Smoke on the water. It’s not just a song lyric when it is hovering over Lake Michigan.
Called sea smoke or sea fog, this phenomenon happens when a mass of very cold air blows over warmer water. It’s similar to what happens when a football player removes his helmet, and “smoke” appears above his head during a cold game.
National Weather Service Chicago meteorologist Ricky Castro says this phenomenon happens often during Chicago winters — even when Lake Michigan is covered in ice, as in polar vortex-influenced winters. “When a cold air mass moves off the land and interacts with the ice cover, then the smoke effect will still occur,” he said. “The temperature of the ice is still warmer than the air above it.”
Castro says the process is aided by wind, “If winds were calm, then the effect might not be as dramatic.”
How sea fog forms
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1. Cold air from the west
blows out from the land
over the lake.
The air
temperature
can be in the
single digits
or lower …
… while
the water
temperature
is in the
mid-30s.
2. When water near the surface
evaporates into the colder air
above, it increases the humidity,
or the amount of water vapor,
in the air.
3. When the air reaches its
dewpoint, or the atmospheric
temperature below which water
droplets begin to condense and
dew can form, the vapor
condenses into fog.
1. Cold air from the west blows out
from the land over the lake.
… while the water
temperature
is in the mid-30s.
The air temperature
can be in the single digits
or lower …
2. When water near the surface evaporates into
the colder air above, it increases the humidity,
or the amount of water vapor, in the air.
3. When the air reaches its dewpoint, or the
atmospheric temperature below which water
droplets begin to condense and dew can form, the vapor condenses into fog.
1. Cold air from the west blows out
from the land over the lake.
… while the water
temperature
is in the mid-30s.
The air temperature
can be in the single digits
or lower …
2. When water near the surface evaporates into
the colder air above, it increases the humidity,
or the amount of water vapor, in the air.
3. When the air reaches its dewpoint, or the atmospheric
temperature below which water droplets begin to condense
and dew can form, the vapor condenses into fog.
Sources: National Weather Service, Chicago; weatherology.com; Tribune reporting
Created by the baiduhai Dataviz team. On Twitter @ChiTribGraphics
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