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5 minutes ago, Snow Dragon said:

Sorry newbie question.

Please can someone explain why on the one chart it shows a reversal of zonal mean winds and on the other it doesn't? Trying to think of why, but I just can't grasp it and it's been bugging me for a few days.

344254615_zonalwindspeedforecast.thumb.png.4a1b7aa2122a2d14dd9ee77fb1723744.png

One chart is from the gfs op and the other from the gefs ensembles ..... 

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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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6 minutes ago, bluearmy said:

One chart is from the gfs op and the other from the gefs ensembles ..... 

Ok thanks for explaining. It makes a little more sense now. I wondered why people weren't posting the GFS Op run and making noises about there not being a reversal  as I see most people posting shots of the GEFS ensembles.

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The 06z fv3gfs had a min zonal wind of +0.1 m/s but it was sporting a convincing looking split -

1100920279_fv318122006384z10.thumb.png.3ec4d5b7302ebb9ed707e49dc6d92b2a.png

Prompted by a tweet, here it is at 1 hPa and 0.4 hPa -

584769686_fv318122006384z1.thumb.png.dbf7525cab35d446d27f448f73943a6c.png1955963305_fv318122006384z0.4.thumb.png.6460f8b5ab86f7e6d688bd875408d464.png

For the lower strat the main vortex heads to Eurasia, but upper strat wanders to N. America.

 

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GFS looks confused, top down or bottom up? 

To the layman it seems ECM is more keen on a split form the top, whereas GFS looks to take the split from the troph to the strat but not making it right to the top. 

Surely troph to strat is more tricky to model as it relies on the less certain troph forecasts to be correct at longer range.

This is a very simplistic view so if I’m way off the ball please let me know.

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8 hours ago, Interitus said:

Those GEOS charts are a bit SD, for HD try the animations (up to 10mb, 240h on 00z 120h on 12z) here - https://fluid.nccs.nasa.gov/wxmaps/?region=nps

Update on minimum zonal winds from last 18z and 00z runs -

GFS -2.0, +3.7 m/s

Para +6.4, +10.8 m/s

Wow!

 

 

Excellent link @Interitus - tremendous discussions kicking off between the esteemed folks on twitter now as to why GFS at odds with it's ensemble, and importantly why GEOS has back tracked. Take it those are 10hPa values.. need Sam Lillo to do one of his cool graphs on this... ?

Good also to see yourself and @Bring Back1962-63 chewing the fat over plenty of stuff, I am not going to arbitrate here, not in a position of expertise to judge. Would only say perhaps a PM will help get you both on same page ?

 

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2 hours ago, supernova said:

I wonder if we're about to see some backtracking? Let's hope not.

 

Screen Shot 2018-12-20 at 16.12.36.png

This chart illustrates what has been bothering me if I'm reading the ensembles right as from all models not just GEFS.  It's like the different models are modelling different systems.  Why?  Something very different about this SSW, maybe?  Previous ones I've viewed, and there haven't been that many since I started model watching, the models were all consistent re the strat at the 10 day out timeframe, if I recall correctly. 

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39 minutes ago, Mike Poole said:

This chart illustrates what has been bothering me if I'm reading the ensembles right as from all models not just GEFS.  It's like the different models are modelling different systems.  Why?  Something very different about this SSW, maybe?  Previous ones I've viewed, and there haven't been that many since I started model watching, the models were all consistent re the strat at the 10 day out timeframe, if I recall correctly. 

Interesting observation Mike. Seems there’s speculation GFS is inaccurately forecasting and/or missing essential obs re the Ural high. Interesting paper supporting your point re early predictability of major SSW’s here, highlighting subsequent importance of Ural blocking accuracy (if I’ve interpreted correctly). Thx to Dr Butler for sharing (Twitter). ://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081091?af=R&

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3 minutes ago, karlos1983 said:

Is that behind a paywall Tony, or can we see it ?

You can see it but tomorrow morning, bookmark this site, you can see loads of strat related stuff but unfortunately just the ECM op and not the eps.

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html

Updates around 4 or 5am.

This was yesterdays.

[ECMWF 240 hour forecast from December 19 2018 12 UTC to December 29 2018 12 UTC: 10 hPa geopotential and temperature]

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8 minutes ago, Singularity said:

ECM might well be the tortoise in this modelling race.

My 'feeling' as expressed in the MOD is that the technical SSW and the split will eventually be one and the same thing rather than a quick displacement of the PV followed by another warming leading to a split.  We will see.

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41 minutes ago, Mike Poole said:

My 'feeling' as expressed in the MOD is that the technical SSW and the split will eventually be one and the same thing rather than a quick displacement of the PV followed by another warming leading to a split.  We will see.

What implications is that likely to have for the UK as opposed to a displacement followed by a split?

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1 hour ago, lorenzo said:

Stop Press - EC remains solid... 

 

image.thumb.png.b02623a6d29da7cc278f57af6777b19b.png

I’m rather more taken by how quickly 30 and 50 hpa begin to look split thereafter ....... has to be a quick downwell to 50 hpa ..... Saturdays Berlin will show more if things stay consistent 

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3 minutes ago, Don said:

What implications is that likely to have for the UK as opposed to a displacement followed by a split?

More reliable signal for possible cold, in that ECM is onto it in a reliable timescale, I would suggest.  And it would nail the split, which would give a higher probability of cold once it has downwelled.  But until we've some more concrete evidence, it is just my speculation at present.

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Just now, Mike Poole said:

More reliable signal for possible cold, in that ECM is onto it in a reliable timescale, I would suggest.  And it would nail the split, which would give a higher probability of cold once it has downwelled.  But until we've some more concrete evidence, it is just my speculation at present.

Thanks for the reply Mike.  A continued wait and see but fingers crossed!

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3 hours ago, Snow Dragon said:

Sorry newbie question.

Please can someone explain why on the one chart it shows a reversal of zonal mean winds and on the other it doesn't? Trying to think of why, but I just can't grasp it and it's been bugging me for a few days.

344254615_zonalwindspeedforecast.thumb.png.4a1b7aa2122a2d14dd9ee77fb1723744.png

Probably something to do with the triple splitting  vortex shown further up the page....it would be interesting to see if this had happened before

 

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Interesting that the 11 Feb 2001 SSW was during phase 5 of the MJO cycle, whilst the upcoming forecast split shown will also likely coincide with phase 5 at similar amplitude. 

Jan-March 2001

 200101.phase.90days.gif.small.thumb.gif.db0098fef4b5b8bd6a9ba0a303bfc92a.gif

Current

rmm.phase.Last40days.gif.small.thumb.gif.45b4c8f76feacb63afb4f6013c5a707c.gif

Forecast

ECMF_phase_51m_full.thumb.gif.34098592e44a785ae2451ca4f2ced834.gif

Not sure if this a coincidence or whether this similarity of sequence of the MJO cycle constructively helped precondition the split.

Anyhow, the 11 Feb 2001 split was followed by a slow response from the trop, but when it did it allowed Atlantic/Greenland height rises and a cold/snow end to Feb and a cold/easterly March

 ERA_1_2001022106_1.thumb.png.89786ccf2b9af08b03b9bdcd7816e3c1.pngERA_1_2001022806_1.thumb.png.6ad1a765670c32d1e949ca9fb4845676.png

Edited by Nick F
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