Anomalous snowfall caused by natural-draft cooling towers

Reports from several sources, including satellite images, suggest that under appropriate circumstances cooling-tower plumes from large electric power generating facilities can generate nontrivial amounts of snow. Tabulation of a number of aerial observations yields the criteria of temperature colder than -13 degrees centigrade and saturation vapor density deficit less than 0.5 gram per cubic meter in the vicinity of the plume for production of such anomalous snow. Numerical simulation with a model describing cloud microphysical processes in considerable detail offers theoretical verification of these empirical criteria. Although the model could be improved by incorporating interactive dynamics and a method to regulate efficiently the introduction of new ice-particle categories, it is in its present form capable of producing much useful information on the microphysical processes within plumes and plume interaction with existing clouds.