Weather Words: Frost Line

Frost covering the ground on a cold morning, or even clinging to structures on a winter day is something most of us are familiar with, however, understanding how far below the surface those freezing temperatures go is very important.

The Frost line is simply the depth below ground the soil remains at or below freezing. This is especially important for builders, as pipes and footing need to be buried below the frost depth (or frost line). If footing for a home is built above the frost line, then as that frozen soil expands, structural damage can occur. If pipes are buried above the frost line, they can burst if the frozen soil expands.

Obviously northern areas will have a deeper frost line than areas in southern regions. But it’s not always the snowiest locations that see the deepest frost lines. Snow acts as a natural insulator, so many times areas with a lot of snow will have a shallower frost line than cold regions without snow.

You can check these maps from NOAA, that are constantly updated, to see places that have soil still below freezing.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.