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Good Friday Low Pressure System

  • 31-03-2010 9:23pm
    #1
    Closed Accounts Posts: 4,279 ✭✭✭


    Our next weather comes early Friday morning as a low pressure system arrives from the west, bringing some snow on hills on its leading edge in the southern half of the country, in a moderate southerly wind.

    The system is currently deepening south of Greenland, as upper divergence increases in the left exit region of a strengthening jet streak.

    109390.gif

    109391.gif

    By 7am Friday morning the system becomes vertically stacked and reaches its minimum pressure of around 988hPa just off the Kerry coast. Precipitation rates will have reached their peak by then and will start to decrease as it pushes eastwards across the country. Still, it will initiall give spells of snow on hills above ~250m, especially in the southwest, but will turn more and more to rain as the warm sector crosses the south.

    100331_1200_42.png

    By midday Saturday, the backbending occlusion should still be giving some spells of precipitation, rain for most, but with snow lowering to around 200m later in the day behind it. By that stage precipitation should be dying out as a transient ridge approaches Saturday night, giving a cold night and a bright start to Sunday.


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Comments

  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    I am wondering if there could be some convective thundery showers developing on Friday afternoon as a slack trough develops on the back edge of the main frontal zone?

    No sure of how unstable the airmass will be on the southern flank of the frontal mass, but at the moment it does look that southern areas esp could be at risk, but all depends on how north the main frontal zone will lodge, and at this very early stage, it looks like it may lodge/pivot over the northern half of the country, which could help lift temps in the southern half of the country if the sun breaks though from any considerable length of time, triggering off an few big mammas!

    Maybe not though. :o

    Edit: Latest DMI HIRLAM I think may be suggesting this as well:

    109400.gif

    although hard to read too much into yet.


  • Closed Accounts Posts: 4,279 ✭✭✭Su Campu


    The Dublin Airport GFS forecast sounding does hint at a narrow window in the late afternoon where a few hundred joules of CAPE may be available, especially with some diabatic heating. Probably most likely in the southeastern third of the country. One to watch

    u3764_10040218_3112.gif


  • Closed Accounts Posts: 4,279 ✭✭✭Su Campu


    Tomorrow afternoon is indeed looking good for some of the biggest showers yet this year. The ingredients are there for an interesting afternoon for the southern half of the country.

    With good boundary level moisture content, where the post-frontal cloud breaks, allowing decent insolation, several hundred Joules of CAPE are likely, and with equilibrium temperatures of possibly -45°C, electrification is highly likely. Heavy downpours of rain and hail could give localised flash flooding.

    The key will be how much insolation we get - if the cloud breaks for long enough, and there is no cirrus shield, surface temperatures of 8°C or more should kick off the show.

    I'm sure ESTOFEX will issue us with at least a thunderstorm area, if not a Level 1, in tonight's forecast.

    109491.JPG

    u3764_10040215_0106.gif


  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    Certainly a notable bank of instability behind that approaching front alright:

    109524.jpg
    Source: http://en.vedur.is/weather/observations/satellites/#teg=iceland


  • Registered Users Posts: 6,827 ✭✭✭pauldry


    Isnt weather great! :)


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  • Registered Users Posts: 2,655 ✭✭✭delw


    typical,i wont b here to see any of it,can any1 tell me what its to b like in holland/belguim for the weekend cheers


  • Closed Accounts Posts: 13,224 ✭✭✭✭SantryRed


    I'm not really into all the stats but just wondering does anyone know what the weather will be like in North Dublin around 3 tomorrow? Suppose to be playing a match...


  • Banned (with Prison Access) Posts: 5,524 ✭✭✭owenc


    im thinking we could get snow or sleet tomorrow with maxes about 4c ...today in the sunshune it was about 4-5c..


  • Registered Users Posts: 1,115 ✭✭✭Takeshi_Kovacs


    Is there still a chance of snow falling on hills 600m and above from this system?


  • Banned (with Prison Access) Posts: 5,524 ✭✭✭owenc


    yes i think we will have sleet here with temps around 3-4c... anyway whats those wee heart things for? snow higher up but certainly not that high up !


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  • Registered Users Posts: 2,832 ✭✭✭NufcNavan


    Let me guess, this will be the apocolypse will it??


  • Closed Accounts Posts: 228 ✭✭wild handlin


    Anyone got anything more to add about the possability of thunderstorms tomorrow??
    What parts of the country could we see a potential? Is it just the south, or could the West bear something??


  • Registered Users Posts: 1,379 ✭✭✭snow ghost


    NufcNavan wrote: »
    Let me guess, this will be the apocolypse will it??

    Hopefully not, I have things to do on Saturday... bloody judgement day always comes around quicker than you expect, and you'd think God could at least wait until the pubs are open. ;)


  • Registered Users Posts: 1,379 ✭✭✭snow ghost


    owenc wrote: »
    anyway whats those wee heart things for?

    Owen, they are the sacred hearts of Jesus - tis easter weekend you know, when Jesus turned rocks into Easter eggs. Everyone with a heart next to their profile when signed in is going to Heaven, anyone without one is doomed!!! :eek:


  • Registered Users Posts: 1,379 ✭✭✭snow ghost


    It's been a beautiful day here all day - was freezing this morning with snow on the mountains and a bit on the side of the road, then sunny all day.

    That said I'm looking forward to heavy rain tomorrow, and hopefully some thunder strikes.


  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    Anyone got anything more to add about the possability of thunderstorms tomorrow??
    What parts of the country could we see a potential? Is it just the south, or could the West bear something??

    Still a hard one to call Will. If heavy showers or thunderstorms do occur certainly the southern half of the country would be most at risk, but as stated yesterday it depends on how far north the frontal zone will move, which even at this stage seems a little uncertain.

    Latest models have the mid western region within the highest threat zone but really could be a nowcast situation, should this situation evolve that is :o


  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    snow ghost wrote: »
    Owen, they are the sacred hearts of Jesus - tis easter weekend you know, when Jesus turned rocks into Easter eggs. Everyone with a heart next to their profile when signed in is going to Heaven, anyone without one is doomed!!! :eek:

    There's none beside mine Snow, I am doomed! :(:o:(


  • Registered Users Posts: 1,379 ✭✭✭snow ghost


    There's none beside mine Snow, I am doomed! :(:o:(

    Get thee behind me satan! :D

    Ay least it's warm in Hell Deep.;)

    Anyway you'll be well prepared for it... living so close to Heavenly Mayo, yet just over the border, must be like purgatory.


  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    snow ghost wrote: »
    Get thee behind me satan! :D

    Ay least it's warm in Hell Deep.;)

    Anyway you'll be well prepared for it... living so close to Heavenly Mayo, yet just over the border, must be like purgatory.

    :D


  • Closed Accounts Posts: 520 ✭✭✭Domscard


    snow ghost wrote: »
    Owen, they are the sacred hearts of Jesus - tis easter weekend you know, when Jesus turned rocks into Easter eggs. Everyone with a heart next to their profile when signed in is going to Heaven, anyone without one is doomed!!! :eek:

    :D:D:D


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  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    The GFS, along with the UKMO, seem to be hinting at a band of potent showers striking the South and Southeast coasts tomorrow night in their last couple of runs also:

    ukprec.png

    this is probably from the main area of instability that is forming on the the back end of the front as we speak as it swings around the forecast slack area of low pressure as it moves to or over the south of Ireland. Saturday could be another day for shower potential too. We'll see.


  • Closed Accounts Posts: 228 ✭✭wild handlin


    Still a hard one to call Will. If heavy showers or thunderstorms do occur certainly the southern half of the country would be most at risk, but as stated yesterday it depends on how far north the frontal zone will move, which even at this stage seems a little uncertain.

    Latest models have the mid western region within the highest threat zone but really could be a nowcast situation, should this situation evolve that is :o

    Many thanks for that Deep Easterly. Hopefully something will develop tomorrow.


  • Closed Accounts Posts: 4,279 ✭✭✭Su Campu


    The postfrontal instability comma system is associated with an upper vort max, which is progged to weaken as it passes to the south early Friday, before reintensifying over northern France later. It should therefore not directly be an issue for us.

    ESTOFEX have gone with thunderstorms for the southern half of the country tomorrow afternoon, basically in line with the ideas posted above.

    109572.jpg
    A cold front crosses UK and NW/N-France during the daytime hours from west to east with a classic postfrontal shower/thunderstorm set-up. A plume of well mixed maritime air and temporarily diabatic heating support adequate updraft strength during peak time heating for showers/thunderstorms. Marginal hail and strong wind gusts accompany those storms with the first risk probably being the more dominant one, given the lowering WBZ level. An isolated waterspout/tornado may develop mainly along the S/SW coast of UK, as LL lapse rates increase somewhat, but there are no indications for a more elvated tornado risk. Onshore activity diminishes after sunset with ongoing activity offshore (e.g. the English Channel). A large thunderstorm area may be the best choice with such a pattern and during a season, where insolation may assist in initiation over various places. Isolated thunderstorms may occur well to the east of the highlighted area over central France, but coverage will be negligible.


  • Registered Users Posts: 1,379 ✭✭✭snow ghost


    Su Campu wrote: »
    The postfrontal instability comma system is associated with an upper vort max

    Bet ya can't say that as gaeilge Su! :P

    BTW, did anyone else see Jean Byrne's forecast after the 9 O'Clock news? Did you see on the graphics "ForeNoon"? Where did that come from? Might just be me, but I've never heard of that before ever - since when did the 'morning' become known as 'forenoon'???:confused:

    New one on me.

    Bring on the rain tomorrow forenoon, can't believe I'm missing heavy rain.


  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    One thing that is not favourable for intense shower set up tomorrow is the actual surface temps.

    Friday's max temp forecast:

    109577.jpg

    Forecast maxes of 8c to 10c across the country, with perhaps a degree or 2 leverage either side. With cold uppers forecast, this may not be a huge problem but ideally a 12c to 14c range at least at surface level would be more encouraging in creating imbalance and volatility.

    Really hard one to call for tomorrow to be honest, but I really hope some of us see something. It is about time some big fecker showers started bubbling up over the country.


  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    snow ghost wrote: »
    can't believe I'm missing heavy rain.

    With you Snow, been a very very long time since we had a proper spell of proper heavy rain. Bring it on!


  • Registered Users Posts: 5,096 ✭✭✭nilhg


    With you Snow, been a very very long time since we had a proper spell of proper heavy rain. Bring it on!

    Yeah, Monday was a long, long time ago..........


  • Closed Accounts Posts: 5,150 ✭✭✭Deep Easterly


    nilhg wrote: »
    Yeah, Monday was a long, long time ago..........
    Did it rain heavy on Monday? News to me..


  • Closed Accounts Posts: 4,279 ✭✭✭Su Campu


    Tá ceart agat, níl clue ar bith agam! :D

    I plotted a GFS forecast sounding for roughly the centre of the area of interest (52.5N 8W, or just west of Cashel) for 4pm tomorrow afternoon. A surface temperature/dewpoint of 8.3/5.6°C is giving 400J/kg of CAPE. With the GFS usually underdoing surface temperatures during solar heating by a degree or two, this CAPE is probably a conservative value, and in reality we could be talking 500-600J/kg. We need to keep an eye on how temperatures are reacting tomorrow afternoon, if we get above 8 then we're in business! But with wet ground, we will need prolonged solar heating to get this to happen, so it is indeed a close call.


    109586.gif




    File start time : 10 4 1 18 0
    File ending time: 10 4 9 6 0
    Chosen date in meteorological file: 10 4 2 15

    YR: 2010 MON: 04 DAY: 02 HOUR: 15 AT POSITION: 353.0 143.5 LAT.: 52.50 LON.: -8.00
    PRSS: 0.9770E+03
    MSLP: 0.9891E+03
    TPP6: 0.9766E-03
    UMOF: -0.9656E-01
    VMOF: -0.3564E+00
    SHTF: 0.7500E+02
    DSWF: 0.6240E+03
    RH2M: 0.8320E+02
    U10M: 0.4700E+00
    V10M: 0.5325E+01
    T02M: 0.2814E+03
    TCLD: 0.6100E+02
    SHGT: 0.9791E+02
    CAPE: 0.4000E+03
    CINH: 0.0000E+00
    LISD: 0.2710E+03
    LIB4: -0.1237E+01
    PBLH: 0.1199E+04

    PRESS HGT(MSL) TEMP DEW PT WND DIR WND SPD
    HPA M C C DEG M/S
    E = Estimated Surface Height

    977. 98. 8.3 5.6 185.0 5.3
    975. 120. 7.5 3.6 187.4 6.2
    950. 333. 5.4 1.8 190.2 7.9
    925. 550. 3.3 0.7 191.8 8.2
    900. 772. 1.3 -0.3 193.9 8.5
    850. 1229. -2.4 -4.3 199.0 8.6
    800. 1707. -5.4 -12.0 204.1 8.4
    750. 2210. -8.8 -15.4 204.0 7.8
    700. 2740. -13.1 -17.4 205.8 7.8
    650. 3300. -17.7 -21.4 209.8 7.4
    600. 3893. -22.6 -25.0 214.5 7.2
    550. 4524. -27.7 -29.4 215.1 7.8
    500. 5202. -33.0 -35.5 209.9 8.1
    450. 5934. -37.9 -46.3 187.7 8.5
    400. 6738. -42.3 -59.0 159.3 8.8
    350. 7632. -46.5 -63.1 148.8 8.8
    300. 8647. -49.3 -65.8 172.7 6.7
    250. 9839. -49.9 -66.0 217.3 6.8
    200. 11298. -49.8 -273.1 242.0 10.6
    150. 13167. -52.0 -273.1 255.4 10.7
    100. 15787. -53.0 -273.1 266.4 10.0
    50. 20203. -57.3 -132.8 273.7 12.1
    20. 25946. -59.2 -273.1 269.2 22.9


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  • Registered Users Posts: 5,096 ✭✭✭nilhg


    Did it rain heavy on Monday? News to me..

    This is the nearest AWS to me that I know of, 30mm between Monday and Tuesday morning.


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