Weather
Pennsylvania Winter Weather: Why 1 Inch of Water Can Mean 20 of Snow
Philadelphia, PA – As Pennsylvania prepares for another winter season, residents from Philadelphia to Pittsburgh may notice something surprising about snowfall forecasts. Two communities can receive n
By Jenna Hartley · 2026-11-10T07:32:57.853Z
Philadelphia, PA – As Pennsylvania prepares for another winter season, residents from Philadelphia to Pittsburgh may notice something surprising about snowfall forecasts. Two communities can receive nearly identical amounts of moisture from winter storms but experience dramatically different snow accumulations. Under certain atmospheric conditions, just 1 inch of liquid precipitation can produce approximately 20 inches of snow.
The difference comes down to a measurement known as the snow to liquid ratio, which helps meteorologists estimate snowfall accumulation based on the amount of moisture in a storm.
Why One Inch of Moisture Can Produce 20 Inches of Snow
A traditional forecasting guideline uses a 10 to 1 ratio, meaning 1 inch of liquid water produces approximately 10 inches of snow.
However, actual snowfall ratios can vary considerably.
Heavy, wet snow may have a ratio near 5 to 1, producing roughly 5 inches from 1 inch of liquid precipitation.
Colder, fluffier snow can sometimes reach a 20 to 1 ratio, producing approximately 20 inches from the same amount of moisture.
Philadelphia and Pittsburgh: Why Snowfall Totals Can Differ
Philadelphia's location in southeastern Pennsylvania can expose the city to relatively warmer air during certain coastal winter storms, sometimes resulting in rain or heavy, wet snow.
Pittsburgh, located farther west near the Appalachian Plateau, experiences different weather patterns influenced by elevation, storm tracks and colder air moving across the Great Lakes region.
Higher elevations across central and western Pennsylvania can also experience colder temperatures that favor different snowfall characteristics.
In northwestern Pennsylvania, lake effect snow from Lake Erie can create additional snowfall differences, especially when cold air moves across warmer lake waters.
What Pennsylvania Residents Should Know
Wet, heavy snow can place additional stress on trees, power lines and rooftops, increasing the potential for damage and outages.
Lighter, fluffier snow may accumulate more deeply while containing less water per inch.
These differences can affect travel along major highways, including Interstate 76, Interstate 80 and Interstate 81.
Understanding snow to liquid ratios helps explain why snowfall predictions sometimes change even when expected precipitation amounts remain similar.
For Pennsylvania residents, snowfall depth depends on more than how much moisture a storm brings. Temperature, wind and snow density can make a major difference in final accumulation totals.