If a specific post was interesting or useful to you, we recommend that you Like that post. It tells the post author, and others, that you found the information valuable. Clicking Like is another way to let others know that you enjoy it without leaving a comment.
Log in to join the conversation and Like this content.
Think about all the dust, smoke particles, etc. that get caught up in the snow over the course of the winter. When it melts, the dust/dirt gets more concentrated (that's my theory).