I'd always heard the story about how Apollo 12 was struck by lightning and wondered why they let it head up in a storm. They always check the weather before a launch, and if there is any chance of even a little rain they delay the flight. What was the reason for Apollo 12's exception?
From NASA's own website:
With a half hour to go, Merritt Island was experiencing peak winds of 14 knots, light rain showers, broken clouds at 240 meters, and overcast skies at 3,000 meters. But the ceiling exceeded the minimum requirement of 150 meters, and the ground winds were within limits. The Apollo design permitted launch during rain. The possibility of lightning concerned Launch Operations Director Kapryan, however, and he considered a hold.
(...) A weather report from the Eastern Test Range helped Kapryan make up his mind. An Air Force plane reported only mild turbulence and no indication of lightning within 32 kilometers of LC-39. Moonport, Ch22-2
If you want more information on why they continued to launch during the special weather conditions, see these links:
- "Lightning Strikes" (NASA Moonport, Ch22-2)
- "Why and Wherefores of Lightning" (NASA Moonport Ch22-3)
As response to Uwe's anwser:
After the launch some newspapers suggested that President Nixon's presence influenced Kapryan's decision. The launch director denied it. Moonport, Ch22-2
Apollo 12 actually was not struck by lightning, despite the common misconception. It did fly through rain, and was the only manned spacecraft to fly through rain. In that flight, there was a massive static electricity buildup that lead to the two electrical events. Source
There was a rule, 1-404, that states:
“The vehicle will not be launched when its flight path will carry it through a a cumulonimbus (thunderstorm) cloud formation.”
That in fact was not violated, as it was not actually struck by lightning. The controllers realized they were close to violating that rule, but opted to go ahead and fly the mission. Still, they learned, and as mentioned earlier, this was the last time they attempted to launch in rain, let alone a potential thunderstorm.
May be they did not delay the flight this time because President Richard Nixon attended the launch, see https://en.wikipedia.org/wiki/Apollo_12 and the discussion here http://www.collectspace.com/ubb/Forum29/HTML/001509.html