FAILURE OF THE PILOT TO OBTAIN A PRE-FLIGHT WEATHER BRIEFING, AND HIS IMPROPER IN-FLIGHT PLANNING/DECISION, WHICH RESULTED IN AN IN-FLIGHT ENCOUNTER WITH SEVERE WEATHER AND SUBSEQUENT ENGINE FLAMEOUTS. FACTORS RELATED TO THE ACCIDENT WERE: DARKNESS, THE SEVERE WEATHER CONDITIONS, AND ROUGH/UNEVEN TERRAIN IN THE FORCED LANDING AREA.