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sebastiaan1973

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Posts posted by sebastiaan1973

    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted

    9 minutes ago, Matt Jones said:

    The problem here is we are losing the key ingredients for a decent cold spell, as others have mentioned Greenland heights show at longer range but often diminish as we get closer. I just think we are in for a colder spell of weather, as in more like January should be compared to what we've had in recent weeks then back to something milder.

    At De Bilt this is perhaps the picture. Day 10-15 shows a cluster with warmer weather and a (small) rise in average temperature. 

    Schermafbeelding 2024-01-06 091403.jpg

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    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted

    On 03/01/2024 at 10:46, jules216 said:

    Doesnt matter now. What will matter is the shortwaves which models will see later gaining influence. Only takes a small one to cut off the NE flow to merge through Európe and send cold to far north west. Been here a lot recently in winters sadly. Also MJO is out of synch phase 3 that does usually not mean European wide cold in January.

    Yep, this is the problem for central and northwestern Europe alike. The low countries have besides that, the issue of wind from sea which warms the cold air too much. 

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    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted

    22 minutes ago, Mike Poole said:

    GEM run is a cracker this afternoon, clean as a whistle, straight up there, T240:

    IMG_8301.thumb.png.286ae984b72be48aa0f0ff48a8459946.png

    GFS just looks messy, you have to think it has got something wrong on today’s runs, hope so.

    Well, the cyclone in the southern part of Scandinavia prevents the continental arctic air to move southeastwards. 

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    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted

    45 minutes ago, Singularity said:

    Important to view the Sun-Tue ‘might be’ easterly as independent from the -NAO driven one being signalled for mid-month.

    By comparison it’s a lot more fragile, so to speak, due to it depending on precisely how the high shapes up and orientates. Still feasible that it could do so in a manner that allows a decent cut-back of low 850s across S UK; we may as well pick options out of a hat regarding such a highly sensitive detail.

    As far as I can deduce, the subsequent retrogression signal is connected to a combo of the minor SSW and lagged response to MJO phase 3 coupled with AAM not falling very low due to El Niño.

    At this lead time the signals from those will dominate how the modelling behaves so yes, as always, well run the ‘finer details gauntlet’ nearer the time - but it’ll take a more substantial spanner in the works to totally derail it, compared to this coming Sun-Tue.

    You mean phase 1 of the MJO?

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    Model Output Discussion - Into Winter

    in Forecast Model Discussion

    Posted

    Excellent development, a British anticyclone. Blocking in that area. 

    Abstract

    Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular in the North Atlantic–European (NAE) region. While the stratospheric forcing often projects onto the North Atlantic Oscillation (NAO), the tropospheric response to SSW events, if any, is highly variable, and what determines the existence, location, timing, and strength of the downward impact remains an open question. We here explore how the variable tropospheric response to SSW events in the NAE region can be characterized in terms of a refined set of seven weather regimes and if the tropospheric flow in the North Atlantic region around the onset of SSW events is an indicator of the subsequent downward impact. The weather regime analysis reveals the Greenland blocking (GL) and Atlantic trough (AT) regimes as the most frequent large-scale patterns in the weeks following an SSW. While the GL regime is dominated by high pressure over Greenland, AT is dominated by a southeastward-shifted storm track in the North Atlantic. The flow evolution associated with GL and the associated cold conditions over Europe in the weeks following an SSW occur most frequently if a blocking situation over western Europe and the North Sea (European blocking) prevailed around the SSW onset. In contrast, an AT regime associated with mild conditions over Europe is more likely following the SSW event if GL occurs already around SSW onset. For the remaining tropospheric flow regimes during SSW onset we cannot identify a dominant flow evolution. Although it remains unclear what causes these relationships, the results suggest that specific tropospheric states in the days around the onset of the SSW are an indicator of the subsequent tropospheric flow evolution in the aftermath of an SSW, which could provide crucial guidance for subseasonal prediction.

    How to cite. 

    Domeisen, D. I. V., Grams, C. M., and Papritz, L.: The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events, Weather Clim. Dynam., 1, 373–388, https://doi.org/10.5194/wcd-1-373-2020, 2020.

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