[Model Output Discussion - Into November 2019]

29 minutes ago, Ed Stone said:

Most of the scatter, in today's GEFS 06Zs, is in SLP -- temperatures don't wander 'too far' from what the operational run is suggesting -- and today's run seems to broadly follow yesterday's 06Z, with its relatively mild easterlies...?

   

   

What to make of it?

Step by step, we are watching the huge tropospheric process developing and it takes time. All began last week in the Pacific which now leads to the creation of Scandinavian HP and Aleutian LP. This process is running later than the GFS predicted. Beginning of December/ tail end of November is the current prediction. 

 

This is is how a wave one enters the stratosphere and disrupts the TPV and eventually displaces the SPV. 

 

Pacific is ready to repeat this process but this time it will be during winter proper hence why many are the end of December and beginning of January for the true effects. Asia first then USA will go and Europe last. If all goes to plan.

[Cold hunt - models and chat]

20 minutes ago, Paul said:

Nick's take on the winter so far:

Winter 2018/19: Sudden Stratospheric Warming - But Why No Beast From The East?

Excellent observations from Nick F. In hindsight we all see that the El Niño in conjunction with the WQBO has me believing that  any periods of UK snowfall this winter, was quite an achievement. 

A momumental achievement against those two major forces. Long range models picked up the signal for blocking, although they predicted them to be higher up latitude wise. 

They were in effect correct just not on the exact positions of the HP cells. ( Very rare to see such long periods of HP dominating UK pattern/not to be confused with a Bartlett pattern)

 In my opinion that does not constitute as a forecast failure but simply that they could not accurately predict the effect of the downwelling WQBO and the continued tropical forcing/ thermal energy release from El Niño. 

So we face a transition period, that will only break when the tipping point is reached. What we want now is for this pattern to hold through the summer months.

When the + NOA pattern does break and it will, HLB will become more fesiable. 

If asked. “Will we ever see a repeat of 2010?” My answer would be yes. 

It requires specific parameters I.e solar minimum, EQBO and above neutral ENSO state. 

 

[Model output discussion - 7th January onwards]

1 minute ago, danm said:

Could you explain the implications?

In short form, this cold spell will have significant longevity. It’s the cause of upcoming -AO, cold air cannot return back into Arctic region and so remain in the mid latatudes I.e UK 

[Model output discussion - 7th January onwards]

2 minutes ago, Catacol said:

That's intriguing......what's the trend today? I envy you lucky early data-birds....

Yesterdays data already has shown the ability for high pressure to oscillate between Scandinavia and Greenland regions. I’m intrigued.

[Hunt For Cold: Model Discussion - Heading Into Christmas]

37 minutes ago, bluearmy said:

One would hope he isn’t just referencing a qtr but the probably absence of any downwelling wave in jan

we can all see the lack of a QTR across the modelling 

I don’t expect to see a QTR until wave 2 develops. SSW/wave 1 is not enough, had I not observed wave 2 then I wouldn’t have been confident of a UK cold spell. 7-10 minimum to see true evolution of Stratospheric influences.

[The hunt for cold - Model discussion (late November)]

4 minutes ago, MR EXTREMES said:

quick question would this equal the record breaking feb 2018 ssw ?

Significant but SSW can reach up to 25-30C.

[The hunt for cold - Model discussion (late November)]

11 minutes ago, IDO said:

I thought the current cycle was WAFz going from the trop to strat leading to the PV push in the strat. That downwelling from strat to trop (PCH's) will come within a quick to 14-day time window after the reversal? Is that wrong?

No not at all. Trop lead with EAMT event that sends energy up(20-22nd Dec) Downwelling following reversal  from approx 23-24th Dec to oust the upper PV. Then Trop lead again 24th-26th into pole.

[The hunt for cold - Model discussion (late November)]

2 minutes ago, IDO said:

So from my untrained understanding, zonal winds will reverse between Dec 24 & Dec 29 (as per GEFS variations) and then maybe up to 14 days for a trop response? So by mid-next-week, we should see something showing in the GEFS that we could attribute to the SSW? We are heading into prime Wintertime, so for once an SSW can deliver some wintriness, rather than be wasted on a cool Spring! 

GFS is now showing effects currently. SSW displaces PV which allows Pacific WAA up into pole for negative AO. 

[The hunt for cold - Model discussion (late November)]

March 2018, the ECM failed to factor the effects of SSW and was late to portray the correct displacement effects down to the tropospheric level. Whereas the GFS had the right overall idea but failed with the correct Synoptics at the Trop level. When the ECM corrected its input (4 days later than GFS) it displayed the correct outcome. 

 

At 240z but models are following the same March 2018 resolution in reading SSW effects.

 

 

SSW equals PV displacement equals Pacific WAA equals -AO. That we know is certain. 

Strength of SSW (unknown at present). Is it enough to overcome dampening effect of upper WQBO remain unknown. 

[Model output discussion - The Hunt For Cold]

Why is the ECMWF not following the GFS?

For that you must observe what the ECM is showing for a specific atmospheric geographical region ie is high pressure propagating or does it have opportunity to propagate in the atmosphere above Greenland.

ECM’s data (A day behind on FU Berlin site) says no at present. It reaches 144z in line with GFS but from there it cannot accurately follow suit and retains the HP cell to move from Iceland out west of the Uk region.

So follow the higher levels above 500hPa to attain where and what direction High pressure can move towards. 

WQBO already at the 30 hPa level which does make an obstacle to get HLB but not impossible. 

I’ve been hesitant until I could see this window evolve. My confidence has increased to 65% lilkehood of sustainable cold spell. 

[Model output discussion - Post SSW - Will it turn cold?]

24 minutes ago, Stu_London said:

As I recall, although the Model output at the time was pointing to a coldish outlook, the ECM (and most of it's ensemble set) went for a very extreme outcome for 1 run.

There is far more model agreement this time, both in terms of cross model consensus and consistencies between runs for the same model. Add this to the background teleconnections as a result of the SSW and things look a lot more solid this time round.

It should be noted that there are still 4 or 5 ensemble members on the 06z GFS that don't really ever get that cold, so a complete collapse is I suppose possible until we see those blues and purples heading over the North Sea and the low countries at +72 or so.

What would concern me more based on 15 years or so of model watching, would be that some historic cold spells have shown similarly epic output in the 8-14 day range only for very incremental downgrades to occur in terms of severity or longevity (or both) which has resulted in a bit of a watered down version when the spell actually arrives, albeit with some noteworthy snow events on occasions. The two instances that I can recall the event being as severe as the models were December 2010 and March 2013, the latter event offering some hope to us here as that was also a SSW event.

All factors count, with that in mind it is necessary to look at this event from all levels and not just at the 850 and 500 hPa levels.

 

SSW split the Stratospheric PV. 

That propagated down and was assisted by wave 2 to dominate the entire atmosphere from surface to upper Stratosphere. That opened the Arctic to HP. 

Wave 2 prevents the PV from reforming.

 

As the timings draw closer to surface reactions you only have to look at the Upper Tropospheric charts to observe how the Scandi HP can develop and hold position. 

Observe the 150 hPa. HP dominates the Tropospheric PV and holds the Atlantic via  the block.

 

It is these observable charts that encourage deep confidence with what the 500/850 hPa charts show, to actually come to fruition by next weekend. 

To take that further, you can follow the 150 hPa level charts to see when retrogression will or will not follow towards Greenland and to predict when the cold spell will end. Add a 2 day lag from 150 hPa level to 500 hPa for best results.

Remove the guess work and the confidence in long range prediction is increased. 

[Model output discussion - Post SSW - Will it turn cold?]

3 minutes ago, Daniel Smith said:

276.. 26th February.. still waiting for that cold air to come on over

Synoptically, good charts showing. Cold air wise? Rubbish.

28th February? Can the cold do it?

Nope. 

Minor changes would make big differences, of course. But I don't quite understand the cheering for this run given what is being offered elsewhere, this is a poor halfway house as far as the UK is concerned.

If it transpires with this actual outcome below and with a WAA of this magnitude.

You will see the formation of an Omega block on a magnitude not seen since 2010. You’ve got to realise that the more energy that goes up then the stronger the block when it closes off. 

This would be a very very special event.

[Stratosphere and Polar Vortex Watch]

1 hour ago, knocker said:

No sustained easterly then

 

 

Anthony has picked out a composition that results in best -NAO for the Eastern US. 

March 2013 would have featured had it resulted in a colder outcome for our cousins in the states. 

Watch the migration of the Euro HP- Travels west over UK, into the Atlantic and up towards Greenland. Gave them a late winter in 2001 with large amounts of snowfall.

2018’s -NAO is to travel NE from the Atlantic towards Scandi and then NW towards Greenland. 

Synoptics are very different. Outside influencing factors are also different.

I believe the US will get their West based -NAO in week 1 into week 2 of March, as the tropospheric PV moves Westward and breaks out into lobes. 

 

 

[Stratosphere and Polar Vortex Watch]

1 hour ago, Ruben Amsterdam said:

I do not quite see what you mean here. Surely, EC sees the reversal coming as it is output from the exact same model we look at in Berlin's Strat. plots vs. tropospheric output on meteociel. Perhaps, our current understanding of strat-trop dynamics limits our ability to accurately model responses to SSW events, but that's something different. And there is a possibility that the response is not as we all expect it (i.e. quick response, AO-), right? Not what we all hope for, but a possibility none the less.

The ECM sees the reversal. It’s just not within the range of the 10 day model outputs of this past weekend.

My post was in reference to those that were  writing off the SSW effects by not seeing the tropospheric response showing an Easterly with every output. When the time table was always pointing towards 21st-25th Feb, if all proceeded as expected. 

Minor displacements in the Stratosphere give us a -AO, I expect the same and much more from this event.

I felt that if the ECMWF’s Stratosphere and Troposphere modelling were in sync, that it would show the formation of a significant-AO. That didnt happen and therein lays my sole criticism of the ECM. 

As for the GFS, it sees the signal, it just doesn’t know where and what date to proceed with the correct solution. 

Ive put a timetable of my expectations and upcoming events and expect to die on my sword for trying to be an SSW oracle. All good.

[Stratosphere and Polar Vortex Watch]

Absolutely 100% agree with you as to the ECM’s current model output. It is not even registering the bare minimum of a -AO from this event as the effects of the SSW are out of its range at present. 

Minor displacement event at the beginning of Jan 2018

 

 

Required 12-14 days to register a -AO on the ECM

.

We don’t even have a reversal registering at the 10 hPa level at 60 N as per Berlin. Which will show by tomorrow or Tuesday at the latest.

 

 

So it stands to reason that in reality it does not know that it’s coming. As seen on the 10 Day model forecasts of this weekend.

 

 

Propagation towards the surface on the 14th/15th. 

WAAs to occur around the 17th-20th Pacific and Atlantic routes. 

Shortly after we should see an enforcement of  -AO from the WAAs.

21st-25th for -NAO. Scandi HP to show first until wave 2 dismantles the US vortex and hunts down the meandering Asian lobe.

 

Once that is complete we would be expecting to see retrogression of HP towards Greenland by the beginning of March. As the HP on Tropospheric level gains more in roads into US Trop PV.

 

Apologies for using your post Sebastian to vent on the failure of some to merely stand firm and watch the developments occur. 

 

[Model output discussion - proper cold spell inbound?]

UKMO has a strong -AO at 144z.

 

The GFS is now onto the correct solution. Scandi HP developing. Retrogression to Greenland is on the horizon. (20th approx)

 

[Model output discussion - proper cold spell inbound?]

“How I learned to stop worrying and love the SSW” Dr Strangelove. 

 

I have always attempted to keep my explanations of the atmospheric processes in the most basic of terms. Simplistic, yes but wanting them to be very understandable too.

SSW creates a split at the 10hPa level commencing over the next 24 hours. As seen below.

 

 

 

Inside the gap of the split vortices there becomes an opening for High pressure to locate to that position. 

We have seen several times this winter, the development of a -AO. Displacement of the PV off its natural peg hole- Greenland. 

The wave energy burns out and we see a return of the PV back to its natural position.

What we have now is not only displacement but also destruction of the PV and no return to its default position.

The SSW downwells enough that it allows upwelling from the surface (wave 2) access to an altitude and position that would be unattainable without the SSW.

That easterly winds exist in all levels from Mesopause to the surface. Firstly at the pole= -AO and the lower latitudes. 

Above see how the HP moves into the gap of where the upper Trop PV existed. We have a cross polar link up. 

Allow 2 day lag to make the same positions at 500 mb level. 

 

Then by the 17th Feb the -AO acts as an elbow into the face of the US daughter vortex and pins in down. While at the same time the vortex is attacked again leaving more certainty that the PV will not reform or reposition at its default for approx 4 weeks. That is if it can recover from such a brutal assault. 

The ECM has a better handle on the upcoming surface reactions. Strat/Trop PV is gone and so the -AO opens the way for a -NAO to develop. 

As seen below

 

I feel the GFS is struggling to interpret to upcoming developments and is messy in comparison. 

Hope this explains the quiet confidence of the SSW effects and the incoming surface responses based on logic, physics and the process.

 

 

 

 

[Stratosphere and Polar Vortex Watch]

46 minutes ago, Glacier Point said:

This is going to be a fantastic event to monitor.

A top tercile magnitude MJO event in the Indian Ocean leads to a potential record strength reversal in zonal winds, leads to what tropospheric impacts ?

Omega

[Stratosphere and Polar Vortex Watch]

1 hour ago, chionomaniac said:

No - If you have read all my posts over the last few days ( and I certainly don't blame anyone who hasn't lol !!!) then any Easterly is the first response as the Siberian vortex gets removed by the SSW. The second phase is the area more in doubt and that is whether or not we can get a -ve NAO with blocking to our NW and this very much will be influenced by what happens to the second daughter vortex - currently we are seeing a second phase warming which will reduce its intensity - so hopefully this brings the NAO down too.

Scandi tonic, GIN chaser. 

[Stratosphere and Polar Vortex Watch]

4 hours ago, comet said:

Seems to have backed off slightly from yesterday, it was showing reversal down to -10

Very marginal 1/2 km, it will change again tomorrow for sure.

[Stratosphere and Polar Vortex Watch]

The ECMWF has wave 1 tantalisingly close to full reversal. As it is so close many will have to watch stats up to and after the event.

 

Wave 2  is going to require the same observations

 

[Stratosphere and Polar Vortex Watch]

19 minutes ago, lorenzo said:

Given the similarities to 2009 have gone all geek and ripped some data from MERRA and plotted November to date for 08/09 and this season.

Attached is a pdf of Heat Flux 45 - 75N for 10,30,50 layers and the same again for W1 and W2.

This season the you can clearly see the rhythm and cadence in the heat flux. The W1 forcing significantly stronger.

Then, looking at W2 you get a feel for just how fierce Jan 09 was. Hopefully helps folks take a view of the two, couple of example images below.

 

 

SSW.pdf

 

 

What are your thoughts on Tropospheric responses? 

Decoupling between Trop and Strat PV by 10-14 days.  Then reliance on WAAs to disrupt  the Trop wave pattern into several extending lobes towards the lower latitudes.  As to where I’d only be guessing, very difficult to calculate. 

 

[Stratosphere and Polar Vortex Watch]

1 hour ago, Glacier Point said:

This feels like a long time ago now.

GFS advertising around the 13th February as key date. That's 36 days after Indian Ocean coupled convective wave passage, so the timeline bang on and yet again another example of the slow time scales for stratospheric - tropospheric events.

Who is willing to predict the NH Tropospheric scatter from this reversal. If the GFS is reading to split correctly and both lobes are hit with down welling it is effectively a continuous atmospheric shotgun blast. 

[Stratosphere and Polar Vortex Watch]

[Stratosphere and Polar Vortex Watch]

 

Pleasantly surprised with the energy contained inside the two initial pulses from wave 1 at the 1hPa level.

 

 

GFS is predicting PV relocation towards Eastern Canada a non to common event if it does transpires. Patience is a virtue of stratospherics but all worth it when we arrive at this point.