Please note that further details are available in a detailed post here.
UPDATE FROM TMT'S PETER O'DONNELL:
Put into forecasting terms, this looks like being a gradual north to south replacement of mild Atlantic air now present by snow-chilled air masses seeping into the increasingly easterly circulation from a much colder Britain. The process starts late Friday night when tonight's frontal system stalls and gets pulled back into low pressure near Donegal/Derry. That should place most of Ulster in the colder variety of air masses near -1 C with sleet changing to snow, and there could be heavy falls on higher terrain. Expect 5-10 cm in places but 15-25 cm on some hills in the north by late Saturday.
The seepage continues all day Saturday placing parts of inland Connacht and north Leinster on the cold side of a frontal boundary but also the air mass to the south of the boundary will lose its connection to the milder Atlantic source and will begin to modify itself, with temperatures sinking towards 2 C by late Saturday. That will turn showers in the milder air mass more wintry while snow is pushing south. By late Saturday night the frontal boundary will dissolve and all regions will be getting a roughly equal easterly feed of colder air that will now be modified only by crossing the Irish Sea. I would expect streamers to develop with mixed sleety showers near sea level and heavy snow potential in higher parts of Dublin and Wicklow.
If any stronger low pressure does develop in the Atlantic and begins to interact with all of this, heavy snow could develop, but if not, the process will remain gradual with further outbreaks of light snow here and there across the central and eventually southern counties. The last district to fall to this process would probably be west Cork and coastal Kerry and that might take most of Monday to finish up, with the possibility that one or two really mild spots could stay above freezing throughout.
I think that by mid-day Monday about 50-70 per cent of the country will have snow cover with an average depth of perhaps 2-4 cm and some fairly isolated falls of 10-30 cm are possible. The most likely places to see heavy snow would be hills in south Donegal and about halfway up the eastern slopes in Wicklow and south Dublin (around 350m might see the heaviest accumulations).
I expect reports to be highly variable simply because there won't be strong organization taking place in this colder pattern.
I expect reports to be highly variable simply because there won't be strong organization taking place in this colder pattern.
Overnight temperatures could eventually fall to about -7 C (would say -3 C for Dublin at some point mid-week) so today would be the day to get yourself some de-icing materials for both the vehicle (if you park outside, expect some hassles with frozen locks and iced over windscreens) and the pavement around your home.
Please note that further details are available in a detailed post here.
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