TRENDS for the week of 15 to 21 Jan 2021
-- Temperatures will average 1 to 2 deg below normal, a blend of near normal to mid-day Tuesday 19th, and very cold readings expected towards the middle of next week.
-- Rainfall will average 75 to 100 per cent of normal values, most of it coming in two periods, Friday night, and Monday afternoon to Tuesday morning. Some wintry showers will follow.
-- Sunshine will average 25 to 50 per cent above normal, as several days will have good amounts of sunshine and the average at this time of year is only 2 hours of sunshine a day.
FORECASTS
TODAY will see increasing cloud dimming any early sunshine, once any fog lifts. Some patchy freezing fog and frost in eastern counties will dissipate fairly quickly but the temperature increase will be slow after reaching 3-5 C and it may still be only around 6 C by evening in some areas, 9-10 C in the west where rain will arrive as winds freshen from the south to 40-60 km/hr.
TONIGHT will be windy and wet, with a distinct frontal passage after midnight that might produce a squall line feature, with strong wind gusts and a rumble of thunder possibly. About 15-25 mm rain could fall overnight, winds will veer from south to west-southwest with the frontal passage, peaking at 50-80 km/hr but with potential for higher gusts to develop especially through central counties. This front will be moving into the west coast around midnight and through Dublin around 0300h. Temperatures will be steady near 10 C until the front passes then will fall a few degrees to near 6 C by morning.
SATURDAY will continue rather windy but skies will become partly cloudy with bands of showers feeding in from the Atlantic, 3-5 mm rainfalls are likely from these in western regions, trace to 2 mm further east (after the main band of rain exits). Winds westerly 40 to 70 km/hr, highs near 8 C.
SUNDAY will have some morning frosts, and sunny intervals with cloudy skies at times in the west and north, only isolated showers likely, and a temperature range from lows near -2 C to highs near 8 C.
MONDAY will start out dry and cold in the north and east, while turning quickly milder and overcast in the south and west with light to moderate rain. This may start as sleet on hills in the north around early afternoon. Winds will pick up from the east to southeast, slowly turning more southerly. Lows near -2 C and highs near 8 C.
MONDAY NIGHT and the first part of TUESDAY will be influenced by the warm sector of an Atlantic low pressure system, temperatures will peak at around 11 C and there will be 15-25 mm rainfalls with winds south to southwest about 50-80 km/hr.
TUESDAY mid-day to evening will be a period of strong west to northwest winds 70-110 km/hr and rapidly falling temperatures, with bands of wintry showers developing especially for Connacht and Ulster. Temperatures will be around 2 C by evening and wind chills near -5 C.
WEDNESDAY will be windy and cold with snow showers, some wintry mixtures from these near sea level, but accumulations of 1-3 cm on some northern hills. There will be more frequent sunny intervals in the east and south coast counties where wintry showers may be more isolated. Winds northwest 70-110 km/hr will add considerable chill to already low temperatures, with morning lows near -3 C and afternoon highs near +1 C, possibly a bit higher near some coasts.
Peter O'Donnell for IWO
THURSDAY will continue windy and cold, although winds will slowly abate to the 40-70 km/hr range. There will be more areas of wintry showers and snow on hills, with morning lows near -5 C and afternoon highs zero to +2 C.
FRIDAY could bring some outbreaks of snow, the guidance is beginning to come together recently in terms of an enhanced risk of at least light snowfalls developing in the cold air, which may be at its most chilly state by then, with lows near -5 C and highs -1 to +1 C, in variable winds depending on how weak features evolve and move around the region.
The OUTLOOK beyond that into the weekend of 23rd-24th and the following week remains more uncertain, with guidance still split on how many more days of cold weather might follow, some suggestions would place the transition to milder, rainy conditions over that weekend (with snow at first a possibility), other guidance says the cold will dig in and not get pushed out until mid-week (a trend which could keep falling further on into the future since the reliability factor is getting low by then anyway).