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Thread: Penellype's Weather Channel

  1. #233
    burnie is offline Veggie gardener
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    Not that cold up here today, plus 2 in the greenhouse overnight and 9 degrees outside and a bit of sun, but a bitter cold wind. Was over at my daughters in Perth and the hills were mostly white with snow, but none lower down, saw lots of wildlife driving to and fro, swallows and house martins around and 2 brown hares near our village on the return journey, must get over with the camera and big lens.

  2. #234
    Penellype's Avatar
    Penellype is offline Mature Fruiter
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    The worst of the cold this time seems to have been in the south and west. Showers coming in off the north sea have decayed to cloud for more northern and eastern areas, protecting us from the worst of the cold.
    A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP. - Leonard Nimoy

  3. #235
    Penellype's Avatar
    Penellype is offline Mature Fruiter
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    The cold spell is coming to an end now as the wind backs round to the west. The next couple of days should be reasonable, although the temperatures will be nothing to get excited about and there remains a slight frost risk at night.

    Tomorrow's chart looks like this:

    Penellype's Weather Channel-fri-28-apr.jpg

    Low pressure is in the atlantic with the high building over Scandinavia. This is going to prevent the low from taking its usual track and it will extend southwards instead. This is always tricky to forecast, with the exact track of the low, and therefore the position of any associated fronts and rain, subject to considerable uncertainty. Currently Sunday's chart looks like this:

    Penellype's Weather Channel-sun-30-april.jpg

    The wind is now coming up from the south east so it will be warmer, but with the low in this position it is likely to be wet, particularly in the south and west. Notice the next low waiting to the south of Greenland, and the high curving back towards Greenland - this is the start of northern blocking and will fix the weather pattern for at least the next month or so. The lows are becoming stuck in the atlantic, and the low south of Greenland is about to suck warm air north to join the developing high. As this happens the winds will swing round to the east. This is the position forecast for Thursday:

    Penellype's Weather Channel-thu-4-may.jpg

    In winter this is a classic cold setup - it would be frosty or snowy and bitterly cold. Thankfully in May it isn't so bad, but the air is still coming from the Baltic so it is not going to be a heatwave. However it would be mostly dry, except perhaps for the south east corner of the country.

    The important aspect of this setup is the track of the low pressure systems which are starting to move underneath the blocking high. If they stay to the south of us it should be mostly dry and average to cool. If they establish a track further north we could be in for a cool and wet month or two. Currently the GFS model appears to be favouring the 2nd of these, but this is not the only possible solution from this position.

    This chart, for 9th May, would be cool and pretty wet, especially in the south:

    Penellype's Weather Channel-sat-9-may.jpg

    The ensemble chart for York shows that earlier predictions of a possible heatwave for next week are unlikely to happen, and that the current GFS operational run (thick green line), from which the above charts were taken, is one of the colder ones:

    Penellype's Weather Channel-ens-27-apr.jpg

    Note that the rainfall spikes at the bottom have generally increased in size since the last time I posted one of these.
    A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP. - Leonard Nimoy

  4. #236
    Ms-T is offline Super Moderator
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    Happy to have more rain in the south east we need it badly .

  5. #237
    Penellype's Avatar
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    No rain here today, having had it forecast for much of the past week. It fizzled out around Leeds.

    The models are sticking to the idea of the high pressure building to the north and moving across towards Greenland (retrogressing), but it is slightly further south than in my last post, which reduces the rain risk. However, a worrying development over the past day or so is that around 9th May most of the runs are forecasting another cold snap:

    Penellype's Weather Channel-ens-1-may.jpg

    Some of these runs are pretty cold, quite cold enough for night time frosts and wintery showers. The trouble with this sort of pattern is that it rather easily puts us into a northerly wind:

    Penellype's Weather Channel-tue-9-may.jpg

    This isn't quite as directly from the north as last time (the thick green line is not one of the coldest), but its coming from a pretty cold part of the world and it wouldn't take much of an adjustment to put us directly in the firing line.

    Don't put the fleece away just yet!
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  6. #238
    Penellype's Avatar
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    Everything has been progressing very much as expected, with most places away from the far south west staying dry and the wind coming from the east or north east. Western areas have had plenty of warm sunshine but colder nights, while eastern areas have been cooler and cloudier but with warmer nights. It has felt very chilly at times in the fairly stiff breeze.

    Things remain much the same for the next few days, but the high pressure is gradually slipping away westwards and this will eventually lead to a change in wind direction and possibly some much needed rain as low pressure moves in:

    Penellype's Weather Channel-fri-12-may.jpg

    By Friday the low is bringing up warmer air from the south west, but there would be fronts associated with this bringing rain. Quite how much rain is open to question. After this we have disagreement between the models, with the GFS wanting to keep us wet and possibly fairly windy for a week:

    Penellype's Weather Channel-gfs-tue-16-may.jpg

    while the ECMWF brings back the high pressure:

    Penellype's Weather Channel-ecm-tue-16-may.jpg

    Therefore, although the ensemble chart looks quite wet after the end of next week, I wouldn't bank on this actually happening:

    Penellype's Weather Channel-ens-7-may.jpg

    For the next week or so keep an eye on the forecasts because where skies are clear and winds fall light there is still the possibility of ground frost in vulnerable areas.
    A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP. - Leonard Nimoy

  7. #239
    Penellype's Avatar
    Penellype is offline Mature Fruiter
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    So, the forecast rain has arrived, at least if you live in the western half of the country. We've had light intermittent drizzle here but no measurable rain

    The low pressure that is bringing the rain is moving up from the south, bringing a showery airstream which will persist over the weekend. The showers are likely to be heaviest in the north with hail possible. The low pressure sticks around to the north west of Scotland, with more fronts moving across the country on Monday and Tuesday. There will be drier interludes and the flow is from the south west so it will be warm and probably muggy. The warm spell doesn't last and by Friday temperatures will be nearer average for the time of year.

    Beyond that there is more uncertainty, with this morning's GFS operational run (thick green line) going quite cold, but with little support from other ensemble runs:

    Penellype's Weather Channel-ens-12-may.jpg

    The rainfall spikes along the bottom show the increased risk of rain for the next week or so, after which it seems to mostly fizzle out. Some of this, particularly around 17th-19th could well be in the form of thunderstorms as a cold front moves into very warm air.

    Note how unlevel the red 30 year average line is, illustrating the vast range of temperatures possible at this time of year.
    Last edited by Penellype; 12-05-2017 at 03:55 PM.
    A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP. - Leonard Nimoy

  8. #240
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    Greenleaves is offline The Weed Fairy
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    Penellype, shall we edit the thread title to Spring/Summer or would you like a new sticky thread for that?
    Last edited by Greenleaves; 12-05-2017 at 05:33 PM.
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