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Gary L

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Posts posted by Gary L

    Model Output Discussion - Cold spell ending - what next?

    in Forecast Model Discussion

    Posted

    24 minutes ago, Met4Cast said:

    Comments like this confuse me and I think it's down to a lack of understanding of "background signals" that trigger it. The teleconnections are what drive our weather and create the weather patterns that we see, NWP modelling is based entirely upon these signals. Understanding teleconnections allows you to view NWP modelling in a much broader context. "Too much emphasis" absolutely cannot be placed on the things that literally drive our weather. If anything, not enough emphasis is placed upon them. 

    I think where people get caught up is that they expected certain drivers to produce specific weather conditions outside their front door & unfortunately, that's not how it works. You can use these drivers to get a flavour of the broader, global scale weather patterns but the micro scale, i.e outside your front door is so local & isolated compared to the northern hemisphere that x + y does not necessarily = a snow day. 

    This current cold period & blocking spell we're in the middle of was well advertised weeks in advance. The MJO cycling through phase 1/2 and slowly through 3 helped to generate a Rossby wave packet within the Pacific which led to wavebreaking in the Atlantic & the Greenland high that has brought about the current cold weather. This, in conjunction with a high total AAM state (increased westerly momentum within the atmosphere) led to a perturbed and amplified jet stream capable of generating the HLB we've seen. 

    A strong +EAMT (East Asian Mountain Torque) event created the Pacific jet extension which developed a downstream trough, causing a jet streak which then created a downstream trough, follow this all the way into the Atlantic with each "wave" amplifying the next. We've got a Greenland high, we've got cold weather across the UK, broadscale pattern? Check. The next step is the micro, i.e small-scale weather systems that may or may not bring about snowfall in specific areas, that's something background/teleconnective signals can never help you predict. 

    Ironically, the "downfall" to this cold pattern & the reason for next weeks milder & stormy weather isn't because of a sudden change in background tropospheric forcing but down to the recent SSW. The SSW has helped to displace the Canadian vortex eastwards towards Siberia which has flattened the pattern.  A case of bad timing, again, something teleconnections can never help you predict. 

    This is the thing I have doubts about - If it were so simple we'd have the forecast broadly nailed down weeks in advance, which simply isn't the case. My comments come from a place where there absolutely is a lack of understanding - but I've not seen much to convince me that these indicators produce much certainty in any forecast weeks in advance. It seems to me they tip the balance, but are not definitive?

    • Like 6

    Model Output Discussion - Cold spell ending - what next?

    in Forecast Model Discussion

    Posted

    15 minutes ago, jules216 said:

    There was a lot of wibe around the seasonal forecasts of "back loaded winter" perhaps they meant 20-28.02.2024 period. As currently there is a big overwhelming signal of very mild Europe in next 3 weeks. Currently the best and only really coolish and snowy period date here in central Europe is 25.11-10.12. Which is as front loaded as it gets. The clusters 240-364 on EPS are showing what would be almost a record breaking warmth being summer time. This winter is a very good match of a blend of last 2. Few december promises and almost snowless January,followed by a week of cold in February and then the really cold pattern sets in spring time. This is almost happening every single year since 2017. This trend shouldnt be ignored. As I ve seen very little re-analysis after the wibe ends ",what has gone wrong". My oponion is that its a blend of factors. 1. Haddley Cell expansion - high pressure from north Africa as legacy of hot summers - pushing north creating a wall that prevents cold air to push too much south, and SST once they cool enough its spring when cold synooptics kick in, Late March - April. 

    chart (11).png

    webp-worker-commands-5f6448649f-b7zvg-6fe5cac1a363ec1525f54343b6cc9fd8-E1v7Wc.webp

    webp-worker-commands-5f6448649f-b7zvg-6fe5cac1a363ec1525f54343b6cc9fd8-jeLbNE.webp

    webp-worker-commands-5f6448649f-kz7pp-6fe5cac1a363ec1525f54343b6cc9fd8-XktGFo.webp

    I'm not an expert in background signals but it seems there's far too much emphasis placed on them. I'm assuming they tip the balances by a few % in the direction of some scenarios (e.g. HLB). 

    • Like 1

    Northwest Weather Discussion - Dec 2023 onwards

    in Northwest Weather Discussion

    Posted

    13 minutes ago, Rob 79812010 said:

    No rapid thaw here. Should still be snow on ground tonight which, with any luck, will stick around till weekend. Could be some sneaky snow showers Thursday also. TBH, am banking this one!

    Not convinced. Were always marginal in low areas and no real melt here yet. Even as a kid they often turned to slush

    It would be great to see a modelling study to understand how significant the increase in temperatures would be. Low lying area maybe always would have been marginal, but I'm at 200m and it's likely to rain today at some point!

    • Like 4
    • Insightful 1

    Northwest Weather Discussion - Dec 2023 onwards

    in Northwest Weather Discussion

    Posted

    22 minutes ago, Joe Bloggs said:

    At first glance It looked like there could be some streamer activity first thing up the Mersey but the model isn’t picking up on any accumulation at all on this frame. 
     

    image.thumb.png.da5503748e5b225556158bfcf557b633.pngp

    It's later on on Tuesday N Lancs area where the streamer seems to set up - accumulation charts then show sig. accumulation over high ground.

    19 minutes ago, frosty ground said:

    UKV feeds the the Met office app right?

    My area has light snow, can’t see anything other than a few cm’s at the most.

    Yes I believe so! Not 100% sure but I'd imagine at this range they'll be using the high res model.

    • Like 6

    Northwest Weather Discussion - Dec 2023 onwards

    in Northwest Weather Discussion

    Posted

    11 minutes ago, Joe Bloggs said:

    Also - I know these apps are absolute bobbins most of the time - but this is always a positive sign if the computers are displaying the symbols already. 
     

     

    IMG_5718.png

    Looking good Joe! I haven't lived in Saddleworth for a long time but in my 7 years here I've worked out we need more of WNW to hit Saddleworth's sweet spot! Keeping a close eye on it but looks like we're in with a good chance.
     

    Manchester (particularly South) often does very well in these situations - especially if they get hit overnight/early morning!

    • Like 4
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