He knew the plan before he took off
A couple of years ago, I was flying on a stromy evening with intense, fast-moving CB activity. On the ground, everything for our departure looked good: it appeared that we could fly the same Standard Instrument Departure we always do (straight ahead to the east for a few miles then right by 45 degrees), since everything said it would take us clear of the weather. We duly picked up our clearance, briefed and set off.
By the time we arrived at the holding point on the southern runway - 20 minutes later or thereabouts - the weathed had moved in, much faster than predicted. Our own radar now revealed that EVERY waypoint on our SID was red or magenta - a definite no-go. However, we noticed that there was a hole to the south, so I asked the tower controller to coordinate with Departure to immediatey vector us by 180 degress into a sort of downwind (very non standard there) and then through that gap.
However, it took the controller some 15 minutes to organize such a maneuver, by which time the gap had gone - and worse still, another CB had moved onto the extended runway centerline very close to the field. The only option now was to go north. So we had to wait 20+ minutes more for the controllers to coordinate with their counterparts handling the northern runway to let us swing north east and THROUGH their departures for a few miles and then swing southeast (even more non standard than our previous idea). This finally worked... after burning fuel 50 minutes on the holding point (thankfully, we were tankering, so had loads to spare).
The moral? Plans on the ground and the actual situation in the air can be very, very different, especially during convective activity...