How Does Frost Form Above Freezing?


Frost is a common sight here in North Dakota. But did you know that the temperatures don’t have to be freezing for frost to appear on your windshield? It probably goes against everything we’ve been taught. how can ice form when the temperature is above 32 degrees?

We’ve already seen it happen and we’ll see it happen again before Fall ends.
It all comes down to what’s called the heat capacity.

When the sun sets, the atmosphere cools and so do objects like your car. The car has what’s called a low heat capacity, which means it can’t hold heat for long when the sun sets. Metal has a lower heat capacity than the surrounding atmosphere. So it will cool faster than the surrounding air.

This is why the air temperature can be 36 degrees and the car can be 32 degrees. Then you factor in the moisture source which is the dew point. This is the temperature where dew starts to form.

As the temperature cools overnight, it cools to the dew point. This is saturated air and when dew forms. If the dew forms on the car that’s already at 32 degrees or colder, it forms frozen dew or frost. This happens even if the surrounding air is warmer than freezing. This scenario happens quite a bit in the fall.

Looking for a quick and easy way to get rid of frost when you don’t feel like scraping? Here’s a quick tip. Prepare 1/3 a cup of water and mix it with 2/3 of rubbing alcohol. Spray it on your windshield and you’ll see the frost melt.
Why is this? Alcohol doesn’t freeze easily. In fact, it would take a temperature of 128 degrees below zero to freeze. So you spray this mixture on the frost, it melts the frost instead of freezing.

Other helpful tips to remove and prevent frost:

1). Spray on a deicer on your windshield the night before.  

2). Dehumidify the car. Open your windows for a few seconds before you turn it off. That allows some of the warm and moist air to escape.

3). Don’t leave water bottles in your car overnight. They’re a moisture source.

4). Hand sanitizer can help with frozen locks. the alcohol will melt the ice.

5). Park facing east. The rising sun will melt the frost quicker than if it were facing west.

6). socks over wipers and plastic bags over mirrors help keep frost off of hard to remove places.

7). There’s always the humble scraper!

Copyright 2020 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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