The Great Snow
The most firmly attested natural event was the “great snow”. The Annals of Inisfallen place it between the feast of Brigit on 1 February and the feast of Patrick on 17 March. The Annals of Ulster give an earlier beginning, referring to the feast of Mary in winter, interpreted by their modern editors as 8 December. This may describe snow beginning in December 1046 and continuing into the spring of 1047, or reflect variation within the annalistic tradition. It is therefore safest to say that exceptionally severe winter weather persisted into March 1047, rather than to claim an undisputed starting date.