SaltWire E-Edition

How does frost form on the inside of my windshield?

ALLISTER AALDERS @allistercanada Allister Aalders is the weather specialist for the SaltWire Network, providing forecasts and analysis for Atlantic Canada. #AskAllister

During the last few months, I have written a few columns about frosty windshields.

A few of you have reached out to me following these columns, noting how frost sometimes forms on the inside of your windshield, and were curious as to how this happens.

We know frost forms when water vapour cools and condenses onto surfaces. When temperatures fall below freezing, this condensation freezes.

The same processes can occur on the inside of your vehicle and cause frost to also form inside your windshield. However, it usually takes much colder temperatures with ample moisture for this to occur.

Now, you might ask yourself, where is the moisture inside my vehicle coming from? It can be as simple as leaving a wet coat, mittens, shoes or an umbrella in the vehicle. The moisture that evaporates then condenses onto surfaces. Another moisture source can be melted snow or water tracked into your car from outside or the possibility that your window was left open just enough to let the moisture in. It’s even possible the heat in your vehicle can leave enough additional moisture to condense onto your windshield, especially if it was on high heat.

And much like scraping the outside of your windshield, this, too, is inconvenient. There’s not a whole lot you can do about it except to keep potential moisture sources out of the car. In terms of getting rid of it, your car heater will melt it eventually, but consider referring to the tips I gave in December about creating solutions that can help melt the ice.

Soon enough, though, it will be dewcovered windshields instead of frosty ones.





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