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CINDY DAY: Frosty ferns explained

During the last few nights, light winds, cold air and relatively high humidity came together to produce works of fern frost art on many windshields.
During the last few nights, light winds, cold air and relatively high humidity came together to produce works of art on many windshields. - Submitted

Making weather is a little bit like baking a cake: you need all the right ingredients for it to turn out! During the last few nights, light winds, cold air and relatively high humidity came together to produce works of art on many windshields.

Frost is the coating or deposit of ice that may form in humid air in cold conditions, usually overnight. It usually forms when a surface cools to a temperature colder than the dew point of the air next to the surface. Of course, the temperature of that surface must be below freezing.

There are many types of frost. In my opinion, the most beautiful one is fern frost. Fern frost, also called window frost or ice flowers, forms when a glass pane is exposed to very cold air on the outside and warmer, moderately moist air on the inside. Car windows and paintwork are good heat conductors: they warm up quickly on a sunny day, but release that heat after sunset. The interior of the car, on the other hand, will cool at a much slowly rate. So, one side of the window is cold and the other side is not as cold and more humid… et voilá!

So how do we explain the elaborate patterns?

Water molecules from the air condense on a cold surface. Once a tiny ice crystal forms, it grows across the cold surface. Crystal growth is faster at edges rather than on larger, smooth surfaces. Tiny imperfections like scratches and dust influence the arrangement of the drops of moisture so that, when they freeze, they form beautiful patterns.

Another little masterpiece compliments of Mother Nature!

Today’s weather fact

On April 12, 2015, there was 90 cm of snow on the ground in Truro, N.S., 70 cm of snow in New Glasgow, N.S., and 42 cm in Charlottetown, P.E.I.  Going further back, on April 12, 2001, there was 101 cm of snow on the ground in St. John’s, N.L.

Cindy Day is the chief meteorologist for SaltWire Network.

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