Monday, January 6, 2014

Ice Crystals

Ice Crystals- Click to Enlarge
On days like the last few, it is hard to get interested in going outside, but there are rewards for the hearty.  Larry Gurian sent me a set of pictures taken the day before the last snow hit.  Frost had decorated his back yard, creating a great photographic opportunity.

Click to enlarge- Pictures by Larry Gurian
These crystals are formed when the air is saturated with moisture and the water vapor settles on a solid surface which is below freezing.  Although the ground temperature is usually higher than the air when temperatures drop below freezing, structures such as grass, twigs and dead leaves may radiate enough heat to drop below air temperature.

As cold air settles during the night, the ground temperature may become lower than the surrounding air.  In our deep valley, the flowing water of Bull Creek contributes to higher relative humidity.  Barb reported an interesting example of this when walking our dogs this morning.  I had walked them in the snow before the really hard freezing temperatures hit.  My footprints compressed the snow into the warmer gravel, leaving ice in each print.  When the air temperature dropped to -5 overnight, frost crystals formed in the icy footprints but nowhere else.

Click to enlarge

The magic of the moment was lost on our blind schnauzer Smokey who thought that the unfamiliar jacket was embarrassing, making him look like Snoopy in his Red Baron fantasies.  Lifting each foot quickly to avoid the cold icy frost, he had a hard time remembering why he was out there and just why a bladder is important.

You can see Larry's complete set of frost pictures here, a good reminder to get outside, even when it is subzero.  Now if I could just explain that to Smokey.

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