[Model Output Discussion - Colder but how cold and for how long?]

Just now, Mcconnor8 said:

Looks like the GFS OP run still has the low further North than the ensemble pack next week as it is at the high end of temps for the South.

Yup, another southwards shift on the GEFS mean too. 

Really surprised the Met gave a southerly tracking low a lower probability in yesterdays 10 day trend, it seemed like the fairly obvious "most likely" scenario to me.

[Model Output Discussion - Colder but how cold and for how long?]

Unsurprisingly the low has now trended to the south of the UK across most modelling. 80% chance now the precipitation doesn’t reach the south coast. 

The benefit of this is much colder air remains in place. 

[Model Output Discussion - Colder but how cold and for how long?]

I'm confused why anyone is worrying about the last week of this month when next week hasn't even been resolved yet. Once cold air is in place features & disturbances can pop up within the 12-24hr timeframe. 

What happens 2-3 weeks away isn't really worth focussing on at this stage!

[Model Output Discussion - Colder but how cold and for how long?]

For those mentioning the GFS 18z det being part of a trend..

Yeah, not so much! Very tight cold clustering, det is outlier territory.

[Model Output Discussion - Colder but how cold and for how long?]

Just now, steveinsussex said:

And the Westerly influence towards the end of January? 

I've flagged this possibility a couple of times but just to extract a portion of a post I made on Sunday;

Quote

 

Worth noting the MJO is just 1 variable within the broader windflow (GSDM) budget so shouldn't be taken in complete isolation. I flagged the 20-25th on Twitter as a period where the jet may begin to edge northwards as blocking wanes, this suggests to me the potential for high impact snow events as weather systems hit the colder air across the UK (Indeed, Tamara echoed this in her earlier post here). 

With Atlantic weather systems comes the potential for milder air depending on exactly how/where they track and something that wont be resolved for at least another 7-10 days. A waxing and waning of blocking seems likely but plenty to suggest renewed blocking into February as per @Catacol's (I believe?)  post earlier today.

 

The MJO continues eastwards and blocking is never sustained forever, it will relax and that will allow the jet to nudge a bit further northwards, however; I'd not buy into any output beyond Wednesday next week at this stage, we need to see how any wedges left to our north come into play, this could have fairly big impacts for the weather we see in the UK. 

As outlined earlier today by Tamara, Catacol & Matt though, any waning of blocking will likely be temporary with renewed blocking likely into early February. the mid-extended range remains very uncertain and open to substantial shifts within NWP modelling. Blocking WILL relax, but that doesn't automatically mean mild, wet & Atlantic driven, the jet should remain south shifted..

[Model Output Discussion - Colder but how cold and for how long?]

Just now, steveinsussex said:

@Met4Cast care to comment?

GEFS are a substantial improvement over the 12z with no mild incursion into much of the south and the mean remaining below -5C during the period of interest. Deterministic run is going up.. the mean is dropping deeper into the cold.

[Model Output Discussion - Colder but how cold and for how long?]

Substantial shift south of the low on the GEFS, increasingly likely now that the south will avoid any milder incursion. Snow risk perhaps increasing for areas south of the M4 as stated earlier. 

Trends trends trends. Maybe the tonga eruption is pushing the low south?

[Model Output Discussion - Colder but how cold and for how long?]

Just now, jonboy said:

All the extra water vapour due to hunga tonga will show its hand in shear intensity of any snow fall as I said back in November.  Get your very large shovels ready!!

How will extra water vapour in the stratosphere increase snowfall intensity? 

[Model Output Discussion - Colder but how cold and for how long?]

I think some are letting the excitement get to them, "snowstorm of the century" and comparing this to 1881 are a little silly! 

The concern with the 18z now though is those wedges have completely vanished and we end up with a bit of an Atlantic onslaught, probably a case of GFS blowing up the lows, some of the frames look rather unrealistic to me but slight adjustments south in the mid term is good enough for me, for now. 

[Model Output Discussion - Colder but how cold and for how long?]

1 minute ago, Kasim Awan said:

I wouldn't go so far at this stage.

I would. Another southwards shift with the difference between the 12z and 18z and the precip band barely reaches the UK. 

[Model Output Discussion - Colder but how cold and for how long?]

The broad trend across ensemble suites today has been to shift that low a little further south. I'd expect to see that trend continue overnight & tomorrow, we're probably looking at a south of the M4 event at best, assuming it pushes into the UK at all. 

[Model Output Discussion - Colder but how cold and for how long?]

Just now, Scott Ingham said:

Substantial over Greenland too upgrading heights at very short notice this…. Could this be the start of some last minute upgrades?

 

That low has shifted by a good 200-300 miles and it's much flatter too! Interesting run coming up for sure..

[Model Output Discussion - Colder but how cold and for how long?]

Pretty substantial shift south of that low at just day 5!

[Model Output Discussion - Colder but how cold and for how long?]

Today’s EC46 is a bit.. grim! 

[Model discussion highlights]

EXETER KEEP THE FAITH! 

Extended update via app, they see the block & hold holding on into February! 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005025

[Model Output Discussion - Colder but how cold and for how long?]

Case in point @ICE COLD

These plume charts show that there's a tighter cluster of ensembles that remain cold & don't follow the Det, albeit there is smaller cluster that does. Huge amount of spread as modelling continues to struggle with undercutting energy SE.

To compare with the 00z, certainly a a reduced cluster keeping things cold but with so much spread it's rather difficult to know if that actually means somerthing.

EDIT: Actually the scales are different between the runs, I don't think it's that much of a downgrade looking more closely, entire suite remains a mess though.

[Model Output Discussion - Colder but how cold and for how long?]

3 minutes ago, ICE COLD said:

@Met4Cast now you can tell me the ECM mean is not a downgrade and the trend to around average 850s or slightly above is clear to see . I’m pretty sure we’ve not been chasing the last 6 weeks to have a 2 day tepid northerly. It’s poor set this evening. These are for London so probably better the further north u head . 

Really don't like those charts, they're too simplistic and the "spread" doesn't actually show anything, you can't see where the strongest clusters are etc. 

Will wait for the full suite from the ECM website or wetterzentrale, those TWO ones are pointless.

[Model discussion highlights]

1 minute ago, Lampostwatcher said:

Most of them were Midlands south not south into france

The majority were south of the UK with some into southern England.

Red lines show the position of the warm front across the 00z EPS suite. It'll be interesting to see this chart from the 12z run.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5005760

[Model Output Discussion - Colder but how cold and for how long?]

ECM mean is further south with the low compared with the det.

[Model Output Discussion - Colder but how cold and for how long?]

Once more for those at the back; 

Nothing has changed

Deterministic runs will flop back and forth within the broader envelope of possibilities but at the range we're talking about the ensembles lead the way, more specifically MOGREPS & the EPS.

 

[Model Output Discussion - Colder but how cold and for how long?]

1 minute ago, Bricriu said:

With respect  it's not just one run, it's two models showing a less than desirable outcome with a return  of a westerly influence.  Granted  the GFS might lead to a dumping for some.  I now need to take this opportunity to apologise to this forum. I committed the cardinal sin by telling a neighbour to get ready for the snow. I have my running shoes on....

The GFS that was very much in the mild camp and well above the ensemble mean? That GFS?

People here put far too much stock into deterministic runs instead of looking at the larger picture, i.e the ensembles. Det runs are no more likely to be right in the 7 day range than any random ensemble member you could pick out. 

As stated a few days ago, the polar boundary will shift north and south with each run until models resolve the undercutting & strength of the high. Nothing has changed.

[Model Output Discussion - Colder but how cold and for how long?]

1 minute ago, Lampostwatcher said:

Most of them were Midlands south not south into france

The majority were south of the UK with some into southern England.

Red lines show the position of the warm front across the 00z EPS suite. It'll be interesting to see this chart from the 12z run.

[Model Output Discussion - Colder but how cold and for how long?]

Just now, Weathizard said:

People are just commenting on what we see… this ECM run is woeful, if it showed screaming easterlies everyone would react to that so why shouldn’t people react when it shows dross?

Because to say a single run of a deterministic run constitutes a "trend" is ludicrous. 

[Model Output Discussion - Colder but how cold and for how long?]

I see the standard over reactions to a single deterministic run are in full force!

Meanwhile MOGREPS 12z continues to make little of the mild incursion next week.

[Model Output Discussion - Colder but how cold and for how long?]

Northern members: It's an amazing run

Southern members: Rubbish run

These types of posts aren't overly helpful and just add confusion. Broadscale patterns for now, wait until high resolution comes into range before worrying about snowfall placements/boundaries. I'm still of the opinion that the low wont even reach the UK, let alone bring snowfall or rain.