-- Temperatures will average about 4 to 5 deg below normal, starting off near average and sliding gradually down into the frigid zone of 6 to 8 deg below normal next week.
-- Rainfalls or the liquid equivalent of melted snowfall will amount to perhaps half of the average amount, although the amount of snow will likely be a significant portion of that and obviously above any long term snowfall average.
-- Sunshine will likely average near normal as there will be a few breaks in the overcast most days and possibly some longer spells of wintry sunshine especially over the western half of the country next week.
FORECASTS
Will update the discussion of range of possible outcomes starting with the Monday segment of this forecast section today.
TODAY will see a mixture of cloud and some sunny breaks although mostly cloudy further north with some further outbreaks of light rain giving 5-10 mm locally in Ulster, north Leinster, and 2-5 mm in parts of Connacht and the midlands. Generally dry in the south with isolated showers mostly near higher terrain. Winds generally light to moderate southwesterly although somewhat stronger in the east and north at times. Highs 7 to 9 C.
TONIGHT will be partly cloudy to overcast with outbreaks of light rain mostly confined to the north and some central counties, lows 3 to 5 C.
FRIDAY will have mostly cloudy skies with a few brighter intervals, as rain tapers off across Ulster, but then circulates back around from the north into Connacht, feeding later into parts of the midlands and Clare then eventually further south into west Munster by overnight hours. This rainfall will amount to around 5-10 mm, with the east and south somewhat drier. Highs 6 to 8 C.
SATURDAY will begin to feel the first effects of colder northeast winds with bands of showers, turning somewhat more wintry at least over higher terrain, as temperatures begin to slide down gradually towards 4 C later in the day, still holding around 7 C in parts of Munster however.
SUNDAY will become colder again with mixed wintry showers in moderate northeast winds 40 to 60 km/hr, a growing risk of snowfall accumulating on hills in the east, and temperatures steady in the 3 to 5 C range. At about this point in time the travelling low will have reached northeast France and Belgium where it will stall out and produce a sleety cold rain and snow mixture for eastern England with some heavy falls of all forms possible there.
MONDAY / NEXT WEEK ... For next week, the guidance has begun to cluster more around one unified solution although there is still somewhat of a range of outcomes following on from what we discussed here yesterday ... there will almost definitely be a wintry spell from Monday to late in the week and moderate to severe cold as easterly winds set in at around 40 to 70 km/hr. The more moderate guidance still shows some mixing potential across the south and reserves the colder temperatures for the northern half of the country. The guidance that was more aggressive yesterday has either remained similar or intensified towards more extreme solutions. From all that, these would be the ranges of forecast conditions on a daily basis next week ...
MONDAY will likely be quite cold and windy with some organized snow streamers, possibly mixing with sleet showers near coasts or more likely near the south coast which will get into the action partially, with the strongest wintry shower activity off the Irish Sea into Leinster and east Ulster. These snow (or mixed wintry) showers will sometimes make fairly significant progress across the central counties into some parts of west Munster and Connacht but the tendency will be for more sunshine and dry intervals on the Atlantic coast. Temperatures will start out in the range of -3 to -1 C and rise only slightly to 1 to 3 C, although possibly holding closer to 5-7 C in southwest counties.
TUESDAY and WEDNESDAY will continue similar although if some guidance is correct the cold will deepen by about one or two degrees each day with nights reaching the -6 to -4 C range and days staying about -2 to +1 C (except somewhat higher right near some exposed coasts). More wintry showers almost all of which will be snow are likely and the dynamics may produce localized thundersnow showers. Amounts could reach the 10-30 cm range if some aggressive guidance proves correct. In the more moderate scenario, the snow will be more confined to the northern counties with a tendency to mixtures falling further south (although still snow on hills in that outcome). Temperatures would not be quite as severe in that option.
LATER NEXT WEEK becomes quite interesting too with various scenarios on the table for (a) possibly an extended easterly cold spell, (b) possibly a vigorous battleground scenario with cold hanging on at the surface leading to heavy snow outbreaks, or (c) still the option discussed yesterday of a more progressive withdrawal of the cold towards the north confining any remnant snows to Ulster and changing the precipitation over to rain across large parts of Ireland. At this point I have to say that the middle option (b) seems the most likely of the three as the cold air will be entrenched but with so much of the guidance wanting to re-energize the Atlantic flow to the south, it seems to favour the outcome of occasional snowfalls in that later portion of the cold spell.
Longer term, all kinds of scenarios are on the table and these range from prolonged cold, renewed cold after a brief interruption, mixed spells of cold and mild, or even a bit of a reversal to quite mild and stormy Atlantic dominated weather. I would favour the mixed spells of these options if I had to bet on one, but they all have some valid chance of coming to reality.
So the current "bottom line" is that a fairly severe wintry outbreak seems all but locked in now, with a north to south gradient of probability ranging from near certain in the north to perhaps a 2:1 chance in the south. That would make the odds fairly high for central counties. The duration of the cold spell is perhaps more in question than its arrival which we could say is going to be gradual in stages over the weekend then more like "full on" by Monday or so.
- Peter O'Donnell for IWO