Bullish early-month seasonal tendencies have been well documented both here and elsewhere.  But what happens if we close the month at a high?  Does that sap some of the typical early-month strength?  Or is the market more likely to continue higher?  Below I show all instances since 1995 where the SPY finished a month with the highest closing price of that month.

The numbers are very compelling. Most of the upside edge occurs in week 1, but there is some follow through into week 2.