Rainfall is a fact of life in Ireland. Because of the climate and the proximity to Atlantic Ocean currents, there tends to be some rain falling on a fairly frequent basis. Different areas of the country receive different amounts of rainfall. In the eastern half of the country, the rain totals between 750 and 1000mm annually. The western half of the country tends to have more rain, and receives between 1000 and 1250mm each year. The more mountainous regions of the country receive more rain and can get totals of up to 2000mm of rain each year.
Most of the precipitation that falls in Ireland is in the form of rain. This is mainly due to the fact that the temperature tends to be above the freezing mark. During an average year, the wettest months tend to be December and January, and this does mean that there will be some precipitation in the form of snow and hail. The majority of the country tends to be driest in April although some areas tend to get less precipitation in June.
Frequency of Precipitation
Although Ireland has a reputation for daily rain it does not in fact, rain on a daily basis. However, there are a fair number of wet days during the year. As with the amount of precipitation an area receives, the number of days where precipitation occurs may also vary. In the eastern portions of the country and along the south-east coast, there are usually 150 days annually where more than 150mm of precipitation falls within a 24-hour period. However, in areas such as the western portions of the country, this can increase to about 225 days of precipitation annually.
However, although rain may fall frequently, it does not always fall heavily. There are severe storms which occur from time to time and during these periods hourly rainfalls of more than 25mm may occur. However these are extremely rare and the usual rate of rainfall tends to be in the neighbourhood of 1-2mm per hour. There are also storms where the rainfall may range from 15 to 20mm but they tend to occur no more frequently than every five years.
How Precipitation Is Measured
There are 15 Meteorological Service stations located across Ireland, which measure the amount of rainfall every hour. A standard gauge, which consists of a container and a funnel is used to collect and measure the precipitation.
There are also more than 750 rainfall monitoring stations located throughout Ireland and these stations may not measure the rainfall in their areas quite as frequently. In fact, they tend to check the gauges daily instead of hourly. There are also stations which are located in more remote locations such as very mountainous areas. These may have their gauges read only once per month.
Rainfall Records of Note
• 1887 was the driest year on record, with the Glasnevin weather station recording a mere 356.6 mm during the year.
• 3rd April 1938 to 10th May 1938 marked the period of the longest absolute drought in Limerick.
• October 1996 saw the most rainfall in one month. A total rainfall of 790.0mm was recorded in the Cummeragh Mountains.
• With a total rainfall of 3964.9mm, The Ballaghbeena Gap holds the record for the greatest annual total.
• In August, 1980 in Orra Beg, Antrim, a rainfall of 97mm was recorded in the space of one hour making it the greatest hourly total recorded to date.
• The greatest daily total (243.5mm) was recorded in Cloone Lake County Kerry on the 18th of September, 1993