Everyone's seen a movie (or two or five or a hundred) in which, during the sad, boy-loses-girl scene, the sky decides to cry along with the protagonist. (AKA, it rains.) This happens in books as well, though sometimes it's not as obvious. (Maybe you just imagine it happening if the weather isn't described.) Then, later, after the happy, boy-gets-girl-back scene, it's sunny and bright (or perhaps it's night and fireworks/aurora borealis fill the sky, take your pick).
It makes sense--these weather patterns are often mistaken as the outside world having emotions. Also, pouring rain is considered a sympathy ploy. Poor Mr. Protagonist, he found out his girlfriend was cheating on him AND his socks are getting all wet. Conversely, bright, sunny weather makes you want to skip along and tan and be happy that Mr. Protagonist realized he was actually in love with his best friend the whole time and they're getting married tomorrow and oh, his socks are dry now and also he needs to wear sunglasses if he doesn't want to get a headache from squinting, wahoo.
I, for one, get suspicious if I notice this happening too much. As in, hey, my emotions are being manipulated by meteorological phenomena and not the plot itself. In addition, I find rain to be preferable to sun. So next sad scene I write will take place at noon on a cloudless day in summer, because not only will Mr. Protagonist be sad, he will also be sunburnt and in need of tinted lenses and have sweat dripping uncomfortable down his nose and feel like there's a spotlight on him from High Above and therefore everyone is staring at his misery. And when Mr. Protagonist finds his joyful resolution, it will take place in the middle of a thunderstorm because then he has an excuse to go home and take off his wet socks and get cozy in dry sweatpants and enjoy his happiness in peace.
The idea of the post, beyond my rant about runny days: mix up the weather!