Why all the fog the last week or so? It's simple, it's a temperature inversion!! What is a temperature inversion? It's when temps warm as you go UP in the atmosphere. Typically when you go UP in the atmosphere, at least at the lower layers, temps decrease with height. When you get a temperature inversion (warming temps with height) you can often get fog to develop. Temps at 850 mb (5000 feet) are in the 40s!!!! In the meantime we are in the teens and 20s at the surface. When you have a temp inversion, this TRAPS the cold dense air at the surface along with the fog, pollutants etc. Until we get a change in the weather pattern, and scour out this temp inversion then fog will persist. I do foresee a change coming by the end of the week as high pressure moves in and we finally see some sunshine.