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Unit 11: Winter Weather

Why Bridges Freeze Before Roads

During transition months and especially during the winter months we talk about how bridges ice before roadways, so why is that?

Temperatures during the daytime may be very similar, but when temperatures start to drop, road temperatures drop pretty evenly. The ground below helps insulate them, but when you talk about bridges, there is a lot of open space. Cold air can get above and below the bridge and that can result in a quick heat loss and in turn see any precipitation or wet pavement freeze.

So how about in the case, where temperatures are above freezing, but there are still icy spots of roads, sidewalks, and parking lots. During the night, heat is released into the atmosphere and with a large snowpack on the ground, it keeps the ground colder. The official temperature reading is taken about 6 feet above the ground where it can be a bit warmer, but because of that snowpack, the ground is still a few degrees colder than the actual reading.

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