Snowfall Variations in the Mid-Atlantic: A Tale of Temperature and Air Conditions
Introduction:
Forecasters reported contrasting snowfall conditions in the Mid-Atlantic region following a Tuesday snow event. While the snow in the northern areas of Washington, D.C., was characterized as dry and fluffy, the southern regions witnessed heavier, wetter snowfall. This variation in snowfall characteristics can be attributed to a primary factor: air temperature.
The Role of Air Temperature:
Air temperature plays a crucial role in determining the type of snow that falls. When the air temperature near the surface is below freezing, dry snow is more prevalent. Dry snow is powdery in nature, making it challenging to form into snowballs or snowmen. Additionally, cold air temperatures contribute to lighter and fluffier snow, containing less water per inch.
In contrast, wet snow occurs when the air temperature near the surface is above freezing. This causes the snowflakes to partially melt before reaching the surface. The resulting snowflakes become sticky, accumulating more readily on outdoor surfaces. Wet snow is more challenging to shovel and can pose a higher risk of tree and power line damage.
Wet Snow Accumulation:
Wet snowfall accumulations are typically observed during early and late-season storms, as well as in the South. Such snow is difficult to shovel and can increase the likelihood of downed trees and power lines.
Dry Snow Powderiness:
Dry snow, characterized by its powdery texture, occurs when the surface air temperature is below freezing. This type of snow is unable to form into snowballs or snowmen. The cold air temperatures result in lighter, fluffier snow that contains less water per inch. Dry snowfall is often prone to blowing around in the wind.
Varied Snow Weights:
The weight of snow can vary significantly. A cubic foot of dry, powdery snow can weigh as little as three pounds, while a cubic foot of heavy, wet snow can reach up to ten pounds.
Water Equivalency Myth:
Popular belief suggests that melting ten inches of snow yields one inch of water. While this may hold true under certain conditions, several factors can influence the actual amount of snow produced from a given quantity of water. These factors include the depth of the warm layer between the surface and the snow-producing cloud, as well as the presence of ice in the cloud.
Snowfall Ratios and Environmental Factors:
The factors influencing snowfall ratios include the depth of the warm layer, ice content in the snow-producing cloud, and wind speed. Wind can cause snowflakes to fracture, reducing their "lacy" structure and leading to lower snowfall ratios (snow accumulations relative to the amount of water present). Deep cold temperatures generally promote higher snowfall ratios.
Conclusion:
The contrasting snowfall conditions witnessed in the Mid-Atlantic region can be attributed to variations in air temperature. Dry and fluffy snow is more common in areas with surface air temperatures below freezing, while wet and heavy snow occurs when surface temperatures are above freezing. The weight and moisture content of snow can vary significantly, and understanding the environmental factors that influence these characteristics is important for effective snow removal and preparedness.
