Toward a coherent US-Canada extreme wind climate

The extreme wind speed values used for wind loading in the United States and Canada are currently being evaluated at the National Institute of Standards and Technology (NIST) and the University of Western Ontario (UWO), respectively. The extreme value analyses carried out for the US and Canada make use of historical wind records in the National Climatic Data Center (NCDC) Integrated Surface Hourly (ISH) database and the Environment Canada (EC) hourly weather (HLY01) database, respectively. The databases differ in content, and most importantly, the averaging time used for the estimation of extreme wind speeds between the analyses is different. The analysis of the ISH database makes use of reported gust data, which are used to estimate extreme gust wind speeds, which reflects the use of the 3-second gust wind speed as the reference wind speed in ASCE 7. The analysis of the EC database uses hourly mean wind speeds, which are used to estimate extreme hourly mean wind pressures, which reflects the use of the mean hourly wind speed as the reference wind speed in the National Building Code of Canada (NBCC). As the datasets and methodology used for the two analyses are different, and have been so for previous versions of each code, there is an obvious discontinuity in specified extreme wind speeds along the US-Canada border. Wind data from six meteorological stations were analyzed based on the different methodologies being applied in each country, and the extracted maxima and estimated 50-year return period wind speeds are shown and compared. Differences which exist between the analyses, which likely result from the use of gust and mean averaging times, are discussed. The examined stations provide examples of the possible differences which arise due to the varying methodology, although analysis of additional stations is required to establish a consistent trend. A better understanding of the differences in extreme wind data handling and estimation techniques between the US and Canada is of great importance, and has implications to structures where design wind loads from multiple codes are being compared.