Model output discussion - deep cold inbound?

[northwestsnow]

Thats great news for those further south and indeed for all of us imo.

 

[stodge]

Evening all

A mild and pleasant day here in lowland East London and well done to those further north who saw quite a bit of snow (10-15cm in parts of Yorkshire).

I confess it's with some trepidation I approach the MOD thread this evening. This is the point of the downgrades/backtracks and the "I told you so" comments from the trolls. Apart from GEM to an extent yesterday evening and JMA, all the other models were on board with the Easterly spell due to start over the weekend. The suggestion  was for 7-10 days of colder weather before the Atlantic came back in as suggested by GFS based on a failure of Scandinavian heights in far FI.

As a wise man once said, that was then and this is now so let's see what tonight's meanderings offer:

T+120 takes us to the 7th, T+240 to the 12th, T+312 to the 15th and T+384 to the 18th February

12Z GEM: The T+120 shows the E'ly air flow in across the British Isles. Heights to the north and north west have finally pushed the trough to the south east and the next LP is looking to head SE to France. Uppers below -4 over all parts and below -8 over south east England and northern Britain in general. From there, the trough does indeed ease SE but is still in the southwestern approaches by T+180. The direct flow from Siberia has bene cut off as a small HP has formed over Poland and a weak trough over Northern Scandinavia. Milder air with positive uppers flirting with the Channel coast while pockets of -12 850s sit to the north. From there, the LP to the south west grinds its way NE across southern Britain to be off north East England by T+240 with a cyclonic flow over most of the British Isles. Upstream, a weak Atlantic trough aligns positively and there's a hint of heights rising to the south west and over NE Scandinavia. There's a brief push of milder air across southern Britain but by T+240 uppers are generally slightly negative with the coldest air in the north.

It's good to see GEM finally latch on at T+120 but it's a 3 day cold spell in the south only (longer lasting in the north) and the T+240 evolution isn't encouraging.

12Z GFS OP - a wonderful run in the short and medium term last evening but it broke the cold spell down around mid month with a return to Atlantic dominated weather. At T+120 we haven't got the clean departure of the trough to the south and while the E'ly is in across Scotland, the LP is still centred over Lincolnshire at T+120 with the other part of the trough aligning negatively to the south west. Heights over Greenland and Scandinavia. Apart from the area close to the centre of the LP, negative 850s for all parts but as you might expect, coldest (below -8) over Scotland.  From there, the trough doesn't want to clear away from the south persisting until T+180 and probably cutting off any severe cold flow for southern areas. Further north, the ESE'ly persists with heights building over Scandinavia. The LP is to the west of Biscay by T+180 and milder air with positive uppers has come back to Cornwall but it remains cold over northern Britain with uppers below -8. Moving on and the trough eases up across the UK but the Atlantic starts to become dominant as the Scandinavian heights withdraw and with pressure building near the Azores, the active Atlantic trough aligns positively and it looks all over for cold by T+240. The coldest air has eased north and by T+240 850s are either side of zero generally.

To be honest, a disappointing run for the south where severe cold never takes hold and the issue may not be snow as much as some very large rainfall numbers which would exacerbate existing flooding issues.

12Z Control - no 12Z parallel this evening so we're off to Control for our second GFS fix and at T+120 it's similar to OP.  From there, the trough remains close to or over southern Britain through to T+180 while the ESE'ly is maintained further north. Positive 850s over the far south of England but 850s below -8 over Scotland. Moving on and the colder spell breaks down as heights dissipate to the north and east and a vigorous Atlantic LP approaches from the west though at this point it's got a neutral alignment with no significant height rises to the south or south west. Positive uppers over southern and western Britain by T+240 but negative uppers persisting elsewhere.

Control follows OP with a 3-5 day cold spell at best it would seem.

12Z ECM - at T+120 we have an E'ly over northern Britain while the trough persists further south as a shallow feature over south east England extending south east into Europe. 850s below -4 over the whole of the British Isles with uppers below -12 over Scotland. From there, it's a struggle to get the trough away from the south but by T+192 it has eased south east to Austria and Northern Italy leaving a NE'ly over most parts but with a new large Atlantic system approaching and heights rising over Iberia. 850s below -8 over most of the British Isles by T+192 but the sense of milder weather approaching once again. As expected, the Atlantic trough splits with the main core LP sitting in mid ocean while a lobe of energy to the east and north east forms a new LP which is approaching Ireland albeit on quite a southerly trajectory by T+240 and heights persist to the north. Positive uppers over southern Britain by this time but colder air persists to the north.

Another model cuts the cold spell down to 3-5 days but at least there's some severity for southern areas.

Looking further ahead, GFS OP and Control at T+312 and T+384 respectively:

Neither OP nor Control offers any let up in the unsettled wet conditions and again it's hard to see there's much respite from rainfall even after mid month.

Conclusion: a disappointing night for cold weather fans. We simply can't get the trough to clear to the south to bring in the severe cold from the east or north east. Obviously, the proximity of the trough offers snow fans plenty of hope especially, I'd argue, from the Midlands north and especially over high ground. The one thing I'm not seeing on any model is a period of dry weather - whether it's snow or rain I suspect flooding will continue to be a huge issue in the next fortnight and exacerbated by any snowmelt.

[Valleyboy]

54 minutes ago, kold weather said:

Here is a summery at 144hrs from the ECM,:

Very rough wind flow from the ECM 12z ECM.

Anything above the blue line will have lots of snowfall, especially with several frontal systems wrapping round.

Anything south will see increasingly diminishing returns quite rapidly as the convection dries out. Thats not to to say on the 12z ECM it'd 'dry' BUT its going to be scattered snow showers rather than sustained showers and fronts you see further north.

At least the Atlantic does help the south later down the line.

That chart doesn’t look summery

[Singularity]

 

Neat example on the limitation of 'face-value' viewing of single timestamp charts.

Broadly you could say ECM is suddenly very close to GFS which in turn has moved toward where ECM was a bit.

Yet the journey there has critical differences. 

GFS is still bringing up the Iberian low, dragging its warm sector with it. ECM still takes it east and the warm sector goes east with it.

This is why ECM still keeps conditions cold enough for snow despite the UK low missing its train to Russia and loitering by the southeast for a couple of days while it awaits the next one.

For what it's worth, I expect there would be more in the way of showers and mesoscale disturbances than what the ECM 12z shows for its scenario. The first of those appeared for Saturday night on that particular run. I really noticed that for an obvious reason! Can't take its position literally of course.

[Djdazzle]

I’m assuming that MOGREPS is fully onboard with the easterly, as the Met seem confident.

[kold weather]

The mean is again in this pattern more or less meaningless in determining where a snow event is going to set up this far out.

For example, here is the GFS mean for 120hrs, followed by two members which resemble the mean closely:

The mean is in the middle.

On the face of it, both of the ensemble members flanking it fit very neatly into the mean and therefore you'd expect would both share similar outcomes?

Well one has a big rain event for nearly all of England bar the far north. The other has a large snow event for most of Southern England bar maybe the far SE.

Yet they both fit into the mean very well?

This goes to show why just using the mean is pointless, because the mean is effectively hiding alot of very similar, but very different evolving LPs which in this situation makes the difference between a let down, and a very large event for most.

Edited February 2, 2021 by kold weather

[in the vale]

ECM OP vs. its ENS Mean, GFS Op vs. its GEFS Mean. There's a pattern here that we should recognise when obsessing over detail in Ops runs. N. Wales is IMBY and the Ops show a dusting here. Given the ensemble spreads and likelihood of short-term drama occurring in the ACTUAL weather means I'm not stressed. I suspect we'll all be surprised at what actually happens. Seems another 48 hours is required to nail any level of detail. Great fun!

If the fun stops. Stop. 

[iceman1991]

8 minutes ago, northwestsnow said:

Thats great news for those further south and indeed for all of us imo.

 

 Backs up what recent memory office update saying

[iceman1991]

5 minutes ago, Djdazzle said:

I’m assuming that MOGREPS is fully onboard with the easterly, as the Met seem confident.

Oh yessssss 

[stodge]

Just now, Bartlett High said:

A disappointing night for cold weather fans?? 

Yes, I think so certainly in terms of longevity if not necessarily severity.

All the models are bringing milder air back in by T+240 so that's a 5 day cold spell maximum. I'm struggling to see any model prolonging the cold spell beyond that at this time.

The problem is as the heights in Scandinavia fail and slip SE they stop the trough sliding into Europe and it moves up north over the British Isles.

[Matt H]

Not sure if it has been posted but the JMA 12z is a stonker out to t132.

[Tim M]

16 minutes ago, chionomaniac said:

if you are really unsure of how the output affects your own location then the best place to ask is your regional discussion area.

If we all do that, then we will be less stressed or annoyed about posters taking their own regional perspective about the model output and a lot more sympathetic to each and everyone’s own take.

It really isn’t that difficult to do!

But what if you don't know which regional thread to use :-)... my location - Mansfield -  always falls between 2! Joking aside, I agree re the sentiment though after reading so many 'downgrade' posts when there clearly has not been a downgrade of the cold spell as such, just how it may affect a particular area after a particular run. 

[kold weather]

10 minutes ago, Singularity said:

 

For what it's worth, I expect there would be more in the way of showers and mesoscale disturbances than what the ECM 12z shows for its scenario. The first of those appeared for Saturday night on that particular run. I really noticed that for an obvious reason! Can't take its position literally of course.

 

You never can quite tell with these set-ups, the ECM keeps ramming in disturbances into the NE but I can't imagine they wouldn't rotate around the lows axis.

Historically though its always been very much 50-50. Sometimes I've looked at a set-up and thought that must bring disturbances, and then its bone dry. Equally other times it looks iffy and yet we get disturbances galore come along in the flow.

I'd still argue all day long that your going to be far better off north of the LP core axis than south of it, regardless of whether the LP ends up over norfolk, Belgium or Newcastle. That basic summary holds IMO regardless. Its just how much convection can we bring into the south if the LP is too close and we end up with an overland flow for much of the southern half of the country.

[Bartlett High]

6 minutes ago, stodge said:

Yes, I think so certainly in terms of longevity if not necessarily severity.

All the models are bringing milder air back in by T+240 so that's a 5 day cold spell maximum. I'm struggling to see any model prolonging the cold spell beyond that at this time.

The problem is as the heights in Scandinavia fail and slip SE they stop the trough sliding into Europe and it moves up north over the British Isles.

But you must concede to the fact you are talking about day 10 which is very much subject to change?

[Scandinavian High.]

14 minutes ago, northwestsnow said:

Thats great news for those further south and indeed for all of us imo.

 

That’s good news thanks for sharing maybe might stop some banging on every two minutes about south east not get any snow.

[Frosty.]

I’ve seen enough evidence, more than enough evidence from the models today that there’s a very cold spell on the way from this weekend, tonight’s ECM 12z ensemble mean strengthens my view on this even more!...how long will the freeze last?...that’s above my pay grade but I’m excited about what’s ahead of us..very!

️ 

 

Edited February 2, 2021 by Jon Snow

[Chesil View]

7 minutes ago, stodge said:

Yes, I think so certainly in terms of longevity if not necessarily severity.

All the models are bringing milder air back in by T+240 so that's a 5 day cold spell maximum. I'm struggling to see any model prolonging the cold spell beyond that at this time.

The problem is as the heights in Scandinavia fail and slip SE they stop the trough sliding into Europe and it moves up north over the British Isles.

Only the models we can see none of which have decent verification stats at day 10.

[Kentspur]

5 minutes ago, Scandinavian High. said:

That’s good news thanks for sharing maybe might stop some banging on every two minutes about south east not get any snow.

Nope this suggests I was on to something- only presenting here what the models are showing and its a downgrade from the 0z suite as well as the op being on the colder end of the ensembles for the most part, but I guess it could just as easily upgrade again tomorrow such is the fixed nature of the models.

Anyway enjoy your narnia winter Northerners I'm not jealous

Edited February 2, 2021 by Kentspur

[stodge]

3 minutes ago, Bartlett High said:

But you must concede to the fact you are talking about day 10 which is very much subject to change?

Indeed and if it were just one of the main models I wouldn't be concerned but looking across the board I don't see anything that prolongs the cold spell.

Even the UKMO at T+144 looks poor as does JMA if you want to see the pieces for a prolonged cold spell. I'm not questioning it would be quite severe especially in the north but tonight GFS has backtracked on the severity further south and, as last night, there's no sense of longevity. 

Of course, the block could be more durable and the LP might continue to shift into Europe but I don't see it on the main models at this stage.

[supernova]

Trigger low positioning absolutely crucial to achieve a lasting and expansive result for coldies and as one might expect at this range, we're really none the wiser.

Irrespective of whether the West or Central/Northern regions have had any snow or not this winter (and accepting that Lincs/EA/SE have largely had bugger all), there's still plenty of time for the low to transition to hero or, sadly, zero. Nothing unusual in these "classic" Easterly set ups - often so fickle.

The mean is mostly our friend, at least, not just on the ECM but also the GEM, and the UKMO/Met remains fully on board. That the hi-res Det and Control are bang in the middle of the ensembles until FI also gives me more than a crumb of comfort. Keep the faith. We'll know soon.

Edited February 2, 2021 by supernova

[Sweatyman]

13 minutes ago, Frosty Winter said:

Not sure if it has been posted but the JMA 12z is a stonker out to t132.

opposite of last night then!

[stodge]

2 minutes ago, Broadmayne blizzard said:

Only the models we can see none of which have decent verification stats at day 10.

If something like MOGREPS is showing a prolonged cold spell past T+240 fine, as you say, I can't say it. 

I can only go by what I see and looking at the Mean charts into medium and longer term, the fact is the Atlantic trough aligns positively drawing heights up to the south west and it's a mild SW'ly by T+240.

[Battleground Snow]

As expected la Nina is now in the weak range. This along with AAM rising, MJO in the western Pacific and the strat warmings, it bodes well for the rest of winter, wouldn't take too much notice of models dropping blocking after 216 atm

ECM mean looks very much like the gem to me, still plenty of time for changes with regards to where that low ends up at 120-144

[Griff]

2 minutes ago, Battleground Snow said:

As expected la Nina is now in the weak range. This along with AAM rising, MJO in the western Pacific and the strat warmings, it bodes well for the rest of winter, wouldn't take too much notice of models dropping blocking after 216 atm

ECM mean looks very much like the gem to me, still plenty of time for changes with regards to where that low ends up at 120-144

Specifically, interest with regards to latest strat warming, could be a surprise or two..

[Paul_1978]

37 minutes ago, chionomaniac said:

A bit of moderation advice for everyone.  It is only human nature for all to look at how the synoptic situation affects them at their location.  It is not a crime, or bias for anyone to do this - rather a natural response to those viewing the output. So, we don’t need to hear outcries of bias, selective viewing or anything similar.

When looking at whether someone says that it is a good or bad run it is worth taking into consideration their location alongside any output to get a better understanding of how that run affects them and influences their outlook. 

I am happy for any member here regardless of location to see the weather they desire, but I first and foremost will look at my own location first, and do not begrudge others doing the same.

Especially, as the timeframe we are looking at is not set in stone and subject to substantial changes, whether it be shifts north or south, or west or east. So, don’t get annoyed by anyone’s own location perspective, and if you are really unsure of how the output affects your own location then the best place to ask is your regional discussion area.

If we all do that, then we will be less stressed or annoyed about posters taking their own regional perspective about the model output and a lot more sympathetic to each and everyone’s own take.

It really isn’t that difficult to do!

All excellent points - however a poster's location does not show when browsing the forum on mobiles. Would be good if this could be added to the mobile view.