Low Season (Oct–Nov)
Flash floods often wash out roads in the Andean region Cartagena and the Caribbean coast is disproportionally wet in October Low water levels in the Amazon means excellent hiking and white-sand beaches Prices everywhere are at their lowest
Shoulder (Mar–Sep)
Bogotá, Medellín and Cali suffer a secondary rainy season in April/May Best whale-watching is July to October on the Pacific coast Cartagena shines through April, hard rains begin in May
High Season (Dec–Feb)
Sunny skies and warmish days throughout the Andes Dry everywhere but the Amazon San Andrés and Providencia are gorgeous Prices country-wide are at their highest
Read more: http://www.lonelyplanet.com/colombia/weather#ixzz4DW6Ipxa8