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Vikos

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    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    Let’s wait for the warming to begin. I don’t trust gfs with its keen spring ambitions. May to many influences of statistics going into the midterms? 
     

    warming begins in around 5 days…

    Could contain: Plot, Chart, Map, Atlas, Diagram, Nature, Outdoors
     

    Because extended range skill is higher when there is a SSW in the forecast initial conditions (Tripathi et al. 2015) then SSW events are a potential source of predictability. 

    From ec hompepage 

    things need to get real, then picked up as a initial condition and then we may see a big flip? Who knows? 

    • Like 5

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    2 minutes ago, Nick F said:

    My goodness, it's as exciting as watching paint dry flicking through each model run through the end at the moment. +heights over Europe, low heights to the northwest.

    It's a good job we have the carrot at the end of the stick of the likely major SSW mid-month, but at the moment it looks like a displacement rather than split. February with a displacement since 1980: 28/1980; 23/1984; 17/2002; 23/2007; 22/2008. 1981 and 1984 both featured a cold March, 1984 was cold late in Feb via easterlies. But those other years with Feb displacements there was nothing of note. So don't pin your hopes that the SSW will deliver cold and snow, especially if a displacement.

    Carrot on a stick? What do you mean?

    • Like 3

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted · Edited by Vikos

    7 minutes ago, Mike Poole said:

    That 52% was the 18z.  Must admit, i thought it had gone west!  Back to 84% on GEFS on the 0z.

    And a much stronger warming with a split on the 0z op, with reversal at T240 - at this point we’d be reaching for the Berlin site to see what the ECM op is showing, but sadly it’s not available this year.  (It’s a bit shaky trusting the ensembles of either model due to lower resolution.)

    I wrote Berlin an email but unfortunately I got no answer. Then I called them but you rather get Joe Biden on the phone to talk about bloons made in China then finding someone to talk about stratospheric charts…

    • Like 7

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    1 hour ago, bluearmy said:

    as per the 18z, the 00z also downwells the weaker zonal flow towards the trop at 10hpa - remember, this is the gfs op out to day 16 so expecting it to have the detail correct as the run goes on, especially lower down in the strat is unlikely (although NH zonal flow is not the same as detailed heights ) 

    the point is that for two runs we have more of an impending connect with a weaker strat heading down 
     

    Could contain: Plot, Chart

    BA, is it possible that the lower trop is trying to connect to the strat, like an upwelling? Seems to me like the winds in strat are also calming down a bit, so would there be a chance? 

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    11 minutes ago, Mike Poole said:

    Splat!

    Could contain: Plot, Chart, Map, Outdoors, Nature, Atlas, Diagram, Rainforest, Vegetation, Tree

    This one the reversal occurred at T288.  

    I’m presuming the flush down of westerlies @bluearmy was referring to is still from the previous warming event as it is before this time.  It has been noticeable this morning on most models that the trop vortex is increased in strength over the next 10 days or so, and you’d expect this.  We want that out of the way so that the effect of the SSW can impact quickly.  

    I wonder in the mean time, whether the UK high will hold or surrender - hopefully for a brief period - to wet and windy weather off the Atlantic?  I think I’d prefer some heights to remain in our locale to give the pattern change associated with the SSW (assuming it happens) a nudge in the right direction, if that makes sense.

    Splat? Splat! Take your magnifying glasses and go for it 😂

    Could contain: Ct Scan, Disk

    • Like 1

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    16 minutes ago, Blessed Weather said:

    From what I can see the GEFS mean hasn't been showing a reversal of zonal mean winds at 10hPa (i.e. a technical SSW) over the last few days. But what is interesting is that when comparing the 0Z run over the period, the mean has been getting closer to a SSW with every run. This morning getting very, very close. Weatheriscool estimate the chances of a SSW now 48%.

    Could contain: Chart, Line Chart, Dynamite, Weapon

    Quite a few ensemble members (green) going for a reversal:

    Could contain: Plot, Chart, Smoke Pipe

    Source: http://weatheriscool.com/

     

    Was 61% yesterday… 🥲

    • Insightful 1

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    7 minutes ago, sunnijim said:

    Can somebody advise how long the lag time was after the SSW event in February 2018.

    For some reason I have it in mind the warming had a relatively quick impact on wind reversal and effects 'on the ground' were felt as little as 10 days after the event?

    We hear alot about a warming event taking up to a month to have impacts on our climate, just feel the transition in 2018 was quicker..

    I might be wrong.

    In the reanalysis, two large deceleration periods are observed before the SSW onset (12–19 January and 5–15 February). The zonal mean zonal wind is steady at ~30 m/s between the two periods. It is clear that the [U]60°N, 10hPa decelerates most rapidly in the second period. The westerlies begin to reverse to easterlies on 11 February, and the easterlies persist for more than 2 weeks. The easterlies fluctuate below the zero line from 11 to 28 February, and the maximum easterlies reach ~20 m/s on 15 February. It can be seen that the circumpolar westerlies gradually recover after 28 February.

     

    Source 

    6554b6be8c0d829a8bf63ae0c82cf121_link.pn Just a moment...

    AGUPUBS.ONLINELIBRARY.WILEY.COM

     

    • Like 3
    • Insightful 1

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    6 hours ago, Mapantz said:

     

     

    Some pretty useful stuff here: 

    Just a moment...

    AGUPUBS.ONLINELIBRARY.WILEY.COM

    ❄️

    The link is gold! Thank you! 
     

    Abstract

    A major stratospheric sudden warming (SSW) event was observed in February 2018 after a 4-year absence since the winter of 2013/2014. Based on the reanalysis data, the polar night jet changed from a very strong state to a moderate state during 12–19 January, and the moderate westerlies directly reversed to easterlies during 5–15 February. The intensified East Asian trough, Alaskan blocking, and East U.S. trough amplified the extratropical climatological wave 2, which propagated upward into the stratosphere, leading to a vortex-splitting SSW event. Predictions of the February 2018 SSW event are explored in hindcasts initialized 0–4 weeks in advance by the Beijing Climate Center Climate System Model. Less than 20% of the 28 ensemble members predict the reversal of [U]60°N, 10hPa hindcasts initialized 3 or 4 weeks in advance if a 5-day error is allowed, while this ratio increases to 43% in hindcasts initialized 1 week in advance. Based on the climatological occurrence of SSW events in the forecast system, the maximum deterministic predictable limit of this event is 1–2 weeks in this forecast system. The eddy heat flux and its domination by wave 2 can only be predicted within the predictable time limit. A comparison between hindcast members initialized 2 weeks in advance suggests that the extratropical troughs and blockings are responsible for the upward propagation of waves from the troposphere to the stratosphere. The predictable limit of the stratospheric circulation pattern for the February 2018 SSW, 1–2 weeks, also generalizes to other vortex split SSW events such as the January 2009 and February 1999 cases.

    • Like 4
    • Insightful 2

    Model Output Discussion - Into February

    in Forecast Model Discussion

    Posted

    1 hour ago, phil nw. said:

    Will we ever know where the recent cold GFS runs came from ?

    Yes there are signs of a weakening spv along with it's displacement now underway but the trop.vortex to our north remains stubbornly positioned.With the MJO showing in the warmer phases over the Pacific area an easterly was against the background signals really as well as most other model suites so those GFS runs came out of left field.

    We now seem to have normal service with pretty reasonable agreement with a uk high which may well give frosty nights but compared to what GFS offered recently it is a bump back down to earth for cold  and snow fans.

    What if gfs sniffed something like a true (but tiny little) SSW-mw the days before and had it as a starting parameter leading to scandi-blocking? Now, after the first peak it disappeared from the starting parameters and this leads us to no scandi high?

    • Like 2
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