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

[Smiler1709]

1 hour ago, bobbydog said:

Yep.

And i'lI raise you a 1065mb on the parallel.....!

Funny thing is, the cfs model has shown on a few occasions this possibility going into Christmas week. Maybe just maybe it could be in to something 

[stodge]

1 minute ago, fergieweather said:

UKMO point-out the increasingly bimodal distribution of members in ECMWF Monthly by week 4. This explains the sudden appearance of bland temperature anomalies into that lead time, through a process of cancellation. Interestingly, latest GloSea5 also goes bimodal into same period, with the result that both above and below avg temps are signposted as more likely than climatology and confidence remains very low.

So it's either the shorts and BBQ or the onset of the next Ice Age for the next month or so.

I was going to make the same point about not taking these four week average charts too seriously. Two very cold weeks followed by two very mild weeks could be an average four weeks - I think some people see an average chart and assume it's going to be four weeks of average temperatures.

[EastAnglian]

12 minutes ago, Grimers said:

Well, I'd think if that chart is showing uppers then it'd be too warm for snow anyway.

I think you will find it is showing London 2m temperatures.

[fergieweather]

1 minute ago, stodge said:

I was going to make the same point about not taking these four week average charts too seriously. Two very cold weeks followed by two very mild weeks could be an average four weeks - I think some people see an average chart and assume it's going to be four weeks of average temperatures.

Yes, but they are used seriously but NOT on pure basis of an anomaly chart. Inspection of the individual stamps is essential. Anomaly fields are effectively meaningless viewed in isolation.

[Matthew.]

26 minutes ago, Summer Sun said:

Mean pressure remains high into Christmas week - only a handful of the ensembles take pressure sub 1020mb

The period from tomorrow to Sunday looks the mildest with temperatures more spring-like than anything else

Will be interesting to note Rainfall figures this month as December is usually the wettest month of the year. I wonder if a drought month could be recorded? Pressure high on them charts which is a good sign.

[Grimers]

1 minute ago, Matthew Wilson said:

Will be interesting to note Rainfall figures this month as December is usually the wettest month of the year. I wonder if a drought month could be recorded? Pressure high on them charts which is a good sign.

That looks unlikely...

 

[SMU]

11 minutes ago, fergieweather said:

Yes, but they are used seriously but NOT on pure basis of an anomaly chart. Inspection of the individual stamps is essential. Anomaly fields are effectively meaningless viewed in isolation.

Detail wise though in relation to the EC46 / Glosea runs - it would help us in terms of understanding a bit more detail if you could just extrapolate the bimodel differences WRT -

Is the split more - Cold blocked as per previous runs V the continued mobility we see now or

cold blocked runs V blocked returning however from a southerly quarter --

or a hash of them all- if its this latter then the earlier signal of blocking to the N/NE/NE will be somewhat muted..-

 

best

S

[bluearmy]

4 minutes ago, stodge said:

So it's either the shorts and BBQ or the onset of the next Ice Age for the next month or so.

I was going to make the same point about not taking these four week average charts too seriously. Two very cold weeks followed by two very mild weeks could be an average four weeks - I think some people see an average chart and assume it's going to be four weeks of average temperatures.

I think it's by week 4 rather than the four week period 

If this news (and it appears to be x model) continues on the Friday output,  searching around for the longer term indicators over the next week or two could be enlightening re the direction of travel.  one would say the strat is currently headed generally the wrong way for coldies if there is to be a strat/trop connective but the trop amplification modelled will help to drive waves higher up. 

[Singularity]

51 minutes ago, johnholmes said:

If these charts are anywhere near accurate in the time scales shown then pretty much all the LRF outputs look to be on dodgy ground. Professional and amateur, at least up to Christmas. Much head scratching as to what caused this. The tropical storm over Sri Lanka and SE India has been mentioned but I rather doubt that. One storm seems unlikely to have such a long term effect to me. I could be wrong so please drop your views in here please.

As far as I understand it, the tropical cyclone was part of a broader convective flare-up which has effectively 'hidden' the eastward propagation signal in convective and upper wind anomalies.

The big question now is whether, as the shroud lifts, we find the eastward propagation to be getting nicely underway or failing to meet expectations. The former should encourage a mid-lat block in our vicinity or just to our east next week, as convection could be quite active in the eastern Indian Ocean prior to a suppressed signal as the MJO crosses the Maritime Continent (this relating to regional heat and moisture anomalies). Later it would reach the Pacific and encourage our block to gain more latitude. The GFS 00z is a very good example of this progression (at long last!) and the ECM 00z has shifted notably in this direction. Ensembles will have a spread in propagation speeds so the means will still be significantly muted in terms of the 500 mb  flow - hence I rarely pay them all that much attention beyond the 5 day range in times of bisecting clusters. I wish a cluster-based anomaly chart tool was available online instead of just grand means.

If we find the propagation of the tropical signal to not be up to expectations then we're in trouble, as GLAAM falls, the pattern in the Atlantic-Europe sector flattens, we then lack much forcing with which to combat the downward propagation of the strengthened upper stratospheric vortex and... well, no wonder there are some milder signals in the long range models as well as the cold ones! Though I suspect the models will be too progressive with the downward vortex propagation (I believe there's a bias in there somewhere but I've not yet confirmed this).

So what happens in the tropics over the next fortnight is looking to be incredibly important with respect to the whole 2nd half of Dec 2016. Scary, I know!

[IM NOT REALLY HERE]

Can somebody please explain bimodal to me? 

[Singularity]

11 minutes ago, Grimers said:

That looks unlikely...

 

Models generally show the Thursday band fizzling out by the time it reaches The Southeast, leaving only Saturday in the foreseeable as a possible denier of a drought month in The Southeast, that of course depending on whether the frontal boundary becomes slow moving there while retaining some intensity.

There's still a good chance across much of the rest of England and perhaps even Wales too, given that droughts are based on percentages, not actual amounts.

According to Wikipedia: "A drought is usually defined as an extended period of weather (usually around 3 weeks) where less than a third of the usual precipitation falls."

In CS England it will have been 15 dry days in a row until the slight rainfall on Thursday so, given the increasing support for settled weather to return Sunday onward, it looks like Saturday will make or break an official drought period for 23rd Nov to 14th Dec.

For Dec as a whole it's really too early to say but given the dry signals mid-late month, if Saturday's rain ends up being an isolated appreciably-sized event, Dec is in with a chance IMO.

[Singularity]

Just now, IM NOT REALLY HERE said:

Can somebody please explain bimodal to me? 

Two different groups of outcomes in this case.

In the simplest sense, a bimodal distribution of observations finds something to either be one way or the other, with little or no evidence of anything in between 

 

[Sky Full]

Despite the models lowering the chances of any seriously cold weather before Christmas I take considerable comfort from the lack of any Atlantic storms worth the name being predicted to directly target the UK by either the GFS or the ECM in the foreseeable future.  In the absence of early ice and snow, I will take lower than average rainfall and no storm force winds over the next four weeks as a very acceptable alternative.  I think the models would be seeing an increase in Atlantic storms by now if they were going to happen in December so perhaps we won't see people flooded out of their homes at Christmas for once.

[bluearmy]

Para gfs 00z very amplified again later week 2

[IM NOT REALLY HERE]

7 minutes ago, Singularity said:

Two different groups of outcomes in this case.

In the simplest sense, a bimodal distribution of observations finds something to either be one way or the other, with little or no evidence of anything in between 

 

So basically they haven't got a clue? 

[fergieweather]

3 minutes ago, Singularity said:

Two different groups of outcomes in this case.

In the simplest sense, a bimodal distribution of observations finds something to either be one way or the other, with little or no evidence of anything in between 

 

Or in this case a clear split between the more mobile, milder outcomes versus those that are blocked/colder. As UKMO suggest, what may actually unfold is a hybrid of both: "At this stage, a return to a more blocked pattern is marginally favoured through the second half of the month; however this may manifest itself as slowly evolving transitions between more settled, colder and unsettled, milder periods."

[Man With Beard]

Typical - no sooner do I throw in my towel than the GFS op decides it will follow the colder ensemble cluster!

06Z coming out doesn't quite look as promising as 00Z, but the 00Z parallel looks interesting. D10 - UK High (which had been my preference up until 18 hours ago!)

D16 on the parallel - now you're talking - looks a good match for the ECM D46 at that time (not that I believe it of course  ) and Fergie's last comments on Glossea (not the ones he posted a moment ago).

The trend to look for now is the Atlantic upper low to completely stall south of Greenland. If that can happen, heights will eventually build to its east. But, perhaps as Fergie has just mentioned, it could be a process of several mini-lows going through the pattern as they spin around the upper low, edging heights incrementally into the eastern Atlantic as they pass through - until we get to something like the D16 chart on the parallel

Edited December 6, 2016 by Man With Beard

[Seasonality]

Just now, IM NOT REALLY HERE said:

So basically they haven't got a clue? 

No, not at all. It means the possible outcomes are split into two groups. Put simply, there are two groups of outcomes, one saying cold and one saying mild. So expressed as a mean they then get 'cancel each other out' as average.

[swilliam]

3 minutes ago, IM NOT REALLY HERE said:

So basically they haven't got a clue? 

I think the phrase that used  is highly uncertain until one solution is favoured over the other.

Edited December 6, 2016 by swilliam

[Catacol]

2 hours ago, Frosty. said:

Tomorrow somewhere in the uk should reach 15/16c 60f..BBQ and shorts weather between early / mid Dec..not bad huh!

Hehe - there we go - every cloud has a silver lining! Let's put the gloom of the last few days into the dustbin of history.

Talking of silver clouds - this forecast is good news for all snow hunters. MJO progression back on track... watch for more amplified runs hitting the ops over the next few days.

 

Remember all the MJO forecast sending us spinning down low into 2? Now back around into a higher AAM state. Oh ye of little faith. If the models don't get an initial handle on the most important drivers then op runs have NO chance of being accurate. Human input on this has been superior. Just need the spike to end up a little higher than this below.... probably explains MetO undercertainty in terms of 2 possible outcomes later in the month.

 

Edited December 6, 2016 by Catacol

[Ali1977]

GFS Op looks like sending WAA North at 300, similar to the 00z, with better height on the Alaskan side this could be a good far FI run with a complete PV split.

It's nice to reset and start looking at some more positive post and charts this morning, the ENS may increase this trend further.

Edited December 6, 2016 by Ali1977

[karlos1983]

I wouldn't chuck the 00z Para out of bed 

 

Edited December 6, 2016 by karlos1983

[booferking]

6 minutes ago, Catacol said:

Hehe - there we go - every cloud has a silver lining! Let's put the gloom of the last few days into the dustbin of history.

Talking of silver clouds - this forecast is good news for all snow hunters. MJO progression back on track... watch for more amplified runs hitting the ops over the next few days.

 

Can you please tell us less experienced what we are looking to see in the above charts. Thanks

Im thinking the draining away of heights to the south of us is good for a start?

Edited December 6, 2016 by booferking

[Paul_1978]

8 minutes ago, karlos1983 said:

I wouldn't chuck the 00z Para out of bed 

 

So which version of the GFS should we put credence in? The normal op or the Para? Does anyone know?

[Frosty.]

Well the Gfs 6z operational turns very anticyclonic from mid month onwards with more seasonal temps bringing night frosts and fog..I would settle for crisp fine weather in the run up to xmas. 

Edited December 6, 2016 by Frosty.