What Is the Snow-to-Liquid Ratio?

It's almost spring, but that doesn't mean we're free and clear of the threat of snow in many parts of the U.S. Let's talk about what makes one snowstorm different from another.

Not all snow is the same. One of the first things we’re taught about the weather as kids is that no two snowflakes are alike, but no two snowstorms are alike, either. Different storms often have different characteristics, and the type of snow they produce can vary from light and fluffy to a sloppy, slushy mess that’s almost too heavy to shovel. One of the biggest factors that determines whether or not a winter storm is a nuisance or a disaster is something called the snow-to-liquid ratio, or how much water the snow contains.

SNOW IS SPACIOUS, AND OTHER BITS OF WEATHER GEEKERY

Contrary to popular belief, snow is not just a frozen raindrop. Snowflakes and raindrops are born from related but different processes. All snowflakes begin with a nucleus, which is a microscopic particle (like dust) suspended in the atmosphere. This nucleus serves as a catalyst, allowing supercooled water vapor to freeze to it on contact and begin to grow into an ice crystal. Snowflakes can take on all different shapes and sizes depending on atmospheric moisture content and temperature, but the most common type is the dendrite, or the iconic snowflake that grows with tree-like limbs and branches.

It’s the very make-up of snowflakes that allows even small amounts of snow to make a much bigger mess than an entire day of heavy rain. Snowflakes quickly accumulate into a thick blanket because they’re very spacious—when snow reaches ground that’s below freezing, the relatively enormous amount of space between the landing ice crystals allows snowflakes to pile on top of one another like scaffolding. The other factor is that snowflakes are much drier than a liquid raindrop. In fact, two feet of snow holds just a tiny fraction of the water produced by two feet of rain.

This is where the snow-to-liquid ratio comes into play. You’ve probably heard about this bit of weather geekery without realizing it; if you’ve ever heard someone say that 10 inches of snow is equivalent to one inch of rain, they’re talking about the snow-to-liquid ratio, or the amount of liquid you’d have (in inches) if you melted so many inches of snow. Higher ratios mean the snow has a lower water content. That 10:1 ratio only applies to storms that produce snow when air temperatures are hovering around freezing. The actual ratio can be as high as 30:1 in very cold climates to as low as 6:1 when temperatures are above freezing. The ratio can even change during the course of a storm as temperatures go up or down.

MINNEAPOLIS GETS DRY AND FLUFFY SNOW, WHILE D.C. GETS HEAVY SLUSH 

Julie Falk, Flickr // CC BY-NC 2.0

Winter storms are drier than those we see during the summer because cold air can’t hold as much water vapor as warm air. Snowstorms have much less moisture to work with than a bout of heavy rain on a July afternoon, but snowstorms can use their limited moisture supplies very efficiently. This is why the American Plains can see as much snow from one storm as the East Coast, even though landlocked storms have less moisture to work with than a storm straddling the ocean.

If Minneapolis and Washington D.C. both see a foot of snow, for instance, the snow in Minneapolis is likely to be lighter and fluffier thanks to the higher snow-to-liquid ratio that results from its cold climate, whereas Washington D.C.’s blanket of snow will probably be heavy and slushy due to higher atmospheric moisture from the Atlantic and temperatures closer to freezing. Simply put, if you filled a bucket with D.C.’s snow and melted it down, it would result in more water than if you melted down the same bucket full of snow from Minneapolis.

A very cold storm produces copious amounts of small, dry snowflakes that you can sweep off your car with ease, but they’re conducive to creating snow drifts and blowing snow that can reduce visibility down to nothing. A storm with temperatures close to freezing produces snow with a high water content, allowing snowflakes to compress upon landing, resting closer to each other and even allowing for a little bit of melting. This sticky, slushy snow is great for making snowballs and snowmen, but it’s also one of the many reasons mountainous areas and cities in the north can handle snow better than the rest of the United States—their fluffy snow is easier to deal with than the icy, water-logged mess everyone else is used to seeing.