Expect winter fog into Saturday morning

Weather

SIOUX FALLS, S.D. (KELO) — With snow on the ground, foggy conditions are possible into the morning. 

Over the course of any given winter day, some of our snow melts away, even on cloudy days. As that snow melts, moisture is put into the air close to ground level. On calm nights, that sets the stage for fog.

On nights with bare ground, it’s much more difficult for the air temperature to match the dew point in the winter since our air can become so dry. With snow on the ground, however, it’s easier.

That extra moisture in the air near the surface raises the dew point just enough so the air temperature doesn’t have to drop as far to match it. Once the air temperature matches the dew point, the water vapor in the air can condense into droplets and thus fog develops.

With temperatures below freezing as this fog forms, water droplets can freeze on surfaces. The end result is something called rime ice which can put a beautiful coat of ice on trees as you start the day.

As long as we have snow on the ground and calm nights, we’ll have the chance to see this patchy fog form toward daybreak. Thankfully, with the late February sun angle in place, this fog usually burns off faster than any fog we see in the dead of winter.

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