-- Temperatures will average about 3 deg below normal, starting out colder than that and moderating to near normal by the weekend; however there is some uncertainty about whether the milder air will have the same impact on trends in the east and northeast which could average 4 to 5 deg below normal.
-- Precipitation will be around the normal amount but an unusual percentage of it is likely to be snow rather than rain, that being especially true in the east and north.
-- Sunshine may manage to reach near average in a few spots but in general the cloudy conditions will be frequent enough to hold down totals to near 50% of normal.
FORECASTS
TODAY will be windy and cold with further outbreaks of light snow or in a few cases mixed hail and snow grains, or sleet. These outbreaks are most likely near the east coast, and will extend furthest inland around Meath and Cavan, while also there could be outbreaks of mixed wintry precipitation in parts of west Munster. Winds will be easterly at about 50 to 70 km/hr adding a chill to daytime highs reaching only 1-2 C in the inland west and north, 2-3 C in most other places. Some localized snowfalls of 2 to 8 cms likely, more widespread amounts in the trace to 2 cm range.
TONIGHT will see a push of colder air from Scotland into Ulster that may spill out into parts of Connacht and north Leinster, and lows in these regions will fall to -4 to -6 C. That will have less effect on counties further south and west but it will remain as cold as this current spell has been, with lows -3 to -1 C. Winds may fall off somewhat to northeast 20-40 km/hr in the colder sector further north, while remaining east 40 to 60 km/hr further south. This may concentrate snowfall along a slight thermal boundary extending inland from near Dublin or just north of there towards Offaly and Roscommon. Localized snowfalls of 5-10 cm may develop here, and in a few other places near the southeast coast. At the same time skies may clear partially in areas further west.
WEDNESDAY will be a mainly dry and cold day with the lingering chance of localized snow streamers, possibly affecting the south coast more as winds turn more to the southeast, but also continuing for the east coast and parts of the midlands to south Ulster. There could be some wintry sunshine at times, especially in the north and west. After the cold start in the north, highs may remain below freezing in some areas (-3 to -1 C) while further south the range is likely to remain similar to today at 2-4 C. Winds will turn to the southeast at 30 to 50 km/hr adding some chill to these readings.
THURSDAY will present the risk of a widespread and disruptive snowfall in the 10-20 cm range, starting from early morning in west Munster, and spreading gradually throughout most of the country by mid-day. There could eventually be patchy freezing rain in counties (Clare, Limerick, Cork, south Tipps, west Waterford) closer to a slow-moving warm front that will try to push into west Munster, and rain is only expected in a few parts of Kerry and perhaps southwest Cork. Snow will fall at least intermittently if not continuously from mid-day Thursday to early or even mid-day Friday in some parts of the east and north, depending on how resistant the cold air proves to be. For Thursday, temperatures are likely to remain in the range of -3 to +2 C in the snowfall areas, rising slowly to about zero C in areas further west experiencing sleet or freezing rain, and more rapidly to near 7 C in outer headlands of Kerry, possibly about 3 C in coastal Connacht. Winds will be rather strong from the southeast (40-60 km/hr at least) during the snowfall although an inversion may prevent them from totally mixing down from the very strong winds aloft; those might break through in some coastal areas. The milder sector will have south-southeast winds of about 70 to 100 km/hr and 15-25 mm rainfalls by midnight.
FRIDAY will continue with this regime of snow or sleet in the east and north, mixed falls of sleet or freezing rain pushing further east and north gradually, and the milder sector with rain spreading into most of Munster and Connacht by late in the day. Temperatures will slowly rise from near 2 C to about 7 C in some central regions, and will remain 7-10 C further west, but could be held down for most of the day near the east coast and in east Ulster, to values in the 2-4 C range. Once again, some uncertainty is involved in the timing, the cold air could prove even more resistant than this forecast assumes, or it could prove less resistant (I took the middle course from the guidance available).
The OUTLOOK is quite uncertain and therefore a low-confidence forecast is all we can derive from the rather jumbled signals we're getting, with model runs changing every time out. There could easily be further changes before we get to the weekend or next week, so this rundown is more like a list of possible outcomes than a forecast as such. The milder air may manage to break through to the extent of holding on to control of Ireland and southwest England, if not any further east than that, for a day or perhaps longer, so that Saturday is most likely to remain fairly mild, with a low overcast, rain or drizzle, and highs near 6 C east to 9 C west, strong south winds making it feel rather raw despite those higher temperatures. That could hold for several more days but there seems to be a fairly high chance of the colder air, lurking fairly close after being pushed out, returning slowly towards Ireland and setting up another encounter with the Atlantic by Monday, but whether that one involves cold air or just a renewed rainfall is a question at this point. The most likely outcome seems to be a continued string of alternations between (somewhat) mild air and colder interludes with winds varying from south to southeast during each phase. If the Atlantic does manage to break through it currently does not look capable of bringing temperatures much higher than the 6 to 8 C range.
Peter O'Donnell