TRENDS for the week of 21 to 27 Dec 2020
-- Temperatures will average about 2 deg below normal values. It will be turning much colder near the end of this interval after an earlier cooler period around 23rd-24th.
-- Rainfall will average 25 to 50 per cent of normal, some precipitation will fall in wintry mixtures.
-- Sunshine will average near normal values.
FORECASTS
TODAY will bring a little further rain, mostly across central counties, then variable amounts of cloud with showers more isolated, as winds pick up slightly around late morning to afternoon, from a westerly direction. Highs near 10 or 11 C in the south, 7 C central, 5 C northern counties. Around 5-10 mm additional rainfall expected.
TONIGHT will become partly cloudy to clear in the northern and some central counties, remaining overcast in the south with another interval of light rain possible. Lows near -2 C in the north, +1 central, +4 C southern counties.
TUESDAY will be a cold and almost calm day with cloud spreading a bit further north to obscure sunshine after mid-day in the north. Some light outbreaks of sleety rain or mixed wintry precipitation will develop late in the day across parts of the south. Highs only 2 to 5 C north, 5 to 7 C south.
WEDNESDAY will start out with a light snowfall in parts of Munster and south Leinster, mixing with sleety rain near the south coast, leaving a coating of 1-3 cm in some areas (more likely inland and above 100m asl). It will likely stay dry north of about Clare to north Wicklow, except for any wintry showers that may form over east Ulster and parts of Mayo due to weak bands of streamers. These may move further south later in the day and affect the Dublin region. Winds will increase from light northeasterly to moderate north-northeast 50-70 km/hr, adding chill to temperatures that will be steady in the range of 2 to 5 C.
THURSDAY (24th) will see partial clearing from early morning, with morning lows near -2 C. Sunny with cloudy intervals during the day, except where bands of wintry showers form near east coast and north Connacht, west Ulster; local snowfalls on hills may amount to 1-3 cm in places although many areas will remain dry. A sharp frost is likely after sunset on Christmas Eve, following daytime highs of 4 to 7 C.
FRIDAY (Christmas Day) will start out frosty in parts of Leinster and Munster, east Connacht and east Ulster, where lows could be -2 to -5 C. Any frost further west will likely be removed before morning by a slight increase in westerly winds and cloud cover. Hazy sunshine will follow the frosts in some eastern counties, more overcast further west, but generally dry with moderate westerly breezes setting in. Highs near 4 C east to 7 C west.
SATURDAY (St Stephen's Day 26th) will become windy with temperatures peaking at a rather early hour (possibly during the night of 25th-26th) at around 7-9 C, then it will begin to turn colder in stages with winds northwesterly at about 70-100 km/hr and passing showers, becoming wintry on hills later in the day as temperatures fall to around 3 or 4 C.
SUNDAY (27th) and MONDAY (28th) are looking windy and cold with scattered wintry showers, many of them snow but a few of sleet or hail too near coasts, in strong northerly winds 60 to 100 km/hr, which will add quite a chill factor to temperatures barely above freezing in the daytime (1-3 C). Nights will not be exceptionally cold because of this constant strong wind, but could drop to -1 or -2 C inland.
The OUTLOOK calls for further wintry weather conditions towards New Years with a growing possibility of significant snowfalls, as low pressure areas begin to form in the broad northerly flow providing a focus for more organized bands of snow or sleet at times. Temperatures will be well below average around zero or +1 C in the daytimes and around -3 C at night. Some of the guidance suggests that the cold spell will dig in and persist for some time into January, and there are also some hints of battleground scenarios where Atlantic moisture over-runs the cold air across Ireland leading to more snowfall. Conditions could become quite harsh in isolated higher terrain with blizzard like conditions possibly affecting free ranging livestock. At the same time, I should underscore the fact that there is some uncertainty about details and it seems likely that conditions will be rather variable from place to place in this coming cold spell, not everyone is going to see the same amounts of snowfall for example.
-- Peter O'Donnell for IWO