I'm not sure if anyone noticed, but after you have completed the main story, the weather, for some reason, is permanently set to sunny. That is, no more cloudy, overcast or moody days, every single day has the bland and completely dull blue sky.
I, for one, took a while to notice this. After a good time of playing the game during Chapter 6 on the PS2, I started to notice that the visuals of the game were now somewhat... lacking. For some reason, the game appeared to be more visually appealing before I have completed it. Then one day I noticed that it was because of the sky. There was no more clouds, no more purple, gray or reddish horizons, and this was somehow taking away part of the fun. Of course, it is irrevelant to the amazing gameplay, but I don't know, having the weather being unpredictable was somehow fun, and made the game prettier. And I've always been somehow fascinated with the sky, even in video games, so this was kind of a bummer to me.
Until one day, I finally figured a way how to fix this and bring back weather changes. It was by a complete accident, I simply decided to do something different and did the Lawn Mowing job. And then, after a short while, the sky appeared to be different. Then I stopped to look at it better, and the clouds were there
Then the weather kept changing randomly, it even started to rain! The game was perfect again!
So, to bring back the weather changes, just do any Lawn Mowing job. I recommend you to do the one in the house as it's shorter, but the one in the park also works. I'm not sure if doing any other side mission also activates this, I believe it has something to do with the fact that you're doing a mission, so that somehow brings the game back to how it was when it was not "completed"... I don't know how it works, but it's a neat little glitch that I thought I should share. The glitches lastes as long as you continue to play on that saved file, loading the game again sets the weather back to permanently sunny. So, if you want to always have this, you'll have to cut the grass everytime you load your file. An advantage to this it's that you'll always get an extra $40 everytime you play the game. I have got over $13,000 from doing this everytime I play, and this is after I have burned most of my money on every single garment in the game to achive 100% completion, so I believe that's a lot.
Something cool about this is that the possibily of raining is back, meaning you can get the umbrella back! Of course, there's no way to predict when it'll rain, it may happen immediately, in one, two or five days, or it may not happen at all. But at least the possibility is there again.
Not sure if this works in Scholarship Edition, and I also noticed that the sky in that version is always the same thing regardless of weather, with only the colours changing.
Picture with a umbrella and with Zoe, to prove this is during Endless Summer:
