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Snow and Ice Warning : Saturday(PM)/Sunday 9th/10th Dec - TECHNICAL ANALYSIS ONLY

  • 09-12-2017 11:22am
    #1
    Moderators, Science, Health & Environment Moderators Posts: 7,132 Mod ✭✭✭✭ pistolpetes11


    This is the Technical Scientific thread for discussion on tonight and tomorrows possible snow event, will it snow in my back garden at such and such a time will just be deleted or merged into the other thread which will be linked below



    https://www.boards.ie/vbulletin/showthread.php?t=2057817783


«13

Comments

  • Registered Users Posts: 2,728 ✭✭✭ Rebelbrowser


    I wonder could I ask again a question I posed in the other thread, namely what is different about this set up from normal that gives the big snow risk? I thought you would need deep imbedded cold for such a battleground scenario to occur but I dont see that in the upper temps. What am I missing?


  • Registered Users Posts: 3,316 ✭✭✭ ZX7R


    Technical question, as mentioned in the other thread about heavy perception, would met eairann take into account, evaporation snow fall into account when making there forecast for snow fall tonight, as well as the low temperatures


  • Registered Users Posts: 829 ✭✭✭ Neddyusa


    Anyone care to make lying snow max predictions for ME stations tomorrow and Monday morning?

    Sun - Mt Dillon 16 cm

    Mon - Gurteen 21 cm


  • Registered Users Posts: 4,438 ✭✭✭ 17-pdr


    6Z Hirlam for +24 hrs. Indicates the maximum northward position of the front before it starts pulling away to the south and east again.

    hirlamuk-1-24-0_jtu1.png


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


    It is important to note- that whilst i don't know the actual parameters behind the above snow chart. In general rain/snow type charts will shade in snow even if there is only a small amount of the precip falling as snow.

    Indeed as of yesterday - the EC was showing 50-50 rain and snow in the precipitation for Dublin region. Inland it was 90%+ snow.


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  • Registered Users Posts: 8,194 ✭✭✭ Gaoth Laidir


    Dublin TAF shows light rain from midnight, tempo sleet from 3 am as light variable winds increase easterly 15 gusting 25 knots from 2 am. The airport may be about the extent of the marine layer, further inland should see more of a snowy nature.

    Knock is hell for leather snow...

    TAF EIKN 091100Z 0912/1012 VRB03KT 9999 FEW010 SCT025
    PROB30 TEMPO 0916/0921 3000 BR BKN005
    BECMG 0921/0924 11012KT 3000 -SN SCT003 BKN007
    TEMPO 0923/1012 1200 SN OVC002
    BECMG 1001/1003 08015KT
    TEMPO 1003/1006 09016G26KT BECMG 1010/1012 05013KT=
    I wonder could I ask again a question I posed in the other thread, namely what is different about this set up from normal that gives the big snow risk? I thought you would need deep imbedded cold for such a battleground scenario to occur but I dont see that in the upper temps. What am I missing?

    You won't see that in the upper charts. Looking at 850 hPa temperatures is useless in this setup as we're not talking about convective snow in normal lapse rates. The sounding below shows how temperature is actually fairly constant with height through the bottom few thousand metres, and is at or below zero. 850 hPa temp is only -2 °C, which would not normally hint at anything other than rain.

    sondagewrf_214_450_24_0_1512808464.png
    ZX7R wrote: »
    Technical question, as mentioned in the other thread about heavy perception, would met eairann take into account, evaporation snow fall into account when making there forecast for snow fall tonight, as well as the low temperatures

    As the whole lower atmosphere is completely saturated there is no scope for evaporative cooling.


  • Moderators, Science, Health & Environment Moderators Posts: 10,455 Mod ✭✭✭✭ Meteorite58


    Raining lightly now near Tralee at 5.1C ( could see the mountains get a bit whiter before they became obscured by cloud ). Will be interesting watch the front move into the colder air as it moves up the country later this evening.

    RAMfbxn.gif

    6V8Jhdh.png?1

    temp_uk_qdg7.png

    3eEtNLc.png?1

    tempresult_gic6.gif

    nmm_uk1-26-35-4_akg6.png

    No doubt driving conditions Sunday/ Monday going to be testing for a lot of people,

    nmm_uk1-32-36-4_sqt7.png


  • Registered Users Posts: 17,664 ✭✭✭✭ JCX BXC


    Temperature quite low here, while Clare is on a yellow rainfall warning I wonder could heavy precip drop the temperature enough to have a flurry?


  • Registered Users Posts: 8,194 ✭✭✭ Gaoth Laidir


    The ECM Extreme Weather Index is high for total precipitation by tomorrow night.

    435700.PNG


  • Moderators, Science, Health & Environment Moderators Posts: 10,455 Mod ✭✭✭✭ Meteorite58


    Frontal rain bearing cloud off the SW

    cDiPyW2.jpg?1


    Dg8ZmbG.gif


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  • Registered Users Posts: 8,194 ✭✭✭ Gaoth Laidir


    The fact that we have a pair of low centres by morning - one off Wexford but another in Galway Bay - could lead to some subtle variations in the exact extent of that easterly marine layer in the east.

    QSg7ZaR0To.gif

    The 12Z ICON has the main bulk of precip back further south, in line with the other models. Note that this model has a known drizzle bias, so it may be overdoing the precip slightly.

    A5hR6bNPmu.gif

    Lastest forecast soundings are still showing heavy (wet) snow for many low-lying areas of the midlands and west during the morning.


  • Closed Accounts Posts: 2,520 nagdefy


    I feel this event is going to be very much a nowcast.

    There'll be surprise falls for some, and others who appeared to be in more favourable areas prior to the event may face disappointment.

    That low off Rosslare could drag some colder air further south east possibly?

    I'm down with flu symptoms and stuck in Portlaoise :( Was looking forward to getting some pics at home as i'd rate our chances of a decent fall at 70% or so.


  • Registered Users Posts: 17,664 ✭✭✭✭ JCX BXC


    Almost forgot about the TAF's!

    Knock:

    BECMG 0921/0924 11012KT 3000 -SN SCT003 BKN007
    TEMPO 0923/1012 1200 SN OVC002

    Light Snow from 9pm, temporarily moderate from 11pm. Gonna be a white out there!

    Shannon:

    TEMPO 1009/1014 3000 -RASN

    Periods of sleet from 9am-2pm tomorrow.

    Dublin

    TEMPO 1002/1009 11015G25KT 3000 RASN

    Periods of sleet betwen 2am-9am

    That's it, nothing for Casement or Cork in the 5pm TAF's other than rain.


  • Registered Users Posts: 8,194 ✭✭✭ Gaoth Laidir


    I'm a bit worried about the extent of cloud cover across the country this evening. With that in place there won't be much cooling in that central slab of the country where snow could fall. Almost everywhere us still above zero at the moment. With cloud on the increase its an uphill battle to hold onto our cold layer. It could swing the wrong side of marginal for low levels, or at least a wet mix. Need it to clear a bit.


  • Registered Users Posts: 8,194 ✭✭✭ Gaoth Laidir


    Snow warning for Knock airport

    EIKN AD WRNG 02 VALID 092200/101000 SNOW MOD 5 TO 10CM FCST =

    Only frost warnings for the Dublin and Casement, and crucially only until 1 am. Nowt after that.

    EIDW AD WRNG 01 VALID 091700/100100 FROST MOD GND AND FBL AIR DEPOSITIONS LIKELY FCST =
    EIME AD WRNG 01 VALID 091600/100300 FROST MOD GND AND FBL AIR DEPOSITIONS LIKELY FCST =


  • Moderators, Science, Health & Environment Moderators Posts: 10,455 Mod ✭✭✭✭ Meteorite58


    The rain proper arriving into the SW now.

    5.8C now in Tralee RH 86% , SE wind avg 29 km/h ,Bar 997.2 hPa Falling Rapidly

    KDzFsMA.png?1

    temp_uk_vdq1.png


    The charts for the next 24hrs.

    qojLmBE.png?1

    juUfWg1.png?1

    3UzPY2a.png?1


  • Moderators, Science, Health & Environment Moderators Posts: 10,455 Mod ✭✭✭✭ Meteorite58


    High cloud moving up the country with a slight rise in Temps in places

    R0PlGiV.jpg?1

    latest-ir-color_fmt4.gif


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


    HIRLAM accumulations by midday tomorrow

    hirlamuk-45-24-0.png?09-17


  • Moderators, Science, Health & Environment Moderators Posts: 10,455 Mod ✭✭✭✭ Meteorite58


    tempresult_kti7.gif

    iconeu_uk1-45-28-0_zhi3.png

    A lot of water falling in one form or another, lucky Monday is set to be mainly dry.

    iconeu_uk1-25-28-0_gck3.png


  • Registered Users Posts: 303 ✭✭ gimpotronitus


    HIRLAM accumulations by midday tomorrow

    hirlamuk-45-24-0.png?09-17

    This shows south dublin around the rathfarnham, ballinteer, tallaght area with a possible covering.

    But goes against what MT was saying in his update.


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  • Moderators, Science, Health & Environment Moderators Posts: 10,455 Mod ✭✭✭✭ Meteorite58


    The Zoom facility on the ARPEGE. That is as much as you can open the page .Not too sure how accurate this is going to be, follow the link below to zoom in closer.

    http://www.meteociel.fr/modeles/arpegezoom.php?mode=45&x=384&y=384&ech=26&zoom=2.1


    2496_far0.png

    8382_hfp6.png


  • Registered Users Posts: 4,044 ✭✭✭ arctictree


    The map of Wicklow does not seem to take local topography into account. For example, there is high ground to the east of roundwood (where I live). Also there are valleys with huge differences in elevation across only a few linear miles e.g Glendalough.


  • Registered Users Posts: 2,023 ✭✭✭ Donegal Storm


    That's because of the resolution of the model, it's only got 10km grid squares, no model has high enough resolution to take individual valleys into account. I'm not sure how they model height, if they take the average across a grid square or the highest point.


  • Registered Users Posts: 8,342 ✭✭✭ Speak Now


    tempresult_kti7.gif

    Almost laughable in that sequence the reluctance of the rain to turn into snow when it hits Waterford at KilkennyWexford boundary. Is it snow or Liam McCarthy!!!!!


  • Registered Users Posts: 4,044 ✭✭✭ arctictree


    That's because of the resolution of the model, it's only got 10km grid squares, no model has high enough resolution to take individual valleys into account. I'm not sure how they model height, if they take the average across a grid square or the highest point.

    Sounds about right. Although take Glendalough for example. Average height would probably be much higher than the places where people live.


  • Registered Users Posts: 10,347 ✭✭✭✭ MJohnston


    The WRF NMM is the best resolution model I think we have for Ireland, but the 18z is taking forever to roll out, here's the current latest frame available:

    nmm_uk1-45-7-4_egj2.png


  • Registered Users Posts: 2,023 ✭✭✭ Donegal Storm


    Arome is 1.3km, no idea how reliable or accurate it is but this is what it's showing for the morning. A patchy and fairly light covering for most at lower levels, a few favoured areas getting a good dumping though

    aromehd-45-14-0_wtx2.png


  • Registered Users Posts: 213 ✭✭ MetLuver


    I'm a bit worried about the extent of cloud cover across the country this evening. With that in place there won't be much cooling in that central slab of the country where snow could fall. Almost everywhere us still above zero at the moment. With cloud on the increase its an uphill battle to hold onto our cold layer. It could swing the wrong side of marginal for low levels, or at least a wet mix. Need it to clear a bit.

    I was thinking the same thing since this morning, it's nice to hear someone else mention it. The models cannot take these details onto account and so it may be a good idea to take snow depth charts less seriously with this in mind.


  • Registered Users Posts: 10,347 ✭✭✭✭ MJohnston


    WRF run is a bit more complete now:

    nmm_uk1-45-19-4_bbd6.png


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  • Registered Users Posts: 2,617 ✭✭✭ Rougies


    MJohnston wrote: »
    WRF run is a bit more complete now:

    It's very bullish on the shadow effect of the Blackstairs and Slieve Bloom mountains!


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