Fog is just a cloud sitting on the ground, and it forms for a simple reason: the air has cooled to the point where it can’t hold any more moisture.
That point is the dew point. When the temperature drops to within a degree or two of the dew point, water vapour starts condensing into tiny droplets, and you get mist, then fog. On a calm, clear night, that can happen fast.
When to expect fog in Lethbridge
- Calm nights after a day with melting snow or rain, when there’s plenty of moisture near the ground
- Low spots first: the river valley, the coulees, and fields along the Oldman
- Early morning, just before and after sunrise, when it’s coldest
- Freezing fog in winter, which can leave a coating of frost on roads, windshields and power lines
Fog isn’t the only thing that cuts visibility here. Blowing snow, blowing dust and wildfire smoke can be just as bad, and they come with wind rather than calm.
What to do
- Use your low beams, not high beams. High beams bounce off the fog and make it worse.
- Slow down and leave more room. Visibility can drop from fine to near zero within a few hundred metres, especially dropping into the river valley.
- Assume roads may be icy in freezing fog.
- If visibility is changing quickly, delaying a trip by an hour often solves it. Fog usually burns off by mid-morning.
You can compare the temperature and dew point live at westlethbridgeweather.com. When they’re close and the wind is light, fog is likely.
Related: Live conditions at West Lethbridge Weather · How to Read the Weather
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