Weather is a constant although it is so commonplace that we don't always notice it. Rain. Snow. Fog. Sun. It all affects us in some way - the clothes we wear, the route we take to work, and how we feel when we step out of the door on a morning. It can also be a mood setting device in our writing.
Dark clouds can bring a feeling of impending doom. Floods suggest the loss of control. Snow can be magical or a blanket over what is buried beneath it. Sunshine lends optimism. Victorian smog added to the element of mystery and something unpleasant lurking unseen in Gothic novels. There are so many ways that weather can be used to affect the reader.
Write an opening paragraph where the weather creates a mood.