Have you ever heard of "freezing fog?"
This is what is looks like - that white layer on trees and grass on the side of the road.
The National Weather Service issued a freezing fog advisory for several areas in central Texas Wednesday.
Freezing fog is formed when tiny droplets of water in fog freeze on exposed surfaces.
That's especially dangerous when it happens on roads, where freezing fog can create black ice.
Advice from forecasters is - drive slowly if you believe freezing fog could be in your area.