When talking about each of the precipitation types that make up a “wintry mix”, it is important to understand that temperature and moisture content of all layers of the atmosphere is critical. You see it’s not enough to know the temperature and moisture conditions on the ground. But you have to know what the conditions are like all the way up through the clouds, which can extend more than 30,000 feet above the surface during the wintertime.

We’ll start with the most common precipitation type here in Kentuckiana, RAIN. Rain is simply melted snow. That’s right, it always starts out as snow. As you probably are aware, the atmosphere usually gets colder as you go up, and this time of the year, it is almost always below freezing at cloud level. Therefore, snowflakes are produced instead of rain up in the clouds. As the snow falls, however, it eventually encounters warmer air on the way to the ground causing it to melt and form rain.

Now another common wintertime precipitation type is SLEET. Sleet, looks like tiny balls of ice and are sometimes called ice pellets. The formation of sleet is a bit more complicated than that of rain. Sleet initially forms the same way that rain does, as snow. Also, like rain, the precipitation eventually encounters warmer air on the way to the ground changing it to rain. Its plight doesn’t end there, however.

You may have noticed a few paragraphs back that I said that the atmosphere “usually” gets colder as you go up. That is not always the case though. In the case of sleet, which starts as snow, then changes back to rain, will then refreeze once it travels through a layer of subfreezing air on its way to the ground. I haven’t lost you yet, have I? This refreezing process converts the rain into what we know as sleet or ice pellets.

The point that I am trying to make here is that there may be several below freezing and above freezing layers of air as you travel from the cloud to the ground… or from the ground to the cloud, depending on which way you go. This is important because FREEZING RAIN also encounters multiple layers of air.

Freezing rain looks like rain, smells like rain and tastes like rain, but it’s not rain! In fact, freezing rain and rain are very similar with only one major difference. The difference is that rain doesn’t freeze on contact with the ground like freezing rain does.

Just like rain, freezing rain stars as snow then melts into rain on the way to the ground. Similar to sleet, it then encounters a layer of subfreezing air as it approaches the ground. However, this layer of cold air is not sufficiently deep enough for it to refreeze into sleet before it reaches the ground. Therefore it falls as rain. Not just any rain though because the water droplets are “supercooled”. Meaning that the droplets are actually below freezing as they reach the ground. The only thing they need to freeze is something to freeze onto. And that something, unfortunately, is any object they encounter that is also below freezing, such as trees, power lines and roads. Freezing rain is the most dangerous of all wintry precipitation types.

SNOW is actually the simplest of all precipitation types because it doesn’t change form. It starts as snow in the clouds and reaches the ground in the same manner. For this to occur, all layers of air between the cloud and the ground need to be at or below freezing. This seems to rarely be the case in Kentuckiana, however. A change of a couple degrees in any layer of the atmosphere between the cloud and the ground can make all the difference between a heavy snow and the proverbial “mixed bag” or “wintry mix” of precipitation.

As for what the rest of this week will hold, you’ll need to stay tuned to that all-important First Alert Storm Team Forecast.