Weather
Washington Snow: Why 20 Inches Can Start With Just 1 Inch
Seattle, WA – Winter storms across Washington can produce dramatically different snowfall totals, even when communities receive similar amounts of moisture. From Seattle to Spokane, just 1 inch of liq
By Natalie Brooks · 2026-11-10T08:04:32.212Z
Seattle, WA – Winter storms across Washington can produce dramatically different snowfall totals, even when communities receive similar amounts of moisture. From Seattle to Spokane, just 1 inch of liquid precipitation can sometimes produce 5 inches of heavy, wet snow or as much as 20 inches of lighter, fluffier snow.
The difference comes down to the snow to liquid ratio, which measures how much snow accumulates from a given amount of liquid water.
Why One Inch Can Produce 20 Inches of Snow
A commonly used forecasting guideline is the 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 approximately 5 inches from 1 inch of liquid precipitation.
Under atmospheric conditions favorable for fluffy snow, ratios can sometimes reach 20 to 1, producing approximately 20 inches from the same moisture.
These ratios describe possible snow densities, not expected snowfall from an approaching storm.
Seattle and Spokane: Why Snowfall Can Differ
Seattle's proximity to Puget Sound and the Pacific Ocean often brings relatively mild, moisture rich air during winter storms.
As a result, precipitation that falls as rain in Seattle may arrive as snow at higher elevations nearby.
Spokane, located east of the Cascade Mountains, experiences a more continental climate with colder winter temperatures that can favor accumulating snow.
Washington's Cascade Range creates another major influence.
When moist Pacific air rises over the mountains, it cools and can produce substantial precipitation, including heavy mountain snowfall.
Areas east of the Cascades generally receive less precipitation because of the rain shadow effect, although individual winter storms can still produce significant snow.
What Washington Residents Should Know
Heavy, wet snow can weigh down trees and power lines, increasing the potential for damage and outages.
Lighter, fluffier snow can accumulate more deeply and create visibility problems when strong winds develop.
Travel conditions can change quickly along Interstate 5, Interstate 90 and mountain passes, particularly around Snoqualmie Pass.
Snow levels may also rise or fall rapidly as temperatures change during Pacific storms.
Understanding snow to liquid ratios helps explain why snowfall forecasts can change even when expected moisture amounts remain similar.
For Washington residents, snowfall depth depends on more than precipitation alone. Temperature, elevation, Pacific moisture and mountain terrain all influence final accumulation totals.