Weatherz School: Frost formation

The frost scraper is back in season. Soon, factoring in a few minutes to clean the windshield before hitting the road will be part of the morning routine. You can plan ahead if you know what causes an icy windshield. For starters, you don’t even need a morning temp as low as 32°F.

In forecasting for and measuring the minimum temperature, we’re interested in the air temperature. The official temp is recorded about 5 feet off of the ground. Cold air sinks, so the ground temperature can be 32 while the air temp is 36.

This is how you can have frost while the temp is in the mid-30s. The same can be said for your roof and windshield. Metals and glass cool to the frost point much more efficiently than the air.

Water molecules in the air touch the frozen surface and freeze forming ice crystals. It’s interesting to note that true frost is when the moisture goes straight from water vapor to ice. If the water vapor becomes liquid and then freezes, it’s technically frozen dew.

The favorable conditions that allow frost to form are clear skies and light winds. It also helps if there’s moisture in the air and on the ground. The temperature has to be at least in the mid-30s.

With all of this in mind, you can plan ahead so that a frosty car doesn’t mean running late in the morning. Of course, we’ll help you prepare for it, too!