Model Output Discussion - Christmas and New Year

[TSNWK]

What is the creditability of GFS control run please?

[Battleground Snow]

7 minutes ago, Mike Poole said:

Do you mean from the strat?  If so, no it’s too early for that, earliest would be 2 weeks after reversal of winds in the strat.  I think the blocking is trop led, and is actually accelerating the split (if there is to be one) in the strat, if that makes sense.  

Sorry, I meant the warming that's due to take place shortly is weakening the usual dominant westerly flow at this time of year, allowing for increased blocking, I understand it won't go easterly for a while yet

[Griff]

3 minutes ago, Djdazzle said:

Won’t get mush snow with those temps - not with frontal snow anyway.

I heard a rumour that 'they' are not limiting the weather to daylight hours this year, which is currently... 

Might it be colder at night? 

[Mike Poole]

Just now, TSNWK said:

What is the creditability of GFS control run please?

It will be less good than the op because it is run at a much lower resolution.  It is the ensemble member that has the same starting conditions as the op (all the others have random perturbations), that is what it’s for.  It is best used in conjunction with the ensembles, often it is posted in here as an op run in its own right, which it isn’t.

[chris55]

Control showing a massive ppn spike for London Monday! 
 

The track and intensity of the ppn Monday, rain or snow, is still loaded with potential. 
 

 

[Djdazzle]

1 minute ago, Griff said:

I heard a rumour that 'they' are not limiting the weather to daylight hours this year, which is currently... 

Might it be colder at night? 

Depends on how cloudy it is.

[Howie]

1 minute ago, chris55 said:

Control showing a massive ppn spike for London Monday! 
 

The track and intensity of the ppn Monday, rain or snow, is still loaded with potential. 
 

 

The mean is staring to dip below -5

[Kentspur]

3 minutes ago, chris55 said:

Control showing a massive ppn spike for London Monday! 
 

The track and intensity of the ppn Monday, rain or snow, is still loaded with potential. 
 

 

❄

[Mike Poole]

3 minutes ago, Battleground Snow said:

Sorry, I meant the warming that's due to take place shortly is weakening the usual dominant westerly flow at this time of year, allowing for increased blocking, I understand it won't go easterly for a while yet

The normal westerly flow is pretty much gone and has been for a while, the jet is meridional upstream (GFS T96):

The blocking looks like it will wax and wane with the jet, leading to rinse and repeat pattern, until the SSW and effects of that down well maybe last third of January.  After that...here be dragons

[Griff]

Just now, Djdazzle said:

Depends on how cloudy it is.

Yeah, I know, I'm just teasing. No doubt a marginal setup but not too hard to imagine daft over sized snow flakes following an initial period of rain and evaporative cooling. Caught my other half out on a journey from Reading back over the Chilterns, as it happens, 2 years ago. No problem turned into the usual traffic chaos in only a couple of hours... 

[BLAST FROM THE PAST]

5 minutes ago, Kentspur said:

❄

But surely...surely not.  There’s been steadfast proclamation on here that Scottish and northern peaks ONLY have a chance?

It’s getting cold and really cold and snow will crop up anywhere in the UK and Ireland 

Merry Christmas 

 

BFTP

[chris55]

Here’s the chart showing that ppn spike on the control for London. You folks in the south east are in the sweet spot! 

Still open to movement and many places in the south are in the mix for some Snowfall at some point Monday  

 

Edited December 25, 2020 by chris55

[Skullzrulerz]

2 minutes ago, chris55 said:

Here’s the chart showing that ppn spike on the control! You folks in the south east are in the sweet spot! 

Still open to movement and many places in the south are in the mix for some Snowfall at some point Monday  

 

And of course the South West misses out again

[TSNWK]

16 minutes ago, Mike Poole said:

It will be less good than the op because it is run at a much lower resolution.  It is the ensemble member that has the same starting conditions as the op (all the others have random perturbations), that is what it’s for.  It is best used in conjunction with the ensembles, often it is posted in here as an op run in its own right, which it isn’t.

Thank you.  I don't get why post a control run in isolation if run at lower resolution than an op. 

Op run and how it aligns within  ensemble pack is my mantra and I find the spaghetti plots really helpful in that.

[jay1lk]

2 minutes ago, Skullzrulerz said:

And of course the South West misses out again

The Kernow snow shield at work again

[Methuselah]

4 minutes ago, BLAST FROM THE PAST said:

But surely...surely not.  There’s been steadfast proclamation on here that Scottish and northern peaks ONLY have a chance?

It’s getting cold and really cold and snow will crop up anywhere in the UK and Ireland 

Merry Christmas 

 

BFTP

There has? I think we all realise that we're headed into a spell of wintry weather? 

Merry Christmas, anyway, Fred!

[Guest]

14 minutes ago, Kentspur said:

❄

Unfortunately this front will be mostly of rain, with any snow on the back edge but unlikely to settle away from 200m. All in my opinion as a humble human being with experience. 

Happy to be proved wrong! 

[MATTWOLVES 3]

The tasty synoptics just keep on coming....short term...mid term...long term....All aboard the cold train folks...

[Frosty.]

Looking at the GEFS 12z mean there’s strong support for a cold / very cold start to 2021..and beyond that there are still some cold members..my hope is that wintry hazards become widespread and something more severe will develop next month!!!..in my unbiased opinion of course!  

[Kasim Awan]

Cracking ECM for snow early Monday

The track is far from resolved, whole of central UK at risk with 1st area Mon 2nd early Tue

[Mike Poole]

2 minutes ago, TSNWK said:

Thank you.  I don't get why post a control run in isolation if run at lower resolution than an op. 

Op run and how it aligns within  ensemble pack is my mantra and I find the spaghetti plots really helpful in that.

Yes, the purpose of the control run as I understand it is to give confidence or otherwise in the ensembles.  If the control goes off massively different to the op, it suggests the lower resolution is to blame, and therefore the entire ensemble suite is dodgy.  If they are similar, however, then the differences seen between ensembles will be due to the random perturbations, not the reduced resolution, so one can have much more confidence in the ensemble suite representing the uncertainty.  

[Man With Beard]

ECM 12Z, Now this was much more like what I was expecting for Monday morning

A much more substantial area of precipitation for southern England - this is 11am, it had passed through the cotswolds & west midlands in previous hours. It will work it's way through the SE in the hours after, maybe even pivoting to give a heavy fall somewhere.

Still too far out to pinpoint exact locations where this will happen, but in general areas between west midlands and south coast is at risk of heavy snow and/or a wintry mix if parameters are ever so slightly on the warm side (e.g. ARPEGE 12Z).

Further north, frequent wintry showers with not a small risk if further organised bands of sleet/snow

 

[sheikhy]

Cracker jack ecm at 144 hours!!!!!!parameters are pretty much perfect for snow sunday night monday for the midlands!!!!got -5 850s to boot!!!

[Ben Sainsbury]

ECM 12z has been a cracker so far! Better advection of the high towards Greenland and a good orientation so that we sit under northerly winds throughout. Colder uppers too!

[Battleground Snow]

@Tim Bland sorry 

Still chopping and changing run to run even at this range.