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Oregon Winter Weather: How 1 Inch of Water Can Become 20 of Snow
Portland, OR – Winter storms across Oregon can produce dramatically different snowfall totals, even when communities receive similar amounts of moisture. From Portland to Bend, just 1 inch of liquid p
By Owen Prescott · 2026-11-10T08:07:34.273Z
Portland, OR – Winter storms across Oregon can produce dramatically different snowfall totals, even when communities receive similar amounts of moisture. From Portland to Bend, 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.
Portland and Bend: Why Snowfall Can Differ
Portland's location in the Willamette Valley exposes the city to relatively mild, moisture rich Pacific air during many winter storms.
However, cold air moving through the Columbia River Gorge can occasionally help produce snow or freezing rain around the Portland metropolitan area.
Bend, located east of the Cascade Mountains at a higher elevation, experiences a colder and generally drier winter climate.
The Cascade Range creates another major influence.
When moist Pacific air rises over the mountains, it cools and can produce substantial snowfall at higher elevations.
East of the Cascades, the rain shadow effect reduces overall precipitation, although cold winter storms can still bring accumulating snow.
What Oregon 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 blowing snow when winds strengthen.
Travel conditions can change rapidly along Interstate 5, Interstate 84 and U.S. Highway 97, particularly near mountain passes and higher elevations.
Freezing rain is another concern in western Oregon, where dangerous ice can develop even when snowfall totals remain low.
Understanding snow to liquid ratios helps explain why snowfall forecasts can change even when expected moisture amounts remain similar.
For Oregon residents, snowfall depth depends on more than precipitation alone. Temperature, elevation, Pacific moisture and mountain terrain all influence final accumulation totals.