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o0herbie

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    South West and Central Southern England Regional Weather Discussion 09/12/2017 onwards

    in Regional Discussions

    Posted

    8 minutes ago, Frosty hollows said:

    A surprising amount of snow here. The M4 is literally the cut off between warm and cold sectors!

    You're not wrong - I live a couple of miles south of Junction 12, at above 100m. 1cm of snow has been washed away by the rain. They have a few inches of snow in Reading, just 5 miles away and 40m high - although north of that road!!

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    Model Output Discussion - cold spell to end Autumn

    in Model Discussion Archive

    Posted

    13 minutes ago, Quicksilver1989 said:

    Right, I've had a look at the charts today and thought I'd offer my interpretation of where things go from here. A lot going on but will summarise the three potential routes we are most likely to go down at this point.

    The first scenario is exactly what the GFS shows, we have this broad synoptic pattern at T144 with the GFS

    GFS at T144                                               Ideal scenario following on                    Further down the line

    image.thumb.png.8341250ccaccd37da4c144a3b917f64e.pngimage.thumb.png.0d2bc1ea874345a4c14a3f9e3f69165c.pngimage.thumb.png.095d93b22f21e7d3440ede8ad9ea3106.png

    Which is very good as it halts the displacement of the cold uppers to the east and we get a potential channel low. If we get the perfect undercut we could get the ideal scenario of heights improving to our North and a displaced Azores high moving north and pumping warm air to Greenland. Getting something like this requires everything to fall in the right place though.

    The GFS is actually pretty close to this, the Scandi low hovers around for a bit before the Azores and arctic high link up . The net result is a very cold easterly flow making its way across the UK. The 06z gets a 9/10 from me. There's a fair chance to get to the middle panel (may take a few tries), I'd rate the chances around 30-40% because the GFS is being consistent with the cut off high again.

    ECM meanwhile still has the undercut but further east, the result being a less cold flow over the UK, though I think the next logical step would be to get another northerly, though with a PV lobe around NE Canada ridging may be a bit troublesome. This would probably mean repeated NW'y winds until an opportunity for a displaced Azores high occurs. It's a 7 out of 10 run from me because we get that cold northerly in the end of the week at least! I'd guess a 50% chance of this path being taken.

    ECM at T144                                              
    image.thumb.png.5002e795f621d3dac731f4ad15a8e200.png

    Finally, thankfully looks unlikely now but this was the worst case scenario

    image.thumb.png.a516a501db9104b2603c1b3bce50b3d8.png image.thumb.png.cf99a55f3d7d1716098806a6e4ec4e4a.png



    Hence my fear from the 18z last night. However the pressure didn't build enough and it wasn't that bad a run. So I was probably a bit quick to fear the worst. I think this scenario only has a 5-15% chance of verifying now.

     

     

    As a long time lurker and non-poster, I'd like to highlight this post as one of the most useful I've ever read on here and implore other posters to use this as an example of something that helps those of us who don't completely 'get it'. Thank you Quicksilver1989

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