Costco Wholesale Corporation gapped up into blue skies on Thursday and rose about 2 percent of the open to reach a new all-time high of $603.78. All-time highs generate excitement and interest that can translate into increased buying pressure and above-average volume. When a stock reaches an all-time high there is no oversupply, meaning every trader and investor in the stock is in a green position and there are no bag holders. Because the stock has never traded in the range, there is also no price history to act as resistance. This can equate to some traders making emotional-based decisions, which can lead to unexpected share price behavior. When a trader has a position in a stock in blue skies there are a number of signals that can be watched to guide a trading plan: RSI The above average volume on a stock reaching a new all-time high often raises …