The density of snow varies as a function of temperatures. The density of snow is heavily dependent upon the liquid content of snow. Two classifications for snow are "wet snow" and "dry snow". Wet snow occurs at temperatures near freezing in the PBL and/or with soil surface temperatures above freezing. Wet snow is partially melted and is therefore denser. Wet snow typically has between a 10 to 1 and 5 to 1 liquid equivalence. This is the snow that makes great snowballs, is tough to shovel, and is not easily drifted by the wind after it reaches the surface. Flakes of wet snow more easily stick together in flight and are not broken apart as much by the wind. Dry snow occurs when the warmest temperature in the PBL and aloft is less than 28 F and the soil surface temperature is below freezing. Dry snow is less dense and can therefore accumulate to a higher depth. Dry snow is easily drifted by the wind and is difficult to make snowballs with. The liquid equivalent of dry snow ranges from 15 to 1 to greater than 30 to 1. Dry snow is easier to shovel due to its lower density. The flakes from dry snow tend to be smaller but more numerous. Warm soil will tend to compact snow over time by giving it a higher liquid content. Gravity also compacts snow over time. Wet snow will compact more significantly than dry snow. A dry snow falling onto a warm surface will allow it to take on characteristics of wet snow. The perfect combination for snow lovers is a wet snow falling on a below freezing soil surface. |