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  • Penellype
    replied
    A very windy afternoon and night coming up, especially in Scotland and the western half of the UK, where it will also be very wet. There are multiple yellow and amber warnings, the amber ones for rain and yellow for wind and rain.

    https://www.metoffice.gov.uk/weather...ate=2021-02-23

    After this storm (which I don't think has been named) there will be a change to higher pressure with much less wind and rain. Temperatures will be pleasant during the day especially in any sunshine, but nights will be colder with a risk of frost and possibly fog.

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  • Nicos
    replied
    Good to know Pen - thanks, much appreciated!

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  • Penellype
    replied
    Thanks for the vote of confidence! Remember, I am self-taught and have no meteorological training whatsoever. I can, therefore, misinterpret things or misunderstand what I am looking at.

    I think it is fairly clear that the rest of February is likely to continue to be mild (sometimes very mild especially in the south) and often windy with bands of rain and showers crossing the country from the west. This is similar to a typical weather pattern of low pressures following the jet stream in a westerly flow and results in warm and muggy sectors (one coming up over the weekend) and cooler, often clearer and showery sectors following the rain as the low moves away (like yesterday). The wind is generally coming from the south west, with a long sea track, hence the air is generally mild and wet. I say it is "similar to" because the jet stream is behaving somewhat oddly at the moment, with very steep loops, which have resulted in the catastrophically cold conditions in the southern USA and snow in Saudi Arabia. There is high pressure to the south of us which will build to the east over the next few days, a process called warm air advection. The flow around this high will draw cold air into Eastern Europe down the eastern side of the high.

    As always, forecasting further into the future becomes less reliable. As usual the weather will depend on where the high pressure goes. Warm air advection has a habit of swinging the wind round from the south to the south east and then to the east as it inflates the high further north. The further north the centre of the high goes the more likely we are to find ourselves in a cold easterly wind. The models are flipping between scenarios where the high remains over or to the south of us, drawing up mild air (although if the skies are clear under high pressure in February it will be cold enough for night frost) and the high moving to Scandinavia and turning the wind back into the east, with upper air temperatures plummeting to various degrees depending on how far north the centre of the high goes. Worst case scenario would be the high going far enough north for the easterlies to tap into the very cold air that has sunk into eastern Europe, which would give us another "beast from the east". Yesterday's midday run of the GFS model produced exactly this scenario at the end of the run (3 weeks away), whereas this morning's midnight run keeps us in a generally westerly flow, cooler than the current south westerlies, but with the very cold air well away to the east. Looking at the models is therefore not giving any sort of consistent guidance into March.

    So, expect mild but often wet and windy weather for the rest of the month, wettest in the west, with some flooding likely, probably becoming drier especially in the south later in the month. After that, at present the possibility of another very cold (and possibly snowy) spell cannot be ruled out, although on balance staying milder looks slightly more likely.

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  • Nicos
    replied
    ^^^ very true!!!

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  • sandspider
    replied
    Things seem to be warming up now, but getting wetter.

    If you have time for a wee update that would be appreciated, Pen? Your efforts are more reliable than my various weather forecasts!

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  • Penellype
    replied
    Originally posted by Nicos View Post
    My daughter is due her first baby any time now and she lives in rural Cumbria

    Lets hope she doesn’t get snowed in!
    Fingers crossed. Initially at least the worst of the snow is likely to be east of the pennines, so Cumbria may be out of the firing line somewhat. Always hard to be specific with showers though.

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  • Nicos
    replied
    My daughter is due her first baby any time now and she lives in rural Cumbria

    Lets hope she doesn’t get snowed in!

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  • burnie
    replied
    We are still free of snow on the Angus coast, but go inland and up a few feet and there's a foot of snow apparently.

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  • Nicos
    replied
    Oh wow! Thanks for warning us Pen.

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  • Penellype
    replied
    After a lot of uncertainty we finally have a definite answer to what happens next. The weather is about to turn MUCH colder from the north with some places seeing large amounts of snow.

    Expect temperatures to plummet on Sunday with daytime maximums around or below freezing and severe and penetrating overnight frosts. It will be windy too, with a bitterly cold easterly wind adding significant wind chill. Snow showers are very likely to arrive from the east, and expect these to penetrate significantly inland. Any snow that settles is likely to stay as it will be too cold for it to melt (although snow does sometimes slowly evaporate). Weather apps are likely to be appalling at predicting where and when the snow will fall, so use the radar eg https://www.netweather.tv/live-weather/radar to see what is heading your way. Because of the nature of showers, some places may see very little snow, others may be under "snow streamers" - bands of showers merging into longer spells of snow. The south coast may be mild enough to see sleet or rain rather than snow.

    A more organized area of snow is likely in the southeast on Sunday. There are Met Office warnings of snow in the east from Saturday lunchtime through until Tuesday (likely to be extended), and already an amber warning in Scotland, which is already buried in places.

    The models are still divided about when it starts to get milder. The GFS model, on which many weather apps are based, has a low pressure introducing warmer air from the west on Thursday. Other models delay this until the weekend or later, with only western areas becoming milder before the end of the weekend (too far ahead for any certainty anyway). Whatever happens, when a low moves into the freezing cold air that will become established over the country, there are likely to be further large falls of snow before it turns to rain.

    So in summary, expect it to become bitterly cold with windchill making it feel like minus double figures and the potential for disruptive snow for at least 5 days, possibly much longer.

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  • Chippy Minton
    replied
    Definitely been winter here, most snow we've had for years, chilly but not proper cold (-3C minimum I guess). A beast from the east would not be welcome as we hope to start getting out more.

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  • Penellype
    replied
    The cold winter continues, with some rain and snow for parts of the southern half of the country over the weekend. Remaining cold until Monday night into Tuesday, when a band of rain and snow moves in from the west warming things up for most areas. The snow should turn to rain south of Scotland as the warmer air arrives.

    A couple of milder days are very likely to be followed by a cold spell starting next weekend, and what happens next appears up for grabs. Some of the models have a few days of cold followed by milder weather, others have a very cold "beast from the east" type setup with a strong easterly wind blowing snow in from the north sea. The models are really struggling with this, with massive swings between runs at times. Therefore take any newspaper stories about the upcoming cold with the usual helping of salt, as nothing is at all certain beyond about a week.

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  • Penellype
    replied
    After a brief short interlude of tolerably pleasant weather today and tomorrow, things are about to turn nasty again. A band of rain looks like getting stuck over the middle of the country on Tuesday and Wednesday with quite a few places seeing upto 48hrs of relentless rain with a serious risk of flooding. It will turn quite mild while it rains. On Thursday a vicious little low winds itself up across the country to add gale force winds to the mix and the rain is likely to turn to snow in the north as the low moves away to the east (some model runs have this further south). It then looks likely to turn colder again for the weekend.

    There are warnings in force already for rain and flooding for Tuesday, Wednesday and Thursday, with an amber warning for the likely worst hit area, mainly in Lancashire and West Yorkshire.

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  • Nicos
    replied
    Wow! Very interesting Pen. Much appreciated

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  • Penellype
    replied
    The SSW is currently occurring and the temperatures over the pole have rapidly warmed:

    Click image for larger version

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    Image from Meteociel.fr.

    The north pole is in the centre of the image, where the warmest temperatures are. The polar vortex (blue) has been split in half. The models show the polar vortex reforming somewhat over the next week or so but remaining displaced from the pole, before possibly weakening again as another warming may occur.

    With regard to cold weather resulting from this, there are plenty of ifs and buts. It is always hard to pin the cause of a weather event down to a specific thing. There appears to be a relationship between a SSW and northern blocking (high pressure over the pole), which can, if it is in the right position, lead to very cold weather here. The important point is that the position of the blocking matters enormously. The winds flow clockwise around a high pressure system which means that any high to our west pulls down a northerly wind, and high to our north pulls in an easterly - both of these are cold. There is therefore a good chance, if high pressure is over the pole, that it will pull in cold winds. However, if the blocking is to our east, or more towards Canada, it can either pull in a southerly wind or have little effect at all, and even if it is to our north, if the Azores high is ridging over Spain any effects from the blocking may be small.

    In addition it can take weeks for the warming to start affecting the troposphere (where weather takes place), and sometimes this seems not to happen at all. There are also complications this year in that the stratosphere has in general been disconnected from the troposphere with a strong polar vortex, usually an indication of low over the pole, and yet large amounts of northern blocking, so there is no guarantee that it will reconnect, and the northern blocking is already giving us some cold weather. This is somewhat unusual, and the effect of a SSW on the current pattern might be different from its affects on the more normal pre-SSW pattern of high to the south and low to the north. We will simply have to wait and see.

    Currently we can expect the weather to remain cold and in general drier than usual (but not completely dry) for the remainder of this week as the wind is generally easterly or northerly. Towards the end of the week the models are favouring high pressure from the west collapsing over us, which would remain cold at first, but if the high moves further south this could allow in milder westerly winds. This is not a certainty and where it goes from there is anyone's guess, particularly with the uncertainties from the SSW thrown into the mix.

    Leave a comment:

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