Another wet and windy year in west Donegal? Of course, but all the more impressive as the McGlinchey weather station records its first hurricane force winds!
The year wasn’t quite as windy or wet as 2015, but we’re certainly starting to see some consistency year to year in the weather recorded at the McGlinchey Weather Station. The climate around Sheskinmore has an annual average temperature of around 10ºC, and annual rainfall between 800 and 1000 mm. The wettest month varies, but guarantees a deluge of over 100 mm, that doesn’t necessarily coincide with the wettest day when more than 30 mm falls. We can be fairly confident though that the warmest days of the year occur in July – nicely timed for the school holidays!
The annual average wind speed of around 4 m/s (about 9 mph) is equivalent to the starting operating speed for most wind turbines. But of course, we experience much windier periods, with gale force winds occurring at least 13% of days. On this basis, 2016 wasn’t as windy as previous years. In fact, 2016 doesn’t break many records in the (albeit short-term) McGlinchey record, but it tested the wind vane and anemometer of our Davis weather station with gusts of up to 33.5 m/s (75 mph) during Storm Gertrude at the end of last January – the maximum speed we have recorded to date. The wind speed threshold for hurricanes (on the Beaufort Scale) is 32.5 m/s … quite remarkable that west Donegal has experienced Hurricane Force winds! Given the relatively sheltered position of the weather station landward of Magheramore dunes, it is likely that the wind speed experienced at Rosbeg and Tramore were greater still.
It is no surprise that the dominant wind direction is from the west, and all maximum speeds recorded routinely come from the 90º sector between south and west. But year to year, we also see a strong presence of southeasterlies; these account for the more frequent, but lower wind speeds. There are changes year to year, but our short-term records don’t show any significant shifts at the moment.
Comparison with the Met Éireann weather stations at Malin Head and Finner (north and south Donegal respectively) – using monthly means or sums – shows that the McGlincheys weather station, and indeed both north and south Donegal, are in good agreement over the last 3 years. There is little to separate the annual temperature between the three sites, but there are some differences in rainfall over the years. We noted last year that the McGlinchey gauge doesn’t record the level of rainfall experienced elsewhere in Donegal, something that has been recognised as an issue with Davis weather stations before. This is particularly noticeable during the 2015-16 winter, a period when we experienced a lot of storms and high wind speeds that sometimes prevent the capture of rainfall in our gauge. Otherwise though, Donegal is quite united in its precipitation record.
As for wind speed though – as impressed as we are with our hurricane force gusts, we are not capturing anything near the average wind speeds recorded at Malin Head and Finner. This is most probably a consequence of vertical setting. We installed the McGlincheys weather station on a vertical timber beam not much more than 2 m high above a base elevation of 4.8 m above mean sea level. Most national wind recording instrumentation is installed on 10 m tall structures to reduce the influence of frictional resistance on the wind near the ground. These are quite significant structures and rather challenging for a small group like ourselves to install. Furthermore, the Malin Head weather station is installed at a site 22 m above sea level, and Finner is at a site 33 m above sea level. Basically, the McGlinchey station is very low (elevation and instrument height) meaning we are not quite capturing the winds that the more formal network of weather stations manage to record. But we can already see that the variation month to month is very similar, so we know that our weather station is working effectively, but we might just need some corrections to deliver an equivalent 10 m height record … a task for another day!
There were 8 named storms during 2016, starting with Storm Gertrude at the end of January, and the last of the year was Storm Conor in late December. Like last year (2015), each storm had its’ own signature of high wind speeds, heavy rain around a distinct drop in atmospheric pressure.
The lowest pressure recorded (961.6 mbar) coincided with Storm Imogen in early February, the second of two dips in the pressure during the 6th-8th February. Despite being only 36 hours apart, the low pressure systems brought an increase in rainfall and elevated wind speeds. Using the tide level observations from the Marine Institute Aranmore tide gauge, we can also see the impact that these low pressure systems have on coastal water levels. In the figure below, the increase in tide range over the 6th-9th February reflects a shift from neap to spring tides, but superimposed on this is also the low pressure affect – a distinct positive surge. The surge peaked early on the 9th February, bringing tidal levels around 0.8 m above their normal level – quite significant, but perhaps less remarkable because it didn’t coincide with a spring high tide.
Do you record weather observations? Do you make other observations about sea state, frosts, surges and storms? Would you like to share your data with Friends of Sheskinmore? We are interested in collating a more complete understanding of weather in west Donegal, and in particular how it differs from the national weather stations. If you have any information that can contribute to this, or comments or questions, we would love to hear from you … so get in touch!