The movement of the SPX are reflected in the VIX (volatility index) but the signal seem to arrive when the SPX index is already too advanced in the retracement. The SKEW signals earlier on. The signal from SKEW starts with lower lows, then the volatility increases and SPX dips.
Sell when the SKEW starts hitting lower highs, then BUY when the VIX index is peaking.
Sell when the SKEW starts hitting lower highs, then BUY when the VIX index is peaking.