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40 minutes ago, Met4Cast said:

Wave 2 is still being forecast by GFS data which is nice to see, I suspect this is the reason for the forecast reduce in zonal winds

169853722_Wave2.thumb.png.1b78090741018079a2388654d24c4e9a.png

I believe this is based on GFS operational data however so I wouldn't take it as gospel, good to have CFS supporting though, even if it does tend to take things a little too far 

Indeed, nothing more than a waiting game ATM.  However, I was hoping the long range models would have started to back off their zonal winter predictions by now, rather than remaining bullish.

Edited by Don
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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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59 minutes ago, Met4Cast said:

Wave 2 is still being forecast by GFS data which is nice to see, I suspect this is the reason for the forecast reduce in zonal winds

169853722_Wave2.thumb.png.1b78090741018079a2388654d24c4e9a.png

I believe this is based on GFS operational data however so I wouldn't take it as gospel, good to have CFS supporting though, even if it does tend to take things a little too far 

Ecm 12z ops now available on Berlin and in agreement 

93E1143C-9039-4710-AA05-C62EC318BEA7.thumb.png.91b3238e73fc56c9c953e7ef685d6d0c.png

 

 

Edited by bluearmy
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Charts from stratobserve.com today (based on GFS) continue to suggest an increase then decrease in vortex intensity, yesterday's 0z run, and today's side by side:

image.thumb.jpg.3fe503b0af76929a4480cf1ed9254c4d.jpgimage.thumb.jpg.d2e987b0b6f207a8ca15500597e4dea3.jpg

Please note vertical scales are different. So yes, it may briefly exceed 40m/s but after that it is on the way down, for a few days at least.

Again the NAM index plot (which is similar to the + or - AO but at all levels of the atmosphere, not just the surface, as I understand it) suggests a disconnect between the strat and trop vortices as far as we can see.  Which is all good.

image.thumb.jpg.173b5c59f94d81ca4c7def6b14c116e0.jpg

Edited by Mike Poole
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21 minutes ago, Mike Poole said:

Charts from stratobserve.com today (based on GFS) continue to suggest an increase then decrease in vortex intensity, yesterday's 0z run, and today's side by side:

image.thumb.jpg.3fe503b0af76929a4480cf1ed9254c4d.jpgimage.thumb.jpg.d2e987b0b6f207a8ca15500597e4dea3.jpg

Please note vertical scales are different. So yes, it may briefly exceed 40m/s but after that it is on the way down, for a few days at least.

Again the NAM index plot (which is similar to the + or - AO but at all levels of the atmosphere, not just the surface, as I understand it) suggests a disconnect between the strat and trop vortices as far as we can see.  Which is all good.

image.thumb.jpg.173b5c59f94d81ca4c7def6b14c116e0.jpg

Interestingly the disconnect looks stronger on that run with -2 anomalies vs the -1 anoms. The strength of the vortex doesn't matter too much as long as the disconnect continues, though I don't think it'll last too long with models converging on Wave 2 attacks and the decreasing strength.

Some GEFS members (green) take the vortex below average interestingly

G.thumb.png.bc7bd99991ef799d2521efb20c3a82c8.png

CFS (pink) has been showing a rapid weakening for a while, but I'm always wary of those 

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Is there any truth it what goes up must go down, i.e. a very strong PV can quickly snap.. or is more likely too? like an elastic band it stretches as far as it can go then snaps, if it stretches far enough.. or is this too simple logic.. same with strat, a very cold Stratosphere can induce a strong warming all of a sudden..

There is logic in the Cold air advection and warm air advection combo.

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4 hours ago, damianslaw said:

Is there any truth it what goes up must go down, i.e. a very strong PV can quickly snap.. or is more likely too? like an elastic band it stretches as far as it can go then snaps, if it stretches far enough.. or is this too simple logic.. same with strat, a very cold Stratosphere can induce a strong warming all of a sudden..

There is logic in the Cold air advection and warm air advection combo.

Statistically all things tend to regress to the mean, so record strong vortices will weaken and record weak vortices will strengthen (like what happened mid December 2017)

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1 hour ago, s4lancia said:

Wave 2 activity certainly seems to be pepping up towards mid month. GFS and ECM on the same page.

ecmwfzm_ha2_f240.thumb.gif.3a657bd0e120954630294171c8db6757.gif

ecmwfzm_uv2_f240.thumb.gif.34f512f385cfb0c52bc8ea2c0bf84a16.gif

ecmwf10f240.thumb.gif.b8af347f97ce83bb84c6828309e8c296.gif

Just what a growing yet fledgling vortex does not need right now...

 

my memory isn’t what it used to be but is a decent thrust of wave 2 activity commonplace for first half nov?  Seems to have been a lot of wave 1 (if any) from what I recall ....... we can see the stronger zonal flow headed down in the upper strat and will be interesting to see how this wave 2 interacts with it - certainly a very odd gfs op this morning in the trop ......

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1 hour ago, bluearmy said:

my memory isn’t what it used to be but is a decent thrust of wave 2 activity commonplace for first half nov?  Seems to have been a lot of wave 1 (if any) from what I recall ....... we can see the stronger zonal flow headed down in the upper strat and will be interesting to see how this wave 2 interacts with it - certainly a very odd gfs op this morning in the trop ......

I'd say although it terms of amplitude November can expect to see only half of what can be achieved through January, yes it has been fairly commonplace to see early season wave#2 action. Possibly moreso in the past 10 years or so as well. 

Last year, taking it at 10mb / 60N, there were two (near or actual, it was close) record amplitude spikes (relative to the date) during November. 

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46 minutes ago, s4lancia said:

I'd say although it terms of amplitude November can expect to see only half of what can be achieved through January, yes it has been fairly commonplace to see early season wave#2 action. Possibly moreso in the past 10 years or so as well. 

Last year, taking it at 10mb / 60N, there were two (near or actual, it was close) record amplitude spikes (relative to the date) during November. 

I had saved 17/18 somewhere 

7AE0344C-5EB6-403E-AD8D-0A25853D2E72.thumb.jpeg.ab54d1a61012c5d28bb1dfd750606141.jpeg
 

35909F19-D6B7-4D31-96F6-9E476DC83B67.thumb.jpeg.b54a73fcc34a343ff00eaecb29e95b22.jpeg

Edited by bluearmy
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1 hour ago, bluearmy said:

I had saved 17/18 somewhere 

7AE0344C-5EB6-403E-AD8D-0A25853D2E72.thumb.jpeg.ab54d1a61012c5d28bb1dfd750606141.jpeg
 

35909F19-D6B7-4D31-96F6-9E476DC83B67.thumb.jpeg.b54a73fcc34a343ff00eaecb29e95b22.jpeg

Good find. Trouble is Wave#2 never looks that impressive up against Wave1.


This highlights it quite well up though...

wave2-1819.thumb.jpg.9216efdcc6557887bbf71d18ade621ad.jpg

 

Interesting looking at other parameters,how wave activity and flux in general then dropped right off during the actual SSW period in January. I wonder if then consequently Uwind was then 'allowed' to gather speed up rapidly, which of course it did, through to mid March.

Edited by s4lancia
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Hmm this is all making for distinct problems with regards to a winter forecast. The easy option is to assume that the semi permanent North Pacific High will force another cold trough driven winter for central US and fire up the jet as it pushes out over warm Atlantic water. = connect between strengthening Greenland vortex and downwelling strat vortex. Once connected bye bye winter at least for the first half because ENSO forcing looks like playing little role in driving us out of a neutral and rather Nina-esque atmospheric predisposition.

And yet....the position of the Scandy anomaly is helping create the wave 2 forcing a few of us were taking about a couple of weeks back, and modelling isn’t yet picking up on a direct strat/trop connection. In addition we have that nagging feeling that a -NAO has dominated our recent calendar, and heights to the NW may yet hold tight for a while. Ocean temperatures as they stand at the moment also favour a jet on a more southerly trajectory, and our solar TSI record minimum at the moment looms over all analysis.

I remain uncertain how this will play out, but the clock is gradually ticking around to the point where some answers will emerge.  Will wave 2 forcing become strong enough to significantly perturb the vortex and maybe even split it (Cohen keeps mentioning this...) or will the Scandy anomaly flatten out as Crewecold alluded to this morning and heights to our north become dominated by low pressure and a coupling of strat/trop vortex?

My instincts still lean towards a December that will be more westerly than northerly as wave 2 fails to have a substantial impact early and the Atlantic takes hold....but that later in the season arctic forcing works to hit the vortex again and give us back loaded cold possibly via a reversal. However all is still up in the air really.

 

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2 minutes ago, Catacol said:

Hmm this is all making for distinct problems with regards to a winter forecast. The easy option is to assume that the semi permanent North Pacific High will force another cold trough driven winter for central US and fire up the jet as it pushes out over warm Atlantic water. = connect between strengthening Greenland vortex and downwelling strat vortex. Once connected bye bye winter at least for the first half because ENSO forcing looks like playing little role in driving us out of a neutral and rather Nina-esque atmospheric predisposition.

And yet....the position of the Scandy anomaly is helping create the wave 2 forcing a few of us were taking about a couple of weeks back, and modelling isn’t yet picking up on a direct strat/trop connection. In addition we have that nagging feeling that a -NAO has dominated our recent calendar, and heights to the NW may yet hold tight for a while. Ocean temperatures as they stand at the moment also favour a jet on a more southerly trajectory, and our solar TSI record minimum at the moment looms over all analysis.

I remain uncertain how this will play out, but the clock is gradually ticking around to the point where some answers will emerge.  Will wave 2 forcing become strong enough to significantly perturb the vortex and maybe even split it (Cohen keeps mentioning this...) or will the Scandy anomaly flatten out as Crewecold alluded to this morning and heights to our north become dominated by low pressure and a coupling of strat/trop vortex?

My instincts still lean towards a December that will be more westerly than northerly as wave 2 fails to have a substantial impact early and the Atlantic takes hold....but that later in the season arctic forcing works to hit the vortex again and give us back loaded cold possibly via a reversal. However all is still up in the air really.

 

Personally speaking.Winter is ruined if Nov and Dec turn out mild wet and windy which is why the next 2 or 3 weeks in the strat are really important for me.

A SSW in jan for example will leave us grasping at straws for cold in Feb/march.

No thanks ?

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1 minute ago, northwestsnow said:

Personally speaking.Winter is ruined if Nov and Dec turn out mild wet and windy which is why the next 2 or 3 weeks in the strat are really important for me.

A SSW in jan for example will leave us grasping at straws for cold in Feb/march.

No thanks ?

On that basis, the UK has only had a handful of decent (in terms of cold) winters over the past century or so ?

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2 minutes ago, MattStoke said:

On that basis, the UK has only had a handful of decent (in terms of cold) winters over the past century or so ?

Well, i can recall plenty of cold spells between christmas and new year matt.

If we are relying on an SW in Jan/feb its looking grim.

Edited by northwestsnow
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Just now, MattStoke said:

On that basis, the UK has only had a handful of decent (in terms of cold) winters over the past century or so ?

Tend to agree. Dec 10 was a bit of an outlier. 79, 81, 85, 87, 91, 96, Jan 10, 12, 13 (grrrr no snow for me), 18 = all post New Year cold. Anything in December raises an eyebrow for me.

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1 minute ago, Catacol said:

Tend to agree. Dec 10 was a bit of an outlier. 79, 81, 85, 87, 91, 96, Jan 10, 12, 13 (grrrr no snow for me), 18 = all post New Year cold. Anything in December raises an eyebrow for me.

Surely Dec is a winter month catacol?

Are we now suggesting getting cold weather in Dec is unlikely?

Not a dig  just a genunine question.

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Just now, northwestsnow said:

Surely Dec is a winter month catacol?

Are we now suggesting getting cold weather in Dec is unlikely?

Not a dig  just a genunine question.

Hi NWS - a winter month by definition and for me largely due to low sun. Any snow in December won’t melt in the sun. But in my life I have seen very little December snow, and I lived in Scotland until I was 12. Plenty of wind and rain (Atlantic is nearly always strong in December and lengthening wavelengths tend to favour westerlies) and occasional omega blocking splitting the flow and giving some very cold frozen ground, but snow in short supply. Later in the season sees wavelengths begin to shorten as we move past the equinox, and this encourages retrogression of any high pressure signal over Scandy/Europe = possibility of undercut snow. Also oceans cool until March so later in the season sees less ocean modification. In general blocking is more prevalent later in the season.

So December is definitely a winter month, but in my experience by far and away the least productive in terms of snow, and without checking the records too closely I wouldn’t be surprised if the UK has more snowfall in March than it does in December. Perhaps someone with quick access to records could confirm or disprove that statement...

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5 minutes ago, northwestsnow said:

Surely Dec is a winter month catacol?

Are we now suggesting getting cold weather in Dec is unlikely?

Not a dig  just a genunine question.

Hi NW,sorry for butting in.Imo and getting old in my exp cold or very cold Dec do seem a rare beast or Jan -feb being the more wintry and cold.ive read that march is stats wise more wintry than Dec but that could be my sanilaty man.calnder wise Dec is a winter month imo

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7 minutes ago, northwestsnow said:

Thanks guys..

I don't disagree with anything you have written.

Which is why current events strat wise are crucial for December itself.

 

If I had to pick a month for a big freeze it would be December.Long nights , low sun and the festivities of Xmas !! January’s big freezes are offset by the gloom of returning to work after Xmas, Febs often fail and have been chased for months,  and March brings slush!!

Fingers crossed the signs of a big neg AO stick!! 

 

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Can look at average days of snow falling/lying per month in different regions of the UK here: 

tomtemps.png
WWW.METOFFICE.GOV.UK

Summaries of the climate characteristics of 11 regions of the UK

In general, I find that March tends to have more days of snow falling than December but less days of snow lying which makes sense given solar radiation. December is my favourite month to be wintry and cold as a result but unfortunately it rarely works out for cold/snow compared to the other winter months. 

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33 minutes ago, northwestsnow said:

Well, i can recall plenty of cold spells between christmas and new year matt.

If we are relying on an SW in Jan/feb its looking grim.

In my lifetime I can only remember December 2010 being cold. December is normally more like an extension of Autumn.

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