Usually I can tell by the beginning of the day whether it's going to be a "good mood day" or not.
But my triggers are usually the weather (esp. in this cold, cold, michigan winter), or even if it's cloudy or rainy. It won't ruin my mood if it is cloudy for just one day, but if it persists, I will gradually get more and more depressed. I have bipolar 1, so I have many more depressive episodes than manic.
Thinking about big issues such as the war, future generations, the economic situation, etc.. also may leave me depressed for a long time after I'm even thinking about them. Maybe days. Maybe a week.
Just thinking about things can get you reeeaaaallly down. If you are having swings, I suggest you try to occupy your time with things that aren't going to make you stop and brood over things. That's just my suggestion.