Late October, first light, Gores Landing. The air is cold enough to see your breath, there isn't a ripple on Rice Lake, and the whole surface is covered in little white wisps curling straight up, as if somebody lit the lake on fire overnight.
Late October, first light, Gores Landing. The air is cold enough to see your breath, there isn't a ripple on Rice Lake, and the whole surface is covered in little white wisps curling straight up, as if somebody lit the lake on fire overnight.
Even the National Weather Service reaches for that picture. It says this kind of fog "takes on the appearance of wisps of smoke rising off the surface of the water." (How fog forms, National Weather Service)
It's called steam fog, and the lake doesn't have to be warm for it. It only has to be warmer than the air sitting on top of it.
It Isn't Steam
The word sends people in the wrong direction. Nothing is boiling. What you're looking at is a cloud of tiny water droplets sitting right on the lake.
Here's how it builds. The water is warmer than the air, so moisture evaporates off the surface into the layer of air just above it. The Met Office explains that this evaporation also warms that thin layer, so it rises and mixes with the colder air passing over. As the warm, moist air mixes with the cold air, it cools until it can't hold the moisture as vapour anymore. The Weather Service puts it plainly: the moist air "cools until its humidity reaches 100% and fog forms." (What is fog?, Met Office; National Weather Service)
The wisps rise and curl because that's the mixing you're seeing. Warmer air coming up, colder air coming across.
The important word is relative. Rice Lake in late October is far too cold to swim in. It can still be a lot warmer than the air on a clear, calm morning after a frosty night. So when we say "warm water" here, we mean warmer than the air. Please don't test it with your feet.
Why It Shows Up in the Fall
You can get steam fog any time cold air moves over warmer water. The Met Office's own examples are steam fog over heated pools, and "when cold air moves over warm seas in autumn." (Met Office)
That second one is the Rice Lake version. There are only two ingredients: air that got properly cold overnight, and water that's still warmer than that air. A late-October morning on the lake can hand you both.
The Met Office adds one more thing worth knowing: evaporation fog often brings freezing fog, or sometimes frost. Freezing fog is made of droplets that stay liquid below 0°C (32°F) until they touch something they can freeze onto. The Weather Service says anything freezing fog touches gets coated with ice. On a dock, that means boards, cleats and rails. (Met Office; National Weather Service)
Not Every Foggy Lake Has Steam Fog
A white layer on the water isn't always the same thing. Fog comes from a few different processes, and they tell you different things about the weather.
| Fog type |
What starts it |
| Steam (evaporation) fog |
Cold air moves over warmer water and mixes with the moist air above it. |
| Frontal fog |
Warm raindrops evaporate into a cooler, drier layer of air near the ground. |
| Advection fog |
Warm, moist air moves across a colder surface and cools. |
| Radiation fog |
The ground cools overnight and chills the moist air sitting on it. |
The Weather Service groups steam fog and frontal fog together as the two kinds of evaporation, or mixing, fog. (National Weather Service fog guide)
The easy tell for steam fog is the wisps. If it's rising off open water like smoke, the Weather Service description fits.
The Same Thing, Seen From Space
On January 6, 2014, a mass of Arctic air pushed south over the Great Lakes. As it crossed the relatively warm water of Lake Michigan and Lake Superior, NASA's Terra satellite caught steam fog forming over both lakes and streaming southeast with the wind. NASA ran it as an Image of the Day two days later. (Steam fog over the Great Lakes, NASA Earth Observatory)
It's the same physics as the wisps off our dock, at the scale of a whole region. Seeing it from orbit makes the cause easy to follow: cold air in, warmer water underneath, fog trailing downwind.
Lakes Michigan and Superior, January 6, 2014. NASA Earth Observatory image by Jesse Allen and Robert Simmon, using LANCE/EOSDIS Rapid Response data. This is an archival Great Lakes example. https://science.nasa.gov/earth/earth-observatory/steam-fog-over-the-great-lakes-82777/
If You're Heading Out in It
The name of the fog matters a lot less than how far you can see.
Transport Canada lists visibility, wind, water conditions, traffic, your boat's manoeuvrability and nearby hazards like rocks and stumps as things to weigh when you pick a safe speed. It also says to be especially careful going into or coming out of a fog bank. (Speed and impaired boating, Transport Canada)
On Rice Lake that's real. The lake has shoals, weed beds and old railway remains near Tic Island, and fog takes away the shoreline you normally steer by. A few questions before you leave the dock:
- How much of your route can you actually see from here?
- Do you know the water well enough to run it without landmarks?
- Is the fog thinning, or are you hoping it will?
If the answers make you hesitate, have another coffee and wait. The lake will still be there at ten o'clock.
What We See at HBW
Late October is haul-out season here, and some boats come to our ramp by water instead of on a trailer. A smoking lake is one of the best sights of the year from our shore, and it's also a good reason to wait an hour before you run across. Our Rice Lake boating guide covers how we think about running the lake, and the Rice Lake boat launch guide helps if you're starting from a public ramp.
If your boat's coming out for the winter, put the request in at hbwservice.ca and bring it over when the fog lifts.
Sources
Phone: 905-342-2153
Address: 5369 Harris Boat Works Rd, Gores Landing, ON
Service: hbwservice.ca
Sites: harrisboatworks.ca | mercuryrepower.ca
