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Posted
  • Location: Worcestershire
  • Weather Preferences: Forecaster Centaurea Weather
  • Location: Worcestershire

    Here's the importance of the wave 2 attack that is happening right now. That is opening the channel and the low frequency forcing that will manifest itself during the early and middle part of December will keep that (Scandinavian) channel open. 

    So when the next phase of vortex disruption takes place, the response time will be a whole lot faster than the strat warming which was associated with the strong MJO last middle February.

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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

    Posted Images

    Posted
  • Location: caernarfon(gwynedd)
  • Location: caernarfon(gwynedd)
    5 minutes ago, Glacier Point said:

    Here's the importance of the wave 2 attack that is happening right now. That is opening the channel and the low frequency forcing that will manifest itself during the early and middle part of December will keep that (Scandinavian) channel open. 

    So when the next phase of vortex disruption takes place, the response time will be a whole lot faster than the strat warming which was associated with the strong MJO last middle February.

    What impacts do you reckon this is likely to be for the UK gp?? What your thoughts on next month

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    Posted
  • Location: Netherlands
  • Location: Netherlands

    I think this new report of KNMI might be useful for get an insight of the impact in the tropshere. 

    http://bibliotheek.knmi.nl/knmipubIR/IR2018-05.pdf 

    Summary
    In this study a new classification has been developed to classify Sudden Stratospheric Warmings
    (SSWs) based on their vertical depth. This new classification was developed because the depth of a
    SSW has been found to be important for the magnitude of tropospheric impact (Gerber et al., 2009;
    Palmeiro et al., 2015), and the official SSW classification does not tell anything about the vertical
    extent of a SSW.
    The new classification adapted from a previously developed classification of Kramer (2016; hereafter
    referred to as K16)). It prescribes that the zonal mean zonal wind between 60N and 70N should
    reverse over a depth of at least 80 hPa between 10 and 100 hPa for at least two days in a 5-day
    period. This classification was termed a ‘Deep Stratospheric Warming’ (DSW).
    In the stratosphere, the new DSW classification was compared to both the SSW-classification and the
    K16-classification. However, the K16-classification included events that were too weak to be
    considered important for tropospheric impact. Coupled to the fact that K-16-events did not contain
    any information about the vertical depth of SSWs, this classification was not taken into account in
    subsequent analyses.
    Compared to the official SSW classification, it appeared that DSWs were less frequent; whereas SSWs
    occurred about 6 times per decade, DSWs were found to occur only 4 times per decade.
    Furthermore, the SSW and DSW classifications were connected: most DSWs occurred a few days to
    weeks after the SSW date. This was explained by the behavior of SSWs and DSWs: first a warming at
    10 hPa took place (the SSW date). After that, the wind reversal extended downward in an irregular
    fashion, during which after some SSWs at some point the wind reversal extended sufficiently far to
    the lower stratosphere to cause a DSW to be classified.
    Connected to the differences in classification date, the DSWs were rarely located close to the
    moment of rapid warming in the stratosphere. Thus, unlike SSWs, the DSWs did not show the
    ‘sudden warming’ behavior. Rather, (most of) the DSWs seemed to be a result warm anomalies in the
    mid-stratosphere that developed sometime during or after the SSW and subsequently downwelled
    on a timescale of about a week.
    In terms of upper tropospheric impact, the DSW classification resulted in a similar response
    compared to the SSW classification: anomalously high temperatures near the pole and a southward
    displaced jet stream. Furthermore, the jet stream was found to become slightly more meridionally
    oriented in the midlatitudes and slightly more zonally oriented in the subtropics, but this signal was
    fairly weak. The main difference between the DSW and SSW was that the DSW effects were mostly
    stronger in magnitude than the SSW effects. Thus, a DSW results in stronger upper tropospheric
    impacts compared to a SSW.
    A similar story was found in terms of surface impacts. Both the SSW and DSW classifications resulted
    in positive pressure anomalies over the pole and generally negative pressure anomalies in the
    midlatitudes (indicative of a negative Arctic Oscillation); but the anomalies were more pronounced
    after a DSW. The surface temperature response after both a SSW and DSW was chaotic, though,
    showing that the DSW classification did not result in a stronger or more structured surface
    temperature response.
    Finally, a thermodynamic perspective was presented to explain why the DSW classification resulted
    in a stronger tropospheric response compared to the SSW classification method (only in terms of a -
    AO and a weaker jet stream in the midlatitudes). The cause was speculated to be that the warming

    accompanied by a DSW extended further to the upper troposphere. This is important for two
    reasons, being:
    1) A deeper warming causes the pressure surfaces to be less tilted from the midlatitudes to the
    pole, resulting in a more pronounced weakening of midlatitude westerlies, including the
    polar jet stream.
    2) A warming that extends more towards the troposphere exerts more pressure on the
    underlying air, because the density of air closer to the troposphere is higher. This results in a
    higher surface pressure. `
    In short, the new DSW classification enables to better assess the zonal mean timing and intensity of
    tropospheric impact compared to the SSW classification. However, no specific conclusions could be
    drawn about the zonally asymmetric effects of DSWs.

    Edited by sebastiaan1973
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    Posted
  • Location: Hoyland,barnsley,south yorkshire(100m asl)
  • Weather Preferences: severe storms,snow wind and ice
  • Location: Hoyland,barnsley,south yorkshire(100m asl)

     

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    Posted
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow
  • Weather Preferences: continental climate
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow

    @Glacier Point I think this tropospheric pattern would be promising for further attacks on SPV from both Pacific and Atlantic sectors

    FB_IMG_1542893084477.jpg

    Edited by jules216
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    Posted
  • Location: @scotlandwx
  • Weather Preferences: Crystal Clear High Pressure & Blue Skies
  • Location: @scotlandwx

    Sliders tend to create excitement on the NWP - never really considered following the wave breaks through on the NASA plots to see how they map over to NWP- a) if at all, b) if there is a lag c) do they lead the NWP and at what stage.

    This to me looks like it has the shape and track to be classed as a Strat-slider..https://acd-ext.gsfc.nasa.gov/Data_services/Current/arctic/anim_EPV_0320.html So will try and keep an eye on when it gets nearer verification date on how it looks at this level of the atmosphere and at what time we can gauge this playing into modelling...

    EPV_2018113000_F216_320.thumb.png.126bb09a4711b191100713b34ecaff0d.png

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    10 hours ago, lorenzo said:

    Sliders tend to create excitement on the NWP - never really considered following the wave breaks through on the NASA plots to see how they map over to NWP- a) if at all, b) if there is a lag c) do they lead the NWP and at what stage.

    This to me looks like it has the shape and track to be classed as a Strat-slider..https://acd-ext.gsfc.nasa.gov/Data_services/Current/arctic/anim_EPV_0320.html So will try and keep an eye on when it gets nearer verification date on how it looks at this level of the atmosphere and at what time we can gauge this playing into modelling...

    EPV_2018113000_F216_320.thumb.png.126bb09a4711b191100713b34ecaff0d.png

    It will be basically the same as the NWP - the 320K potential temperature is used as an indicator of the dynamic tropopause. For the polar region it tends to be just above the tropopause in the winter half of the year and just below in the summer - the UTLS region in general. In the chart above and animation, the shading shows the potential vorticity which is much higher in the stratosphere than the troposphere because of the increase in static stability. So in this particular chart the green and blue colours show where the air with 320K theta is in the troposphere (< 2 potential vorticity units) and the oranges and reds where it is in the strat (>2 PVU).

     

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    Posted
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow
  • Weather Preferences: continental climate
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow

    More strat. warming advocated by GFS in FI, also we have reasonable wave 1 amplitude higher up.

     

    ECMWF looks like it may produce +EAMT event day 11-14?

    In the same time MJO could be passing Indian ocean with strong amplitude come mid month

    I would say this is a very good position coming in to best part of winter, also we seem to be keeping the Scandi-Euro high anomaly.

     

    gfsnh-10-384.png

    00.png

    image.png

    image.png

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    Posted
  • Location: Hoyland,barnsley,south yorkshire(100m asl)
  • Weather Preferences: severe storms,snow wind and ice
  • Location: Hoyland,barnsley,south yorkshire(100m asl)

    Jma.

    JN264-5.thumb.GIF.2bc1999006dddafdf45798090c11d901.GIF

    10hpa,are we going to see this rise further tomorrow?

    pole10_nh.thumb.gif.cb19a158999721e2448fd5550cb284ec.gif

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    Posted
  • Location: Santry, Dublin, Ireland. 50 metres ASL.
  • Location: Santry, Dublin, Ireland. 50 metres ASL.
    1 hour ago, Allseasons-si said:

    Jma.

    JN264-5.thumb.GIF.2bc1999006dddafdf45798090c11d901.GIF

    10hpa,are we going to see this rise further tomorrow?

    pole10_nh.thumb.gif.cb19a158999721e2448fd5550cb284ec.gif

    Indeed,  but a lower than usual starting point? 

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    Posted
  • Location: Netherlands close to the coast
  • Location: Netherlands close to the coast
    1 hour ago, Weather-history said:

     

    And only yesterday Judah Cohen tweeted the exact opposite happening 

    https://twitter.com/judah47/status/1066685721933750273?s=09

    Edited by ArHu3
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    Posted
  • Location: Netherlands
  • Location: Netherlands

    Wintertime high-latitude blocking is associated with persistent changes in temperature and precipitation over much of the Northern Hemisphere. Studies have shown that the Madden–Julian oscillation (MJO), the primary form of intraseasonal tropical variability, significantly modulates the frequency of high-latitude blocking through large-scale Rossby waves that alter the global circulation. However, the characteristics of MJO teleconnections are altered by El Niño–Southern Oscillation (ENSO), which modifies the global flow on interannual time scales, suggesting that the MJO influence on blocking may depend on the ENSO phase. The characteristics of MJO Rossby waves and blocking during ENSO events are examined using composite analysis and a nonlinear baroclinic model. The ENSO phase-dependent teleconnection patterns are found to significantly impact Pacific and Atlantic high-latitude blocking. During El Niño, a significant persistent increase in Pacific and Atlantic blocking follows the real-time multivariate MJO (RMM) phase 7, characterized by anomalous enhanced tropical convection over the East Indian Ocean and suppressed west Pacific convection. The maximum Atlantic blocking increase is triple the climatological winter mean. Results suggest that the MJO provides the initial dipole anomaly associated with the Atlantic blocking increase, and transient eddy activity aids in its persistence. However, during La Niña significant blocking anomalies are primarily observed during the first half of an MJO event. Significant suppression of Pacific and Atlantic blocking follows RMM phase 3, when east Indian Ocean MJO convection is suppressed and west Pacific convection is enhanced. The physical basis for these results is explained. https://journals.ametsoc.org/doi/10.1175/JCLI-D-17-0721.1

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    Posted
  • Location: Netherlands close to the coast
  • Location: Netherlands close to the coast
    7 minutes ago, Glacier Point said:

    Wave amplitudes this cold season are very high.

    Wave 2 first ...

    416971583_wave2current.thumb.png.5326b5e235a2b2d2cb84995036856b3c.png

    Wave 1 now ...

    1156413218_wave1current.thumb.png.90ff4900567f5767b48220956ad6f9bc.png

    Very similar in evolution to 1986, wave 1 likely to be shorter duration this time round though as the Pacifc ridge becomes more of a trop feature in the coming 2 weeks.

    1986wave2.thumb.png.647e58601d6c4f83cf05cac343bac9fb.png1986wave1.thumb.png.810cc0d4fddce69870583fe625647750.png

    GEFS and EPS modelling continues to advertise a steadily weakening stratospheric vortex as we enter the core climatological vortex intensification period. 

    Wave 1 is also very similar to last year unfortunately, it showed a lot of promise until it died off mid December 

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    Posted
  • Location: st albans
  • Location: st albans
    5 hours ago, ArHu3 said:

    And only yesterday Judah Cohen tweeted the exact opposite happening 

    https://twitter.com/judah47/status/1066685721933750273?s=09

     

    5 hours ago, Weather-history said:

    Yes I noticed that but he himself says at the moment its a low probability

    Cohen was talking about a gfs op forecast for 9th dec

    ventrice is talking about an event predicted end this week

    of course we could assume that the latter may not happen if the former occurs but the question needs to be asked if the upper strat will become coupled with the lower as we head through December …...

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    Posted
  • Location: County end Oldham 202 m Above sea level
  • Location: County end Oldham 202 m Above sea level
    13 minutes ago, bluearmy said:

     

    Cohen was talking about a gfs op forecast for 9th dec

    ventrice is talking about an event predicted end this week

    of course we could assume that the latter may not happen if the former occurs but the question needs to be asked if the upper strat will become coupled with the lower as we head through December …...

    Sounds like Exeter are expecting worse case scenario for coldies .. their outlook is rapidly deteriating ..now any high is expected to sink by Mid Dec!!

    Sounds like coupling to me..

    Edited by northwestsnow
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    Posted
  • Location: Hoyland,barnsley,south yorkshire(100m asl)
  • Weather Preferences: severe storms,snow wind and ice
  • Location: Hoyland,barnsley,south yorkshire(100m asl)

     

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    Posted
  • Location: The Netherlands
  • Location: The Netherlands

    The vortex is under attack, indeed. A next heat flux (not visible on the Eddy heat flux plot so far) starting December 12th will likely cause a further displacement towards Siberia and the zonal winds may drop a lot more. It looks like we are heading towards a Canadian Warming, in the second half of December.

     

    Knipsel2.PNG

    Knipsel3.PNG

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    Posted
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow
  • Weather Preferences: continental climate
  • Location: Roznava (Slovakia) formerly Hollywood, Co Wicklow
    2 hours ago, Interitus said:

    There are some similarities with 1986 however there are closer similarities with other years. Some of the analogues are much more interesting than 1986, for example the closest 15-day 10mb wave 1 height to the GEOS forecast for December 6th is 6/12/98 -

    w1.thumb.png.18b7b9ba222836c90cbf29ce7413e074.png

    While the closest combined wave 1+2 is 25/11/81 -

    779437890_w12.thumb.png.1a70e8cbe448716ba3a99924c8f1099d.png

    What happens to the zonal winds from these dates is quite remarkable -

    u1060.thumb.png.579f0ceab8efab0f0af480f5029420cc.png

    In both cases there is a SSW 9 days later - two of the rare December events.

    The dates chosen are for the same time of year to ensure a fairly close time for seasonal vortex evolution, but returning to the wave 1 there is a closer match than 1998 with 17/2/99, which is not just similar to December 6th this year for 15 days but for a full 30 days -

    467758039_w130day.thumb.png.abddf1b5c27ed1bbdeadaac6bb883718.png

    Adding 17/2/99 to the zonal wind chart from above -

    1080980410_u10602.thumb.png.517345f516230939ff9fd15ee12b2152.png

    Incredibly, SSW 9 days later once again.

    There would appear to be something in this, but it isn't clear cut - the SSW of Dec 98 and Feb 99 were very similar while Dec 81 was quite different, little warming and wind reversal (and yet linked to some dramatic weather for the UK). Also many other close analogues don't feature SSW of course.

    Give me February 1999 anytime @Interitus ? 

    kolaz-zima-1999-kosice-kalamita.jpg

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