The S&P 500 is heading into what is historically its strongest season, but a specific set of market conditions is flashing a warning sign for investors in the immediate short-term.While the fourth quarter has delivered the best average returns for the index since 1950, historical data shows that a strong year-to-date performance through September often leads to a flat or negative October, creating a conflicting picture for Wall Street.A Strong Fourth Quarter Is On The CardsData compiled by Carson Research’s ...