Chilbrown, as humans we want to know WHY something happens. If the US markets rise or fall we want to know what caused it.
And so, the most obvious piece of plausible news at the time satisfiies most as the reason. An Obama speech. Eurozone wobbles. Unemployment claims. Whatever.
I believe some news can and does cause spikes, but the day to day stuff.....just look at where your indicators are and you'll know before any "news" what's likely to happen.