EYEWITNESS WEATHER (WBRE/WYOU-TV) — When we venture out in the winter, one of the main concerns on the road is black ice, but there is also freezing fog to consider.
Icy roadways are always a danger in the winter months, and black ice can be some of the most dangerous kind of winter weather that we can actually see.
What exactly is black ice? Well it’s a very thin layer of ice that develops over the top of the pavement when the road temperature is below 32 degrees Fahrenheit. It’s below that freezing mark and it’s the transparency of that ice that lets it blend in with the dark pavement or the sidewalk and can make it very difficult to see, that’s why it’s one of the more dangerous kinds of winter weather.
There are three different ways we can talk about getting black ice, one of the first ways is when we have snowmelt during the day, then is that temperature drops overnight. Everything can refreeze and it refreezes into that thin layer of ice.
Early in the mornings after we’ve had a chance to cool down, we can also get black ice with light rainfall when the road temperature the pavement temperature is below that freezing mark and light rain begins to fall, it can turn into ice.
So that’s why we really pay attention to those road conditions in the winter, because we can be seeing rain, but as it hits the ground, it turns right on the ice.
There’s another way we can see black ice, and that’s called freezing fog. Remember, with fog down at the ground, it just moisture and there’s tiny water drops in that cloud of fog. So once it comes into contact with a surface that’s below 32 degrees Fahrenheit, it freezes into that icy layer of black ice.
We call this freezing fog and it can be dangerous in itself, just on a foggy morning and a lot of the time in the winter.
You see the signs everywhere, some will say bridge ices before the roadway. But why is that the case? We tend to see the bridges freeze first, then the roadways after, and this can be very dangerous in the winter months, the main reason being the roads can be fine.
Once you move over that bridge though, you hit a patch of ice and that can cause some problems. So look at the air temperature dropping and notice that the bridge temperature follows very closely along with that air temperature while the road temperature is actually running much higher than that at 38 degrees Fahrenheit.
It’s because bridges are exposed to colder air from both above and below so that more exposure to the colder air actually lets that temperature drop more rapidly, and follows the air temperature much closer. So that’s why those bridges tend to ice before the roadways.