Snow vs. Liquid Water

Real talk: snow forecasting in the South is one of the hardest things a Meteorologist can attempt, and today you will see why. 

What You Need: 

-a snowy day

-clear jar

-marker

What to Do: (click here to watch my demonstration and hear about the differences between snow and rain forecasting)

-collect snow in the clear jar (you need a good amount - at least one inch of snow in the jar, but the more the better)

-while outside in the cold, set the jar on a level surface and measure how much snow you collected. Mark on the jar with the marker where the top of the snow is. 

-bring the jar inside and allow the snow to melt naturally. When it has all turned to liquid water, mark the top of the water and measure it. Note the difference between the snow and water measurements. 

What This Teaches:

Our forecast models are built to predict liquid precipitation, not frozen. Because there are so many different factors that go into a snow forecast, the computer model cannot handle all of that well. We have to look from the surface all the way up to the cloud for temperature and moisture to make sure it’s all saturated and colder than freezing. At the ground, though, the temperature can be a few degrees above 32F and you still have snow. Since each of the variables we look for has a little bit of wiggle room, a computer that’s working in 1s and 0s isn’t going to solve that problem very well. 

So when we forecast snow, we actually start by forecasting how much liquid water we have to work with. As you saw in your jar, that’s a pretty poor stand-in for how much snow can fall. When we talk about snow on TV, you may have heard us describe it as “a wet, fluffy snow” or a “cold, icy” snow. Depending how cold and moist the air is where the snowflakes form, we can get very different kinds of snow to fall. Have you ever seen the snow sparkle?? That’s generally a lighter snow that’s made of more ice and less liquid water. When that melts you have even less liquid than with the fluffy, wet snow. We call this a higher snow ratio. If you have 4” of snow, you might only have a few tenths of an inch of liquid water. But if the snow you collect is fluffy and wet, that is a lower snow ratio. If you have 4” of that snow, you might have half an inch or more of liquid water.