Light, Fluffy Flakes Or Wet, Weighty Slush: What The Snow Ratio Means For Your Forecast

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By mid-winter, it starts to become obvious that winter storms can produce wildly different amounts of snow, more so than the difference in rain totals from different rain storms. This difference is because of an important factor in forecasting: the snow ratio.

'10 to 1' r​ule of thumb is only a rule of thumb: You may have heard that melting 10 inches of snow gives you an inch of water. While that is valid at times, how much snow comes from an

“inch of water” has many more factors that can significantly alter the resulting snowfall.

The resulting ratio of rainwater to snow is called the “snow ratio.” Determining this ratio plays an important role in creating the forecast for a winter storm, in addition to determining its future path.

(MORE: Why Do Snowfall Forecasts Change as a Potential Storm Gets Closer?)

Snow ratios can far exceed the 10:1 rule of thumb: In the 24 hours ending the morning of Jan. 21, 2024, parts of the Alleghenies saw 2 to 4 inches of snow from just 0.05 to 0.08 inches of liquid water, according to the National Weather Service in Baltimore-Washington.

T​hat's a ratio of 40 inches of snow per one inch of water, or four times higher than the 10:1 rule of thumb, meaning the snow was extremely dry.

(15-minute details: For even more granular weather data tracking in your area, view your 15-minute details forecast in our Premium Pro experience.)

We also have seen examples on the opposite end of the spectrum, like the one below from January 2023 where the snow-to-water ratio was 6 to 1 in the Sierra Nevada.

Temperature plays a critical role in determining the snowfall ratio: Snow that occurs in an environment where there is deep, cold air produces higher amounts of snowfall. That's exactly what happened in the example above from the Alleghenies: fresh arctic air sweeping into the East coincided with the snowfall.

This higher-ratio snowfall is typically dry and fluffier and is often prone to blowing around in the wind. It’s also the worst kind of snow for snowball and snowman construction.

Lower snow ratios result in wet, heavy snowfall accumulations commonly found in early and late-season storms, and often in the South. That type of snow is difficult to shovel and can be more likely to bring down trees and power lines.

(More: Shoveling Snow Can Lead To Heart Attacks)

Temperatures aren’t the only factor for snowfall ratios: High winds can also result in lower snow ratios since larger snowflakes can break apart in gusty conditions, says NOAA.

The ratio is also not set in stone for a storm (it’s more like it’s set in snow). Even as a particular storm is ongoing, snow ratios may increase or decrease to some degree depending on how temperatures evolve in the large-scale weather situation.

(192-hours: Further beef up your forecast with our detailed, hour-by-hour breakdown for the next 8 days – only available on our Premium Pro experience.)

The region can help forecast expected snowfall ratio: Historically speaking, there is variability by region when it comes to snow ratios.

The highest snow ratios historically can be found in the nation's northern tier and the Rockies, based on the map below from a 2005 study by Marty Baxter, an associate professor at Central Michigan University.

Locations from the Rockies eastward into the Midwest and interior Northeast have average snow ratios anywhere from 12-to-1 to 15-to-1. That means one inch of water has produced, on average, 12 to 15 inches of snow in a given storm.

In parts of the northern Rockies, the average ratio is even higher, topping 15-to-1 in some cases.

Locations from New York City southward into the mid-Atlantic have historically seen ratios on either side of 10-to-1.

If you prefer wet, heavy snow, your best bet for where you can find it is in parts of the Southeast, the southernmost regions in the Southwest, and the coastal Pacific Northwest. These regions are historically the most likely to experience storms with a snow ratio below the 10-to-1 rule of thumb.

Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.