The current climate of Ireland is classified as temperate, with warm summers, cool winters and plentiful precipitation throughout the year. The principle factors of influence on the climate include the UK's northerly latitude (which ranges from 50° to 60° N), its close proximity to the Atlantic Ocean and, especially, the warming of the waters around the British Isles by the Gulf Stream. The weather can be notoriously changeable from one day to the next but temperature variations throughout the year are small.

The climate of Ireland is significantly influenced by the maritime tropical, maritime polar, continental polar and continental tropical air masses.

Ireland is at the boundary of convergence between the warm tropical air to the south and the cold polar air to the north. In this area, the large temperature variation creates instability and this a major factor that influences the notoriously changeable and often unsettled weather Ireland experiences, where many or all types of weather can be experienced in a single day.

A deep depression near Iceland on 27 October 2000

Temperature figures are in Centigrade and are based on Dublin.

Seasons

Winter
Winter in Ireland is generally a cool, wet and windy season. Temperatures at night rarely drop below -10 °C and in the day rarely rise above 15 °C. Precipitation is plentiful throughout the season with occasional snow.

Towards the later part of the season the weather usually stabilises with less wind, precipitation and lower temperatures. This change is particularly pronounced near the coasts mainly due to the fact that the Atlantic is often at its coldest during this time after being cooled throughout the autumn and the winter. The early part of winter however is often unsettled and stormy; often the wettest and windiest time of the year.

During periods of light winds and high pressure frost and fog can become a problem and can pose a major hazard for drivers on the roads.

Spring
Spring is generally a rather calm, cold and dry season, principally since the Atlantic has lost much of its heat throughout the autumn and winter. However, as the sun rises higher in the sky and the days get longer, temperatures can rise relatively high and thunderstorms / heavy showers can develop.

There is a fair chance of snow earlier in the season when it is cooler.

Summer
Summer climatic differences are more influenced by latitude and temperatures are highest in southern and central areas and lowest in the north. Generally, however, summer temperatures rarely go much above 30 °C, although temperatures have soared as high as 38 °C.

Summer is a rather dry season on average but rainfall totals can have a wide local variation due to localised thunderstorms. These thunderstorms mainly occur in southern, eastern and central areas and are less frequent and severe in the north and west.

North Atlantic depressions are not as frequent or severe in summer but increase both in severity and frequency towards the end of the season.

Autumn
Autumn in Ireland is notorious for being extremely unsettled. As cool polar air moves southwards following the sun in the sky, it meets the warm air of the tropics and produces an area of great disturbance along which the United Kingdom lies. This combined with the warm ocean, which due to heating throughout the spring and summer, produces the unsettled weather of autumn. In addition, when the air is particularly cold it may actually be colder than the ocean and this can result in significant amounts of evaporation, producing clouds which eventually condense and bring rain to Ireland.

Atlantic depressions during this time can become intense and sustained winds of hurricane force (greater than 74 mph) have been reported. One such intense depression was the great “hurricane” of 1987. (see below)

As such, autumn, particularly the latter part, is often the stormiest time of the year.

Sunshine and cloud

The average annual amount of sunshine for Ireland is relatively low and around 2/3 of days are partly cloudy, occasionly with little sun at all. Southern coasts, however, often have the clearest skies because cumulus cloud formation generally takes place over land, so coastal areas are often cloud free.

On occasions blocking anticyclones (high pressure systems) may move over or near Ireland and may persist for weeks or even months. The cool dry air often results in clear skies and few clouds, bringing frosty nights in winter and hot days in the summer.

A fine summer's day

Average annual daily hours of sunshine range from between one and three hours in midwinter to between five and eight in midsummer.

The Atlantic Ocean

One of the most important influences on the Ireland climate is the Atlantic Ocean and especially the North Atlantic current which brings warm waters from the Gulf of Mexico to Ireland by means of the global conveyor.

This has a powerful moderating and warming effect Irish climate. The North Atlantic Drift warms the climate of the UK to such a great extent that temperatures in winter would be about 10 °C lower than they are today if it didn't exist.

These warm ocean currents bring substantial amounts of humidity with them and contributes strongly to the notoriously wet climate Ireland experiences.

Depressions are another major product of the Atlantic Ocean and roll in towards Ireland throughout the year and are especially intense and frequent in autumn and winter. These depressions can be very severe and often bring in heavy rain and strong winds.

Winds

A high temperate latitude and close proximity to a large ocean on its westerly side means that Ireland is a windy place.

The prevailing wind in Ireland is from the south west but in such a changeable climate it may blow from any direction for sustained periods of time. Winds are strongest near westerly facing coasts and inland areas where there is little topography, such as mountains, to divert the wind.

Gales (which are defined as winds with speeds of 32 to 63 miles per hour) are strongly associated with the passage of deep depressions across or close to Ireland, and both are most frequent in the winter.

Areas of high elevation tend to have higher wind speeds than low elevations, and Great Dun Fell in Cumbria (at 857 meters) averaged 114 days of gale a year during the period 1963 to 1976.

Rainfall

Rainfall amounts can vary greatly across Ireland and generally the further west and the higher the elevation, the greater the rainfall.

The main reasons for high number of rainy days in Ireland are its mid-latitude position, its close proximity to the Atlantic ocean and the warm waters the North Atlantic Drift brings.

Most rainfall in Ireland comes from North Atlantic depressions which roll into Ireland throughout the year and are particularly frequent and intense in the autumn and winter. They can on occasions bring prolonged periods of heavy rain in the north and flooding is not rare.

Temperature

Generally Ireland has mild to cool winters and warm to hot summers with little variation in temperature throughout the year. In Ireland the average annual temperature varies from 8.5 °C in the north to 12 °C in the south, but over the higher ground this can be several degrees lower. This small variation in temperature is to a large extent due to the moderating effect the Atlantic ocean has since water has a much greater heat capacity than air and tends to release it slowly throughout the year. This has a warming influence on coastal areas in winter and a cooling influence in summer.

The ocean is at its coldest in February or early March, thus around coastal areas February is often the coldest month, but inland there is little to choose between February and January as the coldest.

Temperatures tend to drop lowest in late winter nights inland, in the presence of high pressure, clear skies, light winds and when there is snow on the ground. On occasions, cold polar or continental air can be drawn in over Ireland to bring very cold weather.

The warmest winter temperatures tend to occur on the lee of high ground and by the coast and are produced when a moist south or south west wind warms up downwind after the crossing the mountains. Temperatures in these areas can rise as high as 18 °C in winter on rare occasions.

Climate history

The climate of Ireland has not always been the way it is today, and in some periods it was much warmer, and in others it was much colder. One of the greatest climatic events Ireland has experienced was the Ice Age. This was a period of extreme cold weather that lasted for tens of thousands of years and ended about 10,000 years ago.

10,000 years ago Ireland began warming, resulting in the melting of the ice sheets bringing the interglacial period that were are in today. There have been many glacial and interglacial periods in the geological history of Ireland.