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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 ✭✭✭


    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


«13456733

Comments

  • Registered Users, Registered Users 2 Posts: 9,234 ✭✭✭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, Registered Users 2 Posts: 23,900 ✭✭✭✭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: 269 ✭✭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, Registered Users 2 Posts: 6,323 ✭✭✭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, Registered Users 2 Posts: 18,227 ✭✭✭✭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: 936 ✭✭✭WolfeEire
    Clare (410ft asl)


    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.

    www.x.com/wolfeeire



  • Registered Users, Registered Users 2 Posts: 2,682 ✭✭✭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, Registered Users 2 Posts: 2,682 ✭✭✭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: 1,536 ✭✭✭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, Registered Users 2 Posts: 23,900 ✭✭✭✭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: 1,985 ✭✭✭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, Registered Users 2 Posts: 16,958 ✭✭✭✭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, Registered Users 2 Posts: 8,219 ✭✭✭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, Registered Users 2 Posts: 16,958 ✭✭✭✭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, Registered Users 2 Posts: 9,234 ✭✭✭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, Registered Users 2 Posts: 2,682 ✭✭✭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, Registered Users 2 Posts: 1,343 ✭✭✭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, Registered Users 2 Posts: 9,235 ✭✭✭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, Registered Users 2 Posts: 23,900 ✭✭✭✭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: 1,985 ✭✭✭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, Registered Users 2 Posts: 16,958 ✭✭✭✭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, Registered Users 2 Posts: 23,900 ✭✭✭✭Kermit.de.frog


    And the UKMO at 144 hrs

    UW144-21.GIF?23-05

    UW144-7.GIF?23-05


  • Registered Users, Registered Users 2 Posts: 16,958 ✭✭✭✭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, Registered Users 2 Posts: 23,900 ✭✭✭✭Kermit.de.frog


    Temperatures on Wednesday

    132-580UK.GIF?23-0

    Max temperatures on Thursday

    156-580UK.GIF?23-0

    Treat with caution!


  • Registered Users, Registered Users 2 Posts: 16,958 ✭✭✭✭nacho libre


    The UKMO is very snowy:)


  • Registered Users, Registered Users 2 Posts: 16,958 ✭✭✭✭nacho libre


    Temperatures on Wednesday

    132-580UK.GIF?23-0

    Max temperatures on Thursday

    !

    Incredible for the time of year, even if what the GFS shows end up being couple of degree wide of the mark - which is likely given its the GFS. To have temperatures struggling to get above zero at this time of year is exceptional.


  • Registered Users, Registered Users 2 Posts: 23,900 ✭✭✭✭Kermit.de.frog


    GFS ensemble average now sub -12c by Wednesday...which is extraordinary

    gens-21-0-132.png

    The control run is awesome

    gens-0-0-150.png


  • Registered Users, Registered Users 2 Posts: 14,584 ✭✭✭✭M.T. Cranium


    The GFS and GEM have an extremely cold look at 850 to 500 mbs, and both seem to relax the block after about 2-3 March rather quickly, which makes me suspicious because it seems plausible that the block would maintain itself longer over snow covered western Europe (as we should see by then).

    Not too concerned about ICON, GEM did something similar last night and recovered, and Arpege does not follow it. Betting the ECM will be another great run.


  • Registered Users, Registered Users 2 Posts: 14,584 ✭✭✭✭M.T. Cranium


    ECM a touch faster than twelve hours ago (has some parameters a bit further west at 00z than modelled by 12z by 28th) otherwise out to 120h fairly similar looking, not following the ICON in any way. North Atlantic blocking also looks slightly further north by 1-2 deg. Money charts are coming up now.


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  • Registered Users, Registered Users 2 Posts: 23,900 ✭✭✭✭Kermit.de.frog


    ICON has support from NAVGEM now for that quick evolution to a more traditional Greenland high setup that would quickly displace the easterly. Still cold but not the same cold for us.

    I think real caution needs to be applied at this point.

    However, ECM is excellent. UKMO excellent. GFS excellent.


  • Registered Users, Registered Users 2 Posts: 14,584 ✭✭✭✭M.T. Cranium


    You might be more into orange than yellow if there's any red alert and the red could spread just to your south, some output showing heaviest snowfalls well inland like Laois-Kilkenny.

    The way that the polar high is building into northern Scandinavia, I can't see this very fast evolution to only a Greenland high without the 2-4 day interval of cold easterly winds that form the core of the rest of the model output. And even if it did happen that way, it might not be a death blow to the cold/snow potential.

    500 mb winds over Sweden at 00z were showing NNE 70 knots. That sounds more like a slow retrograde sequence. But it shows that the high latitude blocking is beginning to push into the mix. Quite exceptional to see widespread -20 to -30 C near the eastern Baltic but a driving mechanism still building further north.

    The Baltic is still fairly warm too, this is not like 1947 where the entire Baltic had frozen over by late February, and so northern Germany and Denmark might see some locally heavy streamers starting later today or certainly by Saturday.


  • Registered Users Posts: 6,017 ✭✭✭TheMilkyPirate


    Fantastic runs again this morning, If the ICON and NAVGEM were the only models showing the easterly and the GFS UKMO and ECM weren't I don't think we would be too confident so I wouldn't worry too much but it would be nice to see them come back on board before the day is out.


  • Registered Users, Registered Users 2 Posts: 4,426 ✭✭✭PokeHerKing


    ICON has support from NAVGEM now for that quick evolution to a more traditional Greenland high setup that would quickly displace the easterly. Still cold but not the same cold for us.

    Can you post the icon & navgem please Kermit?


  • Registered Users Posts: 1,985 ✭✭✭BLIZZARD7


    EC Snow accumulation chart in inches by Friday 00z - From Nick L on netweather - Dublin in the firing line

    2D761940-D7FB-4112-BB2F-B131F24A0772.png.9a229935601739a7dada799093291bf5.png


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  • Closed Accounts Posts: 248 ✭✭kod87


    BLIZZARD7 wrote: »
    EC Snow accumulation chart in inches by Friday 00z - From Nick L on netweather - Dublin in the firing line

    2D761940-D7FB-4112-BB2F-B131F24A0772.png.9a229935601739a7dada799093291bf5.png

    Snow accumulation chart??? How does snow accumulate on water?


  • Registered Users Posts: 253 ✭✭littlema


    Gfs for next Friday supporting ????


  • Registered Users, Registered Users 2 Posts: 14,322 ✭✭✭✭leahyl


    What's the pink off the south coast?


  • Registered Users Posts: 1,985 ✭✭✭BLIZZARD7


    kod87 wrote: »
    Snow accumulation chart??? How does snow accumulate on water?

    His words, not mine- I suspect it's a total snowfall chart and the assumption is all that falls will stick in these temperatures.

    @leahyl 10-16 inches of snow by the looks of it, that's why Cork does better off a South easterly tilt rather than Northern Easterly.


  • Registered Users, Registered Users 2 Posts: 8,219 ✭✭✭Gaoth Laidir


    kod87 wrote: »
    Snow accumulation chart??? How does snow accumulate on water?

    It's totalling all of the precipitation falling as snow, not the accumulated depth on the ground.

    I would add too that the ECM may slightly underplay the amount of snow showers extending inland as it tends to kill them off too quickly over cold land.


  • Registered Users, Registered Users 2 Posts: 8,219 ✭✭✭Gaoth Laidir


    On the subject of solar heating at this time of the year, it's not negligible compared to say the end of November 2010.

    The maximum possible midday solar irradiation at 53N on Feb 28th is 780 W/m², while on Nov 30th it's around 533 W/m². That means that the sun will be up to 46% stronger next week than it was at the start of the cold spell in 2010. For reference, the June 21st value is 1023 W/m², and the Dec 21st one is around 485 W/m².

    Also, at around 10h45min, daylight will be almost 3 hours longer next Wednesday than on Nov 30th (7h56 min).

    All this means stronger melting between the showers now compared to 2010. Surfaces such as pavements, cars, etc., will heat up much quicker once a small part becomes exposed, melting that edge of snow cover, increasing the exposed area, further melting, and so on.

    Of course these values are on a perfectly clear day. With extensive cloud cover around the difference is greatly reduced, though in scattered cloud conditions spot irradiation can actually be greater (due to reflection of sunlight from surrounding clouds).

    Anyway, just one thing to note when comparing this to 2010. If we look at 8th January 1982, the solar figure is also only around 500 W/m². Every week makes a big difference at this time of the year.


  • Registered Users, Registered Users 2 Posts: 7,219 ✭✭✭pad199207


    On the subject of solar heating at this time of the year, it's not negligible compared to say the end of November 2010.

    The maximum possible midday solar irradiation at 53N on Feb 28th is 780 W/m², while on Nov 30th it's around 533 W/m². That means that the sun will be up to 46% stronger next week than it was at the start of the cold spell in 2010. For reference, the June 21st value is 1023 W/m², and the Dec 21st one is around 485 W/m².

    Also, at around 10h45min, daylight will be almost 3 hours longer next Wednesday than on Nov 30th (7h56 min).

    All this means stronger melting between the showers now compared to 2010. Surfaces such as pavements, cars, etc., will heat up much quicker once a small part becomes exposed, melting that edge of snow cover, increasing the exposed area, further melting, and so on.

    Of course these values are on a perfectly clear day. With extensive cloud cover around the difference is greatly reduced, though in scattered cloud conditions spot irradiation can actually be greater (due to reflection of sunlight from surrounding clouds).

    Anyway, just one thing to note when comparing this to 2010. If we look at 8th January 1982, the solar figure is also only around 500 W/m². Every week makes a big difference at this time of the year.

    So plenty of lethal icicles dangling from roofs and gutters I’d imagine next week!


  • Registered Users Posts: 1,985 ✭✭✭BLIZZARD7


    Oh my god, -15c 850 temps out to Galway Bay on the 06z for Wednesday into Thursday - 1987 levels matched there

    06_144_ukthickness850.png?cb=13

    Top temperatures of -3 to -5c under heavy snowfall - for the 1st of March!!


  • Registered Users Posts: 1,645 ✭✭✭Daniel2590


    GFS 06z

    tempresult_tno3.gif

    tempresult_zfz2.gif

    Nearly have a blob of -18 uppers reaching the east coast :eek:


  • Registered Users, Registered Users 2 Posts: 6,238 ✭✭✭Oneiric 3


    Nice to see you back Wolfe :)

    Seconded.

    For some reason, his return reminded me of this classic...



    Can't for the life of me think why... ;)

    New Moon



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