Model output discussion - Closing in on Christmas

[Cheshire Freeze]

Someone order a SSW?

[Allseasons-Si]

The mean is more impressive than the 06z

12z 204 v's 06z 216

 

[Jason M]

14 minutes ago, Frosty Winter said:

We get it mate, you aren’t impressed by the model output and that’s a perfectly credible position to take. But is it really necessary to come on here after every model run to moan about the same thing over and over?

If the charts keep showing the same issue for run after run, I'd suggest the answer to your question is 'yes' 

I suppose the fact that its so marginal leads to different takes on things. FWIW I'm going for rain on low ground in the south and south east but wintry mix of sleet / wet snow on even moderately high ground. I'd imagine places like Leeds will see snow. We will find out in due course though.

[Drifter]

Just now, CreweCold said:

Someone order a SSW?

For a strat dunce like me, what am I looking for on that chart which means it is a technical SSW?

TIA

[Optimus Prime]

13 minutes ago, s4lancia said:

Irrespective of Arctic warming, climate change, things were better back in the 1700s blah blah blah, there are very simple synoptic reasons why the uppers are what they are. Nothing weird or sinister or strange  or ‘typical’ , the current Northern Hemispheric set up is why.  

 

Except what you've just outlined goes completely against the science. The air in the Arctic is much warmer than it was even 20 years ago. And >40 years ago temperatures would be 1.0 - 2.5° C colder in the arctic regions. It's just a fact and this translates to less cold northerlies when the synoptics grant it.

Edited December 20, 2020 by Optimus Prime

[mother nature rocks]

PLEASE NO MORE TALK OF UPPERS abc The GFS has been counting this down nicely and it now looks like other mods are moving in same direction!! Let’s just get it down to 0z first with a GH High then worry or enjoy the weather that comes with it!! Xmas already looking colder than it was originally so the ‘******’ will cool down nicely nearer the time!!! 

RANT OVER ️️️
 

MNR

[ITSY]

GEM is actually a great looking chart imo. V cold northerly followed by amplification towards greenland with trigger lows at the ready. But it's a finely balanced game with less 'assurance' than the GFS. 

Common theme though: Northerly of sorts, amplifcation towards greenland of sorts, likely secondary bite of sorts, shattered PV. Yes please to all of those

[Radiating Dendrite]

What does history tell us??

1. Things tend to move further east as we get closer to reliable.

2. Uppers tend to upgrade as we get closer to reliable. 

Given these.....expect the trough centred over the Eastern end of the North Sea and -10c uppers being pulled into the flow. 

[Scott Ingham]

26 minutes ago, V for Very Cold said:

You’ll get icicles! 

As long as i don't get Ballsicles!

[Jason M]

2 minutes ago, Optimus Prime said:

Except what you've just outlined goes completely against the science. The air in the Arctic is much warmer than it was even 20 years ago. And >40 years ago temperatures would be 1.0 - 2.5° C colder in the arctic regions. It's just a fact and this translates to less cold northerlies when the synoptics grant it if it were to occur back then.

Absolutely. SSTs are also warmer as a consequence, so add in a long fetch maritime airflow and you have yourself a nicely modified airmass. The current issue is 90% synoptics in fairness but in marginal situations the 10% contributed by AGW in background warming can just nudge things the wrong side of marginal. In truth the real interest probably lies beyond the end of the month as we have a somewhat higher chance of something more interesting down the line. 

[swfc]

Seems we now have "uppers gate" . Looking at the output it's looking going forward that everything from West to east is to be stopped in its tracks. That should in late December be a great boost and looking at the PV being dismantled, ssw building hopefully and a great nhp what's not to like

Edited December 20, 2020 by swfc

[Snowman.]

20 minutes ago, Allseasons-si said:

People stop worrying about the bloody uppers,they will change considerably the closer we get to the time,the synoptic pattern is evolving and i am as much on the bandwagon as anyone else that is wanting the white stuff to fall from the sky

anyway,good consistency from both the gfs and control @174

BTW,...who is ZONA LITY...

 

 

We do need shifts south-east of that low or general weakening of it, if it comes in that strong and that far west the best uppers will go to the west of the UK. Its just how low pressure systems work, the cold will be washed out more on a stronger system.

We only need to look back at the start of the month to see a similar situation.

 

Obviously some got snow but it was a marginal affair for many. 

The charts are on face value good but need a budge SE. As much as the 12z GFS looks nice and pretty I really hope its wrong as it even ends with a west based -NAO. Encouraging signals nonetheless espically higher up in the Strat which completely nukes the PV.

 

 

Edited December 20, 2020 by Snowman.

[Matt H]

3 minutes ago, Jason M said:

If the charts keep showing the same issue for run after run, I'd suggest the answer to your question is 'yes' 

I suppose the fact that its so marginal leads to different takes on things. FWIW I'm going for rain on low ground in the south and south east but wintry mix of sleet / wet snow on even moderately high ground. I'd imagine places like Leeds will see snow. We will find out in due course though.

My point wasn’t about arguing against the importance of uppers in delivering snowfall, indeed all of the factors that are required to produce snowfall are important and need to be discussed. I was just saying that the same people appear after every model run to moan and make the same point that they made only a few hours ago. If you aren’t impressed with the model output then it’s obviously perfectly acceptable to make a post about why you feel that way but people are more than capable of coming to their own conclusions without the same people posting the same message every few hours. I just don’t understand why you would feel the need to repeat yourself if you’ve already made the same point countless times already.

[BlueHedgehog074]

Do feel like it’s best to put this all to rest. Our hoover is getting clogged up with all the little toys we’ve had to suck up from the carpet of this thread. I understand the concerns. Yep, a little shift further East would be nice, but the setup the GFS shows is some distance away to bother too much about the 850 hPa temperatures. Not to mention, it will likely be different nearer to the time

There’s also this great guide here by John Holmes on the ingredients needed for snow:
 

 

[Catacol]

55 minutes ago, Met4Cast said:

I'm still not overly optimistic despite the output. Where is the forcing for a sustained Greenland block? The MJO is currently in the COD & forecasting what that's going to do continues to be incredibly difficult. The CFS does tank the AAM which might give some support for a decent block, however given the lag on that the GFS block would be too fast. 

I think what’s more important is that support for a reversal back to a flat pattern is even less easy to see. The GWO remains in a more Nino than Niña orbit, and that means opportunities for amplification especially given high pacific jet activity and an MJO that is more active than RMM plots suggest. And crucially we have falling vortex wind speeds and ongoing warming. In this context what is going to flatten the pattern? Don’t see much. Of all these drivers the vortex is the greatest of all, and if it splits and reverses - a hope I continue to have - then the second half of winter will hold considerable intrigue.

It is only 20th December - and there is a chance that 2020/21 might turn out to be one of those “memorable” winters.

As a final aside an interesting discussion on Twitter the other day about the index used to define Nino or Niña. It turns out the average used as a benchmark is rewritten every 5 years....and that our -1.2 Niña would have been -0.4 a century ago. I had not appreciated this going into the season, and as others have pointed out there are very warm patches of water just north of the pacific equator. I think our understanding of Pacific Ocean forcing has quite a long way to go, and one negative trap we fell into 6 weeks ago was reading a potentially strong Niña as a link to front loaded cold and back end flat misery. It isn’t turning out that way, our Niña is not behaving like a Niña (but then index changes might help explain this!) and with a weakened vortex we have a real chance of a special spell. There will be plenty of time for hindcast analysis....but right now let’s watch the ridge/trough dance unfold and see if we can get a proper cut off high somewhere to our north. 

[Mike Poole]

Just to comment on the cold air with this (or lack of it) SSTs to both our east and north are warmer than average for the time of year.  This will mean that the cold weather synoptics predicted by the models may take a little time to cool things to give colder uppers later.  

But in the meantime, marginal snow can often be the heaviest!

[Allseasons-Si]

The mean at day ten is a bobby dazzler to me

 

and most of the gefs represent this well.

 

 

[Bricriu]

1 minute ago, Mike Poole said:

Just to comment on the cold air with this (or lack of it) SSTs to both our east and north are warmer than average for the time of year.  This will mean that the cold weather synoptics predicted by the models may take a little time to cool things to give colder uppers later.  

But in the meantime, marginal snow can often be the heaviest!

Yes, and dinner plate snow flakes are nice to look at.

[dragan]

May i be so bold as to ask.....

What is the reason people think the -4ish uppers will actually be colder than that (if these charts verify of course) 

Is it past experience? Genuine question 

[BARRY]

42 minutes ago, Devonshire said:

don't worry: now post-Solar-Grand Maximum, heading for Grand Solar Minimum and new little Ice Age - chill!

2020 total: 208 days (59%)
2019 total: 281 days (77%)
2018 total: 221 days (61%) 

sunspots are still low

[weirpig]

Just to illustrate  the effects a shunt East would result  in.  Please see below one of the ensebles  which ironicly shuts the  lowtoo far east    but you can see the  difference it makes to the uppers.  ass they flood into Europe.

  

[Met4Cast]

3 minutes ago, Catacol said:

I think what’s more important is that support for a reversal back to a flat pattern is even less easy to see. The GWO remains in a more Nino than Niña orbit, and that means opportunities for amplification especially given high pacific jet activity and an MJO that is more active than RMM plots suggest. And crucially we have falling vortex wind speeds and ongoing warming. In this context what is going to flatten the pattern? Don’t see much. Of all these drivers the vortex is the greatest of all, and if it splits and reverses - a hope I continue to have - then the second half of winter will hold considerable intrigue.

It is only 20th December - and there is a chance that 2020/21 might turn out to be one of those “memorable” winters.

 

Indeed, my post was more in relation to blocking in the xmas > new year period. The developments within the strat and the potential that holds come mid-late January continues to interest and excite me. It's great to see the GFS toying with the idea of a split & reversal, in fact, wave 1 activity looks almost record breaking in the coming week. The continued trend within the EPS to weaken the vortex with a few members signalling a technical SSW is great to see too, although interestingly GLOSEA is not interested in an SSW on the more recent outputs, though the wind field profile in Jan is highly uncertain with a large spread.

The second half of winter holds a lot of promise, but I think xmas > new year is probably a little too early for us to be able to 'cash in'. Interesting about the Nina measurements too, I wasn't aware of that.

[Scott Ingham]

28 minutes ago, bumpydogz said:

Still confused. Why does low heights make any difference to the 850s threshold at which we would expect snow?

It brings freezing temperatures lower to the suface. So it takes away the need for as much elevation

[Mapantz]

Can we please keep to model discussion?! We have various other threads to discuss other subjects.

[Chesil View]

2 minutes ago, dragan said:

May i be so bold as to ask.....

What is the reason people think the -4ish uppers will actually be colder than that (if these charts verify of course) 

Is it past experience? Genuine question 

Because years of model watching experience have shown us that models have a tendency to underplay uppers the further away from t0 you go.