Knowing of my interest in weather, and extreme weather, Brenda Turner drew my attention to an article in Ireland XO News on one of the worst storms ever to hit Ireland, 6–7 January 1839. There was immense damage and considerable loss of life in Ireland, Scotland and north-west England"
"every part of Ireland - every field, every town, every village in Ireland have felt its dire effects, from Galway to Dublin — from the Giant's Causeway to Valencia."It's around the time my Irish ancestor John Marmon might have left Ireland.
As a former meteorologist I looked for a weather map and found three in an article Barometric pressure during the Irish storm of 6–7 January 1839 at http://onlinelibrary.wiley.com/doi/10.1256/wea.53.05/pdf which mentioned this storm had the third-lowest barometric pressure recorded in the British Isles.