What's The Difference Between Freezing Rain, Sleet, and Snow?

Sticking with the winter weather theme, I'm going to break down the difference between the three types of winter precipitation: freezing rain, sleet, and snow.  Technically, there are four types of winter precipitation, because it can still just rain during winter!  But everybody knows what rain is, so for this post we'll leave it out.

Freezing Rain

This is a tricky one, because its name is confusing.  A friend of mine said he saw tiny ice pellets falling on the ground around him and called it freezing rain.  If ice is falling from the sky, then yes freezing rain seems like the perfect thing to call it!  But this is in fact sleet, not freezing rain.  Freezing rain is when liquid precipitation falls from the sky and freezes upon contact with the ground, roads, cars, or any other object.  If it's raining outside but you notice patches of ice forming on the ground, that's freezing rain.  Freezing rain occurs when the surface is colder than the atmosphere above.  The surface or object the rain lands on must be at 32 degrees or below to cause the transition from liquid to ice.  However, the air above the surface has to be above 32 degrees for a significant distance in order for the rain to still fall as a liquid.  So, the more accurate term for freezing rain would be "rain that freezes on the surface," but obviously people would get tired of saying that all the time!

Sleet

This is the one that my friend saw falling that day!  Sleet is like hail, only smaller and falls when it's cold, not during a thunderstorm.  If the ice is smaller 0.2 inches in diameter and it's cold outside, it's sleet; bigger than 0.2 inches and warm outside, it's hail.  When the ice that's falling is that tiny, you don't have to worry about it denting your car, but it can still make for very slick roads.  Sleet starts as snow high up in the atmosphere, but if the snow passes through a layer of warm air, it will melt.  If this raindrop then enters another layer of cold air, it will partially refreeze and arrive at the surface as an ice pellet rather than a snowflake.

 

Snow

This is of course the most famous type of winter precipitation and can be common or uncommon depending on what part of the country you live in.  Rather than falling as tiny balls of ice like sleet, snow falls as tiny ice crystals of all shapes, though they typically feature hexagonal symmetry.  Snow can form at any temperature below freezing in the atmosphere, but you typically don't see as much snow formation in extreme cold (below 0 F) because there is usually not enough moisture present.  For snow to reach the surface, the snowflake must not fall through any part of the atmosphere warmer than 32 degrees...as a general rule.  This is why in the southern U.S. snow is so uncommon, because it is rare for the entire atmosphere to be this cold.  However, if the atmosphere is cold enough, snow can still fall when it's above freezing at the surface.  That's because a snowflake can fall for about 1,000 feet in slightly above freezing conditions before completely melting.  If it's warmer than 41 degrees outside though, it's just too warm for snow.

So there's the difference between the three types and hopefully you now have a better idea of just how they form.  Forecasting has improved greatly, but precipitation type is still difficult to predict.  A few degrees difference at any layer of the atmosphere can have a dramatic effect on what type of precipitation falls.  So the next time your meteorologist says it will snow and you instead see sleet falling from the sky, try not to get too angry :) 

Why do You See Your Breath on Cold Days?

We all know that we breathe in oxygen and breathe out carbon dioxide.  But CO2 is not all that we breathe out.  The air inside of our lungs and mouth are very moist and some of this moisture travels outside our bodies in the form of water vapor when we breathe out.  Most of the time we don't notice this, but we can clearly see it when it's cold outside.  That's because when the outside air temperature is cold enough, the water vapor we breathe out is forced to change from a gas to a liquid through the process of condensation.  This is the same process that forms clouds in the skies above, so you're essentially making your own personal cloud just by breathing outside on a cold day!

So how cold does it have to be to make your own cloud?  Well it's not an easy answer because there are a couple of factors involved.  Not only is it dependent on the temperature outside, but also on the humidity.  When you breathe out, your warm, moist breath mixes with the colder, drier air outside.  The combination of your breath and the outside air must reach 100% relative humidity in order for you to see your breath.  100% relative humidity can be reached by lowering the temperature or raising the humidity.  You raise the humidity by breathing out, but if the outside air is warm or really dry (low relative humidity or dew point) it is less likely that you'll see your breath.  If the air outside is more humid, you can see your breath at higher temperatures than you would if the air was dry.  This is why you only sometimes see your breath when temperatures are in the 50s or upper 40s.  If the relative humidity is already above about 50% at these temperatures, the moisture in your breath should be sufficient to bring the mixed relative humidity to 100%.  If the outside relative humidity is under 50% though, even the addition of your moist breath may not be enough to reach 100% relative humidity.  You can even see your breath at 60 degrees, but this is uncommon, as the outside air would have to be at 80% relative humidity or higher to start with which is pretty muggy.

If the air temperature is cold enough though, you are guaranteed to see your breath.  This is right about 45 degrees.  Below this temperature, no matter the outside humidity, your breath will likely supply enough moisture to saturate the air around it and cause the formation of a cloud. 

Now you have a lot to think about the next time you're pretending to be a dragon!

Have a weather related question you'd like me to answer?  Comment below or hit me up on Twitter and I'll be happy to answer your question in a future blog post!