BOISE, Idaho — Cooler temperatures are on their way to the Treasure Valley, meaning snow could soon fall from the sky in urban areas rather than just the mountains.
When people think of precipitation in winter, fluffy white flakes are the first things to come to mind. However, snow is not the only thing that falls from the sky as temperatures cool.
The type of precipitation depends on one key factor: the temperature of the air and land.
Water evaporates into the air and condenses on a regular basis because of energy from the sun. The evaporated moisture will reach freezing temperatures and condense, forming clouds.
When enough of the moisture collects, the resulting particles are large enough to fall to the earth from gravity. The falling frozen particles will encounter warmer air on the way down and melt, resulting in rainfall.
Frozen particles typically fall to the Earth as rain, but what happens when temperatures are colder?
In fall and winter conditions, there are different layers of air temperatures. The frozen particles can encounter warm air as they fall but often a cold air mass at the surface will cause freezing.
The particles refreeze and create freezing rain. Ice then forms on roadways and other surfaces.
Another possibility is the frozen particles go through a smaller warm air mass and melt, then encounter a large cold air mass, resulting in a rain and snow mix also known as Graupel.
This is also commonly called corn snow or, in some cases, large snowflakes.
Finally, if the frozen particles fall and only encounter a cold air mass all the way to the surface, then there is no melting and the result is only snow. If surface temperatures are also below freezing, the result is accumulating snow.
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