DES MOINES, Iowa — With the dawn of the most consistently cold air we've seen since late January (nine consecutive days with a forecast high of 42 or lower), it's time to put our winter caps back on.
First, let's talk about tire pressure as it relates to cold temperatures. For every 10-degree drop in temperature, you'll lose 1-2 PSI in your tires. You'll probably see a noticeable drop in your tire pressure throughout the week, so make sure to head to a gas station or somewhere convenient to fill them back up.
But now to the more complicated part of the winter weather forecast: deciphering winter weather precipitation types — snow, sleet, freezing rain and rain. It's one of the most difficult aspects of meteorology, and one of the most important, as travel can become incredibly dangerous.
Just one or two degrees can make all the difference in what we see at the surface.
With rain, the column of air the rain is falling from stays above 32° — that's common sense of course.
For freezing rain to form, the entire column of air stays above freezing, except near the surface. Common surface temperatures for freezing rain range between 28° and 32°. Freezing rain is arguably the most dangerous aspect of winter weather; it freezes on contact, creating a sheet of ice, typically the most dangerous kind: black ice.
Sleet and freezing rain aren't that much different; with the only difference being the cold layer of air is thicker near the ground. That allows the raindrop to freeze back into a small piece of ice (think of it as a very small piece of hail) right before it hits the ground.
Of course, snow requires the entire vertical profile of the atmosphere to be below the freezing mark.
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