at that day 10 range.

Looks like the evolution since would seem to trend away from this one. Interesting to observe the mood around here over the last 24 hours. As you say plenty of uncertainty beyond day 10, but I'm struggling to find anything beyond day 5 that seems to count down to 0. Constant flux, but no sustained mild period yet. I'm scratching my head a bit, thinking about the long range pro forecasts of a mild November and start to December, but I certainly have my own bias towards a colder, more seasonal winter. The signal for colder than forecast seems apparent however there's little to suggest anything very wintry over the next month...

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One thing that cannot be disputed is that the NH trop vortex looks more threatening over the next 7/10 days than it has (or indeed been modelled to ) over the past month 

if the arctic ridge fails to establish effectively then,  without some amplification upstream, we are potentially looking at some of those long rangers verifying for the rump of December  ....

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8 minutes ago, bluearmy said:

One thing that cannot be disputed is that the NH trop vortex looks more threatening over the next 7/10 days than it has (or indeed been modelled to ) over the past month 

if the arctic ridge fails to establish effectively then,  without some amplification upstream, we are potentially looking at some of those long rangers verifying for the rump of December  ....

I replied earlier saying just about the same thing.

The trend over the last 48 hours or so has been to lessen the effect of the arctic high- coldies need to see this trend reversed pronto.

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9 minutes ago, bluearmy said:

One thing that cannot be disputed is that the NH trop vortex looks more threatening over the next 7/10 days than it has (or indeed been modelled to ) over the past month 

if the arctic ridge fails to establish effectively then,  without some amplification upstream, we are potentially looking at some of those long rangers verifying for the rump of December  ....

A sobering thought but based on the model runs of the last 24 hours, I have to agree. 

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Not surprising if the seasonal models do verify,its way easier to forecast the climatic norm in the winter ,than cold outbreaks .

The models do seem to over amplify everything regarding colder weather  in FL ,then flatten everything out ,when it reaches the semi reliable timeframe.

 

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I see the upbeat mood of yesterday has been brought back down today!

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15 minutes ago, bluearmy said:

One thing that cannot be disputed is that the NH trop vortex looks more threatening over the next 7/10 days than it has (or indeed been modelled to ) over the past month 

if the arctic ridge fails to establish effectively then,  without some amplification upstream, we are potentially looking at some of those long rangers verifying for the rump of December  ....

I would need to adjust my Dec cet pronto then could be way off the mark went with the heart not with the head.👀👀

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4 minutes ago, SLEETY said:

Not surprising if the seasonal models do verify,its way easier to forecast the climatic norm in the winter ,than cold outbreaks .

The models do seem to over amplify everything regarding colder weather  in FL ,then flatten everything out ,when it reaches the semi reliable timeframe.

 

They certainly have been over amplifying. Nothing new as that happens every year. Ecm is the main culprit but a couple of gfs op runs have been guilty as well. 

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2 minutes ago, blizzard81 said:

They certainly have been over amplifying. Nothing new as that happens every year. Ecm is the main culprit but a couple of gfs op runs have been guilty as well. 

Yes - remember the Norwegian shortwave last year, GFS - 138 hours screaming Easterly bust.

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Weak HP over Scandinavia past 240 hours in GFS 06z, needs to be stronger in order for the easterlies to get all the way down central/western europe

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Some coldies won't be happy unless we get a siberian beast but the GEFS 6z mean is again promoting an unsettled outlook with a broadly westerly upper flow with occasional chances of Polar / Arctic maritime shots..compared to this time last year, early winter this year at least looks more interesting with a chance of cold shots..most of last winter was a bore fest..I'm hopeful this one won't be!👍

Edited by JON SNOW

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10 minutes ago, Steve Murr said:

Afternoon / All.

Using the above chart is just one image from a suite of strat plots that can be used.

Its a bit one dimensional being that your just looking at the net speed of the zonal wind> Things you can deduce from this is the notable deceleration from ave & a landing zone probably around 10 M/S for Mid December. 

This means that the thought process & start position for the run through the month is that on the whole the momentum for a 'classic' zonal flow across the NH is lower than average > This is contradictory to the seasonal forecasts ( although these are 3 month blended not just for December )

The main purpose of that image is to determine whether the zonal wind goes negative & Easterly.

Leaving that image aside > you then can choose whether you delve in to the GFS & ENS where they have a bit of a negative bias after day 11 or the ECM. Looking at the ECM & GFS yesterday they were 25 M/S & 30 M/S so similar.

The strat vortex though also has a shape which is normally centred over the pole - With that positioning within that speed you also have to consider the directional component IE Westerly ( moving East ). 

A vortex over centred the pole has the most even distribution of westerly winds over the NH & therefor portends to a positive AO signature.

So why are the models especially the ECM perpetually showing this sharp dive in the jet at day 10 - Well lets look at the shape of the vortex from the ECM & GEFS

3CC9AA07-78C0-4225-B608-5D1F18B588A3.thumb.jpeg.c2c283af825e4a880641ce88393e7423.jpeg

8DC6B46F-460B-45DB-A8C3-AFF463A87EB4.thumb.jpeg.ccccf72a4a4502afddab4f5b08d43f40.jpeg

What appears to be a displaced vortex > well its technically not as the central position needs to be south of 66N

C7A8E94B-3A8D-4C30-B41C-44C7BC6C23AC.thumb.jpeg.d58350399865b2b3ae1e608a6bffbd05.jpeg

So not displaced but whats key is the shape & direction- because the vortex is sitting over Northern Russia the westerly component for the atlantic is now heavily reduced in favour of a Northerly component - meaning the tPV will be deflected.

The alignment is a pretty good match-

C56FF503-95EA-4D8E-A6E9-1725DB87B2AE.thumb.jpeg.8ef3c7999fb62cfd0d4303a13c852241.jpeg

8E1D5940-C4E7-483C-B0FE-27724E4E0615.thumb.jpeg.5469caabfbac77f4d2ef8a657f0b69b8.jpeg

When you look at then in detail then ( as opposed to some who are just posting up the default zonal opinion ) the probability is that we see amplification & reduced Eastward momentum- 

The key is where that easterly momentum stops & shears along the tPV in relation to the UK.

The ECM is very good at 192 / 216 however 240 the point is just to far east ( but far enough away in time that it correct back west )

216 > 240 ECM

3540AEB1-4940-4E96-A1EF-538F6981A40D.thumb.jpeg.a20bd32d300cad0aac4e505b74616970.jpeg0FCFA8B5-C519-40FB-86D0-445D7BAF5FBD.thumb.jpeg.37ad32f3d4558d6323831c4388499434.jpeg

This pattern thats developing FWIW is poorly resolved by the GFS > Especially the 06z & 18z. Much like this current cold spell that incremental bias between 144-192 will nudge everything East & flatter. The ECM could be over amplified > So as explained throughout the last run in to this cold spell the 75% meeting point to the Euro blend will aways be the starting point.

This then makes things very interesting at day 8 that there could be a significant snow event for the North of Uk. The image below is used for locational purposes 

2D242422-337E-451B-BE88-BB95DD7A2A36.thumb.jpeg.efed72a8c698ea2756036685a948c80f.jpeg

D810FB69-4DD5-45AE-9391-9DED0C3A6B0F.thumb.jpeg.19e7cd1c2771f2b60c09f001674ac119.jpeg

NB the GFS isnt as sharp being that the low is out in the northern North sea

D5FC1C1F-6EF9-4CF4-91D4-B1CC860D8813.thumb.jpeg.ca59bee1b74e3d84b1b4256b0391321e.jpeg

Meeting point ~ 75% Track through Northern midlands ....

 

Best

S

PS we don't need the arctic High in this pattern ( it would have been a bonus but not essential )

 

 

A really interesting and well thought out post for me as a newcomer.

The shift in the PV isn't something I have witnessed (well at least picked up on) over the last couple of years of lurking.

@Steve Murr how often have you experienced this? 

My rather naive hope is that the models don't know how to factor this. Certainly following Matt Hugo on twitter it gives cause for interest and possible optimism.

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