Wednesday it was so warm I went running in shorts and a t-shirt; today it’s twelve degrees Fahrenheit, and the gusts of wind push the cold through even our tightly-sealed windows. I’ve noticed that when it’s cold like this the snowflakes are stringy (instead of forming the idealized hexagons you normally think of). Confirming my observation, this page says that no one knows why, but snowflakes do form different shapes according to temperature.