An very unusual steam fog was seen around mid day today
in Savannah. To get steam fog in the middle of the day this
far south in May is quiet unusual.
Steam fog... also called evaporation fog... is created by cold air
passing over much warmer water. The process starts when
evaporation from the water body gets into the low levels of the
air and this creates slight instability near the surface of the
water body. The warmed air rises, where it mixes with the
cold air above the immediate water surface. The mixing cools
the air enough to produce condensation and the water vapor
forms tiny rising droplets... very similar to what you see when
you pour a steaming hot cup of coffee or tea and watch the
steam rise from it.
At the time I took these pics... the air temp was 52... the
water temp is in the middle 70s. The combination of nearly
25 degree difference between air/water combined with cold
and dry low level advection led to its development. Keep in mind
a very basic weather principle... the higher the difference
between warm water and cold air above... the greater the
transfer of heat from water to air.
To get steam in the middle of a May night is pretty hard to get...
much less in the middle of the day! Truly something unusual!
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