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sebastiaan1973

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    In my opinion we were on the right track with this article:

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020RG000708

    "For SSWs that are dominated by EuBL around their onset, cold anomalies prevail over northern Europe, albeit also extending over large parts of central Europe (Fig. 4b). They peak at −4 to −6 K around lags beyond 20 d, which corresponds well with the occurrence of the GL regime. Note that negative T2m' values in the composite for all SSWs are much weaker (see Fig. 4d). The associated retrogression of initial positive Z500' over the eastern North Atlantic to Greenland along with a strengthening of negative Z500' over the southeastern North Atlantic around lag 15–25 d is striking. Furthermore, GL is associated with warm anomalies over Greenland and eastern Canada." 

    In the coming days we do see a second SSW. This time with a European Blocking. In EC46 at least we see this retrogression and strengthening of negative Z500' over the SE North Atlantic. 

    Sciences rocks. 

     

    Schermafbeelding-2023-02-20-211752.gif

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    Schermafbeelding 2023-02-21 173740.gif

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    3 hours ago, sebastiaan1973 said:

    Thanks Cold Winter Nights for the reminder of the Domeisen et al article. In my opinion this part is right now the most important:

    WCD - The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events (copernicus.org)

    Figure 4Surface impact for SSWs with (a) Greenland blocking, (b) European blocking, and (c) cyclonic regimes around the SSW onset, as well as (d) for all SSWs. Shading indicates the composite 2 m temperature anomalies, with stippling (hatching) indicating significance at the 25 % (10 %) level. Blue contours correspond to geopotential height anomalies at 500 hPa in intervals of 50 gpm (geopotential meters). Negative values are dashed. The fields are averaged over 5 d between lags 0 and 25 d with respect to the SSW central date. Note the different scales for temperature in (a)–(c) and (d). The 2 m temperature anomalies are detrended and deseasonalized using 9-year and 21 d running mean filters.

     

    So we need to see European Blocking around the SSW onset. But we see right now cyclonic setting. Which doesn't deliver as we wished it would do. But... in the last days of February there will be a next dip. Then there will be European Blocking. So, I guess we have to wait a little longer, but according to this research and if there is European Blocking, there will be a long impact on the troposhere.  

     

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    Schermafbeelding 2023-02-17 163214.gif

    Well at least the oper of EC is showing a European Blocking. As mentions earlier today, this seems to be important for the impact of the SSW. 

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted · Edited by sebastiaan1973

    Thanks Cold Winter Nights for the reminder of the Domeisen et al article. In my opinion this part is right now the most important:

    WCD - The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events (copernicus.org)

    Figure 4Surface impact for SSWs with (a) Greenland blocking, (b) European blocking, and (c) cyclonic regimes around the SSW onset, as well as (d) for all SSWs. Shading indicates the composite 2 m temperature anomalies, with stippling (hatching) indicating significance at the 25 % (10 %) level. Blue contours correspond to geopotential height anomalies at 500 hPa in intervals of 50 gpm (geopotential meters). Negative values are dashed. The fields are averaged over 5 d between lags 0 and 25 d with respect to the SSW central date. Note the different scales for temperature in (a)–(c) and (d). The 2 m temperature anomalies are detrended and deseasonalized using 9-year and 21 d running mean filters.

     

    So we need to see European Blocking around the SSW onset. But we see right now cyclonic setting. Which doesn't deliver as we wished it would do. But... in the last days of February there will be a next dip. Then there will be European Blocking. So, I guess we have to wait a little longer, but according to this research and if there is European Blocking, there will be a long impact on the troposhere.  

     

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    Schermafbeelding 2023-02-17 163214.gif

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    12 minutes ago, Cold Winter Night said:

    I wouldn't say that March 2013 was the "main event" following that January 6th SSW.
    Mid January 2013 was very cold. Here in Holland, De Bilt counted no less than 12 ice days in a row from the 14th to the 25th, several with snow falling as well. I had a 9 cm snow cover on the 21st.
    If indeed that was the result of a QTR impact, that would have been the main event, in my opinion.

    Like @feb1991blizzard mentioned, then there were more impact waves. After a late Jan milder phase, early mid february onwards was colder again, but not as cold and snowy as January, and after another milder phase early March, that mid-late March cold arrived, mostly very dry, windy cold here.
    But the further out, the weaker the response of SSW impact waves, so can the remarkable cold even late March still be fully attributed to the early January SSW?

    This chart from a Domeisen article (2018, 2019, I think? I lost the link to the original article) shows for an SSW during European blocking a series of downwellings, gradually weakening, and the chart is cut off at Day 60 post-SSW.

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    The current output suggests that we don't have to wait that long to see the impact from this SSW though.

    It's probably too late for ice to skate on, so I personally hope to see more Greenland blocking with big snow events, instead of a Scandi High with bone dry Easterlies like 2013 and 2018.

    Yes Domeisen

    WCD - The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events (copernicus.org)

    https://wcd.copernicus.org/articles/1/373/2020/

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted · Edited by sebastiaan1973

    Good luck to you Matt t. Wish you the best. 

    https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.3017

    or 

    https://www.researchgate.net/publication/313547642_Predictability_of_downward_propagation_of_major_sudden_stratospheric_warmings_Downward_Propagation_of_SSWs

    Abstract

    Major sudden stratospheric warmings (SSWs) are striking phenomena of wintertime stratospheric circulation usually defined as a reversal of zonal mean circulation from westerlies to easterlies. SSWs often have significant impact on tropospheric circulation and cause anomalies in surface climate lasting for up to 2 months. For this reason, dynamics and predictability of SSW receive considerable attention. It is however well-known that not all SSWs cause significant, long-lasting impact on the troposphere. In order to explain differences in tropospheric impacts following SSWs, several reasons have been previously proposed, including differences in type of SSW (split or displacement), persistence of stratospheric anomalies, preconditioning of the tropospheric circulation, and whether or not SSW was accompanied by a planetary wave reflection in the stratosphere. Here we address the predictability of tropospheric impacts by SSWs by seeking early precursors of the impacts. We separate midwinter SSWs into two groups: those which are followed by significant, long-lasting impacts on the tropospheric circulation (defined in terms of anomalous Northern Annular Mode) and those not followed by significant anomalies in the annular mode. We show that SSWs characterised by a more negative Northern Annular Mode index in the lower stratosphere around 150 hPa and enhanced wave activity propagation to the stratosphere during the first few days following the central date have a larger probability of being followed by tropospheric impact, both in reanalyses and in climate model runs. These anomalies play a more important role in the subsequent downward propagation of the signal to the troposphere than the type of SSW: whether it is a split or a displacement, or absorptive or reflective SSW. We propose that using these anomalies as precursors of tropospheric impacts of SSW can enhance climate predictability.

    ---------------

    Right now we see positive AO in the lower stratopshere around 150 hPa by next week. So, according to this study I guess there is less chance for a tropsheric impact. Sorry to say. 😒

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    3 minutes ago, Mike Poole said:

    I’ve posted this up before, it’s a chart of winter weather regimes (+NAO, -NAO, scandi blocking, atlantic ridge) which I’ve hacked to mark the approximate time of all the SSWs with an ‘S’.  A string of -NAO or scandi blocking days after a SSW might indicate a cold spell, +NAO the reverse. Obviously the regimes are wider than the UK, so no guarantee as to exactly what weather the UK experienced.  

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    This one is important as well 😉 

    https://twitter.com/SimonLeeWx/status/1582372470027272192

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted · Edited by sebastiaan1973

    22 minutes ago, Mike Poole said:

    Given the 10hPa winds chart, and reading between the lines a bit, I would say the ECM 46 might be pointing to a potentially easterly setup for the UK from the last week of Feb into Mar if there is a SSW, with a prolonged period where Scandinavian blocking is the favoured regime:

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    Please keep in mind by that time we can/might enjoy the impact of MJO phase 6 perhaps 7.

    Schermafbeelding 2023-02-02 213718.gif

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted · Edited by sebastiaan1973

    Indeed, what an exceptional anti-cyclone. Record for the Netherlands is 1050 hPa. Article by Burt.

    The Highest of the Highs … Extremes of barometric pressure in the British Isles, Part 2 – the most intense anticyclones - Burt - 2007 - Weather - Wiley Online Library

    The all-time UK record is 1053.6 mb recorded at Aberdeen Observatory on January 31, 1902. https://rmets.onlinelibrary.wiley.com/doi/10.1002/wea.35

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