Our weather has become much milder this week following two weeks of very cold weather to start the month of February. Likely unnoticed due to the timing of the arrival of Pacific air, a very subtle transformation has taken place which is a sure harbinger of spring. Snow and ice melt on any sunny day, no matter the temperature. Even if we get another round of subzero weather, sunshine will cause wet spots to form on sidewalks exposed to direct sunlight.
The cause of this change is increased solar radiation caused by the increasing angle of the sun in the sky. The more direct solar rays are better able to penetrate the atmosphere and warm objects on the ground. Bright snow cover is highly reflective and is not warmed very much, but an exposed patch of sidewalk is readily warmed above freezing, causing nearby snow to melt on even the coldest days. Of course, melt water runs freely on the mildest days.