Sunny had become my default, and in books, defaults are dangerous.
Thing is, the weather is just another part of worldbuilding. Your characters will enjoy the weather, fight the weather, have their feelings and plans affected by weather. There's a huge difference in how a first kiss goes if it happens in a forest at night in the rain, in a cafe on a snowy morning, or on a blanket by a river on an unusually warm spring afternoon. A summer day in Savannah will be as warm and wet as walking through soup, your shirt stuck to your back and mosquitoes buzzing in your ears, while a summer day in San Francisco might be windy and cool with ocean breezes and morning fog. Whenever your character walks out the door, you have a chance to let your reader really see what they're experiencing, and that includes their feelings about weather and how it affects their life, including whether or not that bus splashes them with a puddle right as their umbrella blows inside out and flies away.
These days, I automatically build in scenes with weather that will complement or confound the plot. If you need something to mess up your protagonist's life, drop in a laptop fried by lightning or clouds on the day of the big pool party. Screw up everything with a hurricane, like I did in SERVANTS OF THE STORM. Or if you want to spice up their life for the better, I'll let you in on a little secret: My first kiss happened when my first boyfriend was snowed in at my house during a freak storm in Georgia. And now, whenever I'm writing a first kiss scene, I remember running upstairs, heart fluttering, and watching the snow fall on the streetlights, one hand to my lips, amazed.
I'm not saying sunny is bad. Sunny is great, and my favorite kind of weather. But sunny is easy, and easy doesn't keep us reading. Sunny isn't the real life default; there are more cloudy or annoyingly damp days than beautiful ones. Sunny matters more when you've been trapped inside by the snow or rain, wishing for blue skies.
If you show us the bad weather, we'll grin when the sun finally peeks out.