Charles Schwab's Rachel Dashiell analyzes the S&P 500’s (SPX) rebound, warning that low volume and volatility could put key support levels back in play. She sees a bullish breakout in Mastercard (MA), with $600 as an important support level, while BlackRock (BLK) is building an inverse head-and-shoulders pattern after earnings. She says strengthening momentum and volatility could set up further upside in both financial stocks.