P.M. Update: Fog and slippery spots develop overnight.

It’s the last full day of autumn, with winter set to start at 5:02 Monday morning. Widespread fog and some spots of black ice are expected to develop overnight, which will make the final few hours of the season dicey on the roadways. Monday’s forecast is a bit tricky, as low clouds and fog may be tough to shake, which would result in some much cooler temperatures than the currently forecast mid-40s for most of the region.

Through tonight: Temperatures and dew point values will bottom out in the low 30s overnight, which means widespread areas of fog are likely to develop. Given that temperatures will be close to or below freezing, black ice and slippery spots will develop on some secondary roads and bridges. Use care on the roads after midnight, with reduced visibility and slippery surfaces.

Tomorrow (Monday): Fog and slippery spots persist through the early morning, but the low clouds and fog should lift by the afternoon. There is high uncertainty on whether and when the clouds will break, which puts the temperature forecast into question. Right now, it looks like we’ll see enough partial sunshine to push afternoon temperatures into the low and even mid-40s. Chilly again tomorrow night, with lows in the 30s.

https://www.washingtonpost.com/weather/2020/12/20/pm-update-fog-slippery-spots-develop-overnight/?