On predicting maximum snowfall amounts in Alberta

Abstract

Snowfall in excess of 10 cm per day in Alberta is usually associated with large‐scale ascent within a wave cyclone and the maximum amount of snowfall depends on the maximum amount of vapour available for deposition. Using the principle of conservation of water, the maximum snowfall amount is related to the saturated vapour mixing ratio at cloud base and cloud top levels. The inherent uncertainties of the input data allow for numerical approximations that lead to a linear relationship between maximum snowfall and cloud base temperature. To test the validity of the linear snowfall–temperature relationship, the correlation of 24‐hour snowfall measurements with temperature observations from upwind soundings was analysed. The dataset covered all of Alberta (with the exception of the mountainous west) for the period October 1990 to April 1993. The data suggest that the snow amounts have an approximately linear dependence on the 850‐mb temperature with a correlation coefficient of 0.62. We further investigated whether the snowfall–temperature relationship can be used to complement the Quantitative Precipitation Forecast (QPF) available for a Numerical Weather Predicition (NWP) model. Specifically, the snowfall–temperature relationship offered value above that available from the output of the European Centre for Medium‐Range Weather Forecasts (ECMWF) model. The implications of this finding on predicting heavy snowfall for Alberta are discussed.