-- Temperatures will average about 3-4 deg below normal, a blend of 5-6 below to Thursday and near normal Friday and Saturday.
-- Rainfall or melted snow equivalent precipitation will probably begin to approach half of normal or a bit more towards Thursday and Friday after a generally dry start although some localized heavy wintry showers are likely at first.
-- Sunshine will probably be less than half of the normal amount. A few places in the west could do somewhat better however.
FORECASTS
TODAY ... Turning colder in stages, more rapidly in north and east, as a frontal trough develops moving west about as far as a Donegal to Waterford line by late afternoon. This will be the leading edge of arctic air moving west from Britain, but its full effects will not be felt until Monday. To the west of this dividing line, any showers are more likely to be rain or hail than to the east where snow, sleet or hail are more likely (although cold rain showers could still be in the mix near sea level). Temperatures will stall at around 3-4 C in the colder sector and perhaps drop slightly this afternoon, while in the milder west and south, highs near 6 C can be expected. Winds throughout will be east to northeast at about 40 to 70 km/hr, adding several degrees of chill factor.
TONIGHT ... Continued windy and cold with passing wintry showers, a bit of snow accumulation is possible in parts of north Leinster and Ulster, and on hills elsewhere. Lows near -1 C. Winds east 40 to 70 km/hr.
MONDAY ... Windy and cold with a few areas of moderately heavy sea effect streamers containing a mixture of snow, sleet, hail or ice pellets, and cold rain showers. These will be most likely in east Ulster, north and central Leinster, near the Wicklow mountains, and later in the day near the Cork coastline. However, isolated snow showers are possible further west too. Thunder is quite possible with any vigorous showers that form. Local snow accumulations later in the day of 2 to 8 cms are possible but this won't be a widespread covering in all areas, some places may have traces that come and go. Skies will be partly to mostly cloudy with a few brighter intervals. Winds east to northeast about 50 to 80 km/hr in exposed coastal areas, 40 to 60 km/hr elsewhere, although west of Waterford on the south coast, the wind direction may become east to southeast at times. Highs will be in the range of 1 to 4 C.
TUESDAY ... Windy and cold with more outbreaks of showery snow, sleet, hail and (even less likely) cold rain near sea level. Some of these once again could produce thunder. Strong east-southeast winds at times especially near the south coast, early in the day, abating somewhat later on. Otherwise, winds generally east 40 to 70 km/hr. Morning lows near -2 C and afternoon highs 1 to 4 C. Once again, 2 to 8 cm snowfalls are possible in some places, most likely central Leinster and east Ulster.
WEDNESDAY ... Partly cloudy and very cold with brisk east winds becoming southeast 50 to 80 km/hr. Any wintry showers in streamers could be heavy in the morning, then the focus will turn to slowly advancing snow and sleet along warm fronts from low pressure attacking the cold air from the southwest. Morning lows near -3 C and afternoon highs near 5 C south and west, 2 C north and east.
THURSDAY ... This warm frontal passage is expected to be slow and could take all of Wednesday night and part of Thursday before milder air gains much of a foothold in the south and west, with winds turning gradually more to the south near the Atlantic coast, remaining southeast in Leinster and Ulster. There is potential in this phase for 10-20 cm snowfalls to develop in Leinster, inland Connacht, Ulster and some parts of Munster such as Tipperary and Waterford. That could turn over to sleet or even freezing rain before the rain expected further west replaces it by late Thursday. Temperatures could be expected to warm up slowly to around 5 C in the east and 3 C north, while warming more readily to 9 or 10 C in the west.
(some guidance earlier in the last 24h was showing this warming stalling out and not reaching the north and east until Friday, that seems to be replaced now by this somewhat faster timetable but readers should be aware that the whole concept of this breakdown of the cold spell is subject to a lot of variations as we get into the cold spell and even the addition of snow to the scenario is not necessarily a "given" yet, these are the most likely outcomes based on a blend of latest guidance).
That being the case, by FRIDAY the most likely scenario is for a milder south wind and light rain at times, possibly with the existence of some colder pockets remaining in north Leinster and east Ulster with sleet or snow still a slight risk, and temperatures steady near 9 or 10 C with a moderate to strong south wind of 50 to 80 km/hr.
There is of course a slight chance that the cold spell will extend longer and these milder temperatures will be confined more to west Munster and coastal Connacht.
The general consensus of guidance beyond Friday is that high pressure will get even stronger over Scandinavia and after this mild incursion around Friday, the influence of the cold high will filter back into Ireland from the southeast with a slow fall off in temperatures to about 7 C on the weekend of 13-14 Feb and perhaps 3-5 C by Monday 15th. From there on the colder spell might even get back to more severe temperatures with snow potential, or it might stabilize at the cool but not frigid levels expected by Monday 15th, with slight variations until the high breaks down later in the week. Some earlier guidance had been showing this as quite a severe second cold spell with more snow potential, and this may return in later model runs, so all I'm saying here is that at the moment, guidance is giving this more moderate outcome, I wouldn't describe it as more than a medium-confidence sort of outcome.
So once again to give a brief summary, expect it to turn colder in stages, with scattered wintry showers, many of them snow, here and there giving a rather variable result in terms of snow cover during the cold spell which now looks like breaking down slowly from Wednesday afternoon south and west, to Thursday mid-day east and north, with a fairly high risk of a snowfall in the 10-20 cm range at that point (but no guarantees on that yet).