As powdery snowbanks turn to slate-gray slush and El Niño drenches sunny cities with dreary downfall, the risk of cabin fever threatens to reach an all-time high. Perhaps the best way to avoid feeling blue is to ditch the dreariness with a tropical getaway to the sand-strewn beaches of the Caribbean and Latin America. We have compiled a list of five jet companies who provide private transportation to warm-weather destinations, offering a much-needed getaway from freezing temperatures and winter s…