Heavy snow and sleet will accumulate on any surface no matter how warm it is. This is somewhat of an exaggeration but heavy snow and sleet can make up for the fact that air temperatures in the lowest part of the PBL and the ground surface are above freezing. Snow or sleet with heavy intensity promotes the greatest amount of melting and evaporational cooling. Heavy snow or sleet accumulation will easily exceed the melting rate AS LONG AS IT CONTINUES TO FALL HEAVY. Once the precipitation ends and the surface and ground temperatures are above freezing, the accumulation will quickly melt. Duration of snow or sleet is also a consideration. Hours of heavy snow or sleet will be much more significant than a burst of heavy snow or sleet that lasts less than an hour. The greatest amount of melting occurs when the heavy snow or sleet begins when temperatures near the surface and at ground level are above freezing. It is typical for heavy snow or sleet to drop the temperature to 32 F within 15 to 30 minutes of the precipitation beginning when the temperature is above freezing when heavy snow and sleet begins. After this 30-minute time period, accumulation will be more significant if the heavy intensity sustains itself. When the temperature at ground level is below freezing as well as air temperatures being below freezing, snow and sleet accumulation will be a direct function of the intensity and duration of the precipitation. |