I did a study looking at situations where historical volatility has contracted rapidly like it has in the last 3 days. For the study I looked at the 3-day historical volatility and compared it to the 10-day historical volatility 3 days ago. In other words I divided Friday’s 3-day historical volatility by Tuesday’s 10-day historical volatility. A result below 1 would indicate the last 3 days have been less volatile than the previous 10. A number above 1 would indicate a recent uptick in volatility. For the SPX, Friday’s 3-day over Tuesday’s 10-day came in at a very low 0.23.
I then looked to see what the 3-day historical volatility has typically been 3 days later. What does a sharp contraction over the last 3 days indicate you might expect over the next 3 days? What I found is that when the 3-day over the offset 10-day dropped to 0.25 or lower the next 3 days were 5.5 times as volatile as the recent 3 days. This is based on 1,111 trading days since 1960 – or about 9% of all trading days. Going back to just 1999 gave similar results, as the 3-day historical volatility increased by 5.4 times.
This suggests we may see some increased movement over the next few days. A breakout of the recent 3-day range could be very sharp.