"If you don't like it, wait five minutes." That's the mantra Coloradoans mumble when the temperature plummets from 70 to 30 in one day. Important plans get interrupted, and you may sprain your back shoveling two feet of wet spring snow off your deck and have to cancel your tennis match.
The unpredictability of weather and its related conveniences and inconveniences can be useful tools as you plot your story. It’s done with good scene-setting, consistent information, common sense/believability, and excellent timing.
Consistent/Common Sense. It’s clever to tie the weather to your protagonist’s moods. If he’s just suffered from the loss of a loved one, a cloudy sky, dripping rain like teardrops, may be perfect to amplify his grief. However, if every time he’s troubled the sky becomes overcast, it becomes obvious and distracting. And admittedly, humorous, where comedy was not intended.
Scene-setting. A romantic story setting might be, not just sea and surf and sand, but a gentle surf, at sunset, warm, with sound effects--whoosh, whoosh, a soothing, sensual rhythm to the waves. Perfect for that “First Kiss” moment between hero and heroine. Or the surf can be crashing and pounding against the cliffs in that “Life Threatening” moment with rain so heavy the characters can’t see as they stumble along a treacherous path to the castle. The setting can become a critical “Plot Point” when nature becomes the antagonist, as when Leonardo DiCaprio as Hugh Glass fought against a hostile climate to drag himself back to civilization in The Revenant. It can become the “Saving Grace” moment when a vicious clump of space garbage veers just to the right of our hero’s space capsule.
Believability. Was there really an ice storm in Florida in August? Not that you can’t deviate from normal expectations, but everybody and his brother had better be talking about it. I recall visiting Vancouver in March, and the weather was something we in Colorado are accustomed to: blue skies, not one cloud, sunny. The difference was that every person on the street and every DJ on every radio station was marveling and commenting. The DJs encouraged everyone listening to take the day off work and just get out there and enjoy it. The entire city was joyful. Unusual weather works in novels. If you need flowering trees earlier than expected, it can be done. Just acknowledge the rarity through your characters.
Timing. If the weather causes a turning point or crisis, build toward that moment to avoid the deus ex machina factor. If there’s a fog-caused 20-car pile-up in which the villain is killed just before he arrives to finish off the hero, palm to head. It won’t work. Your fan has been loyally reading for hundreds of pages, anticipating this confrontation. For the satisfying ending, the villain needs to arrive mentally and physically strong and able to compete, so the hero can suffer and strive and finally win.
If in the struggle the villain slips on ice, falls and loses his gun, it needs to be established beforehand that it rained and the temperature dropped at sunset, causing treacherous driving conditions, for example.
Most of these are common sense. Considering the weather is one of the joys of writing. No longer are you victim of the weather. Now you are the Wizard, throwing clouds and rain and snow on your people. Just cool it with the lightning bolts.