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Some useful tropospheric developments upcoming which are likely to have stratospheric impacts towards the end of November and more particularly into December. A strong convectively coupled tropic

so after many days the GFS & FNMOC & canadian finally now follow the Euro with 44 out 64 Members with a split at day 9- The ECM is day 8. We will call it - SSW & Split for 1st Ja

For all that watch the zonal winds. Let me urge you to look at the geopotential heights more. At least as far as weakening/strengthening trends go. Because as the polar vortex cries for help, you migh

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A couple of questions

What caused the phenomenal blocking during the second half of March 2013?

NOAA_2_2013031906_1.png

Can a significant SSW have an impact on the following winter? I recall 10 years ago, we had a series of warmings in the stratosphere and then followed almost 3 years of -NAO.

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51 minutes ago, Weather-history said:

A couple of questions

What caused the phenomenal blocking during the second half of March 2013?

NOAA_2_2013031906_1.png

Can a significant SSW have an impact on the following winter? I recall 10 years ago, we had a series of warmings in the stratosphere and then followed almost 3 years of -NAO.

The March 2013 blocking was a result of the Jan 2013 SSW. If I remember right the downwelling of the SSW that year followed the composite picture almost perfectly (on mobile so don't have it), where the biggest and longest downwelling pulse happens a good 45 days after the SSW.

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1 hour ago, Weather-history said:

A couple of questions

What caused the phenomenal blocking during the second half of March 2013?

NOAA_2_2013031906_1.png

Can a significant SSW have an impact on the following winter? I recall 10 years ago, we had a series of warmings in the stratosphere and then followed almost 3 years of -NAO.

A combination of two factors.. 

1) Although zonal winds in the upper stratosphere recovered as expected after the SSW. They remained generally weak closer to the troposphere. 

https://acd-ext.gsfc.nasa.gov/Data_services/met/metdata/annual/merra2/wind/u60n_150_2012_merra2.pdf

(That's as low as NASA will let me go)

2) A significant wave event occurred in mid to late Feb which probably caused the surge of heights over the Arctic and since the tropospheric zonal winds were weak, we saw a good push. 

..

As you'll recall from about Nov 12 though the troposphere was being relatively kind to us anyway so a bit like the winter of 09 or this winter, i think that this was a winter where less of a push was needed. 

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MJO Composites for March. Phase 2 then phase 3. From left to right = 500mb all amplitudes of MJO, 500mb amplitudes >1, surface temp anomaly all amplitudes, surface temp anomaly amplitudes > 1

Phase 2 5a8035a20ab5c_ScreenShot2018-02-11at12_21_21.thumb.png.76a73b32814023352c9f817b4065a5d3.png  5a8035a94d5c3_ScreenShot2018-02-11at12_21_34.thumb.png.084ca7ccadf1d8119681719a5074e8f5.png  5a8035b18f679_ScreenShot2018-02-11at12_21_44.thumb.png.861668b501bf7eca6022e0d471b01908.png  5a8035b9cb007_ScreenShot2018-02-11at12_21_54.thumb.png.d4210d6421537a571399c53f7a476c07.png

Phase 3 5a8035c41f2fa_ScreenShot2018-02-11at12_22_07.thumb.png.0411729ee6861c2d40e6da29fa636a7a.png  5a8035cc4763b_ScreenShot2018-02-11at12_22_18.thumb.png.f069a22d0070f625025be0e102395a79.png  5a8035d1ed7e3_ScreenShot2018-02-11at12_22_28.thumb.png.f931b5e4bd1b2c3ce1ddff3281d40d32.png  5a8035d80a12b_ScreenShot2018-02-11at12_22_36.thumb.png.439687b6c1d1e933cc66932765676dda.png

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How fast the Siberian vortex swoops around to the Canadian one is something I can imagine the models struggling with.

Out if interest, if the stratospheric high over Asia was weaker, would the merger take longer I.e. has the sheer strength of that feature actually impeded the quick response to the initial SSW?

Not sure you see if the flow around such a feature necessarily didctates how fast the weak daughter vortex moves. 

 

I have also noticed that the precise orientation of the Canadian vortex is critical for just how fast the second major warming initiates and also how close to Greenland that becomes focused. Faster solutions with this have tended to block the movement of the weaker vortex west from Scandinavia for a day or two so it has relevance to the quick response potential as well.

Very complicated for the models and then there’s the MJO and changing atmospheric base state... it’s the mother of all conundrums!

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The more I look at this SSW situation the more I am drawn back to the 1999 warming. (I have mentioned this in here previous) A lot of the Trop drivers at the time were the same / similair compared to any other year. The time of year and the SSW type were Split and early / mid Feb. La Nina and E QBO. MJO in same phases with similar amplitude. Eddy heat flux at most height levels and 60N Zonal mean wind reversal similar. 

1999 Eddy heat flux at 10hpa / 50hpa then 150 hpa 5a806d017e661_ScreenShot2018-02-11at16_18_52.thumb.png.83d6e2725379b4a62f6ddf0cfdbc474f.png 5a806d25cc15e_ScreenShot2018-02-11at16_19_30.thumb.png.e5fb4f6034a51978fcc8c4758109a13a.png 5a806d9285b8e_ScreenShot2018-02-11at16_21_17.thumb.png.8f8e8981ebfac5570640270b4531d944.png  

2018.                                                                          5a806df2d5332_ScreenShot2018-02-11at16_22_50.thumb.png.34c46196b5bd567a5aacd53869fdd688.png 5a806e19bb1ee_ScreenShot2018-02-11at16_23_38.thumb.png.4117412409bf2c7e52b16985381adbcc.png  5a806e411f026_ScreenShot2018-02-11at16_24_13.thumb.png.a9bfdceb8d304632dce7be74b6ef4b86.png

 

1999 wind at 60N at 10hpa / 50hpa then 150 hpa.    5a806ed536367_ScreenShot2018-02-11at16_25_45.thumb.png.ead42878fb41fd1b5bf8a4c756924db4.png  5a806edf1e569_ScreenShot2018-02-11at16_26_01.thumb.png.d75804a0192a97afb4ac2fcc6f58facb.png  5a806f10050b5_ScreenShot2018-02-11at16_27_42.thumb.png.830d0b6246af8a57f94be2af09152133.png

 

2018                                                                          5a806f67104ed_ScreenShot2018-02-11at16_28_27.thumb.png.8fe6f76cdb684680182a0de3efb3e0ab.png   5a806f6d95035_ScreenShot2018-02-11at16_28_44.thumb.png.d68256eb575b370474c717dbb206f567.png  5a807e5417fab_ScreenShot2018-02-11at16_28_59.thumb.png.a0f1c0b2e1deffc2996e27bcfa0b0248.png

1999 - To me shows it took 2 hits over the winter to make the split happen, two wind reversal events over that winter both due to limited heat flux events.

2018  - we are having one whooping heat flux event causing the split, does this cause a different trop response to the one in 1999? I hope so because that wasn't great from a cold / snow perspective. Take your pick from any of the February and March BBC weather forecast on youtube to see for yourself.

Anyway here is a GIF of the 1999 split from the Patrick Matanaeu site. very similar in nature, split vortex takes similar paths and note the vortex lobe over Asia make its way back towards the Canadian vortex, similair to what we are seeing this time.

1999_03_01

Of course there are plenty of other trop conditions at the starting point that will be different from what happened in 1999 given the chaotic nature of the atmosphere and all the variables there are, I am not saying its game over for cold / snow. Purely an observation based on past events.

5a807f7bd1b39_ScreenShot2018-02-04at17_31_54.thumb.png.24fff9d4ec8f95e1222d851a217bf543.png the chaos......

 

Screen Shot 2018-02-04 at 17.31.54.png

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Screen Shot 2018-02-11 at 12.12.10.png

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Screen Shot 2018-02-11 at 12.16.07.png

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Screen Shot 2018-02-11 at 12.16.52.png

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I profess to know very little re the understanding of SSW 's  but would like to ask the following question. I am going back many years ,1962 to be precise, was there a SSW that year as the weather patterns from Mid December did behave in what I would describe an unusual manner. In those days I received DWR's from the met office every day and prior the start of that epic winter I had never observed high pressure cells travelling NNE in the manner that they did.

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Here's one for the stratosphere experts!

gfsnh-10-384.png

This is todays 384 hour chart - going out to the end of February now. At no point does there appear to be any re-invigoration of the PV. Gone are the dark blues, there are patches of warmer air floating around Greenland throughout.

I know the PV obviously weakens and disbands as we head into spring and summer, but what is a normal point for major weakening? Is it now unlikely we will see a raging PV re-form?

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9 minutes ago, mb018538 said:

Here's one for the stratosphere experts!

gfsnh-10-384.png

This is todays 384 hour chart - going out to the end of February now. At no point does there appear to be any re-invigoration of the PV. Gone are the dark blues, there are patches of warmer air floating around Greenland throughout.

I know the PV obviously weakens and disbands as we head into spring and summer, but what is a normal point for major weakening? Is it now unlikely we will see a raging PV re-form?

You need to be careful in recognising that the meteociel strat. charts only show temperature, not geopotential heights. 

The vortex is not simply a very cold blob of upper air, it is an area of intensely low geopotential heights.

So if we look at the geopotential heights for the same period on the GFS:

NH_HGT_10mb_384.thumb.gif.39183a740d66e8e2e9b2b29b1e8929cf.gif

We still see our old foe the vortex spinning away over Canada - though surely after continuous warming thrust its way throughout the period, significantly weaker than you might expect.

The good news from the above is the fact that it is displaced away from Greenland, and with a big positive geopotential wave visible across most of the eastern hemisphere it looks favourable for blocking to our North/North East (and, just potentially, our North West too)

However, there are two things to bear in mind:

1. This assumes that the stratospheric synoptic setup imprints itself exactly upon the troposphere (which is far from a given)

2. I'm doing that thing I encourage everyone never to do in dissecting a single operational run out at +384

Complicated all this stratosphere stuff!

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One can certainly envision how the vast stratospheric ridge (or positive geopotential wave as named above) may superimpose onto the usual increased tendency for easterly flows during the spring transition period.

I do wonder if the models are being a bit slow to propagate the effects downward. Especially after reading Kyle Henry's post! :smile:

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41 minutes ago, mb018538 said:

Here's one for the stratosphere experts!

gfsnh-10-384.png

This is todays 384 hour chart - going out to the end of February now. At no point does there appear to be any re-invigoration of the PV. Gone are the dark blues, there are patches of warmer air floating around Greenland throughout.

I know the PV obviously weakens and disbands as we head into spring and summer, but what is a normal point for major weakening? Is it now unlikely we will see a raging PV re-form?

From what I have read polar vortex intensification, growth of polar winds and temperature anomolies happens at a much slower rate than the break up of the vortex during a SSW. The slow growth is related to lower wave activity in to the Stratosphere during the early stages of vortex intensification and is characterised by slow cooling of the vortex via thermal relaxation.

Ive seen a few posts suggesting the polar vortex will now not return due to the time of year, seasonal change etc however this is not necessarily the case as the charts below will show. 

5a815fa985ce4_ScreenShot2018-02-12at09_32_45.thumb.png.4161f1e1090b825062205e215e2d7f39.png  5a815fadb6147_ScreenShot2018-02-12at09_32_28.thumb.png.9a2645b93ceb4fd69129721406856da9.png

Re-intensification is much more likely during La Nina years than El Nino. Currently clinging on to La Nina state. As you can see from the next chart Vortex intensification does occur through into mid march but only on very few occasions. 

5a816065c61db_ScreenShot2018-02-12at09_35_27.thumb.png.4ac06780872986735700616ee7e7fb3a.png

A link to the full study.  

 https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwilxubVgKDZAhVIDcAKHUUkBucQFghAMAM&url=https%3A%2F%2Fatmos.washington.edu%2F~dennis%2FLimpasuvanetalJGR2005.pdf&usg=AOvVaw1Dv6L_6aRC-CV0YIoFXQNb

Hope this helps

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Thanks very much for all of your answers!

My knowledge of the strat is very, very limited - I'm learning all the time, and this really helps! I was aware that we could still have a strong trop PV even with a warmer strat etc, but it's a lot to get your head round. Very interesting though! :)

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11 hours ago, KyleHenry said:

 

 

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.

 

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.

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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.

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40 minutes ago, KyleHenry said:

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.

Pretty good assessment imo. I think the establishment of blocking to our north/northwest may be a few days earlier than you summise. 

The original modelling of the strat split carried the Asian chunk around the growing  block across mainland Europe allowing an easterly to establish quite quickly - slowly but surely, ecm And eventually gfs took this chunk further north until it phased to our northwest  with the Canadian segment extension. I think this is the easiest way to understand why we haven’t seen a quick trop response affect nw Europe.  

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A couple of questions that have bugged me over the last couple of days. i was going to post in model thread but think it might be suited here

Given that all the weather models use hindcast to verify the programming dynamics  before being put into the operational field  it possible that given the size of the deviation and duration that this event may not have been verified ie How will have this scenario been tested if it has never been seen before?

Is it also possible that the scale of the event may lead to a faster response as response is so strong and the understanding of the Strat and Trop is not fully understood but is nonetheless modelled into the NWP   ?

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