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sebastiaan1973

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Posts posted by sebastiaan1973

    Model discussion highlights

    in Forecast Model Discussion

    Posted

    26 minutes ago, Penrith Snow said:

    I a  not sure Singularity is correct about the Iberien High being a response not a cause, its chicken and egg.

    Check out a 100 years of historical data pre 1988 and you won't find such a massive and persistent Iberain/Mediterranean High as we see modelled now, it just didn't happen and of course the current persistant Bartlett is only the latest in a long line since the 1999's.

    IMO, the Iberian High dominance is due to the expansion of the sub tropical Hadley Cell in response to a warming world, the expanse forces the Jet Stream north preventing the PV leaving its natural home ie Greenland, it happens occasionally of course like last week but any change is pushing againt the new normal and is quickly crushed.

    This I feel is the over riding factor and overwhelmes other natural signals that might encourage Northern Blocking, hence the late January early February forecast debacle.

    Watch the MJO if you like but it will make little difference 

    Andy

    Science seems to back your thoughts. 

    he Azores High is a persistent atmospheric high-pressure ridge over the North Atlantic surrounded by anticyclonic winds that steer rain-bearing weather systems and modulate the oceanic moisture transport to Europe. The areal extent of the Azores High thereby affects precipitation across western Europe, especially during winter. Here we use observations and ensemble climate model simulations to show that winters with an extremely large Azores High are significantly more common in the industrial era (since ce 1850) than in pre-industrial times, resulting in anomalously dry conditions across the western Mediterranean, including the Iberian Peninsula. Simulations of the past millennium indicate that the industrial-era expansion of the Azores High is unprecedented throughout the past millennium (since ce 850), consistent with precipitation proxy evidence from Portugal. Azores High expansion emerges after ce 1850 and strengthens into the twentieth century, consistent with anthropogenically driven warming. https://www.nature.com/articles/s41561-022-00971-w

     

    5 minutes ago, Duane S. said:

    It will change of course but thats incredible how the mean, over 6 days, steadfastly refuses to enter phase 8 ! 😁
     

    Amplified P7 should (eventually) at least help our cause 👍 P6 at this stage of winter in this ENSO state is more of a wild card I’d say?

    I guess we all remember BOM in december 😂 


    Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5022912
    • Like 2

    Model Output Discussion - Spring Has Sprung

    in Forecast Model Discussion

    Posted

    26 minutes ago, Penrith Snow said:

    I a  not sure Singularity is correct about the Iberien High being a response not a cause, its chicken and egg.

    Check out a 100 years of historical data pre 1988 and you won't find such a massive and persistent Iberain/Mediterranean High as we see modelled now, it just didn't happen and of course the current persistant Bartlett is only the latest in a long line since the 1999's.

    IMO, the Iberian High dominance is due to the expansion of the sub tropical Hadley Cell in response to a warming world, the expanse forces the Jet Stream north preventing the PV leaving its natural home ie Greenland, it happens occasionally of course like last week but any change is pushing againt the new normal and is quickly crushed.

    This I feel is the over riding factor and overwhelmes other natural signals that might encourage Northern Blocking, hence the late January early February forecast debacle.

    Watch the MJO if you like but it will make little difference 

    Andy

    Science seems to back your thoughts. 

    he Azores High is a persistent atmospheric high-pressure ridge over the North Atlantic surrounded by anticyclonic winds that steer rain-bearing weather systems and modulate the oceanic moisture transport to Europe. The areal extent of the Azores High thereby affects precipitation across western Europe, especially during winter. Here we use observations and ensemble climate model simulations to show that winters with an extremely large Azores High are significantly more common in the industrial era (since ce 1850) than in pre-industrial times, resulting in anomalously dry conditions across the western Mediterranean, including the Iberian Peninsula. Simulations of the past millennium indicate that the industrial-era expansion of the Azores High is unprecedented throughout the past millennium (since ce 850), consistent with precipitation proxy evidence from Portugal. Azores High expansion emerges after ce 1850 and strengthens into the twentieth century, consistent with anthropogenically driven warming. https://www.nature.com/articles/s41561-022-00971-w

     

    5 minutes ago, Duane S. said:

    It will change of course but thats incredible how the mean, over 6 days, steadfastly refuses to enter phase 8 ! 😁
     

    Amplified P7 should (eventually) at least help our cause 👍 P6 at this stage of winter in this ENSO state is more of a wild card I’d say?

    I guess we all remember BOM in december 😂 

    • Like 4
    • Insightful 4

    Model Output Discussion - Cold spell ending - what next?

    in Forecast Model Discussion

    Posted

    Just now, Duane S. said:

     

    Cold spells cannot appear without potential but potenital does not mean it will occur

     

    I think expection management is here the key. For the one who reads the comments and the one who writes them. If one writes about potential, I think it is important to write about the things that can go wrong. For the reader, I guess it is matter to understand this text of Duane S above and realise it is not settled science but developing knowledge. WIP. Work in progress.  

    • Like 5

    Model Output Discussion - Cold spell ending - what next?

    in Forecast Model Discussion

    Posted

    58 minutes ago, Met4Cast said:

    What did previous look like a good chance of sustained high latitude blocking during February is rapidly fading. 

    Despite an increasingly favourable MJO signal into the western Pacific, we’re missing a vital ingredient & that’ poleward propagating +AAM (westerly momentum). 

    IMG_4877.thumb.jpeg.a597a9af9bc5bb0d3cb077b65ac53734.jpeg

    The arrow shows the previous “starting pistol” of +AAM anomalies propagating poleward through December & indeed into early January, this along with the MJO helped to support & sustain the recent blocking we’ve seen around the UK/over Greenland. 

    Unfortunately, this time +AAM is increasingly glued to the equator & we’re not seeing this fluxing towards the pole, this helps (despite the MJO) to inflate the European ridge & indeed, a very strong signal for this within NWP through the remainder of January. A flat, mostly mild end to the month with low pressure systems deflected northwards, potentially stormy at times for Scotland. 

    The reflective wave from the SSW hasn’t helped things either. So.. my hopes for something sustained in terms of cold/snow are rapidly fading. 

    Okay ,thanks. What is need to turn it back as a good chance for high latiude anticyclone?  & don't you think we have to be careful by using these kind of 'forecast' because it not the first time, something went wrong. Like in for the end in december.  

    Model Output Discussion - Cold spell ending - what next?

    in Forecast Model Discussion

    Posted

    56 minutes ago, Mike Poole said:

    ECM clusters this morning, T192-T240:

    IMG_8562.thumb.png.8bc3a2fcb9e591247fce0aa77fac1c07.png

    Generally a flat zonal picture, apart from clusters 3 and 5 which push a ridge up to Scandi, but it doesn’t hold and flattens again.  

    T264+:

    IMG_8563.thumb.png.c8648ce607a6a49ed7322cb02bd4c622.png

    Cluster 1 (21 members) shows the Atlantic ridge scenario on which hopes for more seasonal weather depend.  The other two clusters maintain the +NAO regime.  

    Just goes to show how once this +NAO zonal pattern sets in for the UK, it is hard to shift, there are, and have been, signs of change but they remain at the tail end of week 2 for now…

    Well it is more or less our default setting 😉

    • Like 1

    Model Output Discussion - Cold spell ending - what next?

    in Forecast Model Discussion

    Posted

    55 minutes ago, Tamara said:

    Just a response to this before vanishing into the background again. Musings based on the best information available at the time. Which matched the diagnostic evidence available at the time.

    The SSW blip have been quite unusual with the incredibly powerful reflective nature of the wavebreaking.  Equatorward fluxing, strong Hadley cell, and very strong polar jet. As posted a while back - in these situations +AAM  momentum transport between the tropics and extra tropics to in turn perturb the polar field through +EAMT - will be negated by equatorward fluxing. Instead of poleward momentum higher latitude blocking, the downstream blocking resides instead across Europe. Sometimes these events hedge along fine lines which makes starkly different outcomes to the Annular Mode.

     

    Thanks Tamara, hope you have pleasant days in Portugal.

    Yep, a reflective SSW. I wonder. How long such a period can last? Thanks!

     

    https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JD023359

    Simon Lee wrote in a tweet about this article. If we have a reflective type of SSW (Judah Cohen states the same), this leads to a Pacific blocking and westerlies over the N-A

    Abstract

    Sudden stratospheric warming (SSW) events have received increased attention since their impacts on the troposphere became evident recently. Studies of SSW usually focus on polar stratospheric conditions; however, understanding the global impact of these events requires studying them from a wider perspective. Case studies are used to clarify the characteristics of the stratosphere-troposphere dynamical coupling, and the meridional extent of the phenomena associated with SSW. Results show that differences in the recovery phase can be used to classify SSW events into two types. The first is the absorbing type of SSW, which has a longer timescale as well as a larger meridional extent due to the persistent incoming planetary waves from the troposphere. The absorbing type of SSW is related to the annular mode on the surface through poleward and downward migration of the deceleration region of the polar night jet. The other is the reflecting type. This is characterized by a quick termination of the warming episode due to the reflection of planetary waves in the stratosphere, which leads to an amplification of tropospheric planetary waves inducing strong westerlies over the North Atlantic and blocking over the North Pacific sector. Differences in the tropospheric impact of the absorbing and reflecting SSWs are also confirmed with composite analysis of 22 major SSWs.

    For the reflecting type (the SSWs in February 1979, December 1998, February 2007, and February 2008.), the deceleration of stratospheric zonal winds is confined mainly to the polar region. Warming is rapidly terminated by reflection of planetary waves, which induces downward propagation of the wave packets. Fluctuations, including intermittent warming periods, precede or follow the major warming. The tropospheric response of this type of SSW appears as an amplification of the tropospheric planetary wave in the recovery phase of the SSW. In particular, a deepening trough over the North Atlantic and an enhancing ridge in the North Pacific sector are evident. The latter enhancement provides a favorable condition for a blocking formation over the North Pacific.

    Key Points

    New classification of sudden stratospheric warming during the recovery phase
    Absorbing type warming events induce Arctic Oscillation on the surface
    Reflecting-type warming events produce a Pacific blocking

    • Like 7

    Model Output Discussion - Cold spell ending - what next?

    in Forecast Model Discussion

    Posted

    19 minutes ago, Mike Poole said:

    I think we may get a heads up on this one from the MJO analysis, because looking at today’s:

    IMG_8541.thumb.png.d5230ea16eef6b4814cd79c63d00ed48.png

    Ignoring what the model is predicting, we are right now going into phase 5 at high amplitude.  If that amplitude is maintained, where the models have it decreasing, as we go through phase 5, then I’d be a little more confident it wasn’t going to collapse on us the moment it reaches the ‘good’ phases.

    A big spread of the members. So we have to wait and see till the MJO reaches phase 6.

    • Like 1
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