Today’s Wonder of the Day was inspired by Brajone. Brajone Wonders, “What is a cold front?” Thanks for WONDERing with us, Brajone!
Is it chilly where you live? When it starts to get colder outside, you may hear weather forecasters talk about a cold front moving into your area. Have you ever WONDERed what they're talking about?
In weather terms, a front is the boundary between air masses of different temperatures. A cold front is the leading edge of a mass of cooler air that is pushing warmer air ahead of it out of the way.
As a cold front moves into an area, it displaces warmer air at ground level. Colder air is denser than warm air, so it pushes the warm air higher into the atmosphere. Temperature changes along the boundary of the cold/warm air can be in excess of 50° F (10° C).
As the warm air rises, it causes an area of low pressure along the cold front. The warm air cools as it rises and moisture begins to condense.
If enough moisture is present, a narrow line of thunderstorms and rain can form along the edge of the cold front. If the cold front boundary is unstable, thunderstorms are more likely. Stable systems often just bring steady rains. Very unstable cold fronts can generate hail storms and even tornadoes.
Cold fronts usually move from northwest to southeast. They tend to be strongest in the spring and the fall and weakest in the summer. In addition to rain and thunderstorms, they also bring gusty, shifting winds.
Winter cold fronts might not generate any precipitation at all if there's insufficient moisture in the air. If there's moisture in the air, though, a cold front can bring significant snowfall.
Cold fronts move much faster than warm fronts and can cause sharper changes in the weather. As a cold front is passing through, you will notice temperatures drop quickly and then steadily decline as it passes.
If you're watching the weather forecast on your local news, a cold front will be marked by a solid blue line. The blue line marking the cold front might also include triangles pointing in the direction the cold front is moving.