Model output discussion - Closing in on Christmas

[Ice Day]

4 minutes ago, Scott Ingham said:

Its not needed mate. See posts above. If it was february id agree we need it but not at this point of winter. 1963 didnt have the mega 850s the majority of time. In fact the best snow events were those with higher 850s

Spot on Scott, December 29th 1962 delivered a Blizzard to the south west of the UK with uppers of around -6c (apologies if off topic mods!)

[BLAST FROM THE PAST]

16 minutes ago, Battleground Snow said:

Indeed and more importantly there are a few more ensembles following the OP compared to the 00z run... Could improve the long term mean slightly going forward

Been through the perturbations up to t192....so if there’s more support on the 06z then there must have been next to none on the 00z?  Hardly any support for GHP up to t192.  Trough dropping and ridging is 

 BFTP

Edited December 19, 2020 by BLAST FROM THE PAST

[Battleground Snow]

1 minute ago, BLAST FROM THE PAST said:

Been through the perturbations up to t192....so if there’s more support on the 06z then there must have been next to none on the 00z?  Hardly any support for GHP up to t192

 BFTP

Sorry I should have been more specific... A few more have better amplification near Greenland..  still need them to improve

[That ECM]

2 minutes ago, BLAST FROM THE PAST said:

Been through the perturbations up to t192....so if there’s more support on the 06z then there must have been next to none on the 00z?  Hardly any support for GHP up to t192

 BFTP

 

[Duane S.]

1 minute ago, Scott Ingham said:

Its not needed mate. See posts above. If it was february id agree we need it but not at this point of winter. 1963 didnt have the mega 850s the majority of time. In fact the best snow events were those with higher 850s

Completely agree. The obsession with 850s can get too much at times. @Broadmayne blizzard or me normally post this at least once a year

Yes it was after some entrenched cold, and in February (which is both bad plus good, as in stronger sun but lower SSTs), but this fairly innocuous looking chart gave the biggest snowfall in memory in places on the south coast. 

 

[BlueHedgehog074]

Just want to check, but does GHP stand for Greenland High Pressure? (Sorry for the stupid question and I know it’s not adding much to the thread) 

Edited December 19, 2020 by DiagonalRedLine

[Djdazzle]

Just now, DiagonalRedLine said:

Just want to check, but does GHP stand the Greenland High Pressure? (Sorry for the stupid question )

Yes.

[Youcan'tbecirrus]

29 minutes ago, bluearmy said:

It’s no longer part of the pv but it contains some air that once was ........  have had this discussion before on here - some think it still is part of the pv but I think description of it as such misleads people as to what conditions really would be in winter actually under part of the vortex ....

Out of interest how often has that set up happened before. Not suggesting for one moment it would be the same this time but would the 47/63 winters have come from such a set up ? Was 2010 similar ? From what I recall the 87 event came from the East so I assume that was a totally different set up.  

[feb1991blizzard]

10 minutes ago, Scott Ingham said:

Its not needed mate. See posts above. If it was february id agree we need it but not at this point of winter. 1963 didnt have the mega 850s the majority of time. In fact the best snow events were those with higher 850s

Not obviously expecting them to be -16c by thetime they get here but this -5c -6c will nearly always be wet snow, of course at this time a year increase my temperature threashold to -9c, -10c verg good - ala 2010, -12c will smash the floodgates, i just don't like those marginals, i have seen nothing yet that would give Buxton a right dumping, never mind a City at hardly any feet in a square with 4 x 500ft+ tower blocks less than 50m away, digressing somewhat though because i am looking more and more at the stratosphere and less the troposphere with every run anyway.

[Duane S.]

8 minutes ago, fromey said:

Something else to add into the mix!!

Will it happen?? Only time will tell!

That’s impressive.

And at 60N, an SSW not too far away going by this forecast...

[Scott Ingham]

7 minutes ago, Ice Day said:

Spot on Scott, December 29th 1962 delivered a Blizzard to the south west of the UK with uppers of around -6c (apologies if off topic mods!)

Exactly mate! Backed up by a chart which i struggle with haha! Its optimal time of the year. Remember the boxing day snow 4 or 5 years ago. Its the end of December less ingredients needed 

[mb018538]

4 minutes ago, s4lancia said:

Completely agree. The obsession with 850s can get too much at times. @Broadmayne blizzard or me normally post this at least once a year

Yes it was after some entrenched cold, and in February (which is both bad plus good, as in stronger sun but lower SSTs), but this fairly innocuous looking chart gave the biggest snowfall in memory in places on the south coast. 

 

Yes. 850s aren’t everything! We got 3cm of snow here a couple of weeks ago with very average 850s due to evap cooling and intense ppn. It also hardly ever snows here!

[BLAST FROM THE PAST]

5 minutes ago, Battleground Snow said:

Sorry I should have been more specific... A few more have better amplification near Greenland..  still need them to improve

Me too, added that ridging is there though

[BLAST FROM THE PAST]

5 minutes ago, DiagonalRedLine said:

Just want to check, but does GHP stand for Greenland High Pressure? (Sorry for the stupid question and I know it’s not adding much to the thread) 

Yes

 

BFTP

[Methuselah]

8 minutes ago, Ice Day said:

Spot on Scott, December 29th 1962 delivered a Blizzard to the south west of the UK with uppers of around -6c (apologies if off topic mods!)

Indeed; there are simply too many other factor that need taking into account: height, DP, air-source, intensity of precipitation, wind strength, and so on: I saw sleet in Inverness with 850s of -9C (wind off the sea) yet we saw snow here, in 2013 with uppers of -3C (wind from the Continent) -- only last week, we had snow from 850s of only around -5C... Things do get a lot easier with T850s of -15C, however!

[Penicuikblizzard]

50 minutes ago, Tim Bland said:

Still remarkable to see that chunk of the PV so consistently modeled to sit over us!..

10 days away though the charts are always decent at that range

[fromey]

8 minutes ago, s4lancia said:

That’s impressive.

And at 60N, an SSW not too far away going by this forecast...

Didn’t realise I put up the 65n chart but yes the that one isn’t far away either.

Edited December 19, 2020 by fromey
Spelling

[Scott Ingham]

10 minutes ago, s4lancia said:

Completely agree. The obsession with 850s can get too much at times. @Broadmayne blizzard or me normally post this at least once a year

Yes it was after some entrenched cold, and in February (which is both bad plus good, as in stronger sun but lower SSTs), but this fairly innocuous looking chart gave the biggest snowfall in memory in places on the south coast. 

 

Couldnt be in better agreement. I only look at 850s from a convective perspictive via a north westerly or easterly but when we have a devoloped area of low pressure with low thicknesses and good dew points we atent relying on 850s to create precipitation 

[kold weather]

The GFS is a snow fest on the 06z, whilst 850hpa are marginal your going to have quite active fronts/troughs swinging round and the uppers a re cold, along with a forward wind from Europe. I'm dead sure that would give a big snow event.

However something that is now really worrying me is this slight trend to set-up more of a west based -ve NAO. 

I'm also struggling with why the 00z ECM looks so tame in terms of the 850hpa profile, looks a bit odd to me I've got to say and thats again based on 16 years+ of watching these things.

[Tim Bland]

Still lots of uncertainty at day 10 around Greenland & our ridge. Op is one of the best outcomes. 

[terrier]

So what a we take from the gfs06z output. Well it’s certainly taken a step towards the ecm this morning no doubt about that. Are we going to see a half way house here as we usually do in this situation. The thing that is looking like could happen is we end up with west based -nao which is no use to us. It seems we are back to looking at the 10day charts once again. I’m not so sure we’re we go from here. I’d expect the gfs to keep taking baby steps towards the euros this evening. You certainly wouldn’t bet against the Ukmo and ecm model at such a short range it would take a brave sole. 

[danm]

1 hour ago, Man With Beard said:

Worth recalling a couple of things.

First, it is a good thing that the low at D8 is being modelled a little too far west for optimal cold - corrections are far more likely to push the low further east than west. Check some of model archives in the run up to 20-25 December 2010 - there was worry on here the pattern would go too far west, but come T0 it was bang on target.

Second, a deep low is like a mini altitude boost - 970mb allows snowfall at slightly lower levels than 1000mb, which is part of the reason some SE areas saw snow earlier this month with modest uppers.

No guarantees of course, but I think this pattern has legs

Great post. To expect each and every run leading up to a cold spell to be flawless and to not expect some downgrades as well as upgrades along the way is unreasonable. It doesn’t mean this cold spell is nailed on by any means, but we sometimes forget the rollercoaster model runs we’ve been on for previous cold spells. 

[chris55]

Foehn effect in full flow over the mountains of Norway. Look how the 850s rise on the north west side with no apparent source.
 

Interesting to see

[Scott Ingham]

44 minutes ago, feb1991blizzard said:

Not obviously expecting them to be -16c by thetime they get here but this -5c -6c will nearly always be wet snow, of course at this time a year increase my temperature threashold to -9c, -10c verg good - ala 2010, -12c will smash the floodgates, i just don't like those marginals, i have seen nothing yet that would give Buxton a right dumping, never mind a City at hardly any feet in a square with 4 x 500ft+ tower blocks less than 50m away, digressing somewhat though because i am looking more and more at the stratosphere and less the troposphere with every run anyway.

I dont think it would even be wet snow. If dew points are on the right side it will still be more of the powdery variety. Id agree with if the air mass was coming over the warm north sea from the east. Well have already been very cold from christmas eve at this point with plenty of frost. I see the 850s as a convective element and were not relying on convection. I really dont think youd be disappointed if it played out as forecast. There would be troughs in this highly unstable flow

[Weathizard]

Upper temperature requirement debates are like trying to boil water in a chocolate teapot. There is way too many variables outside of exact 850 temperature, dew points, humidity, evaporative cooling, wind direction.

Lets all worry about getting the day 7 GFS chart to t0 before worrying too much about that, too many other hurdles to overcome first  

The UKMO 144 this morning is not ideal but I would still take that chart as a starting point considering where we were a few weeks ago, it’s totally unscientific but I’ve got that ‘feeling’ that there is a very snowy spell coming up.