Winter Wind Parameter for Snow Drifts

The relationships in ASCE 7 for the determination of roof snow drift size are functions of the ground snow load and the upwind fetch of the snow source area. In a 2019 paper, O’Rourke and Cocca propose a new relationship for snow drift size that includes a new winter wind parameter along with current ground load and fetch parameters. An inclusion of the winter wind parameter would improve the accuracy of snow drift estimates. The O’Rourke and Cocca paper presents the winter wind parameter for about four dozen sites across the United States. For potential use in ASCE 7, one needs a map of the winter wind parameter for the whole United States. In the current paper, the winter wind parameters for 272 locations in the United States are used to develop a map suitable for use in the ASCE 7 standard. The paper also provides information of the expected change in the design drift size if the winter wind relationship were to be used in ASCE 7. It is shown that, on average, there would be a 15% reduction for an upwind fetch of 250 ft (1 ft = 30.48 cm).