another thought on the moisture "characteristic" is that thunderstorms produce SHOWERS as opposed to continuous rain.
Here's what I found on T/O mins, not sure if it answers your question...
Civil airport takeoff minimums. Unless otherwise authorized by the Administrator, no pilot operating an aircraft under parts 121, 125, 129, or 135 of this chapter may take off from a civil airport under IFR unless weather conditions are at or above the weather minimum for IFR takeoff prescribed for that airport under part 97 of this chapter. If takeoff minimums are not prescribed under part 97 of this chapter for a particular airport, the following minimums apply to takeoffs under IFR for aircraft operating under those parts:
(1) For aircraft, other than helicopters, having two engines or less -- 1 statute mile visibility.
(2) For aircraft having more than two engines -- 1/2 statute mile visibility.
Last edited by EvilGN; 11-28-2007 at 07:54 AM.