First, this week I have an update on Hazel the hummingbird who is hanging out at Shelly Horner’s Liberty Lake house. Shelly reports that as it’s gotten colder, Hazel likes to sit on the rim of heat lamp to stay warm.
“She’ll sit there for hours,” Horner said.
I also heard about two more hummingbirds hanging out around another feeder. If you have birds, buy a heated feeder or wrap LED Christmas lights around the feeder to keep it thawed.
Science of snow
Now that we are onto the subject of cold, let’s move to snow. Last Friday proved to be a challenge for many drivers because the temperatures were near freezing, resulting in slick everything.
The reason? The air temperature was in the high 20s, and the air mass coming in had a higher humidity. As a result of the combination, as the snow crystals were compacted by cars driving or people walking, the friction generated by the motion created enough heat to melt the snow into very thin layers of water that resulted in the slippery roads.
Conversely, if you have driven during a few winters here, you know that as our temperatures drop into the teens, the snow seems to dry out and get less slippery. Driving around in snow at 15 degrees is completely different from driving in it when it’s close to freezing. Why is this?
Atmospheric conditions of temperature, humidity and wind determine what kinds of snow will form. Snowflakes in their pure form are six-sided crystals that arrange themselves in infinite patterns, there are no two snowflakes that are alike.
When snow crystals form closer to freezing, the humidity is often higher and thus there is more water available to form flakes. Warm air holds more moisture than cold air.
As it gets colder, the air can’t hold as much moisture and the flakes become smaller. These smaller flakes are surrounded by drier air that insulates them from the effects of friction. When they fall to the ground, the air between the flakes further insulates them and allows the jagged ice crystals to pack together.
As the ice crystals pack together under their own weight, there is “micro thawing.” The moisture created under these circumstances refreezes into the spaces between the crystals linking them together. Because the temperature is well below freezing, the crystals stick together. As a result, cold snow won’t generate as much slippery water when its compressed.
This is also why snow squeaks under foot or a tire when it’s really cold. It is thought that when cold snow is stepped on, the bonds between the ice crystals break and we hear that as a squeak.
For all of you who are new to plowing snow off walks and driveways, remember this. Fresh snow is easier to move than packed snow so don’t wait to get the clearing done. If you are plowing a driveway, push the snow back a to make room for more over the winter.
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