Northern Ireland's climate is oceanic, with quite cold, rainy winters and mild, relatively rainy summers.
The region is a constituent country of the United Kingdom and occupies the northeastern part of the island of Ireland.
Atlantic weather fronts move relentlessly one after another over the country, resulting in a rapid succession of cloudiness and sunshine, rain showers and subsequent improvements. Days with completely clear skies are rare: the weather is more likely to be variable or unstable, and between one disturbance and another you can expect, rather than clear skies, clouds running in the sky.
The wind is frequent and lively, although it is generally stronger between late autumn and early spring.
Rainfall is frequent, even though it is not very abundant, because the bulk of the rains is discharged on the hills of Donegal, in the Republic of Ireland. Rainfall amounts to 850 mm (33.5 inches) per year in Derry, in the north, and 950 mm (37.5 in) in Belfast, in the north-east, while it exceeds 1,000 mm (40 in) in the west. The least rainy city is Armagh, in the southern inland areas, with 810 mm (32 in).

Winter, from December to February, is quite cold but not freezing. The sky is often cloudy, the rains are frequent, and the most intense low pressure systems can cause wind storms. Temperatures are slightly above freezing during the night, while they are around 7/8 °C (45/46 °F) during the day.
On milder periods, under the influence of southerly air masses, the temperature can reach 13/15 °C (55/59 °F).
Cold waves are rare, and are usually short-lived because the westerlies start to blow again after a while. Snow is quite rare as well: on average, it falls for a few days in a year, and may not occur for an entire winter. Night temperatures drop below freezing (0 °C or 32 °F), usually by a few degrees, for about 20 days each year in Portrush (on the north coast), 25 days in Derry (near the north coast), 30 days in Belfast (near the north-east coast), and 50 days in Castlederg, in the western inland areas. However, they drop to about -10 °C (14 °F) only in the coldest winters. In most cases, on clear nights, there can be light frosts, and nothing more.
Most of the region is flat, but there are also hills, in particular, the Sperrin mountains in the west, which reach up to 678 meters (2,224 ft), and the Morne mountains in the south-east, which reach up to 850 meters (2,790 ft). On these hills, the temperatures are a bit lower than in the plains, so the snow, which is rare at sea level, becomes quite frequent here from November to April.

Spring, from March to May, is initially cold, and remains very cool or cold still in April, and sometimes in May; the temperature becomes usually quite mild only by the second half of May, when, however, nights can still be quite cold. In return, spring is the (relatively) least rainy season and the sunniest of the year.

In Summer, from June to August, temperatures are cool: average highs are around 18/19 °C (64/66 °F). The temperature rarely exceeds 25 °C (77 °F), and this happens only in the rare and short periods when the Azores High moves over the country, while it never reaches 30 °C (86 °F).

Autumn, from September to November, is cloudy and rainy, at times windy, with little room for sunshine.

Lough Neagh


Here are the average temperatures of Belfast, the capital city, located on the east coast.
Belfast - Average temperatures
Min (°C)223471011119743
Max (°C)881012151819191713108
Min (°F)363637394550525248453937
Max (°F)464650545964666663555046

The rains are quite frequent all year round. Here is the average precipitation.
Belfast - Average precipitation

The sky in Northern Ireland is often cloudy, so the sun is rarely seen; however, the sunniest month is May. Here are the average daily sunshine hours in Belfast.
Belfast - Sunshine

The sea in Northern Ireland doe not invite you to swim, in fact the water temperature does not go above 15 °C (59 °F) in August. Here is the sea temperature in Belfast.
Belfast - Sea temperature
Temp (°C)87781012141515141210
Temp (°F)464545465054575959575450

Best Time

The best time to visit Northern Ireland is the summer, from June to August, since it is the mildest of the year: the rains are frequent, the air is often very cool (especially in June), it's better to bring a jacket and umbrella (or rather a raincoat as it often rains in the wind), but the days are long, and you can hope to see the sun peeking through the clouds.
In September, the temperatures are still acceptable, but the days are shorter than in the previous months.

What to pack

In winter: bring warm clothes, such as a sweater, a coat, a raincoat.
In summer: bring clothes for spring and autumn, a jacket and a sweater, a raincoat or umbrella.