Here are some clues as to an upward trend day, referencing the Market Delta chart above:
* Price breakout above the overnight trading range on good volume;
* Price staying above the overnight range on pullbacks;
* More volume transacted at the market offer price than at the bid (bottom histogram);
* Price consistently staying above the day's volume-weighted average price (VWAP; red line);
* Accepting value higher by building volume at higher price levels within each bar;
* Repetitive breakouts above areas during the day where volume accumulates (side histogram);
* A very strong intraday advance/decline ratio;
* Persistently positive NYSE TICK, with few readings < -800 and many > +800;
* The vast majority of stocks and sectors trading up from their opening prices.
The earlier you can see these signs, the quicker you'll be able to identify the day structure and adapt your trading strategy accordingly.