Wettest December on record at Armagh, warmest December since 1988 and coolest year since 2010

editorial image
0
Have your say

Armagh Observatory, 5 January 2016: Armagh Observatory reports that December 2015 was much wetter than average, the wettest December on record at Armagh, that is, since records of daily precipitation began at Armagh in 1838.

It was also much warmer, the warmest December at Armagh since 1988, and equal sixth-warmest December at Armagh since records of the daily maximum and minimum temperatures began at Armagh in 1843. The month was slightly duller than average, with 15 of the 31 days having no recorded strong sunshine at all.

Mean annual temperatures (1796-2015). Graph courtesy of the Armagh Observatory

Mean annual temperatures (1796-2015). Graph courtesy of the Armagh Observatory

Total recorded precipitation was 186.1 mm (nearly 7.33 inches), with no trace values, that is, some rainfall was recorded on every single day of the month. The long-term (1838-2010) average December precipitation at Armagh is 77.44 mm and the most recent 30-year (1981-2010) average precipitation is 77.23 mm. This shows that whereas the average December rainfall has hardly changed in nearly 200 years, last month’s record rainfall was 240% of the long-term average.

The five wettest Decembers on record at Armagh are now those of 2015 (186.10 mm), 1914 (181.35 mm), 1876 (170.19 mm), 1978 (165.85 mm) and 1852 (161.20 mm). The wettest day was the 29th with 31.1 mm (1.22 inches) of rainfall, and the second wettest day was Christmas day itself, with a total rainfall of 25.0 mm. This 2015 December 25th was the second wettest Christmas day on record at Armagh (beaten by 1956, with 25.9 mm).

The mean temperature (the mean of the average daily maximum and minimum temperatures) was 7.79 degrees Celsius (46.0 Fahrenheit). This was approximately 3.21 C higher than the long-term (1796-2010) average December temperature at Armagh and 2.86 C warmer than the most recent 30-year (1981-2010) average December temperature at Armagh, making this December the warmest since 1988. The five warmer Decembers at Armagh are those of 1857 (8.5 C), 1828 (8.3 C), 1934 (8.1 C), and 1842 and 1843 (both with a mean temperature of 7.9 degrees Celsius).

The warmest day (highest maximum daily temperature) was 14.8 C. This occurred on the 18th and was the equal sixth-warmest December day on record at Armagh (shared with 2nd December 1985). There were four December days with maximum temperatures above 14.0 C, namely the 18th (14.8 C), the 16th (14.4 C), the 19th (14.3 C), and the 15th (14.0 C). By

Total annual sunshine (1881-2015). Graph courtesy of the Armagh Observatory

Total annual sunshine (1881-2015). Graph courtesy of the Armagh Observatory

contrast, the coolest day was Christmas Day itself, with a lowest maximum

daily temperature of 5.1 C.

There were also several very warm December nights, that is, nights during which the temperature never fell below double figures. These exceptionally warm 2015 December nights were the 2nd and 17th (both with minimum temperatures of 11.1 C and now the equal fifth-warmest December nights on record at Armagh), and the 19th (10.9 C) and the 18th (10.3 C).

There were 13 ground frosts, the coldest of which was -5.2 C on the 13th, and two nighttime air frosts, that is, when the minimum temperature fell below freezing. The coldest night, also on the 13th, had a minimum temperature of -2.1 degrees Celsius.

Total annual rainfall (1838-2015). Graph courtesy of the Armagh Observatory

Total annual rainfall (1838-2015). Graph courtesy of the Armagh Observatory

December 2015 was slightly duller than average with a total of 38.6 hours of strong sunshine recorded at Armagh. This is approximately 95% of the most recent 30-year (1981-2010) average number of hours of strong December sunshine at Armagh (40.45 hours). The sunniest day was the 6th, with 4.5 hours of sunshine and there were 15 days with no recorded sunshine at all.

Taking the year as a whole, 2015 can be described as cooler and wetter than average, but slightly sunnier.

Despite the recent very warm November and December, and to a lesser extent October too, each of the previous months of 2015, namely January to September, were cooler or much cooler than the corresponding most recent 30-year (1981-2010) monthly average. The mean annual temperature for 2015 was 9.52 C (49.1 Fahrenheit), which is 0.19 C cooler than the most recent 30-year mean annual temperature at Armagh (9.71 C) and 0.46 C warmer than the long-term (1796-2010) average, which is 9.06 C. 2015 was the coolest year at Armagh since 2010.

Total precipitation was dominated by a few very wet months, namely May (60% wetter than average), August (approximately 50% wetter than average), and November and December (approximately 60% and 140% wetter than average). In contrast, June, September and October were relatively dry, each with roughly 50% or less than the corresponding month’s most recent 30-year average precipitation. The year as a whole, with a total precipitation of 951.7 mm (37.47 inches), was approximately 17% wetter than the most recent 30-year average annual rainfall at Armagh (813 mm).

The total number of hours of strong sunshine, 1387 hours, was approximately 11% greater than the most recent 30-year (1981-2010) average number of hours of strong sunshine, continuing a recent trend of there being slightly more sunshine at Armagh than the most recent 30-year annual average.

These data refer to observations at Armagh Observatory, which has been recording the weather at Armagh since 1795. The attached graphs show the run of mean annual temperature, rainfall and sunshine over the years since these data have been recorded on a daily basis at Armagh.