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St Patrick's Weekend Snow Risk - Technical Discussion Only - READ MOD NOTE POST #1

  • 16-03-2018 9:16pm
    #1
    Registered Users Posts: 21,797 ✭✭✭✭ Kermit.de.frog


    MOD NOTE

    This thread is for Technical Discussion Only - for everything else use the event chat thread Off topic posts will be moved there.

    It’s also a busy thread and as a result the Mod Team will be taking a zero Tolerance approach to trolling, flaming and personal abuse.

    Don’t say you weren’t warned!!

    And please don’t feed - report & let the Mod team deal with Troublesome Posters/Trolls and thread-spoiling

    Thanks




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    "Event" thread here. :)

    https://www.boards.ie/vbulletin/showthread.php?t=2057851222


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Comments

  • Registered Users Posts: 13,187 ✭✭✭✭ M.T. Cranium


    North German radar loop gives an idea what Irish Sea might produce ...

    http://www.wetterzentrale.de/de/reanalysis.php?map=34&model=rad&var=415&jaar=2018&maand=3&dag=16&uur=2125&h=1&nmaps=32

    remember Baltic is close to 1 C, Irish Sea 6 to 8 C. North Sea now 2 to 6 C in the sector likely to be upwind from Ireland.

    Gusts to 107 km/hr at Arkona (the northern point of eastern Germany).

    The snow further south was produced by an eastward-moving wave on the arctic front and is not part of the forecast scenario.


  • Registered Users Posts: 4,646 ✭✭✭ thomasj


    I'm having problems with that link MT.

    Edit: got it working on the desktop site seems to be problems from the old app


  • Registered Users Posts: 21,797 ✭✭✭✭ Kermit.de.frog



    Gusts to 107 km/hr at Arkona (the northern point of eastern Germany).

    Convective gusts? Pretty much confirms the drifting risk...


  • Registered Users Posts: 829 ✭✭✭ Neddyusa


    Convective gusts? Pretty much confirms the drifting risk...

    Was just going to ask:
    What are forecast windspeeds for Sat night/Sun relative to the last time?

    It was the drifting that caused all the disruption on roads here rather than the amount of snow on the Tuesday - Thursday of the last spell.


  • Registered Users Posts: 7,759 ✭✭✭ Calibos


    Convective gusts? Pretty much confirms the drifting risk...

    Ah Jaysus, dont tell me strong winds are going to both blow the streamers over me too quickly and carry salty sea spray aloft over me onto Bray Seafront and environs ruining any chance I have of more than 5cm of accumulation like they did with Emma?? Say it aint So?


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  • Registered Users Posts: 12,653 ✭✭✭✭ ninebeanrows


    Harmonie showing some sweet spots getting 20-30cm, more generally Leinster 5-15. All streamer line dependent


  • Registered Users Posts: 342 ✭✭ kittyn


    @Weathercheck ....... So where roughly are these sweet spots?


  • Registered Users Posts: 9,183 ✭✭✭ sdanseo


    kittyn wrote: »
    @Weathercheck ....... So where roughly are these sweet spots?

    About as easy to forecast as the winning lotto numbers at this point.


  • Registered Users Posts: 5,359 ✭✭✭ highdef


    kittyn wrote: »
    @Weathercheck ....... So where roughly are these sweet spots?
    In reality, these sweet spots are very much nowcast scenarios. They are virtually impossible to forecast with any sort of accuracy. I managed almost 20cm during daylight hours on the Wednesday of the recent snowy spell. Yet places less than 10km away for hardly anything. That was pure luck for me and could not be forecasted.


  • Registered Users Posts: 256 ✭✭ Mount Vesuvius


    Some places getting a good dumping from streamers. Probably should be Red Alert in areas but impossible to tell where yet untill they form.

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  • Registered Users Posts: 256 ✭✭ Mount Vesuvius


    This is the atmosphere profile for Sunday midday showing
    the 500 hPa geopotential height (contours) and temperature at 850 hPa (shading) from the ECM

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  • Registered Users Posts: 1,591 gabeeg


    This is the atmosphere profile for Sunday midday showing
    the 500 hPa geopotential height (contours) and temperature at 850 hPa (shading) from the ECM

    Curvier the better, right?


  • Registered Users Posts: 1,858 ✭✭✭ Artane2002


    Is this fax chart showing the possibility of heavy, persistent snow clipping the south coast on Sunday? I could be reading this wrong but it looks like a convergence zone to me? This is where two air masses meet causing very heavy precipitation I think. The Boscastle floods of 2004 were caused by a convergence zone from what I've read on Netweather. Professional help would be appreciated. Credit to supernova on Netweather for the image.
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  • Registered Users Posts: 256 ✭✭ Mount Vesuvius


    @Gabeeg
    Position of trough in upper atmosphere at noon. These steer what's underneath so I'm expecting lots of activity especially around 6am Sunday. Instability over Irish sea helping to bolster up some streamers


  • Registered Users Posts: 8,195 ✭✭✭ Gaoth Laidir


    Artane2002 wrote: »
    Is this fax chart showing the possibility of heavy, persistent snow clipping the south coast on Sunday? I could be reading this wrong but it looks like a convergence zone to me? This is where two air masses meet causing very heavy precipitation I think. The Boscastle floods of 2004 were caused by a convergence zone from what I've read on Netweather. Professional help would be appreciated. Credit to supernova on Netweather for the image.
    445730.gif

    Yes, that's a convergence line. The Arpege is picking that up too in the form of an enhanced band of snow running right through Manchester and Liverpool tomorrow night.

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  • Registered Users Posts: 8,195 ✭✭✭ Gaoth Laidir


    The real moneymaker in this setup is to be found at mid-levels, in the form of a concentrated pool of very cold sub-minus 20 air advecting low partial thicknesses westwards. It gets into the east by sunset Saturday, so this will mark the start of the heaviest showers. By midnight to 6 am we're in the core of it, so showers should be reaching their peak by sunrise Sunday, gradually losing intensity throughout the morning and afternoon. Note: the 850 hPa charts don't really show the same level of change, remaining within a degree or two of -10 °C throughout.

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  • Registered Users Posts: 256 ✭✭ Mount Vesuvius


    Nice one Gaoth Laidir.

    Also latest Arpege shows the intense precip zone. Going to be lots of fun and games if these models are correct.

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  • Registered Users Posts: 12,653 ✭✭✭✭ ninebeanrows


    MS paint of Harmonie accumed precip by 18z Sun


  • Registered Users Posts: 3,986 ✭✭✭ giveitholly


    MS paint of Harmonie accumed precip by 18z Sun

    Any chance of getting a countrywide map from harmonie


  • Registered Users Posts: 256 ✭✭ Mount Vesuvius


    Harmonie showing great accumulations there Weathercheck.
    Even taking away 5-10 of rain /sleet early Saturday still leaves loads of white gold.


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  • Registered Users Posts: 13,187 ✭✭✭✭ M.T. Cranium


    Any chance of getting a countrywide map from harmonie

    What location are you interested in?

    Looks like the streamers are predicted to run inland WSW from that guidance.

    Anyway, it's likely to be all over by Sunday night and sea effect snow has a fairly quick settling rate so give it most of Monday and Tuesday to evaporate, should be largely gone by mid-week except in higher parts of the southeast where it may be falling on top of existing snow and a few places could see 50 cm new snow.


  • Registered Users Posts: 13,187 ✭✭✭✭ M.T. Cranium


    The current temperatures in Scandinavia are awe-inspiring given the calendar date:

    http://www.meteociel.fr/observations-meteo/temperatures.php?region=su

    this is the high pressure area that will drift down to Scotland and then Ireland over the next three or four days.


  • Registered Users Posts: 14,307 ✭✭✭✭ nacho libre


    AM_2018316_2118.jpg

    It's coming...
    Heavy snow in parts of Cambridge now.


  • Registered Users Posts: 21,797 ✭✭✭✭ Kermit.de.frog


    No upgrades on this mornings models. If anything, maybe a slight tempering of precipitation potential. This is down to nowcast now anyway...


  • Registered Users Posts: 14,307 ✭✭✭✭ nacho libre


    The hirlam model tends to have a good handle on precipitation amounts. It still looks fairly good to me for the east coast of Ireland

    hirlamuk-45-48-0.png?17-05


  • Registered Users Posts: 13,187 ✭✭✭✭ M.T. Cranium


    Temperatures near the core of the arctic high are quite extreme, -35 C at one location in south central Norway. I see higher pressures than modelled too, but that's probably a false conversion from elevation situation (1047 mbs near that -35 C reading). Winds continue to howl out of the east from northern Poland to the central North Sea and now into Britain too, arctic front appears to be approaching Wales (it is oriented WNW-ESE but will start to form more of an arc this morning and slam into Leinster around 0900h. Somewhat delayed response likely in terms of streamer production, would expect sporadic ones later morning then more organized by mid-afternoon.

    We've had some good entries to our snap contest, if you missed it, join in. I plan to get a moderator to lock this contest thread at 1201h today then we can open it up for commentary on the results by Sunday morning perhaps.

    Not planning any significant changes to forecast after reviewing all guidance, looks to be on track.


  • Registered Users Posts: 4,964 ✭✭✭ Chris_5339762


    Didn't expect such large streamers in the UK at 730am.....


  • Registered Users Posts: 8,195 ✭✭✭ Gaoth Laidir


    The 06Z radiosonde ascent from Albemarle (just west of Newcastle, England, so upwind from us) shows the inversion at around 700 hPa about 2 degrees weaker than forecast. Actual temperature is -15 while the 00Z ECM had it at -12 to -13 for that area at 06Z.

    This means either the high is weaker/further north than forecast or the cold pool is making slightly faster progress east. This could mean slightly heavier showers earlier for the east this evening.

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  • Registered Users Posts: 8,195 ✭✭✭ Gaoth Laidir


    Didn't expect such large streamers in the UK at 730am.....

    It looks to be more drizzle/snow grains, like the Friday here two weeks ago.


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  • Registered Users Posts: 8,195 ✭✭✭ Gaoth Laidir


    Sub-zero wet-bulb temps making steady progress westwards.

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