This past winter, contractors were faced with mixed precipitation and disagreements with client’s on the type of ground accumulation: snow, ice or a mixture of both. One of the most important things a contractor can do before next season, is make sure contracts and terminology are up to date and accurate based on the services expected to be performed. Understanding precipitation types will help with communicating with customers on the difficulty or work that is needed in each situation.
1. Sleet and hail are not the same! Sleet (small ice pellets) form in a winter storm at lower layers of the atmosphere. Hail (large ice pellets) are formed at much higher levels in the updrafts of severe thunderstorms.
2. Freezing rain can occur even when the air temperature is above freezing. In preceding cold outbreaks, there may be some lag time between the colder, below-freezing ground and the above-freezing air temperature.
3. Snowfall ratios can be less than a 10-to-1 ratio in the case of a very wet snow, or as much as 20- or 25-to-1 in colder temperature profiles (dry and fluffy snow).
4. Compressibility is the compacting of snow (pressing it into a smaller area) resulting in increased density, weight per volume and hardening. A volume of snow can be reduced by as much as eight times through compaction. The pores of cold, dry snow are filled with air and water vapor. In wet snow, the ice grains are coated with water. Thus, the degree to which the snow can be compressed will significantly influence the snow removal effort and the selection of snow removal equipment. Definition by the Snow and Ice Management Association Glossary.
5. Snow equivalency refers to the amount of snow accumulation that would have occurred in a given area if the water content (taken into account for all precipitation types) had fallen as all snow.