Berkshire Hathaway (BRK.B) stock is up just 0.78% for the year and is underperforming the S&P 500 Index ($SPX) by a wide margin. However, the stock gained 3.78% over the last month, which not only helped it turn positive for the year but also helped it bridge its gap with the index. With Berkshire jumping sharply over the last month, let’s examine the stock's outlook in the back half of the year.