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  • Nicos
    replied
    Thanks Pen!

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  • sandspider
    replied
    Thanks very much for typing that out, P, lots of food for thought there. We shall see!

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  • Penellype
    replied
    Originally posted by sandspider View Post
    Do you have time for a wee update, Pen? Very very wet here, not very cold. Would be nice it if was a bit drier in Jan so I can mow my meadow to help the yellow rattle germinate!
    I can try, although there is a lot of uncertainty at the moment (which seems to be par for the course nowadays).

    Very mild at the moment, and continuing mild and wet at times especially in the west, windy at times too, until mid week. By Wednesday a ridge of high pressure in the atlantic starts to push north towards Greenland, with low pressure to the east. It is the behaviour of this setup that is causing the forecasting headaches. The further north the high goes and the further west it is, the more likely we are to be caught in cold northerly winds between the high and the low. Some model runs have us in a screaming northerly by Christmas eve, others keep the high further south and slightly closer to us, with the wind coming round the top of the high from the north west. This is not particularly mild, but it wouldn't be as cold or potentially snowy for northern and eastern areas as the first scenario. There seems to be a consensus that Christmas day is likely to be chilly but probably mainly dry under higher pressure, although frost and showers (snow if cold enough in the north) can't be ruled out.

    Beyond Christmas most of the models seem to be staying chilly or cold, with some building the high over Scandinavia and turning the wind into the east. if this happens it could set up a prolonged cold spell with potential snow, especially in eastern areas. An alternative scenario is for the high to keep to our west, with bouts of northerly winds as low pressures dive south. The amount of rain or snow would depend how close we were to any low pressure systems. A third possibility is that the ridge topples over us and flattens out, letting in a milder, westerly flow, typically wet and windy - this appears to be a minority view at present.

    A complication is the presence on the model runs of a predicted sudden stratospheric warming over the north pole by the end of the month. This often leads to colder weather but it can take weeks or even months to propagate down into the troposphere where weather takes place. This year there has so far been a notable disconnect between what has been happening in the stratosphere and the troposphere, about which I have my own theories, but as I have no scientific basis or evidence for them I won't expand on that!

    With so much uncertainty in the medium range, attempting a forecast for January is virtually impossible. My feeling about this winter has always been that there is more potential for cold than in recent winters, and I think it is likely that we will continue with cold spells and milder interludes for some time yet. It is possible that the Christmas cold will become locked in and extend well into the new year, and this is most likely if the high forms over Scandinavia. However, there is simply too much uncertainty in the models to make any firm predictions at the moment.

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  • sandspider
    replied
    Do you have time for a wee update, Pen? Very very wet here, not very cold. Would be nice it if was a bit drier in Jan so I can mow my meadow to help the yellow rattle germinate!

    Leave a comment:


  • Penellype
    replied
    Not a lot of gardening going on here either. We have had so much rain over the last couple of days that the garden is under water in places. Not great considering that it is about to get wetter!

    Cold weather is likely to last for a few more days, with potentially some more snow in the north, after which the models are in disagreement about where the high pressure goes. Some have more lows diving south with higher pressure building to the north, keeping us cold and unsettled, while others favour the lows breaking through bringing milder, wet and windy conditions before high pressure builds over the top of the UK, which would be drier with the potential frost and fog.

    Personally I think the models haven't much of a clue because things are very, very unusual at the moment. The temperatures high up over the north pole are very cold, which should give us weather like last winter - mild, stormy and with low pressure to the north, but there is a "disconnect" between what is going on in the stratosphere and on the surface, with high pressure trying to develop to the north. In addition, one of the standard atmospheric drivers, the QBO, should be in its easterly phase now but has gone into reverse and is westerly. I think it highly likely that the models don't know how to handle this at all.
    Last edited by Penellype; 06-12-2020, 07:58 PM.

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  • Chippy Minton
    replied
    Originally posted by Penellype View Post
    As always, any forecast for more than about 5 days in the future must be taken with an appropriate dose of salt and everything could look very, very different in 4 weeks time.
    Huge pinch of salt taken and applied to the drive

    Really quite chilly here, greyhound dragged me home and has been ensconced on the sofa for the afternoon, not a lot of gardening going on....

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  • Plot70
    replied
    We had some snow but it did not settle.

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  • burnie
    replied
    We have wind and rain, apparently there's snow in Arbroath and further in land.

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  • Bren In Pots
    replied
    Your snow does look pretty Peanut we've also got snow but luckily ours isn't settling.

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  • Nicos
    replied
    ^^^^ beautiful! ...that"ôs even put a huuuge grin on my face too!

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  • peanut
    replied
    I have SNOW!!!!

    Attached Files

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  • Nicos
    replied
    I seem to have lots of deconstructed snowflakes sploshing down here today!
    Feels cold enough to snow though.

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  • burnie
    replied
    Trying to snow a bit here just now

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  • Penellype
    replied
    Yellow warnings of snow and ice for parts of Scotland now until Friday.

    There is still the possibility of some snow for parts of England and Wales from tomorrow and over the weekend. Snow is incredibly hard to forecast and the conditions are very marginal, but the most likely areas are the western side of the country and high ground. It is possible that eastern areas could see snow too, depending on how heavy the precipitation is - heavier = more likely to turn to snow due to evaporative cooling.

    Regardless of whether or not it snows it is about to get colder and the cold could last for some time, depending on where the high pressure goes. The models are not in agreement over this yet, but some runs are very cold, and if it hasn't happened already, you can expect armageddon -type headlines in the press. A cold and potentially wintery December looks likely, at least for the first couple of weeks, but this is not (yet) a repeat of December 2010, the coldest for 100 years or 100 days of snow (to quote common headlines!).

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  • Nicos
    replied
    Brill explanation - thanks!

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