During the Winter time here in Salt Lake we get this phenomenon called an “inversion.” This is where high pressure squashes the cold, moist, polluted air and forces it to the lowest altitude. The valley acts like a soup bowl containing the foggy air. At a certain elevation you can drive up a road and right into a cloudless sunny day. Drive back below the soup level and you’re in the fog again.
When the inversion happens the temp is cold and the ground stays frozen. The air quality is terrible and it really makes my eyes sore. Last year we had 21 straight days of this soup.
The soup stays until wind or precipitation washes it away.