There's no getting around it, weather plays a big part in our lives. Heat waves make us irritable and tend to increase the crime rate. Too many snow days, like too many rain days, can make us lethargic, while the occasional blizzard that shuts down the city and provides everyone with an unexpected holiday, can be invigorating.
Weather is a close companion to all of us, affecting outdoor types and shut-ins alike, and it should also play a part in the lives of the characters you create. Weather can add depth to your stories. A sunny day can complement or contrast with a character's mood. Rain can dampen spirits or wash everything clean. "The Storm" by Kate Chopin is my favorite use of weather, as the building of a thunder storm mirrors the sexual desires of Calixta and Alcee. More subtle is Chopin's use of weather in her famous "The Story of an Hour" where, after being informed of her husband's death in a train accident, signs of spring signify the promise of a new life for Mrs. Mallard.
"She could see in the open square before her house the tops of trees that were all aquiver with the new spring life. The delicious breath of rain was in the air. In the street below a peddler was crying his wares. The notes of a distant song which some one was singing reached her faintly, and countless sparrows were twittering in the eaves."
If you are like me, the bite of winter can be difficult to conjure during a string of 90 degree days. The muffled tones of a snow day may be hard to recall during a thunderstorm. Yet sometimes the story we are writing cries for different weather than we're currently experiencing. That's why it can be a good idea to keep a weather journal. Either on paper or just in your mind, make note of the weather you experience. While walking down to the mailbox on a close, muggy day, notice how the air feels on your skin, how the leaves hang weighted from the branches, how the neighborhood dogs lumber. Then, when you need just that weather to make your story real, you'll know how to write it.
The main thing is, don't overlook the weather. It's one of the best, and easiest ways to add depth to your writing.