Predictions given by the statistical basis for determining ground snow loads are bounded by an upper and lower limit. The lower limit is 21 psf to meet ASCE 7 minimum guidelines. The upper limit, however, is not as easily determined. Since values are extrapolated rather than interpolated, the estimated values for snow loads at elevations significantly higher than nearby stations sometimes lead to unreasonably high snow load estimates. To mitigate this "peak effect", the predictions in the map are not allowed to extend beyond the highest 50-year station ground snow load, which is approximately 429 psf. The regions where the map is “capped” by the upper limit of 429 psf maximum prediction are indicated in black on the map overlay. In other locations, elevations over 9,000 ft are also considered less accurate due to the limited number of stations at these elevations, and sometimes produce overly-conservative values. Locations where the results are considered less accurate and/or the load has been capped by the upper limit will include a warning note on the report.
The output for the ground snow load prediction includes the elevation used for the prediction. This elevation is approximated using the methods outlined in the report and may differ from the actual elevation at that location, particularly in steep terrain or at hills or valleys. Engineering judgement must be exercised where the predicted elevation greatly differs from the actual elevation at the site.
While great efforts have been made to ensure these predictions are as accurate as possible, designers must use expert judgement to ensure that such predictions are appropriate for their particular project. The SEAU and the authors cannot accept responsibility for prediction errors or any consequences resulting therefrom.