The Irish Meteorological Service Online
Rainfall in Ireland - Download the Report on Rainfall of November 2009 - [PDF] Report
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, in almost all areas are December and January. April is the driest month generally across the country. However, in many southern parts, June is the driest. Hail and snow contribute relatively little to the precipitation measured.
Rainfall amounts are collected by a standard gauge, consisting of a funnel and a container. The 15 Meteorological Service stations around the country measure these rainfall amounts every hour. However, most of the 750 or so rainfall stations around the country read their gauges once a day. A few gauges in remote mountain locations are only visited once a month.
How Often Does it Rain?
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 south-east coasts, to about 225 days a year in parts of the west.
How Heavy is the Rain?
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.
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