Weather Words: Valley Fog

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Valley fog can make for some of the most stunning photos, where fog is nestled in a valley and you can see it rising through the trees. In order for fog to form, the temperature and dewpoint have to be very near or at the same temperature. This is what forms that cloud on the ground that we know as fog. While this is the rule for every type of fog to form, there are different scenarios that help create fog.

During the overnight hours, the daytime heat that’s resting in the valleys begins to lift out, allowing for the denser, cooler air higher up the mountain to slide down into the valley. As this happens, the temperatures near the surface of the valley begins to cool to the dew point, creating valley fog

While it can be beautiful to witness from above, valley fog can be very dangerous or near impossible to travel through. One moment you are driving through picturesque mountains, and the next you could find yourself in valley fog with little to no visibility. Always make sure you check the weather conditions before you begin your journey.

J​ennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.