Pull up a chair and let’s talk snow. Not the pretty postcard kind, but the geeky “what’s actually happening in the atmosphere” kind. And yes, I promise to keep this fun. This is classic winter-weather talk, the stuff I grew up loving in small-town Missouri when a good snow meant school might just shut down and we all got a surprise holiday.
When people see a forecast calling for one inch of liquid equaling 10 inches of snow, they assume it’s a law of nature. It is not. That famous “10 to 1” ratio is more of a suggestion than a rule. The atmosphere is a lot more creative than that. Snow ratios can swing all over the place based on temperature, moisture and how flakes form on their long journey from the clouds to your driveway.
LIQUID-TO-SNOW RATIOS 101
Every inch of snow begins as liquid water in the clouds. A l iquid-tosnow ratio tells us how much snow y o u g e t from one inch of liquid. The famous “10 to 1” ratio is the one everybody remembers, but the atmosphere rarely sticks to that number. Ratios can be as low as 5 to 1 or soar past 25 to 1 depending on how cold the air is, how dry it is and how the snowflakes form on the trip down.
Cold air produces lighter, fluffier flakes and higher ratios. Warmer air produces wetter, heavier flakes and lower ratios. It is basically the difference between scooping powdered sugar and scooping wet cement.
WHAT MAKES SNOW “WET?”
Wet snow forms in an atmosphere that’s right around freezing from top to bottom. The flakes bump into super-cooled droplets, pick up extra moisture and get heavy. This is the snow that sticks to everything, builds snowmen, snaps tree limbs and gives you a backache when you go out to shovel it.
If you’ve ever tried brushing heavy snow off your car only to smear it around like icing, that is wet snow in action.
WHAT MAKES SNOW “DRY?”
Dry snow forms in colder air. The crystals stay crisp, airy and don’t absorb much moisture. You cannot build a snowman with this stuff unless you have the patience of a saint. It blows, drifts, sparkles under streetlights and makes that satisfying crunch when you walk across it.
This kind of snow has high ratios because the water content is so low. A little liquid goes a long way.
“TOO COLD TO SNOW” – WHAT PEOPLE REALLY MEAN
So here’s the fun part. Is it ever literally too cold to snow? No. You can get snow at extremely cold temperatures if the atmosphere has moisture and rising motion. Antarctica, for example, is one of the coldest places on Earth and still gets snow.
But here’s the truth behind the saying:
Very cold air is usually very dry air. When temperatures plunge, the atmosphere cannot hold much water vapor. So, while it is not physically too cold to snow, storms struggle to produce snow when the air is bone dry. It is like trying to bake a cake with no ingredients. You might have the oven, but you do not have the batter.
And when snow does fall in bitter cold, it is often the driest powder imaginable — sugar-shaker snow. It looks impressive piling up, but if you melted it down, you’d get barely a sip of water.
When you hear me say, “Expect a dry, powdery snow” or “Look for a heavy, wet snow,” I am really telling you what the atmosphere is doing above your head. A couple degrees of warming or cooling at just the right layer can completely change the type of flakes, the snow ratio and your final totals.
This is why meteorologists stare at upper-air data soundings like they’re ancient maps and why we sometimes adjust a snow forecast even when the storm track hasn’t changed.
So, the next time someone says it’s too cold to snow, you can smile, sip your Pibb and explain that it’s not too cold… it’s just too dry.
From my window to yours, stay warm and enjoy the next round of flakes, whatever form they take.