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Model output discussion - Post SSW - Will it turn cold?


Paul
Message added by Paul

Please only post model discussion in this thread. 

For more general chat and banter, or moans and ramps loosely around the models, please head to the banter thread:
https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

For general weather chat including about the snow/cold chances around the country, please go to the regional threads:
https://www.netweather.tv/forum/forum/142-regional-discussions/

Thank you!

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Posted
  • Location: Chelmsford, Essex
  • Weather Preferences: Anything interesting!
  • Location: Chelmsford, Essex

As this seems to be inching toward the reliable with cross-model agreement on the broad pattern and hefty ensemble support, can anyone comment on the potential small-scale features cropping up within the +96 period which can cut off or weaken the cold flow? If so, are there specific areas where this is most likely? 

I ask this as a long time lurker who knows an extreme chart when I see one, but not great at the more nuanced stuff.

Cheers.

Edited by Number 23
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Posted
  • Location: West Sussex
  • Weather Preferences: Extreme cold & snow
  • Location: West Sussex

Some T2M later runs are giving minima for London of -15C !

image.thumb.png.ac28b4cdf7de9fb16b9dc397ebb449ba.png

Several ice days before that.

Take several degrees off that for the countryside at least! :clapping:

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Posted
  • Location: Southend-On-Sea, South East Essex.
  • Location: Southend-On-Sea, South East Essex.
14 minutes ago, Number 23 said:

As this seems to be inching toward the reliable with cross-model agreement on the broad pattern and hefty ensemble support, can anyone comment on the potential small-scale features cropping up within the +96 period which can cut off or weaken the cold flow? If so, are there specific areas where this is most likely? 

I ask this as a long time lurker who knows an extreme chart when I see one, but not great at the more nuanced stuff.

Cheers.

Scandinavia/Baltics is normally the killer in terms of shortwave disturbances that kill/dilute/re-direct any cold shots from the E/NE. Someone more knowledgeable than me will be able to elaborate. Nick Sussex loves a shortwave

In short, the less kinks you see in the isobars the better in terms of a clean and smooth transition of colder air from the east. Once the cold air is established then you want to see kinks galore moving west haha

Edited by Southender
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Posted
  • Location: Brighton (currently)
  • Location: Brighton (currently)
1 minute ago, Southender said:

Scandinavia/Baltics is normally the killer in terms of shortwave disturbances that kill/dilute/re-direct any cold shots from the E/NE. Someone more knowledgeable than me will be able to elaborate.

Also, western Norway when the cold uppers reach that area. That's why it is best for the easterly not to be too far north.

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Posted
  • Location: Derry, NW Ireland, 20 to 30m ASL
  • Location: Derry, NW Ireland, 20 to 30m ASL

Does anybody with knowledge know how far the showers would be pushed west? I.e far west of Ireland. The models don't take into account convection do they?

Edited by parrotingfantasist
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Posted
  • Location: Chelmsford, Essex
  • Weather Preferences: Anything interesting!
  • Location: Chelmsford, Essex
2 minutes ago, karyo said:

Also, western Norway when the cold uppers reach that area. That's why it is best for the easterly not to be too far north.

Thanks guys. Presumably, it's the temp gradient which causes these to occur, and the placement and prediction of these can only be ascertained in very near term high-res? Sorry mods if this is taking the discussion away from models, but thought it might be relevant for the less skilled among us.

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Posted
  • Location: Weymouth, Dorset
  • Location: Weymouth, Dorset

I've stopped being greedy. In my book every 6 / 12 hours closer to T-0, without a significant spoiler popping up, should class as an upgrade.

Are we going to see a -20 breached in one of the ens between now and next week I wonder!? I can't believe I've even typed that sentence. Crazy days.

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Posted
  • Location: Brighton (currently)
  • Location: Brighton (currently)
Just now, Number 23 said:

Thanks guys. Presumably, it's the temp gradient which causes these to occur, and the placement and prediction of these can only be ascertained in very near term high-res? Sorry mods if this is taking the discussion away from models, but thought it might be relevant for the less skilled among us.

No need to apologise, I think it is a very relevant question for this thread.

I think the models can pick those shortwaves in the 96 hour range but there can be variation in the exact track. 

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Posted
  • Location: Hertfordshire
  • Weather Preferences: SNOW AND FREEZING TEMPS
  • Location: Hertfordshire
Just now, s4lancia said:

I've stopped being greedy. In my book every 6 / 12 hours closer to T-0, without a significant spoiler popping up, should class as an upgrade.

Are we going to see a -20 breached in one of the ens between now and next week I wonder!? I can't believe I've even typed that sentence. Crazy days.

That's exactly what I am looking out for , -20 is surely not out of the question going on previous runs , in the last few days . 

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Posted
  • Location: Weymouth, Dorset
  • Location: Weymouth, Dorset
5 minutes ago, karyo said:

Also, western Norway when the cold uppers reach that area. That's why it is best for the easterly not to be too far north.

Yep. This is still my only slight niggling worry. With the retrogression signal so strong I just can't see it being shunted too far south this time. Too far north would be much more likely out of the two. IMO.

But but but... that's just looking for problems that aren't currently there. All looking great at the moment though, no need for concern!

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Posted
  • Location: Southend-On-Sea, South East Essex.
  • Location: Southend-On-Sea, South East Essex.
1 minute ago, Number 23 said:

Thanks guys. Presumably, it's the temp gradient which causes these to occur, and the placement and prediction of these can only be ascertained in very near term high-res? Sorry mods if this is taking the discussion away from models, but thought it might be relevant for the less skilled among us.

Yes. small scale disturbances can crop up at very short range and kibosh everything. We have seen it many times before particularly with E'ly types. That is why these epic charts are still being viewed with caution as we have all seen it go Pete Tong at just 96hrs many times before. We all view the output with trepidation at the moment, hoping and praying nothing derails the beast. If we can get to Friday with these charts still showing, then game on in my opinion.

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Posted
  • Location: Cleeve, North Somerset
  • Weather Preferences: Continental winters & summers.
  • Location: Cleeve, North Somerset
12 minutes ago, parrotingfantasist said:

Does anybody with knowledge know how far the showers would be pushed west? I.e far west of Ireland. The models don't take into account convection do they?

I would've thought the Irish Sea plus the uppers would be good for Ireland.

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Posted
  • Location: Southend-On-Sea, South East Essex.
  • Location: Southend-On-Sea, South East Essex.
7 minutes ago, s4lancia said:

I've stopped being greedy. In my book every 6 / 12 hours closer to T-0, without a significant spoiler popping up, should class as an upgrade.

Are we going to see a -20 breached in one of the ens between now and next week I wonder!? I can't believe I've even typed that sentence. Crazy days.

Well going by the deeper cold pool on the 6z GFS, which bottomed out at about -25c 850's moving out of Western Russia into Belarus/Ukraine, who knows. Perhaps we can get the odd ptb with a -20 in the mix.

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Posted
  • Location: Blackburn - 180m asl
  • Location: Blackburn - 180m asl
12 minutes ago, parrotingfantasist said:

Does anybody with knowledge know how far the showers would be pushed west? I.e far west of Ireland. The models don't take into account convection do they?

It's not that they don't take account of convection at all, it's that they are awful at taking it into account.

The inland extent of showers will depend on the depth of cold and the convection rates in the north sea for the mainland and the irish sea for ireland. Could easily see showers pushing across to the west of island, but a polar low set up sweeping from the north sea just north of Newcastle directly across to the Atlantic Ocean to guarantee significant snow on the western coast of Ireland.

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Posted
  • Location: Carryduff, County Down 420ft ASL
  • Location: Carryduff, County Down 420ft ASL
18 minutes ago, parrotingfantasist said:

Does anybody with knowledge know how far the showers would be pushed west? I.e far west of Ireland. The models don't take into account convection do they?

Most models do take into account convection. As you are in the North West of Ireland, you have two hopes from snow from this spell.

1. That the Easterly flow is potent enough such that any snow showers produced as the frigid air crosses the Irish Sea reaches you

2. That there are troughs within the flow giving more organised bands of snow moving East to West.

At this stage, it is impossible to forecast and the models will only give a rough indication.

Edited by mountain shadow
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Posted
  • Location: Chelmsford, Essex
  • Weather Preferences: Anything interesting!
  • Location: Chelmsford, Essex
1 minute ago, Southender said:

Yes. small scale disturbances can crop up at very short range and kibosh everything. We have seen it many times before particularly with E'ly types. That is why these epic charts are still being viewed with caution as we have all seen it go Pete Tong at just 96hrs many times before. We all view the output with trepidation at the moment, hoping and praying nothing derails the beast. If we can get to Friday with these charts still showing, then game on in my opinion.

Cheers. Ha yes, I've witnessed a few over my lurking years which prompted the question, but never really understood why, where and how! It got me wondering whether the depth of cold inbound makes these features more likely to occur. 

Still, without doubt the most impressive runs I've seen on here. My wife is a fair bit younger than me (born in '91!) I did mention the current charts reminded me of the pre-Feb '91 BBC forecast I watched as a lad with a slack jaw - three months to the day before she was born...

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Posted
  • Location: Southend-On-Sea, South East Essex.
  • Location: Southend-On-Sea, South East Essex.

The best thing for me about the charts at the moment, is there is no sign at all of any marginality absolutely anywhere in the UK!......a rare beast and a nice headache not to have.

If there is PPn about, it will be all snow and of the powder kind to even the warmest beach huts down south. Let's hope these epic charts hold for a few more days....and then our only concern is about how rubbish the snow is for building as it's "too powdery" haha.

Edited by Southender
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Posted
  • Location: Matlock Derbyshire
  • Location: Matlock Derbyshire
1 hour ago, Broadmayne blizzard said:

yes seriously it has happened plenty of times before.

Yep can confirm that, 2 feet of snow massive snow drifts 23 March 2013.

check out the archvive charts.

and this spell looks even more severe. :shok:

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Posted
  • Location: Longton, Stoke-on-Trent.
  • Location: Longton, Stoke-on-Trent.

Milder air into the far SW at the end of the GFS 6z. Game over ;-) 

Seriously though. Other than the cold arriving a tad later, the run is faultless.

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Posted
  • Location: Morecambe
  • Location: Morecambe

I think the only concerns I have is the infamous shortwave development and whether the main instability airflow gets pushed too far southwards and into France and Spain. Remember cold uppers and warmish sea temps don't always mean full on convective snow showers, lapse rates are crucial also. I remember a case when i lived on Tyneside where on paper we had a nice easterly flow with -10 uppers but there was a lot of stratus cumulus cloud around with very minor hidden convection in it so its something to keep an eye on. It's why I rather have the easterly slightly further northwards initially rather than the current thinking of it sweeping through Germany/Holland/Southern England and into France as it gives more room for error that way.

All that said, really interesting output, in theory the easterly drift starts this week and we some chilly upper air temps mixed in at times so it's like the starter before the potential main course next week.

Lots of variations still to go though so be interesting what the final outcome will be.

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