Fern frost

If you have leaky windows with semi-moist air on their interior and very low temperatures on their exterior, “fern flowers” or fern frost can form on the inside of the windows.

Such was the case this morning after a sub-zero overnight low:

The sun actually warmed up the thermometer a little; air temperature was -1 F.

The sun actually warmed up the thermometer a little; air temperature was -1 F.

And my kitchen window had grown a lovely crop of fern flowers overnight.

fern frostfern frost

 

Easy to see why it’s called fern frost, since the ice crystal patterns resemble the leaves of a fern.  But why does it take this shape?

Moisture from the air condenses on the cold window, but instead of forming a liquid pool, the very cold window temperature causes the water to go directly from gaseous to solid state.  Ice crystals form around surface imperfections in the glass, like scratches, dust, or dirt (I’m sure there is plenty of that on these windows).  These initial ice crystals then serve as “organizing” points for the further deposition of ice, and eventually, a lacy pattern appears.

The cold morning air didn’t seem to bother the intrepid avian visitors to the feeders though.  They just fluffed up and toughed it out.

American Goldfinch enjoying a morning treat of thistle seed.

American Goldfinch enjoying a morning treat of thistle seed.

Did you even notice how Black-capped Chickadees seem to be almost spherical in shape when fluffing out their feathers.

Black-capped Chickadees seem to be almost spherical in shape when fluffing out their feathers.

7 thoughts on “Fern frost

  1. Great photos, Sue, as always. Love the fern frost! I should be seeing some springtime migrants passing through my yard in the next few weeks. The goldfinches will stay a month or two while molting back into their breeding plumage before heading farther north. I’d love to have chickadees, too, but have never seen any here.

    As for your cold weather, wow. I was wearing shorts again yesterday, though Friday, it was cool enough for a fire in the morning. By afternoon, though, it had warmed up smartly. Today, too. I have to say that once it gets below zero, even I (an ardent fan of cold weather) start to feel like sticking by the fire. So far this year, we haven’t had a freeze in our area, but I’ll bet we drop below 32 before it’s all over for the year. At least for a day or two.

    Thanks again for such cool photos…in every sense of the word.

    • As much as I complain about the cold, I think it makes me appreciate the warm summer days, so I’ll take what nature dishes out just for the variety. thanks. as always, for your great comments.

      • The variety is nice, and I love a change of seasons, something we get very little of here. But minus 12 IS a bit extreme. However, it gives you a good excuse to stay inside, drink hot cocoa, and read. Now what could be better than that?

      • Not to make you feel bad, Sue, but it was 78 here yesterday, and definitely shorts weather again. Today feels a bit cooler, though. It might stay in the 60’s. Mike and I will have to send warm thoughts your way to keep you toasty on such a cold morning!

  2. Pingback: A really cold day | Back Yard Biology

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s