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The Enforcer

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    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted

    4 minutes ago, WYorksWeather said:

    Those are P15 and P17.

    image.thumb.png.f79f41b1deaa96ea5fe5c6d67104db09.png image.thumb.png.25cf865840a3a0aa8219679b8191b0d1.png

    Interestingly they get to mild 850s by different routes. P15 goes for the high sinking downwards, dragging in milder air around the top, so still quite cold at the surface further south but milder actually the further north you go.

    P17 is just a very odd one, the UK high fails almost entirely. We then have high pressure to the NW over Greenland, and moderately high pressure over Iberia and North Africa, which creates a gap for Atlantic weather patterns to just continue streaming in.

    Even P15 is not that bad from a cold perspective as there'd still be frosty nights with it. P17 is vile though.

    Of course, this is just two ensemble members, so it's a low probability event in any case, colder options are now very well favoured at least from the 5th-10th or so.

    For comparison, the mean at this point looks like this. Big area of high pressure centred over the top of the UK, cold and frosty for all.

    image.thumb.png.11c9afa597be6cd42d604cfdceb48b6d.png

    How is it possible to identify which P-numbers those ensembles are from the ensembles chart?

    UK high now appears to be touted as a 'certainty', but not for me until the P17 option has been wiped from the suite. It makes more sense to me to micro-analyse P-numbers that show things going awry than it does to cherry-pick the coldest one(s) in the hope that they become the norm in the many runs that follow.

     

     

    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted

    14 minutes ago, WYorksWeather said:

    Has to be said, unfortunately, that as well as the OP (which is still a mild outlier, and at times quite an extreme one), the ensembles are also a slight downgrade on the 12z compared to other recent runs. The good news is that the downgrades mostly come later in the run, we still see the mean getting down to -5C or thereabouts around the 7th.

    Definitely the way we'd rather have it to be fair, it's far better that than getting downgrades at day 7 and upgrades at day 14, which is what we see far too often.

    gfs-london-gb-515n-0e(12).thumb.png.99eb2b68c469a7a9526aa825e60b37c3.pnggfs-newcastle-upon-tyne(4).thumb.png.5c5182b15ca86e8c8f657735891c04f8.pnggfs-aberdeen-gb-57n-2w(7).thumb.png.b0472e0cc1554a579e8437db530dee37.png

    As long as the signal around the 7th doesn't collapse we're OK I think. Will be interesting to see the ECM 12z ensembles later for comparison.

    Do you know what pattern the orange red/runs on the 8th that reach about +4C are showing at that timeframe?

    • Like 1

    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted · Edited by The Enforcer

    1 hour ago, Met4Cast said:

    And this in itself is the problem.. 

    Far too many people think the GSDM/MJO can be used for UK specific forecasting, it can’t. It’s a global diagnostic tool for broad scale patterns, macro rather than micro. 

    As per Tamara’s post yesterday/the day before, the well advertised south shifted jet & subsequent current -NAO phase has occurred. 

    Next week we will see amplification & cold air filtering across the UK, the high now unlikely to be amplified enough to allow for widespread deep cold/snowfall but that has never really been on offer, though granted clearly there has been a shift SE in the placement of high pressure, again. 

    Getting a decent synoptic pattern really is like pulling teeth these days, it’s becoming increasingly difficult & frustrating. 

    OK, but presumeably the jet has shifted south at the longitude in which the UK resides?

    In terms of actual weather I can't say I have seen any difference: rain, wind, overcast when not raining and hardly any sun - the same as last week and the three weeks before that.

    • Like 3

    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted · Edited by The Enforcer

    19 minutes ago, AO- said:

    Good evening all,

    Does Anyone know what "is wrong" with the GFS operational?  It has been leaving the "bunch"  for three runs in a row now. It is clearly (again) an outlier. Synoptically it is on its own for quite a while now. 

    gfs-leeuwarden-knmi-nl-5.jpeg

    After the GFS operational spews out a series of mild outliers, it has a tendency to show a colder solution, just at the point where its ensembles and other model sets decide on a milder outcome after all.

    Model Output Discussion - Into 2024

    in Forecast Model Discussion

    Posted

    3 hours ago, Catacol said:

    I’d describe it as a diagnostic tool probably more than a forecasting tool. The fact the MetO don’t use it illustrates its one weakness, namely that the GSDM approach is itself the product of other forecasts. So…if pressure patterns don’t develop to allow a mountain torque spike, or if the pacific wave is derailed or lowered in amplitude then GSDM forecasts, like any other, can bust. The ENSO profile can suggest the likely direction of the GWO orbit, but - as we have seen in recent years - the atmosphere can fall into a pattern that disconnects from this forcing and perhaps most significantly the GSDM approach produces a shape of wind flows to the hemisphere and this doesn’t factor in locally relevant features that can overtake it on a local level.

    However, what it does do is provide the context within which NWP forecasting sits. So….we can be pretty confident in a period of low momentum and coupled Nina season that amplification will be significantly less likely to occur than a higher momentum profile coupled to a Nino ENSO. We know that momentum spikes produce meridional responses and the phases of the MJO help give a clue as to where the peak/trough pattern will setup. So GSDM diagnostics help provide an understanding of higher or lower probabilities of events occurring.

    Finally - to show its value the GSDM approach correctly “forecast” the cold at the end of Nov/early Dec. It also correctly forecast the flatter period through the middle of the month. It didn’t quite get the latter third of December because the MJO didn’t play ball…so 2 from 3 there. And now we have a period of blocking on the horizon that GSDM analysis diagnosed as likely a fair while ago. 3 from 4? Useful.

    I'm glad you agree it's useful. As for performance, it all depends as to what was actually diagnosed - blocking of the jet stream away from the UK or polar air flow over the UK (accepting that it does not cover the type of details that in any event often prevent snowfall from occurring)? Either way, it is not possible to conclude on round 4 until it has actually occurred or indeed hasn't occurred.

    Model Output Discussion - Into Winter

    in Forecast Model Discussion

    Posted

    5 minutes ago, Met4Cast said:

    It’s well advertised across all ensemble suites, regardless of details on snow we are going to be entering a prolonged period of below average temperatures, continuing to cool as time progresses. That much is clear. 
    IMG_4159.thumb.png.ca2d1d0ca18b5b328c24b6edac8ed314.png

    Ah yes, another 10 day+ chart. However, I could be persuaded after a further 20-something runs.

    • Like 1

    Model Output Discussion - Into Winter

    in Forecast Model Discussion

    Posted

    9 minutes ago, Met4Cast said:

    Just because you don’t understand something or don’t want to take the time to learn, it doesn’t make it “waffle” 👍🏻 

    The GSDM is firmly based in science & is a diagnostic tool to understand the drivers and subsequent atmospheric response, those that follow the GSDM have been flagging this cold period far longer than NWP modelling has. 

    I am sure GSDM is a useful forecasting tool, but there hasn't been a cold period yet.

    • Like 1

    Model Output Discussion - Into Winter

    in Forecast Model Discussion

    Posted

    9 hours ago, The Enforcer said:

    I tend to look at mild outliers differently. It matters not if they are the operational run or one of the pack. Their existence serves to illustrate that a cold spell, even if promoted by the vast majority of runs, could still 'go wrong'. And in my experience, when the possibility remains that it could 'go wrong', it usually does.

    I'd actually go a stage further and argue that not all ensembles are equal, such that those closest to the average line for the time of year ought to be weighted more heavily compared with those further from the average line. For arguments sake, let's say the average was 0C 850 then an outlier at 0C would be the equivalent of 5 runs at -5C and 10 runs at -10C.

    Model Output Discussion - Into Winter

    in Forecast Model Discussion

    Posted · Edited by The Enforcer

    1 hour ago, Battleground Snow said:

    Relentless GFS op outliers

    See you at 4am overnight crew

    gfs-london-gb-515n-0e (2).png

    I tend to look at mild outliers differently. It matters not if they are the operational run or one of the pack. Their existence serves to illustrate that a cold spell, even if promoted by the vast majority of runs, could still 'go wrong'. And in my experience, when the possibility remains that it could 'go wrong', it usually does.

    • Like 2

    Winter 2023/24 Chat and Discussion

    in Spring Weather Discussion

    Posted

    26 minutes ago, MJB said:

    image.thumb.png.78956204f73d10148eee795c99a05197.png

    Control is shaping up nicely 

    There's a Blackadder quote that can be paraphrased for every situation: "E-E-Exactly! And that is what so brilliant about it! We will catch the watchful MOD thread totally off guard! Doing precisely what we have done eighteen times before [show a cold spell at T+some high number only for it to disappear by T+120] is exactly the last thing they’ll expect us to do this time!"

    • Like 2

    Winter 2023/24 Chat and Discussion

    in Spring Weather Discussion

    Posted

    9 minutes ago, January Snowstorm said:

    It's not unusually wet for mid Winter. Nor is it very stormy despite all the hype. Indeed even though we are flying through storm names we've had little interest in what's being thrown 

    It's not the overall amount of rain that's the issue, it's the incessantness of it. No respite at all.

    1. Fronts don't clear properly, leaving 'baggage' behind.

    2. Troughs appear in gaps between fronts at T+0

    3. Regardless of the direction of the flow, the outcome is the same: rain. Even high pressure brought rain when there were no trapped fronts and nothing on the radar.

    4. Virtually no sun, any breaks in the cloudcover always overnight, so everything stays waterlogged and never dries out.

     

    • Like 4
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