Wednesday, 10 February, 2021
Forecasts for Ireland
(Blog format today, trends are generally upward in temperature and precipitation and same old flat line for sunshine)
Cold air has deepened its presence somewhat overnight especially in the northern counties, and it now stands ready to battle the Atlantic which will be returning to its familiar haunts with a number of forays planned over the next three or four days.
Today, expect mostly cloudy skies but the odd sunny break possible especially away from the streamers which will be generally most frequent in these areas -- the southeast and near the south coast, central and northern Leinster occasionally into the midlands, and east Ulster as well as a persistent band near the north coast of Derry moving across Inishowen in north Donegal. All of these streamers can be described as mainly light but occasionally moderate in their intensity, and capable of dropping 2-5 cm snowfalls in their life cycles. Otherwise the day will be largely dry in quite a few places that don't see any streamer activity. Highs today will likely reach about 2 C again in most places, but could be held down a degree or two on higher terrain. Winds will start out easterly, but with a slow veering towards southeast late in the day, in the 40 to 70 km/hr range mainly. This will add about 3-5 deg of wind chill to actual temperatures.
Tonight, winds will be southeast 40-70 km/hr except in west Munster where they may increase to 60-90 km/hr. Cold air will be holding strong in most areas overnight and there could be some local clearing although some streamer activity and resultant snowfall will also continue, with the south coast becoming somewhat more prolific as a source due to the wind shift. Parts of Leinster and Ulster could see localized 2-5 cm snowfalls also. Lows will probably drop a bit from previous nights due to some clear patches developing, -4 to -2 C seems probable.
THURSDAY will start out cloudy and raw with southeast winds of 50-80 km/hr. Some locally heavy snow streamers could develop ahead of the main storm event but many areas will have a dry morning. Snow turning to sleet near coasts will move into west Munster; the snow will likely be heavy on higher ground in Kerry and Cork, but wet and sporadic on lower terrain. In that region, the sleet may turn to rain by afternoon and temperatures could rise rather steadily to around 7 C. Otherwise the cold air will be much more resistant (at first) and snow could break out around mid-day in many counties between the south coast and through the midlands into Connacht and south Ulster. Amounts by evening could be 5-10 cm and this could cause considerable travel disruption especially for inter-city road travel. This snow is only likely to change to sleet right along the south coast and a few kms inland at low elevations. Any hills in this zone could see 10-20 cm snow amounts. By late afternoon or evening heavy snow is possible in the southeast and up the east coast towards south Dublin. Amounts of 5-15 cm are possible, 10-25 cm on the higher ground in the southeast. Much of the guidance suggests that Dublin (city) will be in somewhat of a snow shadow situation due to downsloping from the nearby hills, and snow amounts there could increase more slowly than in other areas (this remains to be seen). Temperatures during the snow event will likely be in the range of -2 to +1 C. Winds will be southeast 40-70 km/hr although sometimes in periods of heavier snow, east 20-40 km/hr. Any onshore flows such as would be expected in central Wicklow and parts of Wexford or Carlow would have a potential to see enhanced amounts.
By THURSDAY NIGHT this snowfall will probably be weakening in general and also its western flanks will be changing over to sleet then rain as somewhat milder air creeps slowly further east, reaching perhaps a Sligo to Waterford line by about midnight or so. The rain in most cases will be rather light at first, becoming heavier later in the night in west Munster. Winds will continue southeast 40-60 km/hr where it is snowing or sleeting (and this activity will also be weaker in many cases), and will become south 50-80 km/hr in the milder sector with the rain. Temperatures will remain about zero to +1 C in the snow/sleet areas of east and northeast, and will rise to 4-5 C with the milder air oozing in (over snow that is melting, so some fog is likely with that).
By FRIDAY some areas of sleet and snow may still be present especially in North Leinster and Ulster, and the further push of mild air will come to a halt for a time, with temperatures 0-2 C in the northeast, and 5-8 C elsewhere. Rain may become heavy at times in the south especially near hills. Winds southerly 50-80 km/hr. Friday night could see a brief push back to the west of the colder air which will be taking advantage of a weaker portion of the incoming Atlantic frontal system at that time. This may turn the rain back to sleet or wet snow in some areas of Connacht and the midlands.
Then on SATURDAY the milder air will slowly start to gain further control but in doing so renewed snowfall or sleet could develop over parts of north Leinster and rain will spread further north and east once more. Eventually most of the guidance now agrees that milder air will push all the cold air out of Ireland and some parts of western Britain before running into greater resistance around central to eastern England. So for Ireland on Saturday, would expect most areas to be overcast with periods of rain and strong southerly winds 60-100 km/hr, with 20-40 mm rainfalls near the south coast, considerably less most other places, and temperatures 7-9 C.
SUNDAY and MONDAY will likely continue with the rain, wind and milder temperatures, and rainfalls could become heavy to excessive near the south coast. Where this rain falls over hills that develop a heavy snow cover, strong melt-driven runoff could lead to stream flooding in the southeast, south central and parts of the southwest as well as possibly Connemara. Temperatures will be near 8 C much of the time.
Now it should be said there is still a slight chance that most of this guidance is wrong about the mild victory over the cold and that the cold might put up a longer or more effective fight, so that needs to be watched, but the chances seem fairly good that mild is going to win based on the current model consensus. There will be times later in the week when renewed Atlantic systems come in but with some cooling of the general south to southwest flow between systems, they may not be starting off as mild as the previous system ended, so temperatures could fall back to the range of 2-5 C then go back up at intervals to around 8-10 C. Just looking at the guidance in broad general terms I would say there is likely a chance of one more cold spell taking place late in the month or more likely into early March. So I don't think this will be winter's "last hurrah" before a spring pattern dominates.
My local weather on Tuesday was sunny and briskly cold at -12 C, and by late evening it had fallen to near -20 C, the coldest night we have had this winter so far. We are on the outer edge of a vast frigid air mass covering almost all of Canada and the northern half of the central to eastern U.S., and readings as low as -45 to -50 can be found well to our north, while -30 is common across the prairies and -25 C in the U.S. midwest. A frontal boundary running from around Oklahoma to Virginia is creating weak disturbances that could bring snow along that path in the next few days, and it's a bit milder to the south (although not above regional normals, near 10 C in the southeastern states is near or a bit below their average at this time of year). The air mass reaching Ireland has its origins in Russia and came across the Baltic regions as well as Poland and Germany. In central Germany this morning some lows near -20 C are being reported, and -10 readings extend into parts of Belgium and the Netherlands. There are also some places in Scotland below -10 C at this hour although -5 C is a ballpark average there.
Unless I want to make a substantial change to the snowfall outlook for Thursday-Friday, there won't be an update issued but that will be assessed around 4-6 p.m. from later guidance.