How Momentum and MACD Histograms to Predict Prices
by Boris Schlossberg
Momentum, as signified by the MACD histogram, can provide clues to the underlying direction of the market. Using the assumption that momentum precedes price, the thesis of the set-up is simply this: a new swing high in momentum should lead to a new swing high in price, and vice versa. Let's think about why this makes sense. A new momentum swing low or high is usually created when price makes a sudden and violent move in one direction. What precipitates such price action? A belief by either bulls or bears that price at present levels represents inordinate value, and therefore strong profit opportunity. Typically, these are the early buyers or sellers, and they wouldn't be acting so quickly if they didn't believe that price was going to make a substantive move in that direction. Generally, it pays to follow their lead, because this group often represents the "smart money crowd".
Source: http://www.investopedia.com/articles/forex/05/MomentumMACD.asp