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comet

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Posts posted by comet

    Model output discussion - heading into 2018

    in Forecast Model Discussion

    Posted

    Again the charts offer some optimism during the Christmas holidays with the Alaskan ridge morphing into an Arctic high and applying enough force to send the jet further south leaving some areas prone to the possibility of some wintriness. For more southern areas we would need to see the jet modelled even further south whether that is achievable is jet to be seen. The ECM is not very inspiring tonight it has to be said but that is just one op run.

    Something maybe afoot in the far reaches of FI with a reasonable warming being forecast and making inroads into the Arctic rather than skirting round the surf layer. Of course it could quite easily disappear but something to watch.

    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted

    2 hours ago, Weathizard said:

    Hmmmm... arctic high much stronger on this run. Seems to be getting stronger every run

    IMG_8671.PNG

    It comes as no surprise, have been banging this drum for several days now and hopefully we will either see better ridging in the Atlantic in coming days or the Arctic high forcing energy further and further south, If and its a big if things went our way we could see some very wintry charts developing in the days ahead. But one step at a time.

    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted

    23 minutes ago, Nick F said:

    But is that of evidence of downwelling though? They are anomaly charts you posted rather than geopotential height structure of the polar vortex at different heights in the stratosphere.

    Certainly the strat forecasts from GEFS and EPS to day 10 suggest the SPV will stay displaced off the pole and centred towards the Barents and Kara Sea areas north of Russia by New Year, though extended forecasts from GEFS take it back to the pole.

    My concern would be if the SPV becomes elongated and aligned with the tropospheric PV close to our NW, as if they become coupled, it would keep low heights intact to our NW for a protracted period in January. Though no evidence of this yet ... with signs of the -EPO ridge building heights toward Greenland, which will help drive the jet stream south. The question is, will the cross polar heights be sustainable into the New Year?

    I was of the thinking that by showing the anomaly charts you could see where any forcing is taking place rather than the broad brush of the mean. The wave breaking several days back at the 10mb level is without doubt the reason behind the Alaskan ridge and cold surge that we engulf a number of states in America over the coming days rather than MJO, Glaam , GWO etc.

    • Like 1

    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted

    Way to much emphasis in here on EPS, GEFS, GloSea, Met etc etc they have all proven to be wrong many times in the past including the not to distant past and they will be again. The trend in the operational runs of the nwp  models look quite positive and so does the progression of downwelling in the strat. I would expect to see  further increases in northern blocking and a much colder pattern developing post Christmas. below are 30mb composite charts from the 14th and 16th this forcing downwelling from 10mb. This forcing started from wave breaking around the 8th and another slightly  weaker one around the 16th.

    Composite PlotComposite Plot

    Below the composites for 50mb

    Composite PlotComposite Plot

    below the composites for 100mb on the 14th and 16th

     

    Composite PlotComposite Plot

    • Like 2
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    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted · Edited by comet

    Fully expected to see a stronger ridge pushing into the Arctic and would expect to see further strengthening in the runs to come. This courtesy of wave breaking into the strat several days ago and downwelling into the trop, Regardless of the AAM and GWO budgets. Models could, repeat could look very different in a couple of days time. Not in time to prevent a green Christmas though for most people.

    • Like 1

    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted

    49 minutes ago, swfc said:

    Wow what a diff a week makes weather and mood wise.Possibly GP or Tamara could post and steady the ship.Any looks like a fired up pv is looking to build ete  after a week of milder weather.Anyonewith altitude may do well if the said spell transpires and any move north of west may spring a few suprises.Nothing cast in stone tbh so maybe a few twists and turns yet giving the current volatility in the output

    Not knocking GP or Tamara but all they do is offer their own views of where the different teleconnects etc are taking us rather than just using the models in isolation. As such they can like the met or any other longer range forecaster be wrong as we have seen in the past and will likely see in the future. The models do not offer great viewing at this present time that's for sure. Hopefully this will change in runs to come.

    • Like 1

    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted

    Positive changes in model output so far today. Ridge from  Alaska looking stronger with each run could mean the UK finding  itself in a colder wintry pattern within the next 10 days as pressure builds to the west north/west allowing a growing nw/se trajectory. With more changes expected in the near term rather pointless looking to far ahead. As some have said a white Christmas or at least snow falling could now be on the table for some at least.

    Stratosphere and Polar Vortex Watch

    in Spring Weather Discussion

    Posted

    3 hours ago, Interitus said:

    The ESRL PSD composites automatically create the scale which can make direct comparisons difficult, but the scale can be overridden to make the plots consistent -

    geop1.thumb.gif.15d9ed1ac6ad35fe76f9f353a873835b.gifgeop2.thumb.gif.a0085bdfd57e99ee74e6438f4bb8fddb.gif

    This shows the heights have fallen over Eurasia, but the height rises over Canada is not quite as intense. Comparison should be made with the mean charts which show that at first the vortex was being perturbed by a large eastward and poleward displacement of the Aleutian anticyclone causing a large wave break, but then the anticyclone weakens southwards allowing the vortex to recover -

    geop3.thumb.gif.c71d0356df7831bcad46fbdcdc111824.gifgeop4.thumb.gif.e221e8413095d1ebbad8760542a48448.gif

     Would be interested to know how to override the scale. As you say the plots look more consistent and less confusing. Didn't think to check the mean my bad. Thanks.

    This wave breaking will hopefully provide some fun and games when it works its way down into the trop.

    Stratosphere and Polar Vortex Watch

    in Spring Weather Discussion

    Posted

    Trying to make sense of these two composite charts below. The first is from Dec 9 and the second Dec 13. The composite anomaly charts seem to show geopotential heights increasing with time over northern most Canada while decreasing over northern Europe and Russia yet when you look at the scale on the right this seems contradictory. Am I missing something here.

    Composite PlotComposite Plot

    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted

    22 minutes ago, The PIT said:

    Well after a few weeks of interesting weather it looks like in for a spell of boring nothing type of weather with mild temperatures and grey laden skies. Bonus if we get any sun next week. Deep lala land does show a bit more interesting weather. GFS with it's normal deep lows blowing the uk away while the ECM doesn't go quite so extreme as it doesn't so far out but at least we do have some transient cooler slots with may produce some wintry weather. Hopefully we will get more application and different types of weather everyone will find interesting. However the emphasis is on the mild side of things.

    It has been a great start to the season with several weeks of very entertaining model output and just recently the coldest and wintriest spell of weather for many in the UK unfortunately the timing could not be worse heading towards Christmas to see a pattern change to much more mobile and milder conditions. Hopefully strat forcing will see a return to much more interesting weather and model watching post Christmas into the new year. A fair number of the 06z gefs show what could be around the corner so not all doom and gloom.

    • Like 1

    Model output discussion - winter proper underway

    in Forecast Model Discussion

    Posted

    34 minutes ago, comet said:

    Could be in for a good tale end to the 12z ecm tonight. Will no of course in another 20mins.

    Didn't quite go according to plan but the t240 chart shows a lot more promise going forward than the muck the gfs op produced. Amazing how the gefs can vary from raging positive AO and NAO to a tanking AO, NAO I suspect myself this is to do with the recent warming and geopotential heights that are working their way down from the mid strat into the lower strat and thicker denser troposphere and also rate and which they are likely to do this. Patience may be the key here although I would of thought that a cold pattern response to this would reveal itself by month end hopefully. This is not always the case though but I would rather hedge my bets on this than on the effects of the MJO which as we have seen in previous winters can be a red herring although if the atmosphere (QBO) etc is in a favourable state then the benefits of a strong MJO event can be very rewarding.

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