The years 2018 and 1798 featured some odd similarities in one way or another. Let's compare the two going by the Central England Temperature (CET) and England & Wales Precipitation (EWP) figures.
January
2018: 5.3°C and 104.5mm
1798: 3.6°C and 72.4mm
February
2018: 2.9°C and 53.7mm
1798: 4.0°C and 44.6mm
March
2018: 4.9°C and 113.6mm
1798: 5.1°C and 32.8mm
April
2018: 9.8°C and 91.6mm
1798: 10.4°C and 56.3mm
May
2018: 13.2°C and 52.0mm
1798: 12.9°C and 47.6mm
June
2018: 16.1°C and N/A (very dry)
1798: 16.9°C and 31.0mm
To add onto these figures for May/June 1798, the PDF for that period from 1798 given by Met Éireann prove that it was a very dry and warm or hot start to the Summer or late end to Spring. It states:
The weather of late Spring and early Summer of 1798, when most of the fighting took place, was exceptionally dry and warm, typical of a prolonged spell of anticyclonic weather. Evidence for this comes from a number of weather observations from the period as well as contemporary accounts of the rebellion. This weather was probably of most benefit to the rebel armies, who lived for weeks outdoors during the battle; it also delayed the arrival of ships carrying government reinforcements from Britain.
One of the most detailed surviving accounts of the weather of 1798 is the record kept by Maximilian Faviere at Eccles Street, Dublin. Faviere made a daily weather entry in the pages of his 'Gentleman's and Citizen's Almanc' between the years of 1781 and 1812. This record shows that the period between May 23rd 1798, when the ill-fated Dublin uprising took place, and the battle of Vinegar Hill on June 21st coincided almost exactly with a spell of fine weather between May 19th and June 19th. During this period, Faviere records only one day with 'showers of rain', while most days are described as 'sultry, dry and very fine'. Another Dublin observer of the time, Richard Kirwan, recorded around a quarter of the normal May and June rainfall. Dixon, in his 1953 account of historical weather records of Dublin, cites the Annals of Ballitore, Co. Kildare, where the Summer of 1798 'seems to have been outstanding and was still remembered in 1818, when an even finer one occurred'.
One effect of the fine weather on the course of the rebellion was to facilitate the Wexford rebels and their families, numbering up to 20,000, who lived outdoors for several weeks and marched on foot over long distances. On the government side, the director general of military hospitals wrote later that 'the weather was so favourable that the regiments upon service underwent considerable fatigue during the Summer, and often slept in the open air, with no disadvantage to their general health'. The anticyclonic conditions and resultant light winds caused delays for the ships carrying reinforcements to Ireland from British ports, the first of which sailed from Portsmouth on June 3rd. The Viceroy Camden expressed his concern to London when no reinforcements had arrived by June 15th. It seems certain that any French invasion fleet at the same time, widely expected on both the rebel and government sides, would have suffered similar delays. By the time the small French fleet under Humbert arrived at Mayo in late August, the outcome of the rebellion had already been decided.
Although the fine weather had some influence on events during the Summer of 1798, stormy weather was much more significant eighteen months earlier, when the attempted French invasion of 15,000 troops under Marshal Hoche failed at Bantry Bay. After initial favourable easterly winds which allowed the fleet to break through the English blockade off Brest, severe storms during the last week of 1796 led to the dispersal of the invading fleet and caused the landing to be abandoned. The loyalist medal struck by landlord Richard White of Bantry House for the Bantry Garrison and Friendly Association was subsequently inscribed with the words 'Deus afflavit et dissipantur' - God blew and they were scattered.
https://www.met.ie/cms/assets/uploads/2017/08/Summer1798.pdf
Summer 1798 took place during Solar Minimum of Solar Cycle 5 - the first of two solar cycles which made up the Dalton Minimum period. It is clear here that the minimal solar activity had a major influence in the anticyclonic conditions of early Summer 1798 during the Irish Rebellion and the blocking just happened to occur over us during the period.
The CET and EWP figures suggest that July and August 1798 were much more unsettled months with July being a very wet month in England & Wales. For that time period, they would have been relatively mild months but using the averages nowadays, they would be average to rather cool months. June was one of the hottest on record in contrast and was over 0.8°C warmer than June 2018 for the CET.
1798 had a similarly warm and dry May to 2018, a similarly cold March to 2018 (though 2018 was far wetter), a similarly dry February to 2018 and a similarly warm April to 2018. All these similarities are very interesting and the fact that 1798 was the beginning of the Dalton Minimum era is also intriguing. Forecasts have been expecting a Grand Solar Minimum to occur following Solar Cycle 24 and if it were to turn out that way, it would be amazing. Years ending in "8" tend to have poor Summers especially since 1878 of the 19th century but Summers such as 1798, 1868 and 2018 show that this is just a statistical quirk and or coincidence more than anything.
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