The Reassessment of Monthly Minimum and Maximum Temperature Extremes Across Ireland

At Met Éireann, the Irish Meteorological Service, part of our mission is analysing Ireland’s climate. This involves the assessment of Ireland’s climate extremes which include monthly maximum and minimum air temperatures, highest sustained wind speeds and highest wind gusts, highest and lowest monthly rainfall, sunshine duration, and highest and lowest atmospheric pressure. However, as our historical climate records span nearly 200 years, many of these climate extremes occurred when observations were reported in hand-written observer logs and are therefore unsuitable for our current validation methods. As such, herein we use a novel standardised operating procedure (SOP) for verifying the monthly minimum and maximum temperature extremes across Ireland. This includes a comprehensive search of archival newspaper records and meteorological reports published at the time of the records. We also employ data rescue techniques when needed and use contemporaneous observational and synoptic reports to investigate the larger scale atmospheric conditions observed during the period in question to see the favourability of inducing the extreme weather reported. Finally, we completed a thorough statistical analysis using a generalized extreme value distribution to put the record into context against a longer observational record. Through this standardised approach we have verified the veracity of 11 out of 12 of the original monthly minimum air temperature records, including the all-time low temperature record for Ireland of -19.1°C which occurred at Markree Castle in January 1881. Our methods resulted in the rejection of the standing March minimum record and has since been replaced by a new verified record for the month. Ten out of 12 of the monthly maximum air temperature records were validated, including the all-time high temperature record for Ireland of 33.3°C which occurred at Kilkenny Castle in June 1887, but March and December were rejected and replaced by newly verified records. This presentation will give a brief overview of this standardised approach, followed by case studies of a record that stood up to the SOP and one that was rejected by it.