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

[bluearmy]

12 minutes ago, karlos1983 said:

ECM ensembles appear to show a steep drop off at the end of the run! 

Was just thinking that the ecm extended temps  are the least suppressed set that we've seen recently !!

[feb1991blizzard]

They've gone back below 5c max's on the mean, the trick now is not just for the mean to bottom out where it is for a bit, its for the ladder continuing to be lowered by way of more members jumping to the cold cluster.

[Due South]

Can anyone explain the effects of a negative WPO. And what effects it will have on our side of the pond

[Glacier Point]

So, talk of the MJO showing some eastward propagation. That's not entirely the full story as it's more a case of the convective forcing located in the West Pacific showing greater influence rather than the index racing to catch up.

No doubt the composites will be wheeled out. But, crucial to consider the impact of the Global Wind Oscillation (GWO), which captures tropical and extratropical domains. We also need to consider potential reinforcement of high pressure signals and high latitudes over Northern Scandinavia and Kara Seas due to exceptional Arctic surface temperatures, weak zonal wind anomalies across the North Atlantic sector and polar vortex centred slightly displaced towards the Canadian interior with a secondary lobe over Siberia.

The GWO is centred in phase 6-7, with an amplitude of +1SD reflecting a high disconnect with the ENSO state.

The net impact of tropical convection in the Indian Ocean will lead to a downward correction in the next week. I have significant doubts on GEFS forecast for this though, so a drop to around near average climatology seems more likely.

With the MJO showing greater tendency towards the Western and Central Pacific, westerly inertia will be added to angular moment budgets. Note the consistent signal here for lowering velocity potential anomalies to develop in the Western Pacific with +ve anomalies over the Indian Ocean. That is a weakening (suppression) of the destructive interference on the base pattern and constructive enhancement.

Mountain torques will induce a fair degree of downstream amplification on the back of this.The GWO will show an attraction to phases 4 and 5, then 6 (duration of this uncertain), before a tendency towards phases 7 and 8.

Composites for these phases for December with El Nino years removed.

 > > 

So if we proceed as seems likely, the MJO shift in tropical forcing will signal lowering heights over Europe (I would shift the low further south and east to allow for adjustments for +ve heights over Scandinavia given polar vortex location). Thereafter, a retrograde and greater amplification signal for pressure rising to the north and north-west. Perfect timing. Note the strength of the anomaly for phase 6 !

The weak spot here is the Indian Ocean. If we see renewed convection here, that would be a signal for those warmer ensemble members but for now, if wheels are in motion, there's no way back until the MJO swings back through its traditional 30-60 day cycle.

The last para from current UKMET guidance:

"However, there will probably also be some milder, unsettled interludes too, and as we head into the New Year this may become more of a feature in our weather". 

I would be selling this position right now.

Edited December 6, 2016 by Glacier Point

[Iceaxecrampon]

Well after this weeks ridiculousness at least the ensembles are heading in the right direction.

CUMBRIA

Edited December 6, 2016 by Iceaxecrampon

[SteveB]

5 minutes ago, Glacier Point said:

So, talk of the MJO showing some eastward propagation. That's not entirely the full story as it's more a case of the convective forcing located in the West Pacific showing greater influence rather than the index racing to catch up.

No doubt the composites will be wheeled out. But, crucial to consider the impact of the Global Wind Oscillation (GWO), which captures tropical and extratropical domains. We also need to consider potential reinforcement of high pressure signals and high latitudes over Northern Scandinavia and Kara Seas due to exceptional Arctic surface temperatures, weak zonal wind anomalies across the North Atlantic sector and polar vortex centred slightly displaced towards the Canadian interior with a secondary lobe over Siberia.

The GWO is centred in phase 6-7, with an amplitude of +1SD reflecting a high disconnect with the ENSO state.

The net impact of tropical convection in the Indian Ocean will lead to a downward correction in the next week. I have significant doubts on GEFS forecast for this though, so a drop to around near average climatology seems more likely.

With the MJO showing greater tendency towards the Western and Central Pacific, westerly inertia will be added to angular moment budgets. Note the consistent signal here for lowering velocity potential anomalies to develop in the Western Pacific with +ve anomalies over the Indian Ocean. That is a weakening (suppression) of the destructive interference on the base pattern and constructive enhancement.

Mountain torques will induce a fair degree of downstream amplification on the back of this.The GWO will show an attraction to phases 4 and 5, then 6 (duration of this uncertain), before a tendency towards phases 7 and 8.

Composites for these phases for December with El Nino years removed.

 > > 

So if we proceed as seems likely, the MJO shift in tropical forcing will signal lowering heights over Europe (I would shift the low further south and east to allow for adjustments for +ve heights over Scandinavia given polar vortex location). Thereafter, a retrograde signal for pressure rising to the north and north-west. Perfect timing. Note the strength of the anomaly for phase 6 !

The weak spot here is the Indian Ocean. If we see renewed convection here, that would be a signal for those warmer ensemble members but for now, if wheels are in motion, there's no way back until the MJO swings back through its traditional 30-60 day cycle.

Lets hope There's no renewed convection in the Indian ocean then...........

[jvenge]

21 minutes ago, Due South said:

Can anyone explain the effects of a negative WPO. And what effects it will have on our side of the pond

I think it supposedly increases the chances of a colder than average winter for the US West Coast. 

[Due South]

1 minute ago, jvenge said:

I think it supposedly increases the chances of a colder than average winter for the US West Coast. 

Thank you for your reply

[Singularity]

As usual, excellent input from GP and Tamara to ease the nerves a little  

So where I was saying eastward propagation I should be saying the dominant signal switching to the W Pac. That'll be where the Hendon-Wheeler MJO plots can lead to false impressions - I was imagining the upper wind anomalies journeying from one convective centre to the other as the relative magnitudes changed around. You live a little, you learn a little .

I wonder if anyone knows of a site that plots model data for the Indian Ocean? I'd like to investigate what the ensembles are suggesting over there to try and gauge the risk of seeing renewed convection in that region. TIA 

[Gael_Force]

2 hours 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 

 

Hence the means mean very little if this is the case.

[Walsall Wood Snow]

27 minutes ago, Glacier Point said:

 

"However, there will probably also be some milder, unsettled interludes too, and as we head into the New Year this may become more of a feature in our weather". 

I would be selling this position right now.

Do you mean by this, has of things stand, you're expecting January to be mild and unsettled?

[karlos1983]

15 minutes ago, Singularity said:

As usual, excellent input from GP and Tamara to ease the nerves a little  

So where I was saying eastward propagation I should be saying the dominant signal switching to the W Pac. That'll be where the Hendon-Wheeler MJO plots can lead to false impressions - I was imagining the upper wind anomalies journeying from one convective centre to the other as the relative magnitudes changed around. You live a little, you learn a little .

I wonder if anyone knows of a site that plots model data for the Indian Ocean? I'd like to investigate what the ensembles are suggesting over there to try and gauge the risk of seeing renewed convection in that region. TIA 

This is an interesting site - http://tropic.ssec.wisc.edu/

Not sure if you find what you need, but you could end up in the right place. I got there by luck more than judgment 

 

Edited December 6, 2016 by karlos1983

[Glacier Point]

Can't comment on that time scale for professional reasons, but for first week of Jan, I would not be mild and wet. Instability yes.

[Walsall Wood Snow]

Just now, Glacier Point said:

Can't comment on that time scale for professional reasons, but for first week of Jan, I would not be mild and wet. Instability yes.

Thanks GP 

[Banbury]

2 hours ago, Frosty. said:

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. 

one of the milder options to be fair

[Frosty.]

So basically it's going to be generally unsettled and on the mild side for the most part until around mid month but with a nw / se split developing next week with the most unsettled and windier weather across the nw with the se having the longer dry and brighter spells between rainbands. From mid month high pressure starts to take over with temps returning closer to average and then anticyclonic conditions intensify with temps dropping below average / cold with widespread frosts and freezing fog..possible milder unsettled interludes but generally cold and blocked during the run up to and including the christmas period..could be worse!

Edited December 6, 2016 by Frosty.

[Guest]

11 minutes ago, Glacier Point said:

Can't comment on that time scale for professional reasons, but for first week of Jan, I would not be mild and wet. Instability yes.

Fronts disrupting against a block?

[Bristawl Si]

14 minutes ago, Walsall Wood Snow said:

Do you mean by this, has of things stand, you're expecting January to be mild and unsettled?

"Selling this position right now" i.e. Stuart doesnt support the meto pos re the New Year - i think i've interpreted correctly.

[Cleeve Hill]

1 minute ago, More Snow said:

Fronts disrupting against a block?

Thats the way I read it. 

[Catacol]

2 hours ago, booferking said:

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?

Darker blue colours represent cyclogenisis. In simple terms when these areas of convective activity reach the area north of Australia travelling eastwards the MJO is moving into phases 4/5/6. This is the cue for a more amplified northern hemisphere pattern in winter.

[Frosty.]

11 minutes ago, Banbury said:

one of the milder options to be fair

Compared to last Christmas the Gfs 6z would be great, crisp sunny days and frosty nights..perfick!

Edited December 6, 2016 by Frosty.

[tcc]

2 minutes ago, Bristle boy said:

"Selling this position right now" i.e. Stuart doesnt support the meto pos re the New Year - i think i've interpreted correctly.

GP's comment in question:

The last para from current UKMET guidance:

"However, there will probably also be some milder, unsettled interludes too, and as we head into the New Year this may become more of a feature in our weather". 

I would be selling this position right now.

----

Based on GP's above comment I think he meant to say "wouldn't" instead of "would" otherwise that would make it sound like he agrees with the Met guidance?

[bluearmy]

1 minute ago, tcc said:

GP's comment in question:

The last para from current UKMET guidance:

"However, there will probably also be some milder, unsettled interludes too, and as we head into the New Year this may become more of a feature in our weather". 

I would be selling this position right now.

----

Based on GP's above comment I think he meant to say "wouldn't" instead of "would" otherwise that would make it sound like he agrees with the Met guidance?

no, he's selling that. he doesn't want to be holding mild beginning jan 

[Glacier Point]

Selling, the opposite of buying ! Quite simple!

[Man With Beard]

GEFS ensembles - hopelessly split, as has become the recent theme. T240 - except just to our south, not much difference between these two charts considering the time-scale, yet possibly all the difference too: