I've mentioned the NYAD before (NYSE advance/decline line) as one of the most reliable short term market momentum indicators. The high frequency trading algorithms that account for over 80% of typical daily trading volume can't manipulate this number like they can with the TICK and the TIME & SALES numbers. It's one of the few windows of transparency that are still available to the retail trader focused on short term trading and most data platforms symbolize it as $NYAD, or NYAD.X, or similar. It's definitely worth tracking if you are a short term trader.
The reason I profile the NYAD here is that its recent action illustrates why I recommend NOT trading the open of the market session to put on new trades, but instead waiting at least 30 minutes.
Now, selling a long position into the open is an entirely different story and, it should be pretty clear that opening gaps to the upside have been routinely knocked down during the first 30-60 minutes, so this is a good time to close Long positions.
The charts shown below are in Schwab Street Smart Pro platform format:
It also displays an overlay line chart of the VIX (volatility index) and a parabolic indicator (white dots).
The chart below is a 14 day chart on 65 minute bars showing the consistency of the morning fade pattern. Why 65 minute bars? The trading day is 6.5 hours = 390 minutes/6 bars = 65 minutes. Many technical traders use hourly bars (60 minutes) but I have found that a 65 minute chart delivers considerably improved results for short term trading as it divides the trading day into 6 equal parts not 6 1/2 parts.