It's really important when choosing the right club for your approach shot to factor in the conditions.  If you're playing in the middle of summer, the golf ball will not only bounce further once it hits the ground, it can travel a lot further through than it would when it's cold.  Likewise, in very cold conditions don't expect the ball to fly nearly as far so make sure you club up.  Rather than thinking you always hit your 7 iron 150 yards, remember this can vary enormously  either way in differing weather conditions.

Consider this story about my Dad, the legend.  Every time we play on his home course, on the 2nd hole, a par 3, he reaches for the 6 iron.  It doesn't matter if it's the height of summer and downwind or there is snow on the ground and into a gale, 6 iron every time!  When it lands 40 yards short in the brook, he says I always hit 6 iron here.

Check the wind and allow for the conditions, it could make all the difference.