The magic number that Irish weather enthusiasts hope to achieve on a maximum temperature in Summer time is 30°C but this figure is quite a rare number to reach. Many years tend to not even record 27°C in Ireland, never mind 30°C. 30°C has been achieved in Ireland in 2018, 2016, 2013, 2006, 2005, 2003, 1995, 1990, 1989, 1983, 1976, 1975, 1948 and 1921 from the data I know of. It is possible that 30°C was also recorded in 1955, 1949, 1947, 1934, 1933 and 1911 but the problem lies in the lack of data available and the lack of stations that were in operation during them years. As can be shown here, 30°C happens at least in 2-3 years per decade in Ireland. This is in contrast to the UK where 30°C occurs in at least one occasion per year though there are still a good few years that failed to reach 30°C, the most recent occasion when writing this blog post being 1993.
It is even rarer to have consecutive days of 30°C in Ireland. These are the three longest runs of consecutive days with 30°C in Ireland that I know of:
5 days at Boora, Co. Offaly from 28 June to 2 July 1976
4 days at Kilkenny from 11 to 14 July 1983
3 days at Shannon Airport from 27 to 29 June 2018
It's rare again that 30°C is recorded in Ireland in two or more consecutive years. The last time this has happened up to this point in 2018 was 2005 and 2006 when both July 2005 and July 2006 achieved the 30°C mark. The two other most recent occurrences were 1975 and 1976, 1989 and 1990.
To successfully reach 30°C somewhere in Ireland, you need to have a few set parameters that can vary from the following:
An anticyclone builds over top of the country for multiple days building up the heat in the strong Summer sunshine with variable wind direction. Unlike in Winter when dry air is likely to bring frosty conditions especially with clear skies, in Summer, this can translate to higher temperatures. July 2013's 30°C was achieved by this setup as an anticyclone from the Azores established itself over Ireland from the 4 July onwards with the first 30°C being recorded on the 8 July. This was helped by a rather dry June for most places and the persistence of the anticyclone allowed temperatures to relatively rise somewhat over the days of July 2013 with 30°C being recorded somewhere over Ireland between the 8th and 12th. 30°C was again reached on the 19th/20th with Dooks, Co. Kerry topping out at 31.0°C - the highest temperature in Ireland at this time since July 2006.
Southerly to southeasterly winds bring hot and humid air from Iberia and off the European continent in general. The problem with this for Ireland is that usually in these situations, Ireland is on the knife edge with the low pressure parked just to the west which results in the highest temperatures for the UK rather than Ireland. There is the rare occasion that the low is out far enough for skies to be clear and temperatures rise to 30°C in the sun. One such example was 2 August 1990 when Phoenix Park, Co. Dublin reached 31.5°C in a southeasterly airstream with air coming off the continent. This setup favours the UK a lot more than Ireland in the majority of times and usually gives away to the UK breaking their temperature records such as 10 August 2003 and 1 July 2015.
Conditions need to be absolutely perfect to get 30°C or more in Ireland as history shows. It doesn't happen very often in the country and when it does, it tends to be a short period of time for over an hour or so. Rarely, you can receive 30°C for a few more hours such as on 28 June 2018 when Shannon Airport did go below 30°C for 15:00 to 19:00 which is crazy for Ireland.
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