http://www.metoffice.gov.uk/learning/fog/difference-mist-and-fog They're not 100% interchangeable but I use fog if the 'cloud' is too dense to see through and mist if it only somewhat obscures my vision. Morning fog in San Francisco vs. the mist in a rain forest

If i go outside on a foggy day, my vision will not be good but i will stay dry. If i go outside and it is misty, my vision may or may not be very good and i will get a little bit damp(wet).

Fog doest get u wet. But a mist will get u wet.