Model output discussion - Closing in on Christmas

[mulzy]

1 minute ago, mountain shadow said:

So, a 1 or 2 day cooler spell with perhaps some frost on Christmas Day then back to chasing something interesting in FI.

Manyana manyana.

Frost in the new snow perhaps? 

[That ECM]

23 minutes ago, West is Best said:

The likeliest progression is that a couple of days before the colder snap the 'northerly' will get slacker and slacker and turn into a damp squib. The ECM points the way here I suspect.

Sorry to be a grinch but we've all seen this sooooooooo many times. It needs to pep up considerably for the inevitable downgrade to retain potency.

You may be right and we will see but we can only go by what we can see not our hunch. Gfs mean has -4 over majority. Ecm has upgraded the day on the latest run. 
 

As I say we will see.

Edited December 17, 2020 by That ECM

[IDO]

I have seen worse 0z runs. 

We are now more confident of the first ridge and that it will be a transitory topple; all models agree and for example, gem:

Post d8 models are not dissimilar. With the upstream amplification on the wain we see how the tPV chunk near Greenland forces the pattern for the our region. The NH synoptic remains mobile so it will hustle and bustle against the Siberian high and the Azores High. Dropping into a ScEuro trough is within the bounds of options.

D10 for ecm, gem and gfs:

With no MJO signal apparent, the loss of the Arctic high and relying on the trop to blend a cold solution, the ScEuro trough is possibly our best shot at cooler conditions now the Atlantic ridge is not standing?

[BlueHedgehog074]

How interesting. Even though there was still always room for things to improve again regarding the possible colder snap/spell towards Christmas, a nice surprise to see the models more amplified this morning. Using examples from the 00Z GFS, 00Z ECMWF and 00Z GEM for Christmas Day (192 hours): 

00Z GFS

00Z ECMWF

00Z GEM

The mid-Atlantic ridge does still topple quite quickly on both the ECMWF and GEM leading to something more flatter (although the GEM does re-amplify upstream again towards the end). The GFS the most amplified of the 00Z runs for Christmas Day. Hence the High takes longer to topple - if you can even call it that, as the mid-Atlantic High ridges over the top of the Italian Low Pressure attempting to link up with the High over Russia. The Vortex does also try to gang up on Greenland... but it has two enemies! The Russian High and renewed amplification in the Atlantic, which forces the beast to drain away South-Eastwards with the upper trough dropping over Eastern UK. The North-Westerly to Northerly flow comes back for revenge!

Compared to the 12Z runs yesterday for Christmas Day (204 hours), which have posted underneath, the runs above are a step in the right direction. The 00Z GFS and 00Z ECMWF, in particular, would bring some wintry showers into Northern and Eastern areas on Christmas Day. These I imagine becoming more concentrated towards Eastern/South-Eastern areas on the 00Z GFS as the flow turns more to the North-East.

12Z GFS

 

12Z ECMWF (had to use an earlier chart at 192 hours due to their being no 204 hour chart. But you’ll still notice that for Christmas Eve mid-day the toppling ridge to our West is a touch further East than it is on the 00Z ECMWF for Christmas Day)

 

12Z GEM

 

Probably likely to continue being a transient affair. However, considering the improvements the operational models have made with some better Atlantic amplification, then not impossible this could become more of a cold spell, rather than a snap. Especially with some of the models wanting to bring another bout of amplification upstream to our West (although things becoming less amplified/flatter again couldn’t be discounted). The Russian/Siberian High, if close enough, might also aid in Low Pressure systems to our West to be forced South-East into mainland Europe along with a displaced Azores or Atlantic High. This directing the Jet Stream on a more North-West to South-East path at times, which could keep the UK locked into a cool setup

[mulzy]

3 minutes ago, IDO said:

I have seen worse 0z runs. 

We are now more confident of the first ridge and that it will be a transitory topple; all models agree and for example, gem:

Post d8 models are not dissimilar. With the upstream amplification on the wain we see how the tPV chunk near Greenland forces the pattern for the our region. The NH synoptic remains mobile so it will hustle and bustle against the Siberian high and the Azores High. Dropping into a ScEuro trough is within the bounds of options.

D10 for ecm, gem and gfs:

With no MJO signal apparent, the loss of the Arctic high and relying on the trop to blend a cold solution, the ScEuro trough is possibly our best shot at cooler conditions now the Atlantic ridge is not standing?

Yes, this is what the extended eps has been broadly hinting at - Euro toughing with a strong Azores High displaced slightly north - mean flow north of west.

The GEFS a bit better with the Atlantic profile in deep FI.

 

 

[carinthian]

I think of all this mornings model runs, the UKMO provides the best prospects of prolonging a colder Christmas period. The low out to SW is shown to fill and be less progressive than shown by the other models. That would support the Mid Atlantic ridge and keep the British Isles in a more meridional  flow . Looks like the jury still not decided on this outcome at the moment !

C

 

[Sky Full]

Snow actually appearing in the ‘precipitation type’ chart for Christmas Day!  That’s got to be a result in itself!  Can’t remember seeing this for years and years.....

OK - I know it’s not a nationwide Christmas blizzard which some would love to see, but at least there’s a chance for some of us.  How often can we say that at this time of year...?

[terrier]

So looking at the gfs & ecm this morning we have a 2 to 3 day cold spell  with a few frost. How desperate it shows we have become in the U.K.. Then the high looks to topple and we are getting milder air moving in. Ala the met office long range updates. So it seems like we are then hoping a ssw to do us a favour. But as we all know even a ssw doesn’t guarantee us cold. Call me pessimistic but haven’t we been here before hoping for a ssw event. 

[Daniel*]

ECM op was an outlier with delaying cold northerly flow.

[georgiedre]

6 minutes ago, terrier said:

So looking at the gfs & ecm this morning we have a 2 to 3 day cold spell  with a few frost. How desperate it shows we have become in the U.K.. Then the high looks to topple and we are getting milder air moving in. Ala the met office long range updates. So it seems like we are then hoping a ssw to do us a favour. But as we all know even a ssw doesn’t guarantee us cold. Call me pessimistic but haven’t we been here before hoping for a ssw event. 

Met office says the West will be driest and East wettest so that wouldn't mean mild air would it? 

[chris55]

Models still undecided on how this Atlantic low develops. How much impact the modelling of this has on developments once we get past it is unclear. 
 

More runs needed, 

UKMO vs ECM at 144

Edited December 17, 2020 by chris55

[carinthian]

4 minutes ago, chris55 said:

Models still undecided on how this Atlantic low develops. How much impact the modelling of this has on developments once we get past it is unclear. 
 

More runs needed, 

UKMO vs ECM at 144

Spot on Chris55. Think the position and movement of the low will be crucial to the Christmas forecast and how the Atlantic ridge is supported.

C

[alexisj9]

3 hours ago, Bartlett High said:

Does seem a bit odd when you compare it to the 18z ...like chalk and cheese.

It reacted to the American low changing, and didn't know what to do, so just went zonal I think. I'm talking t0 not fi.

[alexisj9]

1 hour ago, carinthian said:

A bit of a difference showing between the UKMO and latest ECM op run at 144h.  ECM makes more of a feature of the Low and holds much of England and Wales in the milder air mass longer. So looks like UKMO may be out on its own this morning.  Who will be right or none of the main models out at 144t  ? Keep watching folks !

C

That's the low I've been watching, we want it as south as possible, it seems to produce more amplification that way. South and shallow seems best from what I've seen so far in the out put.

[sheikhy]

It all hinges on that low to the south west at 144 hours!!!deeper low then most probably you can forget about any meaningful cold!!slacker and further south maybe a better outcome?

[TSNWK]

24 minutes ago, terrier said:

So looking at the gfs & ecm this morning we have a 2 to 3 day cold spell  with a few frost. How desperate it shows we have become in the U.K.. Then the high looks to topple and we are getting milder air moving in. Ala the met office long range updates. So it seems like we are then hoping a ssw to do us a favour. But as we all know even a ssw doesn’t guarantee us cold. Call me pessimistic but haven’t we been here before hoping for a ssw event. 

Morning terrier.. serious question if I may please. Do you have posts saved on a virtual clipboard which you trot out each winter.

TIA

[Radiating Dendrite]

1 minute ago, TSNWK said:

Morning terrier.. serious question if I may please. Do you have posts saved on a virtual clipboard which you trot out each winter.

TIA

Think he is a glass half empty type of chap 

[I remember Atlantic 252]

31 minutes ago, Sky Full said:

Snow actually appearing in the ‘precipitation type’ chart for Christmas Day!  That’s got to be a result in itself!  Can’t remember seeing this for years and years.....

OK - I know it’s not a nationwide Christmas blizzard which some would love to see, but at least there’s a chance for some of us.  How often can we say that at this time of year...?

00Z GFS will be wrong in deep FI, shows perfect snow setup for me on new years Day, last white new year was in '97

[frosty ground]

16 minutes ago, I remember Atlantic 252 said:

00Z GFS will be wrong in deep FI, shows perfect snow setup for me on new years Day, last white new year was in '97

Yes it's a cracking chart, the G?Fs has been keen to introduce a second northerly after the first.

[nick sussex]

The latest curveball upstream is the shortwave which shows up on the ECM off the eastern USA which then phases with the developing shortwave running east across the mid west .

That impacts the ridge ahead and also the low sw of Iceland .

The models later seem to want to re-invigorate the PV over Greenland and then edge that eastwards .

Whats not certain is how much if any trough disruption occurs as that happens .

The GFS is more progressive there , the ECM by day ten keeps that further to the nw.

There is a lot going on upstream as the pattern amplifies next week so things aren’t set in stone.  

[BarometerCat]

Interesting GFS ensembles...for the less than Knowledgeable like me this shows in a nice graphic form the spread of options (and uncertainty) after only 21st. Loads of great posts pointing this out and why.  The operational line represents the rollercoaster of emotions over the next few days..   

[captaincroc]

1 hour ago, Daniel* said:

I found progression quite odd 192 > 216 the ridge just collapses into main heights it seems rushed to me. 

GFS for same timeframes at 192 it’s really not that dissimilar different in Atlantic sector. And well 216 looks very different.

 

From what I’ve seen there’s flexibility to get a little more out of this than ECM 00z depicts.

 

Morning Daniel, I actually was going to reply with two points and you just made one for me. I am not hope casting but, like you, for me the ECM towards the latter stages looks wrong. Not just because the ridge is being flattened, but how the pressure looks around it.  It looks like the models are struggling so, yes mild could come in but I have never seen such constantly confused models with this high pressure on the pole.

Point 2...haha. I have been here many a year (as CreweCold will also know...) and I have never seen a genuine piece of the PV drop straight onto us. I have seen it sink south and have 'polar westerlys' which again has produced some wet snow (plenty of hill snow) but the PV still remained slightly to our north with gales etc. I have never seen it drop south with such cold upper and great thicknesses.  If, and i mean, if it drops as per GFS then it would literally be a snowstorm wouldn't it?  Something I have always questioned whether it could happen.  Are there any more more 'mature' posters that know whether this has happened before?

Edited December 17, 2020 by captaincroc

[bluearmy]

1 minute ago, captaincroc said:

Point 2...haha. I have been here many a year (as CreweCold will also know...) and I have never seen a genuine piece of the PV drop straight onto us. I have seen it sink south and have 'polar westerlys' which again has produced some wet snow (plenty of hill snow) but the PV still remained slightly to our north with gales etc. I have never seen it drop south with such cold upper and great thicknesses.  If, and i mean, if it drops as per GFS then it would literally be a snowstorm wouldn't it?  Something I have always questioned whether it could happen.  Are there any more more 'mature' posters that know whether this has happened before?

No need to analyse it captain - it ain’t gonna  happen ! 

[Iceaxecrampon]

Saturday (Wet?) T-shirt weather then the ensembles go only one way.

[captaincroc]

2 minutes ago, bluearmy said:

No need to analyse it captain - it ain’t gonna  happen ! 

Blue, put down your Daily Mail and pick up the Mulled Wine and come join me in Xmas dreaming...