Breakdown: Why there is frost on your windshield

Published: Dec. 29, 2018 at 10:04 AM CST
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MEMPHIS, TN (WMC) - If you’ve ever woken up to frost on your windshield, you know the pain of scraping it off. Have you ever noticed that sometimes the frost is only on your windshield and nowhere else?

With the right weather conditions, frost can develop at night. However, where that frost forms is based on the object’s temperature and/or humidity level.

Some materials, such as metal and glass, cool down more efficiently than others. During the day, the sun heats up the ground and objects around it. Then, that heat is released through radiation at night. Since your car is made of materials that release that heat more quickly, the temperature of your windshield may drop to 32 degrees or below faster than its surroundings. This is also why frost can form on your windshield even when the air temperature is above freezing.

In addition, sometimes frost forms on the grass or trees, but does not develop on other objects. This is because cold air is heavier (in simple terms) and will sink. So, the coldest air is on the ground. The official temperature you see on TV or on your phone is actually measured a few feet above the ground, so the air temperature may actually be a few degrees above freezing, while the ground temperature is at 32 degrees. Another factor is humidity. The grass holds more moisture than metal or concrete, which is needed for frost to develop.

In Tennessee, it is illegal for the view out of your windshield to be blocked by frost or snow. Frost is common in the Fall and Winter, so keep an ice scraper in your car during those seasons.

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