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Model output discussion - Winter approaches


Paul

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Posted
  • Location: Castle Black, the Wall, the North
  • Weather Preferences: Spanish Plumes, Blizzards, Severe Frosts :-)
  • Location: Castle Black, the Wall, the North

Even though I haven’t posted since last weekend, I’ve still been keeping tabs on the mods..I mean models!..and..for example, even though very recent ecm ops have been going for anticyclonic longer term, the mean has been more reluctant and showing more of a NW / SE split..now of course this doesn’t in any way preclude a more settled early / mid December...anyway, I want cold and snaw dammit!!!:snowman-emoji:

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Posted
  • Location: Hertfordshire
  • Weather Preferences: SNOW AND FREEZING TEMPS
  • Location: Hertfordshire
16 minutes ago, Ols500 said:

Can anyne explain how this happens? I get canada is close and all but thats not the reason... Why does the jetstream dip southwards there, I can only think of HP around alaska and a big trough consequently following southwards? Im a noob so thats probably wrong!

I’d have ago but I’ll probably be wrong . Best to wait for a more knowledgeable poster to give you the run down . All I know is it happens year in year out over there . I mean look how far south the cold gets over there . Make you sick . 

265E20BB-D4BA-410A-AF62-33E0E4AC8D74.png

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Posted
  • Location: Bournemouth
  • Weather Preferences: Dry mild or snow winter. Hot and humid summer.
  • Location: Bournemouth

No more tweets in here please. Drives me mad and takes the thread down rabbit holes.

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Posted
  • Location: Castle Black, the Wall, the North
  • Weather Preferences: Spanish Plumes, Blizzards, Severe Frosts :-)
  • Location: Castle Black, the Wall, the North
24 minutes ago, Defector said:

Well Ian Ferguson has just posted this on Twitter - apologies if it is in the wrong thread:

 

Ach nae bother, at least we have the cfs..that’s actually quite a cold southwesterly..yeah rite ., as I said, I’m very new to all this model malarkey!!..oops..lol

3A67A750-B991-4810-A1C1-ED067DA2F3D7.thumb.jpeg.946036e5a03a3f91432b391d584ffe01.jpeg

Edited by Jon Snow
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Posted
  • Location: Rotherhithe, 5.8M ASL
  • Location: Rotherhithe, 5.8M ASL

ECM not interested in very unsettled westerlies this evening after a step towards GFS this morning it takes one step back and we’re none the wiser.

5F4A2394-B3B1-4B6C-AB08-0D0B8436E3CF.thumb.png.bc9991124dbe7bac707c75c70543e553.png

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Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire
8 hours ago, blizzard81 said:

You would think today's 6z 144h chart for next Tuesday would be more accurate than yesterday's 168h chart for the same time. Lets hope so because the 144h chart shows the trough to the west showing a significant negative tilt when compared to yesterday's 168h chart which showed it positively tilted. To anyone who isn't sure what negative tilt refers to then just think of the trough doing a limbo dance

Screenshot_20201120-101519.png

Screenshot_20201120-101430.png

The ECM is doing a limbo dance Friday night special

Screenshot_20201120-185114.png

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Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire
3 minutes ago, northwestsnow said:

image.thumb.png.98f0fbd32967a2869b8981da13f2fb2f.png

Very nice profile to the NE !

If the ecm ext ensembles take a nose dive this evening then....... It's game back on. 

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Posted
  • Location: Scouthead Oldham 295mASL
  • Location: Scouthead Oldham 295mASL
1 minute ago, blizzard81 said:

If the ecm ext ensembles take a nose dive this evening then....... It's game back on. 

The det is eye candy for cold weather fans from Poland eastwards ....

The charts have detieriated over recent days and even Exeter have thrown the towel in for a much needed drying out...

Caution required but a rigid block to the NE has hopefully been underplayed during recent days...

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Posted
  • Location: Cambridge, UK
  • Weather Preferences: Summer > Spring > Winter > Autumn :-)
  • Location: Cambridge, UK
1 hour ago, Ols500 said:

Can anyne explain how this happens? I get canada is close and all but thats not the reason... Why does the jetstream dip southwards there, I can only think of HP around alaska and a big trough consequently following southwards? Im a noob so thats probably wrong!

Just part of the predominant global circulation I’m afraid. You have a semi-permanent Pacific high that often dominates the western USA.

This chart below is a bit extreme as it was from February this year (record wet and record PV)....but you can see that the pacific high is often coupled with a trough across the east. This pours extremely cold air off the eastern seaboard, which is then met with milder subtropical air. Massive temperature gradient fires up the jet stream and deep Atlantic storms.

772A2ACD-65CB-4E9B-94C1-D2332AA45475.thumb.png.1a9702450078c8fecc953bfdaf777ae7.png

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Posted
  • Location: Heckmondwike, West Yorkshire
  • Location: Heckmondwike, West Yorkshire
1 minute ago, northwestsnow said:

The det is eye candy for cold weather fans from Poland eastwards ....

The charts have detieriated over recent days and even Exeter have thrown the towel in for a much needed drying out...

Caution required but a rigid block to the NE has hopefully been underplayed during recent days...

Indeed. However, I saw the comments re meto changing their outlook so had a look for myself. I don't think it has been revised 'that' much to be honest. 

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Posted
  • Location: Scouthead Oldham 295mASL
  • Location: Scouthead Oldham 295mASL
1 minute ago, blizzard81 said:

Indeed. However, I saw the comments re meto changing their outlook so had a look for myself. I don't think it has been revised 'that' much to be honest. 

There appears to be more emphasis on unsettled but that may transpire even with some sort of block to the NE...

I think most coldies would hope the 12z det is onto something with removing the Euro heights ...

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Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl

Far too much volatily in model output in recent days, reliable timeframe 120hrs I say.. sometimes pays well to not look beyond, only adds to frustration. The only trend I can see is for more of a southerly track jet, temps nearer normal than the last 4 weeks. A drying out would be nice, just a spell of sunny dry weather would raise peoples spirits, not much to ask for, alas on average late Nov, early Dec least likely time for such conditions. Is there anywhere as cloudy as UK this time of year, probably not!

More generally, an observation is a sense of complete resignation about the upcoming winter being more of the same, wind, rain and mild. I suspect the general prevailing miserable mood caused by the current situation is having a major impact in this respect, the downbeatness, and more than any other year, many just want to fast forward to Speing and hopefully brighter days. Winter 2020/2021 can we just hibernate from and wake up in March.. 

Edited by damianslaw
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Posted
  • Location: Hoyland,barnsley,south yorkshire(134m asl)
  • Weather Preferences: severe storms,snow wind and ice
  • Location: Hoyland,barnsley,south yorkshire(134m asl)

Well that's a bit rude....

ECH0-240.thumb.gif.00eb80871bcee8b95d8f7a65f46df27d.gif

we have a somewhat very huge Pembrook dangler at day ten through the UK

as for the ECM,a nice profile and there is some gefs ens support regarding the block to our E/NE.

Edited by Allseasons-si
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Posted
  • Location: Scouthead Oldham 295mASL
  • Location: Scouthead Oldham 295mASL

You can see the Atlantic crash out against the brick wall of a block day 7 to 8 on EC det...

There is a few snags though ..its day 8 ,and ukmo looks flatter at day 7 ...

Jury is out !

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Posted
  • Location: sheffield
  • Weather Preferences: cold ,snow
  • Location: sheffield
1 minute ago, northwestsnow said:

You can see the Atlantic crash out against the brick wall of a block day 7 to 8 on EC det...

There is a few snags though ..its day 8 ,and ukmo looks flatter at day 7 ...

Jury is out !

It also showed a ridge on yesterday's 6z and blew it away this morning nw? Zero support imo but we can hope 

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Posted
  • Location: Scouthead Oldham 295mASL
  • Location: Scouthead Oldham 295mASL
2 minutes ago, swfc said:

It also showed a ridge on yesterday's 6z and blew it away this morning nw? Zero support imo but we can hope 

Its probably unlikely in the grand scheme of things but the models have been known to throw curveballs ...

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Posted
  • Location: Epsom
  • Location: Epsom
30 minutes ago, KeegansPerm said:

This is a very simplified answer, and probably not the thread to do this in (feel free to move or removed moderators). Pressure is literally the weight of the earth's atmosphere above a point, hence the higher you get, less atmosphere above you and pressure decreases. Geopotential height is the measure in dm (10*metres)  of a pressure surface (for example 300hPa geopotential height is around 10KM on average) above the geoid (this accounts for the variation in gravity between equator and poles and makes the maths much simpler).  If you think of the earth's atmosphere like a balloon, if you cool a section of it the air molecules will lose energy, move more slowly, and be able to get closer together (increasing density), and the balloon would we seen to deflate, if you heated the air inside the balloon the opposite would be true and it would inflate.

In the earth's atmosphere this means that in areas where the atmospheres mean temperature is cooler, the air is denser and where warmer less dense etc. This means that in a cool area you if you were firing a rocket upwards you may pass through the 300hPa at say 10 KM, whereas in a warm airmass at 10KM the pressure would be higher say 350hPa in this example. This difference is typically at a maximum at the top of the troposphere (the part of the atmosphere where the weather occurs) and hence the jet stream is typically strongest around this height in the mid-latitudes where this temperature/or height of pressure surface gradient is strongest.

In winter at high latitudes the net radiation balance sees energy lost to space....hence net cooling. This is more marked over land than ocean (which has a much higher heat capacity)., and once land snow covered sunlight reflected further cooling etc... As such at the same degree of latitude over land the mean temperature of the airmass (if it persisted here) would reduce and geopotential height of the pressure surfaces would reduce. This would cause a minima in geopotential height to form (a trough)  relative to the surrounding oceans, and the jet stream to dip southward to the southern boundary of this cooler airmass to where the geopotential height gradient is greatest, and then move north to find the gradient nearer Greenland / Iceland / the sea ice edge in the North Atlantic. 

There are other factors such as lee troughs (to the lee of the Rockies) which often favour troughing over North America too. But hope this sort of helps explain the general broad pattern. But note the jetsream on the boundary between cold and warm airmasses, so further south across Asia (large cold continent), and generally shifts north in the Pacific and Atlantic oceans (ECMWF 200hPa height and winds image for today attached).

Screenshot 2020-11-20 at 18.34.01.png

20201120190054-fd43fe09561c993c3412ed6ee476c62f422cb508.png

Wow thanks alot for such an indepth answer. Really appreciate your time writting this.

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Posted
  • Location: Epsom
  • Location: Epsom
32 minutes ago, mb018538 said:

Just part of the predominant global circulation I’m afraid. You have a semi-permanent Pacific high that often dominates the western USA.

This chart below is a bit extreme as it was from February this year (record wet and record PV)....but you can see that the pacific high is often coupled with a trough across the east. This pours extremely cold air off the eastern seaboard, which is then met with milder subtropical air. Massive temperature gradient fires up the jet stream and deep Atlantic storms.

772A2ACD-65CB-4E9B-94C1-D2332AA45475.thumb.png.1a9702450078c8fecc953bfdaf777ae7.png

Thanks as well! Both answers have "answered" many questions in my mind

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