Mostly mild and moist
by Denis Fitzgerald
Ireland is situated on the eastern edge of the North Atlantic Ocean between 51deg.N and 56deg.N latitude and comes strongly under the influence of the westerly windflow of these middle latitudes. The warm waters of the Gulf Stream cause sea temperatures around Ireland to be a good deal higher than the average in this latitude band, and the prevailing westerly winds carry air from over these waters across the country and thereby cause Ireland to miss the extremes of temperature of continental climates and gives the Irish climate its temperate, changerable character. While Atlantic weather systems are the dominant influence on Irish weather, there are times when the winds blow from the continent of Europe, which in Summer usually gives warmer weather, and in Winter, cold weather.
Gentle Rain – little snow
Average annual rainfall varies between 750 and 1000 millimetres (30 to 40 inches) in the drier eastern part of the country, while most other parts have average yearly totals of between 1000 and 1350mm (40 to 54 inches). The intensity of the rainfall is generally low: Dublin Airport’s 750mm per year falls in about 550 hours. In continental areas with comparable annual averages the rain usually falls in shorter, heavier outbreaks.
This rainfall is well distributed throughout the year: the months from February to July form the drier half of the year, but even so they still account for about 40% of the annual total. Months without rainfall are rare. Dry spells can occur at any time of the year but, fortunately, are most frequent in the Spring and Summer months between April and August.
Irish Winters are usually free from widespread, significant snowfalls. In the 1980s there were only two years – 1982 and 1987 – when snow persisted for some days and disrupted the normal pattern of life. January and February are the months when snow is most likely.
Temperate and Humid
The relatively warm seas around Ireland’s coasts exert a moderating influence on both Winter and Summer temperatures. Air temperatures in excess of 25deg.C (77deg.F) have occurred only in the months April to October and 30deg.C (86deg.F) has been exceeded only in June July and August. Daily minimum values of -5deg.C (23deg.F) or lower have been recorded only in the months of October to May; if the threshold is lowered to -10deg.C (14deg.F) the period reduces from November to March. The extreme temperatures reached in over a hundred years of recording range from 19.4deg.C (- 2.9deg.F) to 33.4deg.C (92deg.F) which by continental standards is a modest temperature range.
January and February are the coldest months with mean air temperatures between 4deg.C (39deg.F) and 7deg.C (45deg.F). July and August are the warmest, with mean temperatures of 14deg.C (57deg.F) to 15deg.C (61deg.F). It is unusual for the mean maximum temperature in a Summer month to exceed 20deg.C (68deg.F) and for a Winter month to have a mean minimum temperature below -2deg.C (28deg.F).
Since the air reaching Ireland often has had a long passage over the ocean, relative humidity is generally high. Throughout the year relative humidity averages about 90% late at night and in the early morning. Typical mid-afternoon values range 65% to 70% between April and August and 75% to 85% during the months from October to February. However Ireland rarely if ever gets that combination of heat and humidity which causes indices of heat stress well known in some continental cities; high temperatures here usually occur with low relative humidity. The damp Winters are countered by widespread use of central heating but air conditioning in private dwellings to ensure comfort in summer is practically unknown (and hardly required!) Outdoor sports are played all year round but a fair degree of hardihood may be required to play golf or tennis in Winter.
A Cloudy Isle
Cloud manages to cover three quarters of sky on average and, generally speaking Ireland is not a destination for sun-worshippers. The length of day varies between 16 to 17 hours in late June and 7 hours in late December. The average duration of sunshine is 15% to 25% of the length of the day in December and 30% to 45% in late Spring and early Summer; the higher values in the northwest.
Wind
Situated in the zone of the mid-latitude westerlies, mean annual windspeeds range from 7 miles per hour in inland areas of the southeast to over 15 miles per hour near the northwest coast which averages about 40 days per year with gales compared with just 2 in some sheltered inland areas. Mean speeds are highest in the winter months, December to February, and lowest in July and August.
When is the best time to visit Ireland?
The outstanding characteristics of Ireland’s climate is variability and averages can be misleading on specific occasions.
With that caveat in mind, we can say in general that July and August, the warmest months, are best overall but they are not the months of the lowest rainfall or highest sunshine. The brightest months are May and June when temperatures are also reasonably high. Indeed, spells of very pleasant weather can occur at any time between April and October.
Temperature conversion from Celsius to Fahrenheit:
Multiply by 9, Divide by 5 and add 32
For example: 25deg. C = 25 x 9 = 225 / 5 = 45 + 32 = 77deg.F