Our winter has been on the active side, with snow being the predominant precipitation type. We’ve briefly discussed why snow can be hard to forecast because of models, but there’s yet another factor that meteorologists have to take into account while predicting snowfall totals.
Snowfall ratios are very important for predicting snowfall accumulations. For one inch of liquid, we can see 7 inches of snow or 17 inches of snow. It all depends on the temperature of the atmosphere and the surface.
Wet, heavy snow usually has low snowfall ratios. We typically see ratios below 10:1 - Let’s say it’s 7:1, which means for one inch of liquid, we see 7 inches of snow. Wet snow has a higher liquid content as it moves toward the surface. Snowflakes partially melt before they hit the ground, making it easier for snowflakes to stick together as they fall. Wet snow will consist of larger snowflakes but a lower amount of total snowflakes. If the ground temperature is above freezing, we’ll have a snow event without accumulation on the ground. With the ground temperature at or below freezing, we’ll see more ground accumulation. This snow is hard to shovel, but the best for snowballs.
Dry snow usually has high snow ratios due to the low liquid water content. Ratios will be above 10:1 - Let’s say 17:1, which means for the same inch of liquid, we’ll see 17 inches of snow. Snowflakes are much smaller because of air pockets between all the snow crystals. Since dry snow is not sticky, it’s not good for snowman building or snowball making. The wind will whip the snow around and it will be quite easy to shovel. Dry snow occurs when temperatures in the atmosphere and at the surface are well below freezing. Without the ‘sticky’ quality of the snowflakes, we’ll see smaller but more numerous snowflakes.
Our December blizzard had average snow ratios at 10:1, where one inch of liquid came to 10 inches of snow. However, this past weekend, our temperatures were in the teens and even single digits during the snowfall. With the cold air in place, snow ratios were much higher than 10:1.
Looking ahead to this weekend, temperatures are going to be in the upper 20s and near 30 degrees. Therefore, we would see more wet snow with lower snow to liquid ratios.