Model output discussion - 5th December 2016 - Into Winter we go

[blizzard81]

20 minutes ago, Summer Sun said:

 

Ecm is determined to drag this one out. Fast becoming the attention seeking model

[bluearmy]

Following on from the info that Matt gives, the mean mslp late on the eps is around 1015mb whereas GEFS 1025 mb. Rather than have to guess what the eps mean, we know it's a toss of a coin. 

wonder which way exeter's DECIDER prodict will point? 

[Frosty.]

Tonight's Ecm 12z ensemble mean is not as bullish as the Gefs 're anticyclonic domination further down the road, it looks finely balanced with the atlantic knocking on the door and even entering NW Britain, it looks better the further SE you are.

Edited December 6, 2016 by Frosty.

[knocker]

The anomalies this evening are still very much on the same page and despite all of the so-called mayhem they have been the model of consistency of late. One proviso this evening is they do show a touch more amplification than yesterday evening and this perhaps was reflected in the det. output.

So to briefly reiterate the position. Aleutian HP; Canadian vortex lobe (cross polar connection to other lobe eastern Europe) which continues to advect very cold air into Canada and the US. and the quite influential trough orientated south east into mid Atlantic In the eastern Atlantic the Azores HP is still ridging to the south east of the UK..

Ergo the upper flow will continue to be from the WSW so temps will stay  above average, The aforementioned complex upper Atlantic trough will continue to spawn perturbations that will track NE on a pretty consistent jet ( it tends to get briefly interrupted by the transient ridging of the Azores) and thus the unsettled weather will favour the west and north of the UK. The proximity of the HP is doing us a favor by pushing the fronts and rain NE.

Moving on to the 10-15 period where the position is more iffy although it has to be said they are still singing the same song if not completely in tune.

The disagreement is around the orientation of the Atlantic trough and the Azores HP. The upshot is they cannot agree on where to ridge the Azores HP, over the UK or further to the east but given the timescale involved not a concern at this stage.Conclusion. Little change with perhaps the upper flow veering a tad, remaining changeable with temps returning to around average

Edited December 6, 2016 by knocker

[bluearmy]

NOAA shows a likely continental flow for eastern England knocks? Given that's a 7 day mean, looks like it could be a pretty chilly period for a fair chunk of the country. (The ec op was very chilly last few days in se England) 

[phil nw.]

Looking at the gefs clusters for the end of next week day 11 and they are pretty much 50/50 whether the high is far enough north to avoid the south westerly flow across the top.There a 4 clustering groups.The largest at 45% should be just about ok for surface cold but the rest are varying degrees of Atlantic influence over the top. 

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cslp&HH=252&ZOOM=0&ARCHIV=0&RES=0&amp

Would like to see them swing into a majority towards the high a tad further north to swing it towards a cold continental surface flow.

[stewfox]

Another day and another 24 hrs of model watching. 

Last night

Pub was a quite affair given the poor outlook with the microscopic review of any T240 charts , do Lativa have any charts ?

What we watch (long range model output) and what we see (looking out of the window) don’t match. Have they F*** ever ? This seemed to be the theme last night.

This morning

First post was at 6.30am when at this time of year it should be 4.30am

Signs of a subtle shift in the models over night in the medium term. With less of a cross polar flow through the arctic and in turn a chance for pressure to migrate into Greenland.with signs of retrogression on many. That was at D16 but a decent elevated high.

We start to see some reamplification mid month (GFS)

We are reminded it will be barbecue weather tomorrow with 22 supporting charts (thanks for that)

Afternoon

Tweats confirm trough disruption T240 (welcome back trough) some folk suggest up to T240 no sign of anything cold

Fergie confirms “””with the result that both above and below avg temps are signposted as more likely than climatology and confidence remains very low” (ie throw a dice for cold)

Gfs 6z operational turns very anticyclonic from mid month onwards with more seasonal temps (ie cold rain)

Several  pages of  discussion re what GP means re early Jan outlook re day 26-33 and additional ‘debate’ over discussing anything post D16. Although to be fair no evidence yet of any posts "will it rain sorry snow in my garden on xmas day"

Evening

ECM pops up and post T240 is showing upstream troughing

However despite the bullish GFS ENS the 12Z EC ENS clusters are split 26/25 the 26 a very mild SW'ly type the 25 the blocked evolution so all to play for.

2/10 Cold (0 for background signals)

Positives. No heavy rain or wind

Negatives: 7 pages today , no strong signal for cold or anything that can push the model pages upto a respectable 20/30 pages .  More straws required to clutch onto

 

 

[Frank Trough]

3 minutes ago, phil nw. said:

Looking at the gefs clusters for the end of next week day 11 and they are pretty much 50/50 whether the high is far enough north to avoid the south westerly flow across the top.There a 4 clustering groups.The largest at 45% should be just about ok for surface cold but the rest are varying degrees of Atlantic influence over the top. 

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cslp&HH=252&ZOOM=0&ARCHIV=0&RES=0&amp

Would like to see them swing into a majority towards the high a tad further north to swing it towards a cold continental surface flow.

As a rank amateur (really rank),can I ask what will determine whether the high is far enough north to avoid the westerly influence? Will it be how much "propping up" there is, how much goes over the top, how the split happens at t+96? Or something else - perhaps my wife will ultimately decide? She's good at that. She's got Christmas sorted.

[Seasonality]

1 hour ago, mountain shadow said:

Retrogression to where? All i see is the bulk of the PV at Day 10 in the worst place possible, namely the Greenland local.

More spread out by day 16 though.

 

[karlos1983]

Nobody knows the answer or apperently it's poker and you can't show your cards. Fantastic 

[knocker]

13 minutes ago, bluearmy said:

NOAA shows a likely continental flow for eastern England knocks? Given that's a 7 day mean, looks like it could be a pretty chilly period for a fair chunk of the country. (The ec op was very chilly last few days in se England) 

Yes indeed blue. Depending precisely where the HP cell is residing a southerly or south easterly surface drift quite possible.

[fergieweather]

41 minutes ago, mulzy said:

Short ECM ensembles for De Bilt illustrate the high level of uncertainty past 120 hours

 

Yes, and so it continues...

That period remains the key point of divergence still: 12z EC DET ultimately traces towards it's lower range of ensemble spread for SFC temps (taking Reading as representative) and a cursory perusal of stamps further out by T+168 suggests only around 12 members in unequivocal support of the truly anticyclonic deterministic run.

Essentially it's another of these will-it-won't-it chapters of low confidence, of which we've seen a few recently into similar model lead times. The bimodality of clusters further on through 12z EC's run is striking and has been a theme of recent output from that suite further into December (as with GloSea). Trend heads to below avg temperatures further into 15d timeframe, but (as yet) unconvincingly so and with scant sign of anything desperately cold anyway (not that we expected any sudden appearance of pronounced cold, based on GloSea and EC Monthly).

Edited December 6, 2016 by fergieweather

[phil nw.]

1 minute ago, Certain kind of fool said:

As a rank amateur (really rank),can I ask what will determine whether the high is far enough north to avoid the westerly influence? Will it be how much "propping up" there is, how much goes over the top, how the split happens at t+96? Or something else - perhaps my wife will ultimately decide? She's good at that. She's got Christmas sorted.

Basically more amplification in the upstream Jet so we see Atlantic troughing dig further south and blowing up the high ahead.Something along these lines

Once we see the jet weaken coming east off NA then it's starts to waver or split and this gives the opportunity for downstream better ridging.A strong jet will tend to drive over the top of the high and flatten it ,Currently we are trending towards a mid-latitude high such as favoured by the ens,this indicates a split jet where some of the energy does go underneath to stop the high sinking.

Not very technical but the bottom line is the weaker the jet the more amplification and splitting we see in it's general flow.

[Frank Trough]

So when we sort out t+120 the "bimodality" may disappear? 

[phil nw.]

12 minutes ago, Certain kind of fool said:

So when we sort out t+120 the "bimodality" may disappear? 

I wish it was that simple,lol.Nothing is ever certain with modeling the weather.Once we look beyond around 4/5 days then as we know increasingly different solutions emerge the further out we look.

The stark division in the ensembles is because the Atlantic jet is being modeled to divide it's energy between going north and south rather than a straight forward strong northern arm of the jet over the top.If in future more goes across the north then it would preclude any deep cold and we would likely continue with mild south westerly winds until we see further signs of a change.Of course the other option of the northern arm of the jet being blocked off so it all goes south is what most of us are looking for.

At the moment we are looking at the mid-latitude high solution but the mystery is where this may go later.

As we can see from earlier posts the ens.outputs are very much finely balanced currently.

 

Edited December 6, 2016 by phil nw.

[nick sussex]

No ejection of the shortwave with it attached to the main trough is very bad news. Without that separating from the trough it will need a miracle to save this GFS run.

[Ali1977]

So it's finally balanced, but for what. If it goes Zonal then that's just UK standard stuff , if it goes blocked are we expecting deep cold - don't think so. Hard to get exited about it, but I'd take dry and cold nights any day

[feb1991blizzard]

5 minutes ago, nick sussex said:

No ejection of the shortwave with it attached to the main trough is very bad news. Without that separating from the trough it will need a miracle to save this GFS run.

 

I take it you mean the one that was ejected towards Scandinavia giving a better slither of heights on the last run but has re-phased on this run.

[nick sussex]

5 minutes ago, feb1991blizzard said:

 

I take it you mean the one that was ejected towards Scandinavia giving a better slither of heights on the last run but has re-phased on this run.

Yes you see the reason the ECM was the best of the big 3 early was that it had the quickest ejection of the shortwave which meant the upstream troughing wasn't pulled as far east. The shortwave acts as a tow to the trough. Its frustrating because the GFS has more dig south of that troughing at T132hrs than the earlier 12hrs.

Edited December 6, 2016 by nick sussex

[frosty ground]

2 minutes ago, nick sussex said:

Yes you see the reason the ECM was the best of the big 3 early was that it had the quickest ejection of the shortwave which meant the upstream troughing wasn't pulled as far east. The shortwave acts as a tow to the trough.

Can you explain how the shortwave is the driver rather than  a symptom of the overall pattern? 

[feb1991blizzard]

7 minutes ago, nick sussex said:

Yes you see the reason the ECM was the best of the big 3 early was that it had the quickest ejection of the shortwave which meant the upstream troughing wasn't pulled as far east. The shortwave acts as a tow to the trough.

Yes, I still think though nick we are struggling even with that favourable separation to get anything decent in the near future, I actually think on this occasion we are looking into deep FI for meaningful cold and its one situation where the shortwave track will be the difference between surface cold, perhaps even v.cold at surface or mild s.westerly and we are unlikely to get the sort of cold that delivers meaningful snow anytime before D14-16 regardless of which solution verifies.

Edited December 6, 2016 by feb1991blizzard

[nick sussex]

10 minutes ago, frosty ground said:

Can you explain how the shortwave is the driver rather than  a symptom of the overall pattern?

I'm not saying it is, its like the chicken and the egg. But when trying to explain quickly why the GFS wasn't as good as the ECM rather than writing half a page its easier to just deal with the bellwether which in this case is the shortwave.

I do seem obsessed with chickens and eggs! In this case chicken, the overall pattern, egg the shortwave.

Edited December 6, 2016 by nick sussex

[blizzard81]

Looks like the gfs 18z is going the same way as the 26 ecm cluster members which went mobile westerly. Not the trend I was wanting to witness tonight. The 18z is normally poor with regards to verification. Just watch it be correct this time though, ugh!

Edit - I may have jumped the gun there. First rule of model watching! It did look like the atlantic was about to pounce though.

Edited December 6, 2016 by blizzard81

[jvenge]

21 minutes ago, Ali1977 said:

So it's finally balanced, but for what. If it goes Zonal then that's just UK standard stuff , if it goes blocked are we expecting deep cold - don't think so. Hard to get exited about it, but I'd take dry and cold nights any day

Have to look at where the block was for 2009-2010 (was that the cold one?). The solutions churned out in ensembles show more a south of Greenland or Scandi, which although can deliver cold for the UK, it won't be cold of 2009/2010 winter. 

Just a word on the EPS weekly. It's week 3 evolution is different to the last run and that was different to the run before. For that reason alone I'm not viewing it too seriously. I can't see the individual members though, just control and mean. Maybe there is some clue hidden there among the individual members, but the mean and control are not consistent.

[feb1991blizzard]

This is still a better run long term IMO, higher heights and sharper ridging driving wave breaking nearer to the pole and further upwards in the stratosphere from both sectors.