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swilliam

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Posts posted by swilliam

    Model Output Discussion - 05/01/2016 18z onwards

    in Forecast Model Discussion

    Posted

    12 minutes ago, nick sussex said:

    No but the initial cold blast was forecast well. We're not even in the cold bit yet! lol The disagreements within T96hrs is not something I ever remember seeing with this type of set up before.

    I remember it well - the GFS/UKMO were pretty solid then the ECM churned a couple of runs where the low that came southwards went SW and W based -NAO was shown. This then suddenly changed back again to dropping S.

    Model Output Discussion - 05/01/2016 18z onwards

    in Forecast Model Discussion

    Posted

    43 minutes ago, bluearmy said:

     

    Sorry but the parallel ops are leading the way on the west based NAO and low upper cold not embedding so strongly beforehand.  Due to the Atlantic trough hanging back for too long. the most recent runs less favourable for lasting cold than the previous.  However, this is a snapshot in time and must be viewed as such. The ens give us an envelope to work within and the pendulum can just as easily swing back somewhat through the next few op runs.  tbh, we know the unreliability of ops post day 6. 

    this is is a tricky evolution with the polar high and n American trough both of paramount importance in how plays out.  We should see the way forward with some reliability over the weekend. if we arrive at the 20th without a decent snow event on low ground somewhere over the UK then it will be a big surprise. 

    Actually this was shown first on the 18Z GFS on Wednesday. I pointed out during the run that the initial ridge was too far W and thin which could lead to breakdown of the block at was then +240 (see below). This was the evening of the 1st stellar runs so I was then told by several people not to analyse every run, that the means were showing this etc. not to get upset (which I was not doing). All I did was point out what was shown and that we did not want this to become a trend. It confirms to me that no runs should be binned because we do not like what they are showing - just accept that they are one solution (especially beyond t120) which should be accepted as a possible if maybe unlikely outcome. the same applies when it is the other way round with everything showing zonal and then we start to see odd runs and ensemble members showing something different.

     

    gfsnh-0-156.thumb.png.b4f8f3b568804cd1bd

    Back to the current and as I see it the problem with the initial ridge being to far W and/or thin is that the 2nd surge of WAA does not really happen because of the orientation of the 2nd low in the US. So this low begins to head more NE instead of NW and interacts with the Azores low. This basically comes under the ridge instead going NW into the US. It is pretty much game over then in terms of prolonged cold for us although we my get a big snow event,

    However as has been said this phase is currently completely undecided and anything could happen at this stage so we will just have to wait and see. We can look at all the runs (good and bad) and see what the options are. But the main point I feel is that we want the initial ridge bigger and further E and then we want to see the 2nd low to rebuild the ridge rather than going underneath  it. Impossible to call at this stage but the trend has certainly been to move more towards the latter this morning but plenty of time for change to the former.

    • Like 3

    Model Output Discussion - 05/01/2016 18z onwards

    in Forecast Model Discussion

    Posted · Edited by swilliam

    8 minutes ago, Harsh Climate said:

     

    The mean isn't too bad

     

    gens-21-1-180.png

    Yes it is still pretty good but not as good as the 12z. I think this run just shows that it is still possible for it to go wrong. 

     

    I am going to stick with the ECM mean and hope it is still like this in the morning.

     

    EDM1-192.thumb.gif.3910d018062cb51f38d46

    The GFS threw out a funny run on the 18Z last evening.

    • Like 2

    Model Output Discussion - 05/01/2016 18z onwards

    in Forecast Model Discussion

    Posted · Edited by swilliam

    Unfortunately there is quite a bit of support of the Op from the ensemble members - this is reflected in the change in the mean at 192

    12Z

    gens-21-1-204.thumb.png.dda053c9a5aa6022

    18Z

     

    gens-21-1-192.thumb.png.3cc6fc5e1f8f68b4

    Lets hope this is not a trend even though it gives a few days of cold weather still - as the Meto say - still a question on the longevity

    gens-21-1-192.thumb.png.3cc6fc5e1f8f68b4

    Sorry about the extra picture  - seems to be bug if you make a mistake

    gens-21-1-204.png

    • Like 1

    Model Output Discussion - 05/01/2016 18z onwards

    in Forecast Model Discussion

    Posted

    1 minute ago, Mucka said:

    ECM London ensembles.

    Cold looks pretty much nailed on for 5 days thereafter scatter and a bit of a split.

    Latest 15 days ensemble forecast temperature for London

    Who wouldn't of taken those at the end of December?

    Quite - looks rock solid till the 14th and then a few rogue members v. unlikely to verify. Then a bigger split around 17/18 which I would imagine is to do whether the ridge gets reinforced by the Azores low sliding up the W side of the ridge and reinforcing the block.

    Model Output Discussion - 05/01/2016 18z onwards

    in Forecast Model Discussion

    Posted · Edited by swilliam

    3 minutes ago, Daniel Smith said:

    Yes, let's all get upset over a single operational run. We don't even know if this new "trend" as some are already calling it is supported by it's ensembles.

    This is but a single run, one option of many of what could happen come next week. The trend on the 18z continues to be that colder weather will flood across the UK next week. Beyond that has always been in doubt. Can we maybe try being more objective instead of throwing toys out of the pram because our Atlantic high has been to slimming world?

    No-one said it was a trend and no-one is getting upset - just commenting on the run. I said it was a problem if it became a trend.

    • Like 1

    Model output discussions pm 31/12/15

    in Forecast Model Discussion

    Posted

    2 minutes ago, feb1991blizzard said:

    Yes, another upgrade for those wanted cold on the GEFS, I know respected forecasters on here have told us to look at clusters and ignore means but if the mean is a Greenland high way into the 200's then the cold clusters will look exceptional!!

     

    What was said was that if the mean is showing something close to the climatological average then it is not much use. If it shows a signification deviation from this then it is very useful. This is the case here

    • Like 1
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