Model Output Discussion 01/09/17

[knocker]

Interesting that the ecm has picked up on the explosive cyclogenesis this run. At 12 Wednesday it has a low 999mb  south of Iceland on the western flank of the ridge where it is picked up by the strong jet running north east along the latter and by 12 Thursday is 961mb just south of Iceland.with the associated fronts already bringing heavy rain and severe gales to N. Ireland and Scotland. These quickly track east and south east bringing gales and rain to the rest of the UK as the low tracks ESE to be just north of Thurso by 12 Friday. It then slowly moves down the North Sea veering the wind northerly over the UK.

Edited November 9, 2017 by knocker

[blizzard81]

5 minutes ago, Tamara said:

Best that I interject at this point.

That is a GEFS forecast which has a low angular momentum bias, notwithstanding that the background pattern is inclined to La Nina

In my opinion its rather the opposite way around with regard your post. What has been happening is effectively "destructive interference" with the La Nina state. There is currently a relatively higher GLAMM state than seen since mid summer - but still only taking total global atmospheric angular momentum a little above -1SD.

The atmospheric decoupling from the ocean base state is the result of a significant eastward propagating MJO wave during October

Its feedback loops from the eastward propagating tropical convection in October that added westerly wind inertia into the atmosphere, boosting atmosphere angular momentum tendency. There is a text book lag time of about 3/4 weeks for the amplification mechanisms created by this amplitude convection to manifest in the atmospheric circulation. Look at the massive leap in AAM tendency starting from the beginning of Octobers high amplitude wave which culminated  mid month. From -4SD to +3SD - quite some ying-yang elastic band effect set in motion   NWP is now showing the fruits of the considerable consequential amplification injected into atmospheric circulation taking into account that lag. 

The westerlies added to the system negate the overriding net total of easterly trades in global windflows which are a product of La Nina and consequent low atmospheric angular momentum.

The rossby wave trains from tropical convection propagate polewards and help to perturb a fledgling vortex. On the basis of the size of the October bounce in AAM tendency no surprise to an early season vortex struggle.

The question is what happens when the MJO feedbacks wane, and the downstream tropospheric amplifying mechanism is lost. This allows the typical La Nina pattern(with low atmospheric angular momentum) to dominate with the jet flowing over the anomalous Nina ridges in the Pacific and Atlantic - possibly at the same time as vortex intensification occurs. That is not a ticket to a -NAO/-AO combination in the future. Quite the opposite - we can't be thanking crashing GLAMM for setting in motion the processes for "building blocks" to a sustaining cold pattern

Time will tell of course, but the pattern indicated by the models heading through this month to the approach of start of winter could simply be a vortex pre-intensification phase characterised by cooling upper layers in the stratosphere descending and flushing out the warmer troposphere/lower stratosphere negative zonal anomalies.

There is unlikely to be any further assist from the MJO until later in December, based on periodicity of the next likely amplitude MJO wave (45 to 60 days). And with La Nina consolidating and the wavelengths changed with the new season, a next amplitude wave could well have a lot more on its plate in terms of making headway across the Pacific to help amplify the pattern downstream

The North Pacific ridge, characteristic of La Nina, will likely dictate the downstream pattern to a further Atlantic ridge - and La Nina favours increased polar jet flow heading over the anomalous circumglobal ridges. The ticket to a -NAO is a southern stream c/o rossby waves triggered by convection passing the dateline. That comes with a weak Nino signature which is not at all likely to be present this side of the New Year, at the least

 

So in a nutshell, coldies make the most of the possible end of November cold spell? 

[northwestsnow]

Edit, keeps showing yesterdays ecm day 10 when trying to post todays chart?

All in all , an excellent ecm with plenty of cold seasonal weather to enjoy.:)

Edited November 9, 2017 by northwestsnow

[bluearmy]

1 minute ago, northwestsnow said:

Yes please ecm- all moving along swimmingly for coldies- Atlantic blocked, and snow showers moving into NI/NW scotland, initially likely higher ground only, hopefully extending to lower ground in the north.

So refreshing to see the zonal dirge of the last few late Nov/early Dec being kicked into the garbage bin.

Yesterday's chart ?

 

anyway, the eps dribbling out over the next 40 mins and coldies need to see a better run than this morning. The AO barely below -2 which is about half of where it was showing yesterday. the 12z GEFS is heading close to -5 which is the lowest ens run from any model 

whilst ops are ops and ens are ens, I would not be hanging my hat on a very amplified ecm op against an ens suite which was flatter and clustered poorly to deliver proper cold to nw Europe 

[northwestsnow]

1 minute ago, bluearmy said:

Yesterday's chart ?

 

anyway, the eps dribbling out over the next 40 mins and coldies need to see a better run than this morning. The AO barely below -2 which is about half of where it was showing yesterday. the 12z GEFS is heading close to -5 which is the lowest ens run from any model 

whilst ops are ops and ens are ens, I would not be hanging my hat on a very amplified ecm op against an ens suite which was flatter and clustered poorly to deliver proper cold to nw Europe 

Yes, i edited my post Blue, keeps showing yesterdays day 10, dont know why.

Anyway, while the meto keep the faith so shall I, fascinating model viewing for us geeks at the very least

[Chris.]

ECM 240+  09/11/17  

[Interitus]

21 minutes ago, Tamara said:

In my opinion its rather the opposite way around with regard your post. What has been happening is effectively "destructive interference" with the La Nina state. There is currently a relatively higher GLAMM state than seen since mid summer - but still only taking total global atmospheric angular momentum a little above -1SD.

The atmospheric decoupling from the ocean base state is the result of a significant eastward propagating MJO wave during October

Its feedback loops from the eastward propagating tropical convection in October that added westerly wind inertia into the atmosphere, boosting atmosphere angular momentum tendency. There is a text book lag time of about 3/4 weeks for the amplification mechanisms created by this amplitude convection to manifest in the atmospheric circulation. Look at the massive leap in AAM tendency starting from the beginning of Octobers high amplitude wave which culminated  mid month. From -4SD to +3SD - quite some ying-yang elastic band effect set in motion   NWP is now showing the fruits of the considerable consequential amplification injected into atmospheric circulation taking into account that lag. 

 

There is no time lag in these two charts, they are concurrent. The tendencies just reflect the changes in the global anomaly chart - this is not taking 'til now to be reflected in NWP. A low GEFS bias notwithstanding, the forecast GLAAM anomaly is markedly lower than the chart of past 90-day anomaly.

[chrisbell-nottheweatherman]

3 hours ago, knocker said:

The gfs is like a dog with a bone vis the explosive cyclogenesis albeit it has dropped the more bizarre interpretations. This could still bring blizzard conditions to Scotland if perchance it came to fruition

.

That's a powerful jet streak, Malcolm - presumably the effect is to negatively-tilt the trough, but do you think the heights are insufficient to force the resulting deep low to undercut the high, or will the pressure gradient force overpower it and allow the low to take the left exit at the base of the diffluent trough?

[comet]

30 minutes ago, blizzard81 said:

So in a nutshell, coldies make the most of the possible end of November cold spell? 

I would not worry yourself to much, we had plenty of this in depth analysis during the summer, last winter etc, etc which at times was less than accurate shall we say. There are no experts on this or any other forum that know what lies ahead during the coming months.

[Man With Beard]

So the ECM op has gone from the most extreme mild end of the spread this morning to nearly the coldest end this evening. And very different to last night's D10 too!

My guess therefore is that the precise interaction between the Arctic High and the Atlantic low is going to be a right pain to pin down.

 

[Northwest NI]

53 minutes ago, Tamara said:

Best that I interject at this point.

That is a GEFS forecast which has a low angular momentum bias, notwithstanding that the background pattern is inclined to La Nina

In my opinion its rather the opposite way around with regard your post. What has been happening is effectively "destructive interference" with the La Nina state. There is currently a relatively higher GLAMM state than seen since mid summer - but still only taking total global atmospheric angular momentum a little above -1SD.

The atmospheric decoupling from the ocean base state is the result of a significant eastward propagating MJO wave during October

Its feedback loops from the eastward propagating tropical convection in October that added westerly wind inertia into the atmosphere, boosting atmosphere angular momentum tendency. There is a text book lag time of about 3/4 weeks for the amplification mechanisms created by this amplitude convection to manifest in the atmospheric circulation. Look at the massive leap in AAM tendency starting from the beginning of Octobers high amplitude wave which culminated  mid month. From -4SD to +3SD - quite some ying-yang elastic band effect set in motion   NWP is now showing the fruits of the considerable consequential amplification injected into atmospheric circulation taking into account that lag. 

The westerlies added to the system negate the overriding net total of easterly trades in global windflows which are a product of La Nina and consequent low atmospheric angular momentum.

The rossby wave trains from tropical convection propagate polewards and help to perturb a fledgling vortex. On the basis of the size of the October bounce in AAM tendency no surprise to see an early season vortex struggle.

The question is what happens when the MJO feedbacks wane, and the downstream tropospheric amplifying mechanism is lost. This allows the typical La Nina pattern(with low atmospheric angular momentum) to dominate with the jet flowing over the anomalous Nina ridges in the Pacific and Atlantic - possibly at the same time as vortex intensification occurs. That is not a ticket to a -NAO/-AO combination in the future. Quite the opposite - we can't be thanking crashing GLAMM for setting in motion the processes for "building blocks" to a sustaining cold pattern

Time will tell of course, but the pattern indicated by the models heading through this month to the approach of start of winter could simply be a vortex pre-intensification phase characterised by cooling upper layers in the stratosphere descending and flushing out the warmer troposphere/lower stratosphere negative zonal anomalies.

There is unlikely to be any further assist from the MJO until later in December, based on periodicity of the next likely amplitude MJO wave (45 to 60 days). And with La Nina consolidating and the wavelengths changed with the new season, a next amplitude wave could well have a lot more on its plate in terms of making headway across the Pacific to help amplify the pattern downstream

The North Pacific ridge, characteristic of La Nina, will likely dictate the downstream pattern to a further Atlantic ridge - and La Nina favours increased polar jet flow heading over the anomalous circumglobal ridges. The ticket to a -NAO is a southern stream c/o rossby waves triggered by convection passing the dateline. That comes with a weak Nino signature which is not at all likely to be present this side of the New Year, at the least

 

There's always next year.

[feb1991blizzard]

4 minutes ago, Man With Beard said:

So the ECM op has gone from the most extreme mild end of the spread this morning to nearly the coldest end this evening. And very different to last night's D10 too!

My guess therefore is that the precise interaction between the Arctic High and the Atlantic low is going to be a right pain to pin down.

 

Any news on the ext eps yet? The 240 doesn't look as promising as the GEFS I have to say.

[bobbydog]

7 minutes ago, comet said:

I would not worry yourself to much, we had plenty of this in depth analysis during the summer, last winter etc, etc which at times was less than accurate shall we say. There are no experts on this or any other forum that know what lies ahead during the coming months.

i think it reflects the challenges faced in trying to predict the behaviour of the dynamic, multi-faceted, often chaotic force that is the atmosphere, rather than "less than accurate" analysis on any individuals part....

[weatherguy]

Good evening all, I'm back for another winter of cold chasing!

I know the chart on the right is a beauty and (rightly so) is a stonker for what it could bring, but it's interesting actually looking at the current state of play - atlantic is remarkably quiet for this time of the year when traditionally we should be bearing the brunt of a zonal onslaught just praying for strat developments...

It will certainly be interesting to see how the disconnect between the trop and strat vortices plays out.  Current output highly encouraging stuff!

[weirpig]

15 minutes ago, comet said:

I would not worry yourself to much, we had plenty of this in depth analysis during the summer, last winter etc, etc which at times was less than accurate shall we say. There are no experts on this or any other forum that know what lies ahead during the coming months.

Yes I'm still waiting for that bloody torpedo to land . It's been up there for a couple of years now 

[knocker]

16 minutes ago, chrisbell-nottheweatherman said:

That's a powerful jet streak, Malcolm - presumably the effect is to negatively-tilt the trough, but do you think the heights are insufficient to force the resulting deep low to undercut the high, or will the pressure gradient force overpower it and allow the low to take the left exit at the base of the diffluent trough?

The latter. I can't post the 00 chart but the trough is in the process of becoming negatively tilted here as the strong jet swings NE around the high.

 

[swfc]

5 minutes ago, comet said:

I would not worry yourself to much, we had plenty of this in depth analysis during the summer, last winter etc, etc which at times was less than accurate shall we say. There are no experts on this or any other forum that know what lies ahead during the coming months.

Id agree there.after many years of watching and studying weather it always seems to stump you.given the met ete are reluctant to forecast beyond 7-10 days kind of says it all I guess.obv they punt at a general theme but even pinning down the output run to run daily looks dubious atm.respect to the seasoned posters with the solid back ground signals ete but im more of a suck it and see person.looking at what I can see and a block of sorts looks on the cards but any longevity is anyones guess.to far west and we stay on the wrong side of any polar activity.to far north generally westerly influence .all in all great model watching for early november and zero raging sw winds!!!

[Chris.R]

 

[chrisbell-nottheweatherman]

2 minutes ago, knocker said:

The latter. I can't post the 00 chart but the trough is in the process of becoming negatively tilted here as the strong jet swings NE around the high.

 

As I suspected, thanks.  I think we perhaps forget the tendency of deep lows to swing to the north as they exit the Jet given that even neutrals or those who prefer mild winter conditions get caught-up in the idea of troughs undercutting heights further north.

Edited November 9, 2017 by chrisbell-nottheweatherman

[bluearmy]

10 minutes ago, feb1991blizzard said:

Any news on the ext eps yet? The 240 doesn't look as promising as the GEFS I have to say.

The upper greeny ridge becomes more marked as does the downstream euro trough - looks a bit better than this morning although not sure the AO will be any lower, looking at the arctic profile.

I think it’s time to look at the evolution of the eps from day 11.5 to day 9 over the past five runs to see if there is a correction evident when the eps get within their higher res at T240 

will get back to you on that in half an hour 

Edited November 9, 2017 by bluearmy

[northwestsnow]

1 minute ago, bluearmy said:

The greeny ridge becomes more marked as does the downstream euro trough - looks a bit better than this morning although not sure the AO will be any lower, looking at the arctic profile.

I think it’s time to look at the evolution of the eps from day 11.5 to day 9 over the past five runs to see if there is a correction evident when the eps get within their higher res at T240 

will get back to you on that in half an hour 

Thats pleasing Blue..absolutely hang my hat on the euro low - think Gp has talked about how critical this component is too.

Exciting times .

[Man With Beard]

15 minutes ago, feb1991blizzard said:

Any news on the ext eps yet? The 240 doesn't look as promising as the GEFS I have to say.

8.30pm-9.30pm for individual ensemble members, 10.30pm for clusters. 

[feb1991blizzard]

1 minute ago, Man With Beard said:

8.30pm-9.30pm for individual ensemble members, 10.30pm for clusters. 

Thanks, it confuses me but ive realised now, the times have changed, the means come out a lot earlier than last season.

[Man With Beard]

The mean D10 chart has just come out. That's a beauty for cold:

[feb1991blizzard]

5 minutes ago, Man With Beard said:

The mean D10 chart has just come out. That's a beauty for cold:

I know its a mean but IMO we still need the trough to be further South else even with a  good ens mean pressure signal in Atlantic / Greenland, it will only be glancing blows with a bit of wintriness for Scotland, I actually think that a straight N'ly wont suffice before months end nor will an E'ly, I think a NE'ly with a SW to NE aligned Greeny high smashing right through the pole giving us a few pushes is the best chance.

Edited November 9, 2017 by feb1991blizzard