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Stratosphere and Polar Vortex Watch


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2 hours ago, Raythan said:

Love the confidence ? , the Met Office weekly show on twitter today noted that their Glosea model isn’t seeing a SSW , only the American model’ is , interesting times 

But we had this posted a week ago, so um... :unsure2:

Who knows? My guess would be a significant warming, but not necessarily an SSW.

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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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9 minutes ago, feb1991blizzard said:

Got a feeling going by the models that there will be an SSW but not sure on the type which could be important, i just think the GEFS / GFS may be a bit early with it, i reckon a technical SSW but no earlier than 15th December.

Agree broadly. Wave 2 followed by wave 1 and then a final wave 2 for the knockout blow. Perhaps a little later than Dec 15 - final third for me. First piece in a complex puzzle perhaps....

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Just now, Catacol said:

Agree broadly. Wave 2 followed by wave 1 and then a final wave 2 for the knockout blow. Perhaps a little later than Dec 15 - final third for me. First piece in a complex puzzle perhaps....

Yes 15th at the very earliest i meant, i would have more confidence in my forecasts though if i could see the old GFS op, anyway would love to see your wave 2 come true - split from Pacific straight through Greenland into the Atlantic with a huge gap and the Canadian chunk pushed right out the way please.

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2 hours ago, Catacol said:

I’m suspicious of any 2 month average chart in terms of usefulness....but one thing is clear from all those charts - cold air spills into the 2 significant northern hemisphere continents, and this provides a source that can be tapped into. And returning to an earlier point - for the UK we need to stop the Atlantic in order to do this, and this requires a weakening of the westerly momentum at 60-65N (and higher). Cold spells can happen with other major forcings (eg very strong Nina Dec10) but of all potential forcings a SSW offers us the most dramatic chance of an impact on the default circulation. I can understand the frustration at the lack of a clear and obvious correlation, but at some point we have to apply conceptual understanding as much as statistical analysis and an SSW offers opportunity even if it doesn’t offer a guarantee.

True averages don't mean anything because they can average out, that's why I looked at the hellmann number for my region first. Hellmann numbers never average out but are always additive and for de Bilt ssws were very often preceded by cold periods but not followed by marked cold periods. And iirc cold periods here after a ssw always followed a split but not all splits and never displacements 

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Based previous experience over the last decade, if this were the old GFS, based on the consistency and the temperatures i am seeing, i would certainly be saying that an SSW would be somewhere between highly likely and nailed on.

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8 hours ago, feb1991blizzard said:

image.thumb.png.9b2b2a72f7e1a34636efe78751159111.png

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Legacy is the GEFS v10 version. As it says on the site, it is the pre-December (v11) version. That means it is the pre-upgrade version.

It has 42 vertical levels and model top at 2mb. The v11 version (december 2015-present) has 64 vertical levels and model top at 0.2mb.

So the legacy version is underqualfied to be a useful strat forecasting tool. At least in the modern times.

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3 minutes ago, Recretos said:

Legacy is the GEFS v10 version. As it says on the site, it is the pre-December (v11) version. That means it is the pre-upgrade version.

It has 42 vertical levels and model top at 2mb. The v11 version (december 2015-present) has 64 vertical levels and model top at 0.2mb.

So the legacy version is underqualfied to be a useful strat forecasting tool. At least in the modern times.

What about the op, is the current version or previous version better? are there actually any verification stats for the strat available?

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17 hours ago, Mike Poole said:

So to the upcoming SSW, and I'm assuming that this is going to happen now.  This has to be the focus of attention.  The narrative of winter 2019/20 will now be largely determined by what happens after this event, so it is absolutely fascinating, and this thread will busy in the next few weeks.

hi

am i correct in assuming that if we do have a ssw in mid/late december (or even early new year) and it fails to produce a cold spell for us, then its game over for a stratospheric induced cold spell for this year? do we get only 1 shot per season? or is it possible to get another warming event later in the season ?

 

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5 hours ago, Recretos said:

There is not much hard data to compare the two as far as I know. There likely is data in existence, that was used during the development, testing and fine tuning phases for the new FV3. But those are probably mostly internal. At least I have not came across any comparison data.

On a general note, I kinda feel an anti-FV3 agenda in this thread. Not sure why, because FV3 is a very capable solver. It is actually appropriate for the strat, as a dynamic core. Has anyone noticed when looking at the strat charts, they look much more realistic? Especially the temperature forecast. You can actually get the feeling of fluidity, even at 1° resolution. You can actually see the eddies in the surf zone, and energy and waves in the forecast. That is not due to resolution, but due to the capability of the FV3. Below is a comparison of GEFS and FV3, both on a 0.5°grid. Now you tell me, where can you see the actual fluid dynamics? ?  You really get the feeling that you are looking at water motion, when you look at the GFS with the FV3 core. And that is pretty much what this is. It is like motion of water, combined with waves and circulation.

dddd.png temperatureisobaricensin.png

This does not automatically mean a better forecast, but as far as I am looking by eye, it is not bad at all! It has the same bias as the old one, trending towards a weaker vortex into FI. But all those biases go out the window and are not important when SSW dynamics start.<-Those are mainly influenced by the trop activity, so any error in the trop forecast will reflect in the strat forecast too. Besides, when a stratospheric warming trend starts in the FI, it can swing the warming air mass 1000-3000km left or right with each run, making big differences from run to run. But the forecast is still a success, because it has seen the developing warming for example, which materializes. 

So to me, the FV3 is quite a capable strat solver. Forget the old GFS, it is gone anyways. So far it seems that FV3 is doing a good job. More time will be needed to make proper actual comparisons.

https://www.emc.ncep.noaa.gov/users/Alicia.Bentley/fv3gfs/updates/EMC_CCB_FV3GFS_9-24-18.pdf

The above is a link a to a presentation (2018) where a few comments are about the stratosphere in the FV3 GFS

These points are found on page 53

FV3GFS Temps are similar to GFS in middle and lower stratosphere

• FV3GFS Temps are warmer in upper stratosphere

• FV3GFS Temp fcsts in winter hem upper strat high lats are colder

• Zonal Winds are slightly worse in FV3GFS at longer fcst times

• Ozone mixing ratio analyses and fcsts are similar

• Total ozone anal are diff at high lats, FV3GFS fcsts are slightly better

• Specific Humidity is much more realistic

• FV3GFS is similar to GFS forecasting the 2018 SSW

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