Below are the seasonality stats for the S&P 500 during the Summer months:

• June: Higher 65% of the time in the last 20yrs. Avg % return = 0% (Yes you read that right, 0% is the average return for June)
• July: Higher 45% of the time in the last 20yrs. Avg % return = +0.4%
• August: Higher 55% of the time in the last 20yrs. Avg % return = -0.8%

(Seasonality data from equityclock.com)

I find it interesting that the only month with a positive average historical return (July) was the one in which had the lowest probability of having a positive returns.