What causes the morning frost on your windshield?

LANSING, Mich. (WLNS) — As we continue to see temperatures fall, scraping frost off the car windshield in the morning will, unfortunately, become a lot more common for all of us.

But 6 News Meteorologist Kendall Wilson tells us that not every cold and freezing night can create frost. She has some more details in this week’s Weather Wednesday. 

Oct. 15 marked the end of the growing season in Southern Michigan, so the National Weather Service will no longer issue Frost Advisories or Freeze Warnings until the start of the next growing season in spring of 2024. 

So, even though we have been able to avoid the frosty mornings thus far, we still must make sure that we are paying extra attention to the overnight lows in the forecast, because it is only going to become more common for us to have to start planning extra time in the morning to scrape off our car windshield. 

But did you know that not every cold or freezing night will be able to create frost? For frost to form we need the 3 C’s: cold freezing air, clear skies, and calm conditions overnight. 

When skies are clear, the heating we gain during the day can escape quickly into the atmosphere, so our cool down overnight is maximized. As our temperatures drop down to the dew point, or in this case the freezing point, we create moisture at the surface. And when temperatures of the surface are at or below freezing that moisture turns to frost. 

This is an extremely delicate process, so even something as small as a strong gust of wind can mix up the air and prevent this process from happening. 

Our temperatures overnight can also tell us just how easy scraping off that frost in the morning will be. The general rule of thumb is that when surface temperatures are between 29 and 32 degrees, the frost is easy to scrape off. But when temperatures drop to 25 degrees or below, you must spend a little more time and use a little more elbow grease. 

Thankfully we don’t see temperatures this cool until we reason around Oct. 28. This is still a little over a week away, so in the meantime continue to bundle up, grab the ice scraper and keep them handy.