According to the weather forecast, it should have rained today. Although it rained a little in the morning, it's cloudy now. However, It seems like it's going to rain again. I guess that it will be rain again when I finish work. It always rains when I go out. (If you start the sentence with because, it becomes a sentence fragment) Oh! It's starting to rain now... My estimation was messed up! ("messed up" sounds more natural here. "screwed" sounds a little harsh)

According to the weather forecast, it should have rained today. Although it rained just a little bit in the morning, it's cloudy now. However, it seems like it's going to rain again. I guess that it will rain again when I finish work, because it always rains when I go out. Oh! It's starting to rain now... My estimation was screwed!

According to the weather forecast, it should have rained today. It did rained but just a little bit in the morning, it's cloudy now. However, It seems like it's going to rain again. I guess that it will rain again when I finish my work work. Because It always rains when I go out. Oh! It's starting to rain now... My estimation was screwed!