With southwesterly winds from the Atlantic dominating, rainfall figures are highest in the northwest, west and southwest of the country, especially over the higher ground. Rainfall tends to be highest in winter and lowest in early summer.
The annual number of days with more than 1 mm of rain varies between about 150 in the drier parts and over 200 in the wetter parts of the country.

Sunshine

The sunniest months are May and June. During these months sunshine duration averages between 5 and 6.5 hours per day over most of the country. The extreme southeast gets the most sunshine, averaging over 7 hours a day in early summer. December is the dullest month with an average daily sunshine ranging from about 1 hour in the north to almost 2 hours in the extreme southeast.

Ireland normally gets between 1400 and 1700 hours of sunshine each year. The eastern Sahara Desert, however, which is the sunniest place in the world, gets an average of 4300 hours a year. Irish skies are completely covered by cloud well over half the time. This in turn is due to our geographical position off the northwest of Europe, close to the path of Atlantic low pressure systems which tend to keep us in humid, cloudy airflows for much of the time.

Temperature

Air temperatures are measured at a height of approximately 1.2 m above a flat surface covered with short grass.
The moderating influence of the Atlantic is felt throughout Ireland. The country therefore does not experience the same range of temperatures through the year as more continental countries. Although our inland areas show more variation, even at these there would only be about one day or less per year when the air temperature stays below freezing point. Air temperatures inland normally reach 18 to 20 °C during summer days, but only about 8 °C during wintertime.

Rainfall

Most of the eastern half of the country has between 750 and 1000 millimetres (mm) of rainfall in the year. Rainfall in the west generally averages between 1000 and 1250 mm. In many mountainous districts rainfall exceeds 2000mm per year. The wettest months, almost everywhere are December and January. April is the driest month generally but in many southern parts, June is the driest. Hail and snow contribute relatively little to the precipitation measured.
The general impression is that it rains quite a lot of the time in Ireland but in fact two out of three hourly observations will not report any measurable rainfall. The average number of wet days (days with more than 1mm of rain) ranges from about 150 days a year along the east and aouth-east coasts, to about 225 days a year in parts of the west.
Unlike the rain in many other countries, especially in the tropics, average hourly rainfall amounts in Ireland are quite low, ranging from 1 to 2mm. Short-term rates can of course be much higher: for example, an hourly total of 10mm is not uncommon and totals of 15 to 20mm in an hour may be expected to occur once in 5 years. Hourly totals exceeding 25mm are rare in this country and when they do occur they are usually associated with heavy thunderstorms.

Wind

The wind at a particular location can be influenced by a number of factors such as obstruction by buildings or trees, the nature of the terrain and deflection by nearby mountains or hills. Average annual wind speeds range from 7 m.p.h. in parts of south Leinster to over 18 m.p.h. in the extreme north. On average there are less than 2 days with gales each year at some inland places like Kilkenny but more than 50 a year at northern coastal locations such as Malin Head. Indeed the north and west coasts of Ireland are two of the windiest areas in Europe and have considerable potential for the generation of wind energy.
Since the days of Admiral Sir Francis Beaufort (1774-1857), who introduced the Beaufort scale of wind force, the knot (one nautical mile per hour) has been used as a unit of wind speed. Local radio weather forecasts normally quote wind speed in Km/hr; modern meteorological practice however is to use metres per second (1 metre per second = 1.94 knots = 2.24 miles per hour).