Stratosphere temperature watch - 2016/17

[ArHu3]

23 minutes ago, Weather-history said:

It was the best winter from 1997-98 to 2007-08 for the Manchester area according to the Manchester winter index, though.

I think SW Scotland and NI had two really big snowfalls that winter

I was looking at the Dutch data, perhaps that's why but if it's cold here you can bet it's very cold all through western Europe 

[Ruben Amsterdam]

I can't help but thinking that GFS outer FI is showing the onset of a proper SSW now. Ofcourse, very far away still, but not entirely unlikely given the persistent troposferic pattern. 

 

Edit: the GFS12z operational turned the warming signal slightly down, but it is still there. Meanwhile, we see the dipole pattern rotate somewhat, with main height anomalies over Canada and the cortex core over Northern Russia. I suspect we are very close to reversal at this point. The pattern is also present lower down (30hPa) and, if you would litteraly translate this down to the troposphere, one would expect the lowest gph to move slowly eastward over Scandinavia towards Russia while heights are rising over Greenland again. Do any of the more knowledgeable on the subject have any thoughts about this?

Edited November 2, 2016 by Ruben Amsterdam

[Interitus]

On 11/1/2016 at 01:17, snowking said:

The general strength of the prevailing westerly flow across our shores (think of it as driven by the jet stream) is caused by the thermal gradient (difference in temperature) between the colder stratosphere in the polar regions to our north and the warmer stratosphere of tropical regions to our south. The stronger this thermal gradient (i.e. When the polar regions are much colder and/or the tropical regions are warmer) the stronger the jet stream is likely to be and the less chance we have of colder incursions taking place from a meandering jet stream shape (i.e. The jet stream is flowing rather flatly from west to east).

However, the weaker this thermal gradient (when the polar regions are less cold and/or the topical regions are less warm) the weaker the jet stream and the more chance it has of splitting and meandering (i.e. Flowing from north to south rather than west to east) allowing colder air to flood down from the polar regions across parts of the northern hemisphere.

 

PLEASE NOTE: that's a very simplified definition and the main point to note is that the jet stream isn't necessarily the 'driver' in this situation, it's just the most simplistic way to think about what is happening in the troposphere and the significance of a cooler tropical stratosphere

Of course the jet stream is in the troposphere though, so it is the tropospheric latitudinal temperature gradient which is the primary driver of jet stream strength. However, cooler tropical stratosphere enhances tropical convection and cyclones and associated increased uplift can cool the tropical troposphere so it can possibly alter troposphere temperature gradient.

 

9 hours ago, MattHugo said:

We shall see!...mainly posting this as a reference point so can actually see whether the GFS was on to something here, but SSW forecast...

As pointed out by others though, this is 65°N, but close.

 

On 10/31/2016 at 09:41, Glacier Point said:

So the key question, what happens after that in the stratosphere ? Clearly at some point, any downwelling of easterly zonal wind anomaly from the upper layers will pull down colder air. The vortex will cool.

This statement 'pull down colder air - vortex will cool' is a little unclear. Pulling down colder air warms the vortex - that's largely what an SSW is.

[daz_4]

7 hours ago, ArHu3 said:

Winter 2000-2001 was very unremarkable in W-Europe though. The impressive 78-79 and 62-63 winters saw end januari ssw's 

The same in central Europe. Very warm winter.

[Methuselah]

You've all got me well confused...Could it be that the air moving from the stratosphere to the troposphere is merely warmer than it would otherwise be had no SSW ever occurred?

[Nouska]

5 hours ago, Ruben Amsterdam said:

I can't help but thinking that GFS outer FI is showing the onset of a proper SSW now. Ofcourse, very far away still, but not entirely unlikely given the persistent troposferic pattern. 

 

 

Edit: the GFS12z operational turned the warming signal slightly down, but it is still there. Meanwhile, we see the dipole pattern rotate somewhat, with main height anomalies over Canada and the cortex core over Northern Russia. I suspect we are very close to reversal at this point. The pattern is also present lower down (30hPa) and, if you would litteraly translate this down to the troposphere, one would expect the lowest gph to move slowly eastward over Scandinavia towards Russia while heights are rising over Greenland again. Do any of the more knowledgeable on the subject have any thoughts about this?

That pattern is very similar to what we saw at the end of January/beginning of February. Allowing for the fact we are now going into polar night rather than fully in it - could we expect to see similar on the ground patterns to what we saw in late Feruary and March - ie. finger of troughing through the UK with southerly disruption and a raw, damp continental feed.

[Interitus]

8 minutes ago, Ed Stone said:

You've all got me well confused...Could it be that the air moving from the stratosphere to the troposphere is merely warmer than it would otherwise be had no SSW ever occurred?

It's not the air moving from stratosphere to troposphere (STT) which is the issue here. Stratosphere-troposphere exchange (STE) is limited by the tropopause but of course it is important for circulation of ozone, pollutants etc and with regards to northern hemisphere STT, this appears to be greatest over the north Pacific/Atlantic storm tracks in the winter months, associated with tropopause folding. These folds can have important meteorolgical effects on cyclonicity - but is not really to do with SSW as such.

[lorenzo]

I had a query around the whole 65N or 60N nuance given the old school SSW definition, however given the excellent paper on the variety of definitions and how this sets the stage for where can we go from here in terms of classification, no longer precious about things!

Am just happy after years of teasing and looking, then looking again at the CW mode, we have something substantive to discuss, nice of Berlin to finally join us

 

[Ruben Amsterdam]

This mornings ensemble looks very promising with about 50% of the members opting for a reversal at 10hpa @65N. Only one member shows an "increase" of zonal wind speeds but mind you, that is only just above todays zonal winds which are unseasonably low. 

Edited November 3, 2016 by Ruben Amsterdam

[Glacier Point]

On 2 November 2016 at 17:08, Interitus said:

This statement 'pull down colder air - vortex will cool' is a little unclear. Pulling down colder air warms the vortex - that's largely what an SSW is.

OK, more precisely, NO_x pulled down from the layers above which bond with O₃ and facilitate additional complexes with chlorine and bromine both of which result in an endothermic reaction resulting in cooling.

Edited November 3, 2016 by Glacier Point

[JeffC]

1 hour ago, Glacier Point said:

OK, more precisely, NO_x pulled down from the layers above which bond with O₃ within an endothermic reaction resulting in cooling.

Wow! meteorology and A level physical Chemistry in one forum at the same time!

[Recretos]

I have some access to the extended ECMWF EPS model, with a 3-week lag, so I made an ENS plot of the 65N zonal mean zonal wind forecasts, which show that even tho some members were seeing the weaker vortex, the ENS mean in general was not as "agressive". But in all fairness, a lot of times not even the GEFS is as perfect for 10-16 days ahead.  

The most interesting part is, that the never runs will see the situation better, which might (or pretty much will) influence the ECMWF Seasonal model. 

 

And the latest 12z GEFS, with very good agreement, with the exceptions of members 4,6 and 8. 

And here is a graphic I made, which shows latest GEFS ensemble means, and it shows a decent negative bias from GEFS, which means that in the early forecast hours it underestimates the vortex strength, which mainly has to do with the positioning, and goes too low also in the later stages, which is also a case of positioning. A thing worth noting when interpreting GEFS ens mean forecasts. 

[bluearmy]

Some observations from berlin

strat waves - well above where you would expect to see for th beginning November 

 

temps (day 1 and day 10 - 'surely shum midhtake ed'.). Going the wrong way!!

. 

 

and finally looks like an anomalously warm wave headed into Europe post day 10 which isn't something I can't recall seeing at 10hpa - the upper vortex seems to be headed back to nw Siberia as a N American ridge grows. 

[Singularity]

A warm N America and a strong ridge, opposite a cold Siberia and the upper vortex... boy do the guns seem loaded this month!

I am very interested in seeing what may arise from the Atlantic troughs battling the N. Eurasian ridge later next week and beyond. If I have my thinking straight, this will depend on to what extent we see a mean tropospheric flow aligned to meet the Scandinavian mountains? I seem to recall from an article posted last year (but maybe not on this forum?) this being the reason why a mean trough that fringes into Scandinavia can be good for driving vertical wave activity flux.

[DOdo]

What does all this mean in Lay mans terms?

[Mucka]

1 hour ago, DOdo said:

What does all this mean in Lay mans terms?

The dice are loaded for more MLB and HLB during first half of Winter which would mean cold displaced from the polar regions to the lower latitudes of Europe and a higher probability than usual of cold to the UK.

[DOdo]

12 minutes ago, Mucka said:

The dice are loaded for more MLB and HLB during first half of Winter which would mean cold displaced from the polar regions to the lower latitudes of Europe and a higher probability than usual of cold to the UK.

Thank you

[Recretos]

Zonal mean temperature change, showing the warming strat top, and some (seasonal) cooling in the mid-levels. 

 

And the change of the zonal wind component, mainly showing the polar jet displacement, and a lack of any general polar vortex organisation. 

 

Height wise, as the south pole seasonally "weakens", the north side slowly drops heights, but without any real fast height drop, exccept for the 1-8 day period due to the shifting. Which is kinda obvious by now, from all fronts why.

 

Edited November 4, 2016 by Recretos

[blizzard81]

I guess the forecast ssw is off the table now?

[bluearmy]

2 hours ago, blizzard81 said:

I guess the forecast ssw is off the table now?

We don't need one anyway

i think the Berlin data tomorrow will look quite impressive judging by the 12z height charts. The upper vortex on its travels  back from Greenland to n w siberia. Clearly a connect with the trop as this journey corresponds with the uptick in the n arm. I'll take a mid month Nov let down on cold to get a Siberian vortex from top to bottom for the last third of the month!

Yesterday's run showed a reversal (SSW ) at approx 65 degrees north

 

Edited November 4, 2016 by bluearmy

[lorenzo]

Ebbs and flows on the u65N plot but no denying the vortex is a lightweight at present. 

Merra view of the aggregate U profile and also another round of heat flux forecast.

W1 peaks at 4 days and our vortex miles away from home at Day 10 on Berlin, Siberian wish looking good Nick.

 

 

[bluearmy]

Indeed Tony - struck by the upper zonal flow being deflected towards the equator by the wave activity towards the polar regions

the 06z gfs upper strat profile was rather different to the 00z and tended towards the 00z ecm though not as marked. If the 12z looks like the 00z then Berlin height charts will be worth a look in the morning. We could be drifting towards a pretty special last third of the month (and perhaps beyond). However, if the vortex decides to journey back to the Canadian side then we probably see another quite transient cold spell (with associated model thread let down) followed by a zonal flow or perhaps mid lat high with jet riding over the top. 

[phil nw.]

Looking at the Zonal wind anomaly for this quarter and it's a good illustration of a vortex running only in first gear so far

 

zonal winds around 10m/s which should be ramping up towards 20-30m/s in a stronger vortex season by now.

ECM-yesterday-showing a day 10 forecast at close to a reversal at 10hPa at 70N

not quite an official warming but it would certainly keep the vortex on the back foot. 

Edited November 5, 2016 by phil nw.

[feb1991blizzard]

10 minutes ago, phil nw. said:

Looking at the Zonal wind anomaly for this quarter and it's a good illustration of a vortex running only in first gear so far

 

zonal winds around 10m/s which should be ramping up towards 20-30m/s in a stronger vortex season by now.

 

If the GFS charts the other day would have verified, it could potentially have been running in reverse by mid November, never mind first gear!!

[lorenzo]

Little bit of an uptick and attempt to get in gear, still refusing to commit..

1000m wave extending to 10hPa on latest Berlin update, Vorticity looking light and this is furthest off the pole have seen the vortex programmed this season.

Interesting period ahead as we lose that Aleutian Low, potential AAM roll downhill following the torque events of recent note.

Final third of November an intriguing watch