Abstract/Summary

During 28-29 March 2020, the rapid development of an anticyclone over the North Atlantic resulted in its central mean sea level (MSL) barometric pressure reaching 1055 hPa near 59°N 20°W at 0000 UTC on 29 March. As the anticyclone slipped slowly south-eastwards over the following 12 hours, pressure exceeded 1050 hPa in western Scotland and the north of Ireland, establishing new long-term records at several long-running sites. Several factors combine to make this event unique in British climatology. Firstly, this was the second occasion during the winter of 2019/20 when 1050 hPa was attained within the British and Irish Isles (the first being 19-20 January 2020), following an interval of more than 60 years since the previous such event. No previous winter in at least the last 200 years has seen two such events occur within one season. Secondly, during this event the previous March pressure record for the British and Irish Isles was exceeded, by over 3 hPa: no previous event reaching 1050 hPa over the British and Irish Isles has occurred so late in the winter season. Remarkably, between them the January and March 2020 events established new long-term high pressure records in all four capital cities within the United Kingdom – in London and Cardiff on 20 January, and Edinburgh and Belfast on 29 March.