Due to its island status and location in the north-east of the 2nd largest ocean in the world, the climate of Ireland can best be described as mild temperate maritime which thus puts it under the Köppen climate classification code of ‘Cfb’ (C = moderate temperature; f = moist; b = mild summer)
Temperature in Ireland is largely influenced by various maritime air masses as well as North Atlantic Gulf Stream which have the effect of suppressing wide-ranging fluctuations and extremes within each season. Both these influences are the reason why both Winter & Summer temperatures in Ireland are relatively benign when compared to those that occur in other regions (particularly inland continental areas) located on the same latitude.
Generally speaking, the coldest months of the year are December, January and February (Meteorological Winter), while the warmest temperatures will occur June, July & August (Meteorological Summer). Mean daily summertime maxima averages between 17 – 22 Deg. C, while in Winter, daily maxima typically ranges between 6.0 – 9.0 Deg. C with absolute maxima and minima rarely reaching above 30.0 Deg. C & below – 8.0 Deg. C respectively. Inland regions will generally experience the highest diurnal range in temperature within all seasons. Graphs below shows mean monthly maxima & minima at both Valentia Observatory on the west coast of Kerry & Armagh Observatory in Armagh City. All data courtesy of Met Éireann & the UK Met Office.
Rainfall in Ireland occurs throughout the year and with reasonable frequency. Because the prevailing winds are from the west-southwest, the west of the country will have a higher number of wet days (days with rainfall totals = > than 1.0 mm) than the eastern half of the island in an average year thus will receive higher annual rainfall totals as a result.
The map below shows the annual mean rainfall totals based on the 1981-2010 period. Please note that the data in this chart is based on a low number of low lying synoptic stations which does not take into account the influence of local topography (which can vary considerably between hilly areas and nearby low-lying regions for example) on rainfall totals with each sector. Although much of the rainfall that occurs in Ireland is light (< 1.0 mm/h – < 10 mm/day), heavy downpours do occur with hourly totals > 10 mm/h and daily totals > 30 mm / day being recorded in any given location between 2 and 6 days per year on average.
The wettest period of the year is typically the late Autumn, – early Winter period which is when Atlantic frontal zones tend to be at their most active; while the driest period on average occurs in the from the 2nd half of Spring and into the 1st half of Summer.
The graph below shows the comparative mean monthly rainfall totals (1981 – 2010) between Valentia Observatory on the far southwest coast and Armagh Observatory, located well inland on the northeastern side of the country.
Mean monthly rainfall
Despite the relatively small size of Ireland, mean wind speeds can vary quite considerably from place to place in an average year. By convention, the north of the country is windier than the south; western areas will tend to be breezier than the east & inland locations will be less windier that coastal regions – though day on day variations on this can and frequently do occur, depending on the synoptic situation at any given point in time.
Mean annual wind speeds vary between 16.0 Knots at Malin Head in Co. Donegal to 7.0 knots at Kilkenny in the south midlands. The number of days with recorded gales (speeds > = 34 Knots) ranges from 30 per year at Belmullet on the west coast to just 1 at Mullingar in Co. Westmeath.
Map below shows that annual mean wind speed (1971-2000) based on the linear differences between a small number of official synoptic stations dotted around the country.
The graph below shows the mean monthly wind speed (knots) at Belmullet and Mullingar which are based on their respective 1981-2010 averages: