Model Output Discussion - the cold has arrived

[Tim Bland]

ECM and GFS both show the chance of widespread snow on the boundary between the arctic air to our north and warmer air from the south west late next week.  I get the feeling we are going to play ‘north a bit’ ‘south a bit’ for a few days and the winners prize could be a white Christmas ! 

[Nick2373]

Unless we see a massive flip which is unlikely the week ahead at least is the usual winter setup then. North/South split colder the further North which geographically is expected, and mild to average with rain at times. I can’t help but to think soon as that storm kicked off in the USA it was curtains for the UK cold. 

[bluearmy]

18 minutes ago, Tim Bland said:

ECM and GFS both show the chance of widespread snow on the boundary between the arctic air to our north and warmer air from the south west late next week.  I get the feeling we are going to play ‘north a bit’ ‘south a bit’ for a few days and the winners prize could be a white Christmas ! 

I’d happily take Paris ……

 

[MattH]

Morning...

A troublesome time to be a forecaster, especially for next week, but just quoting the following from the post a few days ahead and, overall, this remains true, currently and looking ahead...

"The 'problem' that NWP will have looking ahead is that we continue to be within a hemispheric regime that is not 'normal'. I used the words 'usual' and 'unusual' the other day in a post, the usual setup clearly being a robust W'ly regime, with connected strat and trop, the unusual setup being what we have had now and, at the moment, will continue to have looking ahead."

Even I, 24 hours or so back, thought we were on to something when both the GEFS and the EPS, for example, generally flatlined on the colder N'ly flow for next week, but, as we have seen many times over the years whether deterministic models or ensembles, they can suddenly flip when the overall evolution is as complex and problematic as it currently is. I won't bark on about AAM this time as, overall, there is no real change there apart from to say that some recovery in AAM is still expected, linked to the movement of the MJO, so that's a positive (no pun intended!) looking ahead.

However...The problem with the run up to Christmas is as I mentioned the other day, the block of late is breaking down and we have a number of conflicting regimes trying to play out. Once again we can put the strat influence to one side, for now, so forget about that, but I am wondering whether it is the MJO, short-term that is actually creating some of the problems next week, in amongst what remains a highly disorganised tropospheric pattern. As I mentioned the other day the recent fall in AAM, if this were a robust W'ly regime with a strat and trop connection then we would be writing off any sig cold for a good while, but that isn't the case.

However, the MJO has been firmly over the Indian Ocean and while you can't take one variable at face value, some of the composite anomalies, especially the often correct regression plots do show a similar pattern to what the models are toying with next week, especially regarding the European high pressure.

We can see the -ve OLR signature over the I/O through the 10th to the 14th (MJO phases 2-3) and the regression plots do show a pattern that is dominated by the european high and low pressure to the NW. Obviously what we have to do, as a forecaster, is add the extra variables in play to adjust that 'black and white' output and suggest that the low pressure to the NW is obviously not likely to be that significant due to the on-going amplification to the troposphere etc. 

 

As many have said on here in recent days it is the European high that is one of the key problems as this essentially stops the pattern from progressing eastwards and clearly stops the low pressure next week from trending eastwards. The 00Z GEM, of course, continues to highlight how if that does happen we end up with a far quicker and more significant way to cold weather once again. The evolution into next week, therefore, is very uncertain indeed, simply because of the all the conflicting signals that are trying to dominate, now that the original ingredients for a prolonged block are waning and there is, IMO, still the chance that the GEM, for example could come off, but, as the UKMO shows, there remains a worst case scenario as well with a SW'ly flow if the european heights dominate.

If we look at this from a model perspective and just taking N England from the 00Z EPS as an example, we can see how compared with yesterday's 12Z ECMWF it is a colder run, but the spread in the box and whiskers plots for the middle of next week is huge(!) and, again, this highlights well how uncertain the forecast is for next week.

Where we go from there remains problematic through to the end of the year, but with the MJO still set to be on the move and with the AAM set to recover once again, with no strat and trop connection then continue to expect some further 'fun and games' from NWP looking ahead. AAM, from the latest EC Monthly does fall into January and *IF* the strat and trop do connect then this could well be the first signs of the +ve NAO development that was always expected for the middle and latter half of the winter without an SSW, for example. It is unrealistic to think that the strat and trop won't connect at some point, but note the predicted recovery through the rest of December, January, meteorologically speaking, is a very long way off especially under the currecnt synoptics and situation.

Cheers, Matt.

 

[East_England_Stormchaser91]

A very interesting battle going on, pretty much all predicated on what that bout of heights does from the Aleutian WAA, and how the residual greenland heights behave. If we can get that link up, that should change the outlook completely. 
Over the past, cold spells have often sprung up very quickly. 2012-2013 during January, it wasn’t until the mid timeframes that a scandi High suddenly built up. None of the models were interested one bit post 180 hours into each run until we got to more or less a week before the event unfolded! That was otherwise looking like a tedious mild winter. 

[Chesil View]

After lots of teasing and the will it? won't it amplify saga of the last few days.  Only the GEM holds out any hope for southern snow lovers this morning.

The rest coalescing around a more mobile outcome albeit with the mild/cold boundary moving up and down the Northern half of the UK.

Saving grace of this Christmas pattern is that it is very similar to Xmas 1978 and those of a certain vintage (like me) know what that went on to produce.

As Matty H points out above there is still some uncertainty going forward. Lets hope it's enough to bring us southern snow lovers into play as well.

Edited December 16, 2022 by Chesil View

[Mike Poole]

ECM clusters T120-T168, there are 5:

Broadly speaking you can put the ECM op in cluster 1 (as it says), the GEM in cluster 2 (11 members), the UKMO in cluster 3, son that would imply over 20% chance of the GEM evolution.  Cluster 4 is poor, cluster 5 rather misses most of UK with the northerly.

T192-T240, and I think the picture is more promising here, which reflects the view of the op runs, 3 clusters - each 17 members:

Cluster 2 has most potential because it budges the euro heights, otherwise cluster 1 is OK, cluster 3 is poor.  

[Anthony Burden]

Morning all,as Matt Hugo stated in his blog a very complicated picture as we run up to Christmas,Gem keen on a channel low keeping cold air well established to the north of the low pressure and a strong possibility of snow to most of England.ECM perhaps keeping the low tracking further north with less cold air over at least the south of the U.K. all still in the unreliable and open to change,prior to that a milder /colder regime looks to be the form horse for next week not seen such a good run up to Christmas for a very long time,white Christmas very much on the cards for some parts of the U.K. 

[IDO]

As expected, the ECM mean highlights that the op was on the milder side for the south:

It also looks more progressive with the pressure drop around D7. I expect the op to separate the Atlantic low for longer in future runs more than the 0z op.

[Day 10]

I only have 2 mins, plenty to play for and great post from @MattH there above.

You can see the difference in output quite nicely at 144 in order of a cold preference from GEM, GFS, ECM to UKMO.

Have a great day all

[Gowon]

1 hour ago, Drifter said:

?? I’m in Hampshire!

I only noticed north east on your profile and missed out Hampshire. sorry.

 

[TEITS]

9 minutes ago, Weather-history said:

That's just not true. I have read Matt Hugo's analyses for some years and he will say it as it is. If its a duck, he will say its a duck. 

I haven't had chance yet to read Matt Hugo's post above but in my opinion he always provides a very honest forecast without any bias towards weather preference. Basically the complete opposite of myself

Back to the models and my word I am glad I do not have to provide forecasts to the bookmakers with regards to the betting on a white xmas. At first the UKMO was very progressive in bringing a return to colder weather from the NW but now the opposite is true. If you take a blend of all the output then the chances of cold returning and the risk of snowfall begins around the 22nd Dec onwards with the greater risk being the further N you are. Obviously Scotland is in the best position at this moment in time.

I will also add that due to the uncertainty and the fact that such relatively small changes could have a big impact. I would be cautious using some charts such as the Anomalies/Ensemble means. Stick with the operational outputs at this moment in time.

[bluearmy]

Those eps clusters have made me wonder whether the trough dropping to our sw will become cut off and allow the Atlantic heights  to connect to the euro ones across the top of it ?? The low anomoly to our sw is common across the ens suites 

 

[Drifter]

1 minute ago, bluearmy said:

Those eps clusters have made me wonder whether the trough dropping to our sw will become cut off and allow the Atlantic heights  to connect to the euro ones across the top of it ?? The low anomoly to our sw is common across the ens suites 

 

Trying to visualise if this would be good for coldies?

[TSNWK]

2 minutes ago, bluearmy said:

Those eps clusters have made me wonder whether the trough dropping to our sw will become cut off and allow the Atlantic heights  to connect to the euro ones across the top of it ?? The low anomoly to our sw is common across the ens suites 

 

Scuro heights... 

1 minute ago, Drifter said:

Trying to visualise if this would be good for coldies?

I don't think so  calm and chilly at best is my take

[carinthian]

3 hours ago, carinthian said:

Wow what a mess at 120t. Who would predict a festive forecast based on this mornings runs ? Basically, Arctic v Sub Tropical and who wins out ? Massive snow potential for some but where ? Basically sit tight and enjoy the ups and downs over the coming days. Experience tells me nothing nailed  . However, that cold up North looking intense but will it flood south ? Hang on to your hats !

C

The 500-1000hpa and mean sea level chart from ECM below for Christmas Day highlights just one example  presently of the difficulties in getting the forecast correct. For us in the Eastern Alps, looks quite simple , dry and mild. However, for you lot back in Blighty you are on the great divide between the two very different air mass types. Looking at the profile chart below you would expect the low to sink slowly SE and allow  Arctic air into Northern Britain with potential snow zone to develop. However, UKMO especially shows a big difference in its out put and indicates milder air pushing back any potential CAA.  Basically, the Festive Forecast remains in doubt until some kind of model agreement. Frankly all looks very messy at this stage with all possibilities on the table. I suppose going by the law of averages, milder scenarios usually win out BUT not all of the time !

C

Edited December 16, 2022 by carinthian

[bluearmy]

4 minutes ago, Drifter said:

Trying to visualise if this would be good for coldies?

 

3 minutes ago, TSNWK said:

Scuro heights... 

cluster  1 on the eps. A hybrid of the gem at day 9/10 

[Jake March-Jones]

Is the 06z delaying the mild a little or is that just me? 

[Captain Shortwave]

24 minutes ago, Drifter said:

Trying to visualise if this would be good for coldies?

Something like this, not good initially for those wanting proper wintry weather.

 

High pressure would build close to the UK and then drift eastwards. However that amplification may help further down the line.

If heights were to build over the top of a sinking trough, it would be far better to have this occur with a deeper trough to our east that could allow the high to build further north and have any northerly backing towards the east later on.

[IDO]

You can see the subtle difference between the GFS and GEM that makes a difference at D6:

GFS 06z:  GEM 0z: 

The more defined wedge between the Atlantic low and UK trough. The knock on for GEM is a sharper more perpendicular UK trough and the suppression of the Iberian high. Meaning a quicker sharper cold flow from the Arctic and more sustainable. Which way will the models trend? So far, a bit towards the GEM by GFS. So on this 06z run a N/S split for cold air at D7 rather than GEM cold nationwide.

[ItNeverSnowsInWindsor]

How do we lose the Bartlett style heights over S Europe ? And replace them with lows ?

[ItNeverSnowsInWindsor]

3 minutes ago, IDO said:

You can see the subtle difference between the GFS and GEM that makes a difference at D6:

GFS 06z:  GEM 0z: 

The more defined wedge between the Atlantic low and UK trough. The knock on for GEM is a sharper more perpendicular UK trough and the suppression of the Iberian high. Meaning a quicker sharper cold flow from the Arctic and more sustainable. Which way will the models trend? So far, a bit towards the GEM by GFS. So on this 06z run a N/S split for cold air at D7 rather than GEM cold nationwide.

GFS has a Bartlett high whereas GEM has much flatter heights.

[Jan 87]

rubbish 06z op. Lets see what the control and GEFS do

 

[frosty ground]

4 minutes ago, prolongedSnowLover said:

GFS has a Bartlett high whereas GEM has much flatter heights.

It has a high over southern Europe and they’ve not been there long enough to be called a Bartlett high. 

[ItNeverSnowsInWindsor]

The whole pattern needs to be a 1000 miles further East.

West based NAO is the worst outcome for us.