Weather report 2015

sandfieldloughIt’s been a wet and windy year again! But while large parts of Ireland have been suffering greatly from the recent heavy rains and storms, Donegal faired slightly better, and certainly in the west, experienced very little flooding. But December was definitely wet – marginally wetter than January, and 2015 was a wet year. In comparison to the Met Éireann monthly summaries for Malin Head (Inishowen) and Finner (Ballyshannon) though, Sheskinmore records lower monthly and annual totals. I noted in last years summary that the McGlinchey weather station might simply under-estimate rainfall totals – recording an annual total of 1094 mm (43.1″) compared to 1484 mm (58.4″) at Malin Head and 1494 mm (58.8″) at Finner. But I have wandered through the dunes at Sheskinmore many times in dry conditions when it seems to raining all around! If the differences were simply under-estimates, then we would expect to see similar patterns with smaller magnitudes – but the McGlinchey gauge implies that November, December and January were very similar, while Malin Head and Finner recorded significantly higher rainfall at the end of the year than at the start. This suggests that west Donegal did not receive the same degree of heavy precipitation observed in north and south Donegal, and across the rest of the country. To note, for those who fancy a visit to Sheskinmore, September is consistently a drier-than-average month! Unsurprisingly, there were now drought periods recorded at McGlincheys in 2015!

2015rainwind2015wrThe 2015 wind climate was dominated by wind from the west and south sectors. In comparison to previous records from McGlincheys, there were proportionately more winds from the west and southwest, and less from the southeast and east. Over the course of the year, wind direction frequency shifted from west-dominated to an increased northerly component, with the year ending with wind mostly from the south/southwest. Stronger winds consistently come from the southwest, with only weaker winds from the north and east. We had stronger winds in 2015 than in previous years, and the weather station recorded its highest wind speed (gust) to date: 31.7 m/s (70.9 mph) on the 15th January. That same day generated the maximum 10-minute average of the year – 19.7 m/s (44 mph). The mean wind speed over the course of the year was 4.6 m/s (10.3 mph), in comparison to 3.8 m/s (8.5 mph) in 2014. It’s worth noting that  Bagnold (1941) determined that 4 m/s (8.9 mph) was the minimum speed threshold for the transport of fine sand (as measured at 1 m height). The McGlinchey anemometer is around 2.5 m high, and beach/dune sands at Tramore are around 0.2 mm in diameter,  so the equivalent threshold for our weather data is 4.5 m/s (10 mph). It’s not surprising then that we see a lot of wind-blown sand across the coast here!

The increase in average and peak wind speeds in 2015 is also reflected in the number of high energy events. The frequency of gale days (days when gale force winds (>17.5 m/s (39.1 mph)) occur in the 10-minute average wind record) is often used to capture the degree of storminess within a year or winter. At McGlincheys, just gale force winds were experienced on 80 days of the year – that is 22% of the year! But most of these windy days fell in January (15), March (11), November (14) and December (20). Since November, Met Éireann and the UK Met Office have named storms impacting UK/Ireland as part of a public awareness initiative, and 6 storms passed across in November and December. Abigail was the first of these; a low pressure of 994.1 mbar hit west Donegal on the 12th November, bringing peak gusts of 25.5 m/s. Barney was next, with a low pressure of 981.6 mbar on the 17th November, but this coincided with a significant drop in wind speed and shift to northerly winds. Clodagh then arrived on the 29th November at 986.6 mbar and 25 m/s gusts. Next was Desmond in early December, responsible for significant flooding across large parts of Ireland and northern England. As we’ve seen already, rainfall at McGlincheys didn’t reach the levels observed across the rest of Donegal and Ireland, and just 27 mm rain fell during this 4 day period. Storms Eva and Frank were wetter, with 4-day totals of 40.2 mm and 43 mm respectively. But Desmond did experience the strongest winds, peaking at 28.2 m/s the day before the minima in pressure. The storm was formed of two parts, the first bringing sustained strong winds throughout the afternoon and evening of 4th December before a drop to almost zero, followed by a second, slightly lower energy peak. Storm Eva brought very unsettled weather and several days of windy conditions and low pressure. Wind directions during these storm periods are largely from the west/southwest except for Storm Frank when the winds came from the south. Like Desmond, this storm had two parts, with a drop in pressure and peak in wind speeds on the 28th December (peak wind speeds of 21.9 m/s) before a further drop in pressure to 980.3 mbar on the 30th December, and peak gusts of 25.5 m/s.

Abigail Barney
Clodagh Desmond
Eva Frank

IMG_7142There has been a lot of reference to 2015 being the warmest year on record, but in west Donegal temperatures weren’t significantly different to previous years, and if anything generally lower. We had some issues with the weather station in November when it became clear that the outdoor temperature and humidity sensor were failing. These were replaced and the weather station was given a mini-service in mid-December (there was quite a lot of blown sand within the various sections that needed cleaning out!), and all is working well now, but we did lose around 6 weeks of temperature and humidity records. The average temperature for 2015 was 10°C, slightly cooler than 2013 and 2014. The highest temperature recorded was a rather low 22.7°C on the 3rd July; the coldest record was on the 4th February, of -4.3°C. We recorded 17 frost days in 2015 in comparison to just 3 in 2014. Met Éireann records from Finner and Malin Head show a similar trend over the year to the results from McGlincheys.

2015temp

A summary table of key records from 2015 is provided below with comparative measures from the McGlinchey weather station for 2013 and 2014. Please do get in touch if you are interested in the results, the data or would like to know more.

2013 2014 2015
Hottest day 19-Jul 28.5°C 25-Jul 25.2°C 03-Jul 22.7°C
Coldest day 12-Mar -7.3°C 03-Mar -2.6°C 04-Feb -4.3°C
Average wind speed 4.2 m/s 3.8 m/s 4.6 m/s
Most frequent direction W W W
Strongest 10min average 18-Dec 18.8 m/s [WSW] 03-Jan 16.1 m/s [SW] 15-Jan 19.7 m/s [SSW]
Strongest gust 18-Dec 30.0 m/s [WSW] 03-Jan 29.1 m/s [SW] 15-Jan 31.7 m/s [SSW]
Lowest pressure 27-Dec 946.1 mbar 08-Feb 946.1 mbar 15-Jan 958.7 mbar
Wettest day 14-Dec 36.8 mm 03-Jan 33.2 mm 07-Mar 28 mm
Wettest month Dec 180.2 mm Feb 153.8 mm Dec 178.2 mm
Annual rainfall 772.4 mm 893.2 mm 1094.4 mm
Number of frost days 35 3 17
Number of gale days 52 56 80
Number of dry days 126 103 82
Droughts 23-Mar to 10-Apr 6-20 Sep

 

References

Bagnold, RA. 1941. The physics of wind blown sand and desert dunes. London: Methuen.

Met Éireann monthly summaries for Malin Head and Finner.

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