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Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

  • 22-02-2018 11:07pm
    #1
    Registered Users Posts: 2,023 ✭✭✭ Donegal Storm


    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



    Not looked at the models since last night but nothing much has changed from what I can see, still expecting a big downgrade every time I have a look but so far so good. The main issue I can still see is the high could sink over us leaving us with a nondescript cold inversion but hopefully hopefully it won't come to that

    Latest GFS pretty much as we were, cold from Monday with snow potential from Tuesday evening. Still pointless looking at smaller details

    gfs-0-114_evy3.png


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Comments

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


    I wouldn't usually cross post in both threads, but 18Z GFS is just beautiful.
    Everything that falls out of the sky from 24hrs through 240hrs is snow or ice.

    96-7UK.GIF?22-18
    162-7UK.GIF?22-12


  • Registered Users Posts: 21,809 ✭✭✭✭ Kermit.de.frog


    Gonzo wrote: »
    it now looks like the cold is definitely locked in at this stage but the snow sure isn't. Sunday/Monday will be a much better idea of how the snow will shape up next week.

    Light snow showers should start moving on to the east coast on current model wide guidance sometime Monday afternoon or evening and continue overnight, getting progressively heavier and more frequent through Tuesday.


  • Registered Users Posts: 1,591 gabeeg


    The GFS is a showing pretty much a steady stream of snow in from the east.

    Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?


  • Registered Users Posts: 256 ✭✭ Mount Vesuvius


    Just checking the GFS mean and all systems are a go for whiteout conditions for a lot of the country. That if it verified. Starting out mainly on Tuesday that little kink should drive lake effect snow showers from the north east for a time before wind changes back more East.

    The Atlantic slider low looks a very promising solution as it has been flagged before and dropped and back again and I feel it is here to stay meandering around our little isle for a few day.

    Buy the bread and freeze it folks cause this could be our epic snowfall event that has eluded us since the 60s 70s and 80s.

    Of course thus is not a forecast but the size and force of this easterly push due to the burrowing of the easterly winds through the atmosphere from the SSW is a remarkable event anyway and we are in the firing line for once to perhaps achieve the perfect winter/ Spring storm.


  • Registered Users Posts: 5,363 ✭✭✭ highdef


    gabeeg wrote: »
    The GFS is a showing pretty much a steady stream of snow in from the east.

    Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?

    Afternoon sun had very little to do with those Irish Sea streamers back in 2010 and the same will be the case next week. One of the main reasons for those showers to develop is due to a large difference in temperature between the sea and the atmosphere. The sun has little or no bearing on their development so the showers can continue on night and day, pretty much 24/7. There are several other factors required for their development but I don't want to go too off topic on this thread.


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  • Registered Users Posts: 17,665 ✭✭✭✭ JCX BXC


    Would anyone care to give their thoughts on the possible convective showers over land building up? While not my area of expertise, I have read online regarding possible over land showers building up as surface temperatures rise quicker in the stronger late February/early March sun.

    It would certainly help get me a dusting here in West Clare if the forecast low pressure systems don't arise.

    On another note, the GFS has a beautiful parting snow front near the end of the 18Z run (+336, around the 8th) dumping possibly feet of snow countrywide. Long way off but as I've said several times before, it's nice to dream

    prectypeuktopo.png


  • Registered Users Posts: 11 ✭✭✭ WolfeEire


    gabeeg wrote: »
    The GFS is a showing pretty much a steady stream of snow in from the east.

    Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?

    A northeasterly wind would favour the northeast, east and southeast.

    As the cold dry airmass flows southwestwards off the northwest coast of England, its' lowest layers get modified enough for cumulus to form. As they continue their track over the sea, these cumulus quickly grow in size, and start producing precipitation by around Angelsea. By the time they reach the east coast they are fully fledged cumulonimbus, complete with hail, snow and graupel, and potentially, thunder and lightning. The distance required for clouds to first start to form is a delicate balance of airmass temperature and dewpoint, windspeed and sea surface temperature. The faster the wind, the further the airmass can travel before clouds can form, and vice versa. Right now, all data suggests this is the likely situation, particularly from midweek.


  • Registered Users Posts: 2,619 ✭✭✭ Rougies


    gabeeg wrote: »
    The GFS is a showing pretty much a steady stream of snow in from the east.

    Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?

    The sun had little effect fueling the streamers in 2010, it was mere coincidence that the other parameters lined up in the afternoon.


  • Closed Accounts Posts: 1,576 patneve2


    The 18z actually brings in -45C temps at 500 hPa for a few hours, insane.


  • Closed Accounts Posts: 1,576 patneve2


    Charts kind of look like a more potent version of the first cold spell at the end of 2010. There was actually a decent continental component at the end of Nov that year with isobars briefly stretching from western siberia to Ireland accompanied by 850s slighly below -10 for a day or two. Whats being modeled now however looks much stronger with a superior air source also.


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  • Registered Users Posts: 2,619 ✭✭✭ Rougies


    JCX BXC wrote: »
    Would anyone care to give their thoughts on the possible convective showers over land building up? While not my area of expertise, I have read online regarding possible over land showers building up as surface temperatures rise quicker in the stronger late February/early March sun.

    It would certainly help get me a dusting here in West Clare if the forecast low pressure systems don't arise.

    On another note, the GFS has a beautiful parting snow front near the end of the 18Z run (+336, around the 8th) dumping possibly feet of snow countrywide. Long way off but as I've said several times before, it's nice to dream

    The effect would be almost non existent due to still relatively low sun strength, dry cold ground and little growth in vegetation. Plants/trees/grasses pump out loads of water vapour when they're growing/in leaf.


  • Registered Users Posts: 1,206 ✭✭✭ typhoony


    the non-computerised Fax chart for next Tuesday...

    http://www.meteociel.fr/ukmo/fax/fax120s.gif?2

    probably just light snow away from the east coast


  • Registered Users Posts: 21,809 ✭✭✭✭ Kermit.de.frog


    GFS ensemble mean does offer quite a bit of support for the more outlandish portion of the 18z run and ECM evolutions. Interesting times ahead.

    gens-21-1-174.png


  • Registered Users Posts: 1,894 ✭✭✭ BLIZZARD7


    typhoony wrote: »
    the non-computerised Fax chart for next Tuesday...

    http://www.meteociel.fr/ukmo/fax/fax120s.gif?2

    probably just light snow away from the east coast

    That nice kink over the Irish Sea should aid convective activity - locally heavy falls by Tuesday evening I would think.


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


    patneve2 wrote: »
    Charts kind of look like a more potent version of the first cold spell at the end of 2010. There was actually a decent continental component at the end of Nov that year with isobars briefly stretching from western siberia to Ireland accompanied by 850s slighly below -10 for a day or two. Whats being modeled now however looks much stronger with a superior air source also.

    So what you are saying is this is about as perfect synoptics wise as we can get here. Cold stretching from high pressure all the way from the Urals. We will marvelling at these charts in the days, months and years ahead.


  • Closed Accounts Posts: 1,576 patneve2


    So what you are saying is this is about as perfect synoptics wise as we can get here. Cold stretching from high pressure all the way from the Urals. We will marvelling at these charts in the days, months and years ahead.

    Yes I would say very close to perfection. It's all kicking into action now with frigid temperatures over E and NE Europe. For Ireland I'd wait another 36 hours before calling it - its still a bit too far out.. but looking more likely as the hours pass


  • Registered Users Posts: 8,200 ✭✭✭ Gaoth Laidir


    This is what we're after. Deep sub-zero saturated profile. Dublin next Friday, according to the GFS, as it has a low moving up and absolutely dumping a shítload of snow on the country.

    Usual disclaimers apply. The value of your snow may fall as well as rise...

    442565.jpg


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


    patneve2 wrote: »
    Yes I would say very close to perfection. It's all kicking into action now with frigid temperatures over E and NE Europe. For Ireland I'd wait another 36 hours before calling it - its still a bit too far out.. but looking more likely as the hours pass

    A lot of us will need to be committed if it were to go bust at this stage. I wish i could just stay away for 36 hours. Maybe i need to get myself banned temporarily:pac:


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


    This is what we're after. Deep sub-zero saturated profile. Dublin next Friday, according to the GFS, as it has a low moving up and absolutely dumping a shítload of snow on the country.

    Usual disclaimers apply. The value of your snow may fall as well as rise...

    442565.jpg

    I guess green is DP but is red air temp or WBT?


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


    WolfeEire wrote: »
    A northeasterly wind would favour the northeast, east and southeast.

    As the cold dry airmass flows southwestwards off the northwest coast of England, its' lowest layers get modified enough for cumulus to form. As they continue their track over the sea, these cumulus quickly grow in size, and start producing precipitation by around Angelsea. By the time they reach the east coast they are fully fledged cumulonimbus, complete with hail, snow and graupel, and potentially, thunder and lightning. The distance required for clouds to first start to form is a delicate balance of airmass temperature and dewpoint, windspeed and sea surface temperature. The faster the wind, the further the airmass can travel before clouds can form, and vice versa. Right now, all data suggests this is the likely situation, particularly from midweek.

    Nice to see you back Wolfe :)



    Full agreement now on the ensembles for cold to arrive on Monday though probably mostly dry until Tuesday evening at least. Daytime temperatures still forecast to be 2-4C both days so doubtful we'll see any lying snow before Tuesday night though sharp frosts. Huge snow potential thereafter but I'd give it until Saturday evening or even Sunday before putting my neck out on that


    Plenty of support for a more prolonged spell now as well, 18z GFS by no means an outlier. A refreshing change from the countess fleeting 'events' so far this winter

    graphe_ens3_xdu1.gif


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  • Registered Users Posts: 2,619 ✭✭✭ Rougies


    sdanseo wrote: »
    I guess green is DP but is red air temp or WBT?

    Yeah green is DP and when green and red align it means saturated air. If green and red are aligned high up into the atmosphere it's a good sign for falling precipitation. And when both are below zero all the way down to the bottom, well I think you know the rest!


  • Registered Users Posts: 1,292 ✭✭✭ OneEightSeven


    gabeeg wrote: »
    The GFS is a showing pretty much a steady stream of snow in from the east.

    Do you reckon this will actually follow a similar pattern to 2010 - with streamers bubbling up in the afternoon sun, or could we be looking at something more continuous?

    This video illustrates what happened in 2010 and what may (hopefully) happen next week:



    Lake-effect or sea-effect snow is similar to steam rising from your piss on a cold night. The greater the difference in temperature between your urine and the air, the more steam it produces.


  • Registered Users Posts: 9,188 ✭✭✭ lucernarian


    Two charts for Thursday at 1800z.

    The 00z last night..
    GFSOPEU00_186_1.png

    And the 18z tonight:
    GFSOPEU18_168_1.png


    This trend is a very snowy one, even if the final details aren't nailed yet. Having a Greenland high in this way lets us have a prolonged blast of cold, past the 5 or so days reliably predicted. It almost seems too good to be true, as even Dec 2010 didn't seem as spectacular at the t+168 range, and the polar vortex has to go somewhere.


    The second SSW event is clearly paying dividends for us. There could be a dry interlude for us, a couple of days of cold and possibly snowy weather over the east coast of Ireland, but then another easterly (edit: northeasterly) blast could be heading our way.


  • Registered Users Posts: 21,809 ✭✭✭✭ Kermit.de.frog


    The ICON model has thrown a real spanner in the works.

    Important to remember as has been repeated over and over that nothing is nailed here. It's on it's own with it's evolution but can't be discounted.

    GFS, UKMO, GEM are fine this morning.

    gfs-0-150.png?0

    gfs-1-144.png?0


  • Registered Users Posts: 1,894 ✭✭✭ BLIZZARD7


    Yeah it goes wrong very early on when it's also very unlikely that GFS/UKMO/GEM are all wrong. For now it looks like an outlier but ECM and ensembles will be important here.

    The other runs all have us in a bitter and very snowy scenario midweek - The ICON keeps us under the ridge sagging down til later in the week but would still be cold.


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


    I will start to worry if the UKMO and ECM follow it. The ICON is a lesser model than those two. I am discounting it for now


  • Closed Accounts Posts: 248 ✭✭ kod87


    GFS continues to have it very snowy towards the end of next week with low pressure to our SE. Serious snow could be dumped just about anywhere but worse the further east and south east you go. Although the uppers are less cold with the low pressure closer. I would not be worried about the ICON model, all the more reliable models have been consistent with what they are showing.


  • Registered Users Posts: 21,809 ✭✭✭✭ Kermit.de.frog


    And the UKMO at 144 hrs

    UW144-21.GIF?23-05

    UW144-7.GIF?23-05


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


    kod87 wrote: »
    GFS continues to have it very snowy towards the end of next week with low pressure to our SE. Serious snow could be dumped just about anywhere but worse the further east and south east you go. Although the uppers are less cold with the low pressure closer

    You mean better, surely:)


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  • Registered Users Posts: 21,809 ✭✭✭✭ Kermit.de.frog


    Temperatures on Wednesday

    132-580UK.GIF?23-0

    Max temperatures on Thursday

    156-580UK.GIF?23-0

    Treat with caution!


This discussion has been closed.
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