Long Range Weather Forecast For Ireland (30 January 2021)


TRENDS for the week of 30 Jan to 5 Feb 2021

-- Temperatures will average near normal in the south to 2 deg below normal in the north.
-- Rainfall will average 50% above normal in the south, trending to near or slightly below normal in the north. Larger portions of the precipitation will be in wintry precip forms further north too.
-- Sunshine will average 25 to 50 per cent of normal.


TODAY will be a raw, windy and wet day in most central counties, and somewhat milder but foggy or drizzly near the south coast. Some of the rain in Leinster could begin to mix with wet snow towards the end of the event mid-day, as colder air mixes in from Britain. Temperatures currently near 5 C in central counties will drop slowly to the 2-4 C range later, and readings 8-10 C near the south coast will fall off slightly also. Ulster and some parts of adjacent regions will escape most of this wintry mixed fall today and could even see some partly cloudy intervals. Winds for all regions will be rather strong east to northeast 50 to 80 km/hr adding quite a chill, not a day you would want to be outside for very long in central counties. About 20-30 mm rainfalls will be total amounts including what has already fallen (in many places about half of that).

TONIGHT will have some clear intervals and a frost in many areas, lows -3 to +1 C. Winds not as strong but still fairly moderate from northeast to east at 30-50 km/hr.

SUNDAY will see a weaker disturbance trying to push along the same frontal boundary which by morning will have slumped a bit further south. This means that a mixture of snow, sleet and rain will begin to fall in Connacht and possibly Clare (inland) before spreading into the midlands by mid-day. Current guidance suggests it won't extend quite as far as Dublin before changing to a cold rain, but probably on higher terrain in Leinster the mix will continue, as temperatures are not likely to come up much from the morning lows. Highs for the day only 3-5 C and that could be during dry intervals, with the precipitation temperatures may be fairly close to 1 C. Not as windy as today but some moderate east winds at times.

MONDAY to WEDNESDAY the guidance generally suggests that a slight Atlantic influence will continue despite the gradual massing of very cold air over northern latitudes of the Atlantic and most of Scandinavia. Even so, some of the rather frequent light rain expected in this first part of the week could easily change over to sleet or snow in parts of the north and on higher terrain, with temperatures generally in the range of 4 to 7 C for most places, and 2 to 5 in the north and on higher terrain. Each day will likely have some intervals of light rain, fog and drizzle, with winds generally rather light as disturbances weaken upon approach from the west. Some intervals of stronger winds could develop near the south coast as these lows die out over Ireland and later south-central Britain or northern France.

From THURSDAY to SATURDAY the guidance generally suggests that Ireland will be on the margins of a large outbreak of colder air with east to northeast winds. Some guidance says that temperatures will fall to very cold values as far west as Ireland, while other guidance limits the spread of this arctic air to eastern England and leaves the frontal zone somewhere near Wales. The latter is of course more likely than not whenever this split is suggested, but the colder guidance is quite robust in appearance so I am calling this a 50-50 proposition, whether or not Ireland gets into the coldest part of this developing arctic northeasterly outbreak. If Ireland does get in, some significant snowfalls are quite likely in Leinster especially. If not, then temperatures will remain in the 4-7 C range like the first part of the week, with drizzly light rain at times.

Around SUNDAY 7th to TUESDAY 9th there seems to be an even greater chance of the coldest air reaching Ireland and this would be the most likely time then for a wintry episode of subfreezing temperatures and snowfalls. But it is by no means "carved in stone" that it would actually become that cold.

Longer term in February, there are signs of further battles between the Atlantic and polar origin arctic air masses with some maps wanting to connect up all known sources of cold air into one gigantic pool of very cold air that would make February quite extreme. I find the parallel to Feb 1895 interesting because at the same time guidance is showing severe cold outbreaks in eastern North America and this combination happened in both that year and 1855, as well as 1917 to a slightly lesser extent. (1917 is remembered in Ireland for a massive snowfall that happened at the end of March and into early April). So let's say this winter has "form" but that alone is no guarantee of an outcome, in more recent decades of course the tendency has been for promising cold to push to the doorstep and then back away (this happened a few times in Feb 2013 before a cold March interval developed, it also occurred in other winters around then).

I like to give you the probabilities rather than just picking A or B and hoping to be right on a coin toss. So you may hear different things from other sources who have decided to go with one or another of these possible outcomes.

The east coast of the U.S. will get a heavy snowfall from Sunday to Tuesday, model predictions are over a fairly wide range but they all have some places getting two feet of snow, the most likely snow jackpot seems to be eastern PA, northeast MD and most of NJ, but anywhere from about southern Virginia to Maine could see heavy amounts. This may prove prophetic or not, but the models showing the most snow are also showing the deepest cold over Ireland, so I'll keep an eye on how that coupling unfolds and whether it proves predictive or just a background noise factor of no consequence.

Just for interest, the degree of cold at present time (as shown for Ireland in 7-10 days) ranges from most extreme on the Canadian model, to medium extreme values on the U.S. (GFS) model, to weak on the European model. However a day or two ago the European model was showing a more robust cold solution and might return to that, plenty of time for models to "chop and change." The feature that seems to be giving the models difficulty is a strong high pressure area near the north pole that is gradually extending towards the Russian side, but some guidance has it pushing towards western Russia and Scandinavia, other sources say central to eastern Siberia. This seems to be making a large difference in the output for Europe.

Peter O'Donnell for IWO