On the whole, Northern Ireland is cloudier than England, because of the hilly nature of the terrain and the proximity to the Atlantic. Even so, the coastal strip of County Down manages an annual average total of over 1400 hours of sunshine. This compares favourably with many coastal areas of England and Wales, though not perhaps with the figures of around 1750 hours achieved by many places along the south coast of England. The dullest parts of Northern Ireland are the upland areas of the north and west, with annual average totals of less than 1100 hours.
Mean monthly sunshine figures reach a maximum in May and are at their lowest in December. The key factor is, of course, the variation in the length of the day through the year, but cloud cover plays a part as well. A feature is the reduction that typically occurs in July and August, accompanied by increased cloudiness.
The graphs show the average monthly sunshine totals for Aldergrove and Armagh, together with the highest and lowest totals recorded in the stated periods.
The highest known monthly sunshine total in Northern Ireland is 298 hours recorded at Mount Stewart (County Down) in June 1940. The highest UK monthly total is 383.9 hours at Eastbourne in July 1911. In the dullest winter months, less than 20 hours have been recorded - a mere 8.3 hours was recorded at Silent Valley (County Down) in January 1996, but there was none at all in December 1890 in central London.
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