It is suggested that you cross mountain passes at an altitude at least 1,000 feet above the pass elevation. Since this altitude will usually put you over 10,000 MSL, the cloud clearance requirement is at least 1,000 feet below the clouds. Hence, you should make sure that you have at least a 2,000 foot ceiling over the highest pass you will cross.
Determining the actual ceiling in the mountains, however, can present some problems. There simply arenžt very many mountain weather reporting stations. Also, those that do exist are almost exclusively in valleys. Reported ceilings at a mountain valley airport may have to be 8,000 feet or higher to give 2,000 feet ceilings at the passes.
Many experienced mountain pilots recommend having at least 15 miles of visibility before attempting mountain flights. Since your navigating will be primarily by pilotage and dead reckoning, good visibility will help keep you oriented in a sometimes confusing array of geographical cues.
Strong winds can cause some of the most dangerous conditionis you'll have to contend with in the mountains. To minimize the chance of encountering dangerous turbulence, mountain flying should not be attempted if the winds aloft forecast at mountain top levels are greater than 25 knots. Above this level, potentially dangerous turbulence, as well as very strong up and down drafts are likely.
IFR and Night Mountain Flights
Experienced mountain pilots recommend that IFR and night flight in the mountains not be attempted. Instrument approaches and departure procedures require a highly skilled pilot and a very high performance airplane. Night obviously obscures most visual navigation cues, making terrain clearance difficult or impossible.