TRENDS for the week of 1 to 7 April, 2021
-- Temperatures will average 2 to 4 deg below normal values, largely because of very cold temperatures expected on Monday and Tuesday, but it will also be rather cool in the east before that arrives, so that is where the average might be as low as 4 below normal, the milder west will build up some above normal averages before the cold arrives.
-- Rainfalls will be about 25 per cent of normal values, or less in some areas, as wintry showers on Monday and Tuesday are not likely to produce heavy precipitation. Some rain late Sunday is the main producer of any totals at all.
-- Sunshine will vary from 25 per cent below normal in some east and north coast counties to 25 per cent above normal in the south and west. These differences will build up in the first half of the interval. Most places will be rather cloudy from Sunday to next Wednesday.
-- Winds will be light to moderate until Sunday afternoon or evening, then rather strong for about a day and a half before backing off to moderate again.
FORECASTS
TONIGHT will feature some clear intervals and the eastern cloud may break to partly cloudy skies, lows 3 to 7 C.
GOOD FRIDAY will be a similar day but likely a bit less cloudy over eastern regions so highs could be more similar to those further west, 10 to 14 C. Both Thursday and Friday, a few places in west Munster may be even warmer than forecasts are saying, a local 17-19 C would not be too surprising since there hasn't really been a strong change of air mass.
By SATURDAY the easterly flow will be replaced by light westerly breezes and this could push in marine cloud layers over parts of Ulster and Connacht, while sunshine prevails further east on this occasion. Lows of 1 to 4 C and highs about 12 to 15 C are expected.
EASTER SUNDAY will start off in this same moderate air mass, but it will be rather suddenly replaced by much colder air arriving mid-afternoon in the north to early evening in the south, on strong northwest to north winds. Morning lows 1 to 4 C, afternoon highs 8 to 11 C north, 11 to 14 C south. Temperatures will fall quickly in the late afternoon and evening, rain turning to sleet or snow in some places, although accumulations expected to be patchy 1-2 cm.
MONDAY will be unseasonably cold with strong north winds 50 to 80 km/hr, some higher gusts in exposed coastal locations adding a chill to near record low temperatures starting out around -1 or -2 C and working back to only highs of 3 to 6 C. Passing wintry showers could lay down some temporary coatings of snow, or graupel (a form of hail) and snow pellets are likely too, some thunder may develop in heavier showers. There will be a few brighter intervals especially across the south. Wind chills may be as low as -4 C in some areas.
TUESDAY will be just about as cold although not quite as windy, and the inland penetration of wintry showers may be somewhat reduced with northern and western high ground seeing more of them, lows -2 to -4 C and highs 3 to 7 deg C.
WEDNESDAY will bring a slight moderation as a weak warm sector develops between this first outbreak and a second one following on, so as winds become briefly westerly at 30-50 km/hr, under cloudy skies with some rain at times, temperatures will recover a bit to 8 or 9 C.
By THURSDAY into FRIDAY and the following weekend, a new batch of very cold air is likely to arrive, not quite as cold as the first round, so highs of 4 to 7 C and overnight lows of -2 to +2 C are expected; more sleety showers but the mix will likely be less snow and more rain than the first interval. This cold spell looks like it will just gradually moderate a degree or two each day until things get back to near normal mid-April weather for a while; however, the pattern looks capable of reloading at intervals with further cold spells so the month as a whole is likely to be quite a bit below normal in temperature, and eventually rainfalls may increase as the Atlantic tries to restore its dominant role with a storm track near or just south of Ireland at times by later in the month. If there was ever to be a repeat of legendary snowfalls of the distant past in April (such as in 1917) this type of cold outbreak is one necessary ingredient, but nothing on the charts suggests an exact duplication of that event (1st-2nd Apr 1917, some parts of southern and western Ireland had very heavy snowfalls -- the culprit was a slow-moving low pressure area that circled around over Britain for several days with air masses at record cold levels pushing in from the northeast and later on from the northwest). Some higher places could see 2-5 cm snow cover during this coming event but they were measuring snow in feet in the 1917 storm. Over in Britain they had their coldest April day in a 250-year interval and in Ireland there were readings colder than on any other April days also.